THE J. PAUL GETTY MUSEUM LIBRARY 
 
 
 
 
 
fj Hl/ 
 
 
 L 
 
THE 
 
 CABINET CYCLOPAEDIA. 
 
 CONDUCTED BY THE 
 
 REV. DIONYSIUS LARDNER, LL. D. F. R. S. L. & E. 
 
 M R. I. A. F. R. A.S. F.L.S. F. Z.S. Hon. F. C. P. S. &c. &c. 
 
 ASSISTED BY 
 
 EMINENT LITERARY AND SCIENTIFIC MEN. 
 
 USEFUL ARTS. 
 
 A 
 
 TREATISE 
 
 ON THE 
 
 ORIGIN, PROGRESSIVE IMPROVEMENT, AND PRESENT STATE 
 
 OF 
 
 THE MANUFACTURE 
 
 OF 
 
 PORCELAIN AND GLASS. 
 
 Cons . 
 
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 V' % >7 
 
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 33fjUa&cIi)I)ia: ' j 
 
 CAREY, LEA, & BLANCHARD. 
 
 1834. 
 
“ The arts may be said to imitate nature, or to help, or to overcome 
 and advance nature: nor are they therefore to be esteemed less noble 
 because more practicable, since our best and most divine knowledge 
 is intended for action; and those may justly be counted barren studies 
 which do not conduce to practice as their proper end.” 
 
 Bishop Wilkins. 
 
 ti 
 
 THE J PAUL GETTV CENTER 
 LBmPY 
 
A 
 
 TREATISE 
 
 ON THE 
 
 ORIGIN, PROGRESSIVE IMPROVEMENT, 
 
 AND 
 
 PRESENT STATE 
 
 OF THE 
 
 MANUFACTURE 
 
 OF 
 
 PORCELAIN AND GLASS. 
 
 PiitlattelpWa: 
 
 CAREY, LEA, & BLANCHARD. 
 
 1834 . 
 

LIST OF WOOD ENGRAVINGS. 
 
 PORCELAIN. 
 
 . Page 
 
 1. Throwing.. 
 
 2. Biscuit Kiln French Improvement.• . 58 
 
 3. Do. do. ib. 
 
 4. Do. do. 59 
 
 5. Making Tobacco Pipes, Roll.87 
 
 6. Do. do. Needle.ib. 
 
 7. Do. do. Mould.ib. 
 
 8. Do. do. Kiln. . . •.88 
 
 GLASS. 
 
 1. Double Furnace. . 128 
 
 2. Glass Pot or Crucible.130 
 
 3. Gathering Rod.137 
 
 4. Blowing.ib. 
 
 5. Pontil.138 
 
 6. Transferring from Gathering Rod to Pontil.ib. 
 
 7. Procello.139 
 
 8. Fashioning.ib. 
 
 9. Annealing Oven, front view.142 
 
 10. Blowing Crown Glass.146 
 
 11. Circular Plate.147 
 
 12. Casting Plate Glass.160 
 
 13. Blowing do. Gathering.167 
 
 14. Do. do. Cylinder.ib. 
 
 15. Do. do. Punching.168 
 
 16. Do. do. Opening.ib. 
 
 17. Do. do. do.ib. 
 
 18. Do. do. Cutting.. ib. 
 
 19. Do. do. Transferring ... .... 169 
 
 20. Do. do. Opening.ib. 
 
 21. Do. do. Cutting . ..ib. 
 
 22. Do. do. Spreading.170 
 
 23. Thermometer Tubes, Drawing.176 
 
 A 2 
 
CONTENTS. 
 
 PART I. 
 
 PORCELAIN MANUFACTURE. 
 
 CHAPTER I. 
 
 HISTORICAL NOTICES OF THE RISE AND PROGRESS OF POTTERIES 
 AND THE PORCELAIN MANUFACTURE. 
 
 Probable Origin of the Art.—Ancient Brick-making.—Roman Bricks.— 
 The Potter’s Wheel, an Implement of high Antiquity.—Indian Earth¬ 
 enware.—Roman Water-pipes.—Introduced into Britain.—Remains 
 of Ancient Pottery in the Kingdom.—Roman Potteries in Stafford¬ 
 shire.—Earthenware made in an Island formerly existing near Mar¬ 
 gate.—Antiquity of the Art in the East.—Porcelain first brought to 
 Rome.—Figures found with Egyptian Mummies.—China Wares 
 brought by Portuguese Traders.—Erroneous Notions concerning their 
 Composition.—Corrected by Pere d’Entrecolles.—Discovery by De 
 Botticher in Saxony.—Manufacture attempted in France.—Investiga¬ 
 tions of Reaumur.—Proper Materials discovered in France.—Jonas 
 Hanway’s Account of Collection at Dresden.—Works established at 
 Berlin.—English Potteries.—Dr. Plot’s Account.—Improvements in 
 Glazing.—White Stoneware.—Advantages of Mr. Wedgwood’s Im¬ 
 provements.—Largo Exportations by Mr. Wedgwood.—His principal 
 Inventions.—Characteristics of true Porcelain.—First made by Mr. 
 Cookworthy in England.—Importance of the Manufacture.—Porce¬ 
 lain of Derby.—Of Coalport.—Of Worcester.—Of Rotherham.—Duty 
 on Stoneware.—Its Unproductiveness and Impolicy.Page 17 
 
 CHAP. II. 
 
 GENERAL DESCRIPTION OF INGREDIENTS USED IN THE 
 MANUFACTURE. 
 
 Different Branches of the Art.—Ingredients used.—Properties of Alu¬ 
 mina.—Its Infusibility.—Contraction when exposed to Heat.—Wedg¬ 
 wood’s Pyrometer.—Composition of Gems.—Great Abundance of 
 Clay.—Properties of Silica.—Its great Abundance.—Sea Sand.—In¬ 
 capable of artificial Solution in Water.—Dissolved naturally.—Springs 
 at Carlsbad.—Boiling Fountain in Iceland.—Fusion of Silex.—Kinds 
 of Clay used in Potteries.—Their various Merits.—China Clay of 
 Cornwall.—Mode of its Preparation.—Its Analysis.—Cornish Fel¬ 
 spar.—Its Fusibility.—Steatite.—Earth of Baudissero.—Its Analysis. 
 —Cornish Sopestone.—Spuma Maris.—Its Employment in Porcelain 
 Works in Spain.33 
 
Vlll 
 
 CONTENTS. 
 
 CHAP. III. 
 
 ON THE PREPARATION OF MATERIALS. 
 
 Dilution of Clay.—Chemical Examination of Water necessary.—Rain 
 Water.—Carefulness of German Manufacturers.—Blunging.—Ma¬ 
 chinery.-Preparing Flints.-Burning.—Baking.—Grinding.—Dry 
 
 grinding.—Brindley’s improved Mill.—Chert.—Care required in se¬ 
 lecting Grinding Stones.—Dilution of Flint Powder.—Affinity of 
 Alumina for Silica.—Slip.— Slip-kiln.—Method of evaporating super¬ 
 fluous Moisture —Working the Paste.—Time necessary for temper¬ 
 ing it.—Proportions wherein Clay and Flint are united.—Difficulty 
 of ascertaining this.—Slapping.—French Manufactures.—Proportions 
 of Ingredients used by them.—Ivao-lin.—Flint.—Gypsum.—Broken 
 Porcelain.—Calcined Bones.—Tender Porcelain.—Its Composition. 
 —Porcelain Earth used in Berlin.—French Potters buy their Ma¬ 
 terials ready mixed.—Advantages of this Plan.—Ineligible in Eng¬ 
 land..40 
 
 CHAP. IV 
 
 ON THE FORMATION OF UTENSILS. 
 
 Throwing.—Potter’s Lathe.—Thrower.—Mode of Proceeding.—Pro¬ 
 files.—Slurry.—Gauges.—Turning Lathe.—Turning and Smoothing. 
 —Moulding Dishes, &c.—Tools.—Steam Machinery.—Engine Lathe. 
 —Milled Edges.—Handler.—Formation of Handles, Spouts, &c.— 
 Pressing.—Small Ornamental Figures.—Mode of affixing them.— 
 Method of making Moulds.—Boiled Plaster.—Great Use of Gypsum 
 in making Moulds.—Stoves.—Modelling.—Qualifications requisite 
 for a Modeller.—Increasing Skill of Artists.—Fostered by Wedg¬ 
 wood.—Mould-maker.—Method of his working.—Casting.—Careful¬ 
 ness required in Drying..48 
 
 CHAP. V. 
 
 ON THE PROCESSES OF FIRING AND GLAZING. 
 
 Seggars.—Proper Materials for these wanting in England.—Not so in 
 France.—Nungarrow Work.—Why discontinued.—Great Estimation 
 of its Wares.—Cause of Superiority.—Use of Seggars.—Their Forms. 
 —Mode of using them.—Sevres Manufactory.—Improved Furnace. 
 —Its Advantages.—Description.—Chinese Method of Firing.—Con¬ 
 struction of their Kilns.—Care required in Baking.—Duration of Pro¬ 
 cess.—Oven-man.—Trial Pieces.—Annealing.—Biscuit.—Wine-cool¬ 
 ers.—Glazing.—Composition of Raw Glazes.—Bad Effects of some of 
 these.—To the Public.—To the Workman.—Pernicious Use of Ardent 
 Spirits.—Glazes invented by M. Chaptal.—By Mr. Rose.—Porcelain 
 Glazes.—French Glazes.—Pallissy.—His Experiments in Enamel- 
 
CONTENTS. 
 
 IX 
 
 ling.—His Perseverance and Sufferings.—His Success, and continued 
 Firmness under Persecution.—Inferior Glazes.—Low-priced Wares. 
 —Gloss Oven.—Regulation of Temperature.—Qualities that deter¬ 
 mine the Excellence of Porcelain.—Stone Ware.—Its Composition.— 
 Lambeth Potteries.—Modes of Glazing.55 
 
 CHAP. VI. 
 
 ON THE ART OF APPLYING COLORS AND ENGRAVINGS TO 
 EARTHENWARE. 
 
 Antiquity of Enamel Coloring.—Specimens from Ancient Egypt.— 
 From the Royal Works at Sevres.—Painted Ware of Worcester.— 
 Of Staffordshire.—Of Derby.—Of Yorkshire.—Great Services of Mr. 
 Wedgwood in this Branch of the Manufacture.—Mystery observed 
 in the Preparation of Colors.—Publication of Processes by M. Brong- 
 niart.—Metallic Oxides.—Addition of fluxing Bodies necessary—And 
 why.—Colors employed for tender and hard Porcelain.—Vehicle 
 used with the Color.—Mode of their Combination.—Description of 
 Colors.—Purple and Violet.—Red—Yellow—Blue—Green—Brown 
 —Black—White.—Compound Colors.—Precautions necessary in 
 forming those Compounds.—Gilding.—Lustre Ware.—Preparation of 
 Colors.—Enamelling Kilns.—Trial Pieces.—Method of Gilding and 
 Burnishing.—Copper-plate Engravings.—Mode of transferring Im¬ 
 pressions to Earthenwares.—How performed in France.68 
 
 CHAP. VII. 
 
 ON THE MANUFACTURE OF TOBACCO PIPES. 
 
 This Manufacture prosecuted to a great Extent.—Description of Ma¬ 
 terial.—Rolling.—Boring.—Moulding.—Polishing.—Baking.—De¬ 
 scription of Kiln.—Of Crucibles.—Manufacture in Holland.—Origin¬ 
 ally conveyed there from England...86 
 
 CHAP. VIII. 
 
 ON THE PORCELAIN MANUFACTURE OF CHINA. 
 
 Obscurity wherein its Origin is shrouded.—Chiefly practised at King- 
 te-ching.—Supposed Superiority of old China Ware.—Materials em¬ 
 ployed.—Koa-lin.—Pe-tun-tse.—Their Preparation.—Oils or Varnish¬ 
 es.—Their Composition.—Hao-che.—Its Superiority to Kao-lin.— 
 Analysis of Kao-lin.—Extent of Factories at King-te-ching.—Great 
 Number of Workmen employed.—Preparation of Materials.—Method 
 of fashioning Utensils.—Moulds.—Division of Labor.—Deficiency of 
 Chinese in the Art of Design.—Their excellent Colors.—Numerous 
 Hands employed in decorating each Piece.—Bad Effect of this Sys¬ 
 tem.—Blue long the only Color used for painting China Ware.— 
 
CONTENTS. 
 
 Mode of preparing various Colors.—Chinese ignorant of Chemical 
 Science.—Umiam.—Tsou-Tchi.—Kia-tsing.—Method of forming it. 
 —Chinese Furnaces.—Passion for old Porcelain.—Ku-tong.—Mock 
 Antiques.—Reasons for Costliness of China Ware in Europe.—High 
 Prices formerly paid in China.—Finest Specimens not brought to 
 Europe.—Porcelain Tower at Nan-King.—Chinese Potters prepare 
 Materials for the Use of their Descendants.-Common Wares made 
 in China.—Attempt of the Emperor to transfer the Manufacture to 
 Pekin.—His want of Success. 90 
 
 PART II. 
 
 GLASS MANUFACTURE. 
 
 CHAPTER I. 
 
 ON THE NATURE AND PROPERTIES OF GLASS.-THE HISTORY OF 
 
 ITS INVENTION, AND MANUFACTURE. 
 
 Nature of Glass.—Its various Properties.—Its Utility to all Classes. 
 The Assistance it lends to Science.—Admiration of the Ancients— 
 Excessive Prices formerly paid.—Origin of its English Name. Aris¬ 
 totle’s Problems.—First invention ascribed to the Phoenicians.—Glass 
 known to the Ancient Egyptians.—Manufactories of Alexandria— 
 Utensils found in Herculaneum.—Urns in British Museum.—Mal¬ 
 leable Glass.—Taxon Glass, by Alexander Severus.—Portland Vase 
 —Glass employed in forming Windows.—Not much used in Eng¬ 
 land till the Eleventh Century.—Privileges granted to Manufactur 
 ers in France.—Plate Glass casting.—Establishment at St. Gobain.- 
 Its early Failure—And Revival.—Manufacture commenced in Eng 
 land.—Of Flint Glass.—Of Plate Glass.—Establishment of Britisl 
 Cast Plate Glass Company.—Chinese unacquainted with Glass-mak 
 ing.—Importance of the Manufacture in England.—Glass made i 
 Source of Revenue.—Bad Effect upon Consumption.—Increase of 
 
 DiRy._Consequent Decrease of Manufacture.—Diminution of Dub 
 
 on Plate Glass.—Increase of Quantity made.10; 
 
 CHAP. II. 
 
 ON THE VARIOUS INGREDIENTS EMPLOYED IN MAKING GLASS 
 
 Glass always composed of Silex with Alkali.—Different Description 
 of Glass.—Sea Sand—Soda and Potash—Pearlash.—Barilla--Kelj 
 
 -Wood-ashes—Nitre—Litharge—Minium—Manganese—Arser 
 
 jc.—Borax.—Chalk.H 
 
CONTENTS. 
 
 XI 
 
 CHAP. III. 
 
 ON THE CONSTRUCTION OF FURNACES, ETC. 
 
 Stability of Furnace essential.—Fritting Furnace, or Calcar.—Its Use. 
 —Working Furnace.—Double Furnace.—Proportionate Dimensions 
 of Furnace and Pots.—Wood Furnaces.—Comparative Consumption 
 of Fuel in Wood and Coal Furnaces.—Annealing Oven.—LierPans. 
 —Glass Pots.—Their Formation and Seasoning.125 
 
 CHAP IV. 
 
 ON THE MANUFACTURE OF FLINT GLASS. 
 
 The most beautiful and costly Kind of Glass.—Importance of its Qual¬ 
 ity for Optical Purposes.—Experiments for its Improvement.—Under¬ 
 taken by the Royal Society.—Promoted by Government.—Distin¬ 
 guishing Properties of Flint Glass.—To what owing.—Different Com¬ 
 positions.—Process of Melting.—Glass-gall.—Its Use.—Curious Phe¬ 
 nomenon.—Implements.—Collecting Glass on Rod.—Marver.—Parai- 
 son.—Blowing.—Reheating.—Elongating.—Pontil.—Fashioning.— 
 Detaching.—Removal to Annealing Oven.—Moulding.—Annealing. 
 
 • —Why indispensable.—Bologna Phials.—Rupert’s Drops.131 
 
 CHAP. V. 
 
 ON THE MANUFACTURE OF CROWN GLASS, BROAD GLASS, AND 
 BOTTLE GLASS. 
 
 Description of Crown Glass.—Harder than Flint Glass.—More difficult 
 to fashion.—Its Composition.—In France.—In England.—Fritting.— 
 Cullet.—Refining.—Sulphate of Soda.—Vegetable Charcoal.—Gath¬ 
 ering—Biowing—Reheating—Flattening.—Transferring to Pontil.— 
 Twirling.—Expanding.—Opening.—Annealing.—Nice Regulation of 
 Temperature required in this Process.—Qualities of Crown Glass.— 
 German Glass.—Broad Glass.—Inferior to Crown Glass.—Its Compo¬ 
 sition.—Preparation.—Working.—Bursting.—Opening.—Annealing. 
 —Bottle Glass.—Manufacture checked by Increase of Duty.—Com¬ 
 position.—Restrictions as to Materials.—Their bad Tendency.—Supe¬ 
 riority of Bottle Glass for certain Purposes.—Materials employed in 
 France.—At Newcastle.—Fashioning.—Moulding.—Experiments 
 suggested by Count Chaptal.—Klingstein.—Volcanic Granite.143 
 
 CHAP. VI. 
 
 ON THE MANUFACTURE OF PLATE GLASS. 
 
 Different Descriptions of Plate Glass.—Blown Plates limited in Size.— 
 Cast Plate Works at Ravenhead.—Difficulties of the Process.—Ma¬ 
 terials.—Various Compositions.—Borax.—Mixing Materials.—Frit- 
 
Xll 
 
 CONTENTS. 
 
 ting.—Furnaces and Crucibles at St. Gobain.—Potts.—Cuvettes.— 
 Regulation of Firing.—Casting Tables.—Arrangements of Foundery 
 at Ravenhead.—Annealing Ovens.—Process of Casting Plates.— 
 Annealing.—Squaring.—Grinding.—Economical Improvement.— 
 Smoothing.—Emery Powder.—Comparative Value of large and small 
 Plates.—Polishing.—Silvering.—Preparation of Amalgam.—Mode 
 of its Application.—Blowing Plate Glass.—Punching.—Partial Cut¬ 
 ting.—Transfer to Pontil.—Completion of Cutting.—Opening.—An¬ 
 nealing.—Sizes of Plates.—Effect of Sun’s Rays in discoloring Plate 
 Glass.154 
 
 CHAP. VII. 
 
 ON THE COMPOSITION OF ARTIFICIAL GEMS. 
 
 Great Interest formerly attached to this Subject.—Different Composi¬ 
 tions for artificial Gems.—Mode of Preparation.—Rock Crystal for¬ 
 merly employed.—Not superior to Sand.—Diamond Pastes.—Selec¬ 
 tion of various Pastes for imitating different Gems.—Reasons for 
 such Selection.171 
 
 CHAP. VIII. 
 
 ON THE MANUFACTURE OF GLASS FROM CALCINED BONES. 
 
 Preparation of Bones.—Their Vitrification.—Process known to Becher. 
 —Concealed by him.—Curious Suggestion as to its Employment.— 
 This Glass highly electric when newly made.175 
 
 CHAP. IX. 
 
 ON THE USE MADE OF THE BLOWPIPE, AND ON VARIOUS SMALL 
 MANUFACTURES OF GLASS. 
 
 Thermometer Tubes.—Manner of giving to them an elliptical Bore.— 
 Blowpipe and Apparatus described.—Materials used.—Method of 
 working.—Sealing Tubes.—Bending and Joining Tubes.—Bulbs.— 
 Spun Glass.—Watch Glasses.—Lunette Glasses.—Glass Beads.— 
 Manufactory at Murano.—Striped Tubes.—Mode of forming Beads. 
 —Sorting them.—Numerous Kinds of Beads.—Mock Pearls.—Man¬ 
 ner of their Invention—And Formation.—Dial Plates.—How form¬ 
 ed.—Lettering and Figuring.176 
 
 CHAP. X. 
 
 ON THE FORMATION OF LENSES. 
 
 Preparation of the necessary Tools.—Choice of Glass.—Grinding.—Pol¬ 
 ishing.—Curdled Lenses.—Means used for avoiding this Defect... 189 
 
CONTENTS. 
 
 Xlll 
 
 CHAP. XI. 
 
 ON THE PRINCIPAL DEFECTS OBSERVABLE IN GLASS. 
 
 StricE.—Render Glass unfit for Optical Purposes.—Threads.—Render 
 Glass fragile.—Cause of this.—Tears.—One of the greatest Defects. 
 —Render Glass useless.—Knots.—Bubbles.—Whence they proceed. 
 —Do not much affect the Quality of Glass.—Objects to be attained 
 for avoiding these Defects.—M. Guinand.—His humble Origin.—En¬ 
 ergy of Character.—Examines Telescopes and constructs others.— 
 Unable to procure Glass of good Quality.—Is incited to examine into 
 the Causes of Inferiority.—His extraordinary Perseverance amidst 
 Accidents and Difficulties.—His ultimate Success.—Accident lead¬ 
 ing to further Improvement.—Prosecutes his Art in Bavaria.—Re¬ 
 turns to Switzerland, and further pursues his favorite Object.—Dies. 
 —Frauenhofer.—Rises from Obscurity by his Talents.—His Scientific 
 Acquirements.—Produces Specimens of perfect Glass.—Dies at an 
 early Age.—Respect paid to his Memory.192 
 
 CHAP. XII. 
 
 ON THE SPECIFIC GRAVITY OF GLASS. 
 
 Importance of this Quality.—Experiments of Loysel.—His Reasoning 
 and Formulae.—Specific Weight augmented by Lime.—Mixed Glass¬ 
 es.—Their specific Weight.—Method of determining this.—Influ¬ 
 ence of Temperature on the specific Weight of Glass.202 
 
 CHAPTER XIII. 
 
 ON THE ART OF COLORING GLASS. 
 
 Antiquity of this Art.—Specimens of Roman Mosaic.—Analysis of these 
 by Klaproth.—Metallic Oxides.—Gold Purple.—Its great coloring 
 Power.—Kunckel.—His Proficiency in coloring Glass.—Yellow Col¬ 
 or.—From Silver.—From Lead.—From Tartar.—From Beech Wood 
 Charcoal.—From Oxide of Iron.—Green.—Black Glass.—Blue.—Di¬ 
 rections found in old Authors.—Imitation of the Garnet.—Of the 
 Amethyst.—Of the Emerald.—Of Sapphires.—Opaque Glasses.— 
 Black.—White.—Opal.—Ancient Pictures formed of colored Glass.— 
 How executed.—Description of Ancient Mosaics.—Most recent Pro¬ 
 secution of this Art.—Accidental coloring of Plate Glass at St. Go- 
 bain.—Ineffectual Attempts to reproduce this Effect..208 
 
 CHAP. XIV. 
 
 ON THE ART OF STAINING AND PAINTING GLASS. 
 
 This Art more recent than that of coloring.—Encouraged by the Monks. 
 —Early Specimen at St. Denis.—Art never much cultivated in Eng- 
 
 • B 
 
XIV 
 
 CONTENTS. 
 
 land.—Splendid Paintings at Gouda.—Directions given by old Au¬ 
 thors for composing Colors.—Fluxes.—Vehicles for diluting Colors.— 
 Description of various Stains.—Method of floating these.—Of Paint¬ 
 ing on Glass.—Imitation of Ground Glass with transparent Patterns. 
 —Description of Kiln employed.—Method of Firing.—Second and 
 third Firing.—Ancient Method of fixing different-colored Glasses on 
 each other.223 
 
 CHAP. XV. 
 
 ON THE ART OF CUTTING, ENGRAVING, AND ETCHING ON GLASS. 
 
 Origin of the Art of cutting Glass.—Implements.—Manner of their Em¬ 
 ployment.—Frosting.—Patterns produced by Moulding.—Engraving 
 on Glass.—Executed with the Diamond.—Etching.—Schwanhard.— 
 Difference of his Practice from that now used.—Method of Etching. 
 —Fluoric Acid.—Glass Incrustations.—Origin of the Art.—Improve¬ 
 ments therein._.235 
 
 CHAP. XVI. 
 
 ON THE DEVITRIFICATION OF GLASS. 
 
 First observed by Neumann.—Experiments of Reaumur.—Substance 
 known as Reaumur’s Porcelain.—Inappropriateness of this Name.— 
 Uses to which the Substance may be applied.—Common Bottle Glass 
 most proper for this Conversion.—Method of effecting the Change.— 
 Produced solely by Heat.—Experiment of Dr. Lewis.—Revitrifica¬ 
 tion.—Experiments of Sir James Hall.—Proposal suggested thereby. 
 —Observations of Guyton-Morveau.—Artificial Intaglios.—Mock 
 Onyxes.—Power of devitrified Glass to bear sudden Changes of Tem¬ 
 perature.—Experiments with colored Glass.—Glass devitrified by 
 burning Lava.—The Process promoted by multiplying the Ingredi¬ 
 ents of Glass.—Devitrified Glass conducts Heat more perfectly than 
 when vitreous.—Becomes a Conductor of Electricity.—Retains this 
 Property when revitrified.243 
 
MANUFACTURE 
 
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 PORCELAIN. 
 
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 OF THE 
 
 MANUFACTURE 
 
 OF 
 
 PORCELAIN. 
 
 CHAPTER I. 
 
 HISTORICAL NOTICES OF THE MANUFACTURE. 
 
 Origin of the Art.—Brickmaking.—Potter’s Wheel.—Indian Earthenwares. 
 —Roman Water-Pipes.—Remains of Ancient Pottery.—Roman Potteries 
 in Staffordshire.—Antiquity of the Art in the East.—Porcelain first 
 brought to Rome.—Figures found with Egyptian Mummies.—China- 
 Wares brought by Portuguese Traders.—Discovery by De Botticher in 
 Saxony.—Manufacture attempted in France.—Investigations of Reau¬ 
 mur.—Jonas Hanway’s Account of Collection at Dresden.—Works at 
 Berlin.—English Potteries.—Plot’s Account.—Improvements in Glazing. 
 —White Stone-Ware.—Wedgwood’s Improvements.—Exportations by 
 Wedgwood.—His Inventions.—Characteristics of True Porcelain.—Porce¬ 
 lain of Derby.—Of Coalport.—Of Worcester.—Of Rotherham. 
 
 The formation of earthen vessels capable of containing fluid 
 substances is an art of the very highest antiquity. In the 
 rudest stages of society, the want of such vessels would call 
 forth the inventive powers of mankind ; and, probably, the 
 hard shells of some vegetable productions, such as gourds and 
 the larger descriptions of nuts, would be first adapted to the 
 purpose. The pliant and infrangible nature of the skins of 
 animals taken in the chase would, at a very early period, point 
 them out as convenient recipients for fluids ; but the prepara¬ 
 tion of these, as well as the fashioning and hollowing of 
 wooden bowls, supposes a previous knowledge of some manual 
 arts, and implies the possession of tools. After even these 
 had been attained, and supposing that the existence of fire, 
 and its use in preparing food, had become known, vessels 
 formed of wood, or of the hides of animals, would be of little 
 use in rendering that knowledge available. Some savage 
 tribes thus circumstanced, have, indeed, made wooden bowls 
 subservient to this purpose, by throwing into the fluids which 
 
 B 2 
 
18 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 they contain, stones previously heated in the fire. This man¬ 
 ner of boiling water, and of cooking provisions, is, however, at 
 best, hut an inconvenient process, and would be immediately 
 abandoned upon the discovery that certain earthern substances 
 were endowed sufficiently with the quality of resisting the 
 action of fire. 
 
 It must continue matter of doubt, whether the fashioning 
 and hardening of clay was practised first by the brickmaker or 
 by the potter. We know that bricks, thoroughly burned, 
 were used at the building of the tower of Babel, 2200 years 
 before the commencement of the Christian era, and 600 years 
 prior to the carrying away into captivity of the Israelites. 
 That the use of bricks, for the purposes of building, must have 
 become exceedingly common at this last-mentioned period, is 
 evident, from the great numbers of the captive Jews who were 
 compelled by their Egyptian task-masters to prosecute the 
 manufacture. It appears that the bricks then made were not 
 artificially burned; the chopped straw which entered into 
 their composition, and which served to hold the mass together, 
 would, in such case, have been destroyed. Specimens of very 
 ancient Egyptian bricks, which have been brought to this 
 country, confirm the supposition that the heat of the sun was 
 alone employed in baking them. 
 
 Many centuries later, the Romans conducted the manufac¬ 
 ture of bricks with a great degree of perfection. A compari¬ 
 son of very ancient Roman ruins, with buildings of modern 
 elevation, will show at once how superior are the bricks em¬ 
 ployed in the former, both as regards solidity and beauty. 
 Specimens of the potter’s art, if even any such existed at an 
 equally early period, could not be expected to continue in be¬ 
 ing for so many ages ; if, indeed, they had withstood the de¬ 
 stroying hand of time, and descended to the present day, they 
 would not bring with them any direct testimony of their date 
 of production, and could throw little or no light upon the ques¬ 
 tion of priority. It is certain, however, that, in very remote 
 ages, the potter’s art had attained to a considerable degree of 
 usefulness, since the earliest authentic records allude to the 
 potter’s wheel as to an implement of then high antiquity. 
 
 The same wants would arise in different portions of the 
 globe ; and in all cases, where similar means for their grati¬ 
 fication presented themselves, it is not surprising that these 
 means should be equally embraced by all. Accordingly, it 
 has been found, in newly-discovered countries, and among 
 people comparatively rude and unacquainted with most of the 
 arts which conduce to human convenience, that the use of 
 earthen vessels has been enjoyed for ages before the existence 
 
CHAP. I. HISTORICAL NOTICES. 19 
 
 of the people was even surmised. Among other proofs of 
 this fact, it may he mentioned, that vases have been found 
 among the aboriginal Indians on the Mosquito shore, which, 
 even by those people, were preserved as memorials of antiquity. 
 There is no reason to doubt that these vessels were the man¬ 
 ufacture of the country in which they were found, as the re¬ 
 mains of ancient potteries have been discovered at a considera¬ 
 ble distance up the Black River on that coast. 
 
 There would be little advantage in entering upon an in¬ 
 vestigation to determine the precise degree of antiquity of the 
 potter’s art, if even there existed any sufficient guides to direct 
 us in the inquiry. It will be more profitable at once to fore¬ 
 go all fanciful speculations, and to commence the relation of 
 a few facts, and such only as bear the stamp of authenticity. 
 The detail of these need not occupy much time or space, 
 which may be more advantageously devoted to descriptions of 
 the art as it exists in the present day, than to the building up 
 of theories, the truth of which can never be demonstrated. 
 
 We learn, on the authority of Vitruvius, who wrote in the 
 •Augustan age, that the Romans then made their water-pipes 
 of potter’s clay. This people, who introduced a knowledge of 
 the useful arts practised by themselves wherever their con¬ 
 quests were extended, established potteries in England, where, 
 among other articles, similar water-pipes were made. Some 
 of these, about a century ago, were dug up in Hyde Park. 
 They were found to be two inches in thickness, and were 
 firmly jointed together with common mortar mixed with oil. 
 
 It has been asserted that the ancient Britons were in the 
 practice of making pottery before the invasion of this country 
 by the Romans; and in support of this belief is brought the 
 fact, that urns of earthenware have been taken from barrows 
 in different parts of the kingdom. On the other hand, the 
 concurring testimony of various writers gives reason for sup¬ 
 posing that our ancestors were in those days supplied with 
 such articles by the Venetians. Vestiges of considerable Ro¬ 
 man potteries are discernible in many parts of the island, and 
 particularly in Staffordshire, on the site of the great potteries 
 which have so long been carried on in that county. In sink¬ 
 ing pits for various purposes, remains of Roman potteries have 
 occasionally been discovered there at a considerable depth 
 below the surface. 
 
 Governor Pownall relates, that in his time (1778) the men 
 employed in fishing at the back of the Margate Sands, in the 
 Queen’s Channel, frequently drew up in their nets some 
 coarse and rudely-formed earthen vessels, and that it was 
 common to find such pans in the cottages of these fishermen. 
 
20 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 It was for some time believed, that a Roman trading vessel, 
 freighted with pottery, had been wrecked here; but on more 
 particularly examining the spot, called by the fishermen Pud¬ 
 ding-pan Sand, some Roman bricks were also discovered, ce¬ 
 mented together, so as to prove that they had formed part of 
 some building. Further researches showed that, in Ptolemy’s 
 second book of Geography, an island was designated as existing 
 in the immediate vicinity. Such pans as were recovered in a 
 sound state were of coarse materials and rude workmanship— 
 many having very neatly impressed upon them the name of At- 
 tilianus; but fragments of a finer and more fragile description 
 of pottery were likewise brought to the surface; and little doubt 
 remains that, during the time of the Roman ascendency in 
 England, a pottery was established here upon an island which 
 has long since disappeared, and that the person whose name 
 has been thus singularly preserved was engaged in its man¬ 
 agement. 
 
 The high antiquity of the art in China, and the proficiency 
 which had been acquired in its pursuit, several centuries be¬ 
 fore the produce of their manufactories found its way to Eu¬ 
 rope, will be shown in a future chapter. Porcelain of superior 
 quality was likewise made in Japan at an equally early period; 
 and we learn from Propertius, that at a very remote date, the 
 art was commonly practised in Persia, the vessels manufac¬ 
 tured there joining to all the excellencies possessed by the 
 porcelain of China, the quality of resisting the action of fire 
 to a degree which fitted them for being used in the prepara¬ 
 tion of food. 
 
 Most authors who have noticed in any way the state of 
 commerce among the ancients, have referred to the Vasa 
 Murrhina particularly described by Pliny,* and mentioned by 
 various Greek and Roman authors. The general opinion was 
 long in favor of these vases having been the true porcelain of 
 China. This opinion has, however, been examined with con¬ 
 siderable industry and erudition by M. l’abbe le Bland and M. 
 Larcher, in two dissertations,! whereby it is rendered evident 
 that the Vasa Murrhina were formed out of a transparent stone 
 dug from the earth in some of the eastern provinces of Asia.J 
 There is abundant evidence to show that Oriental porcelain 
 was not uncommon in Europe during the first century. The 
 pieces of this manufacture which, according to Pliny, were 
 first seen in Rome, were brought there from Pontus in Asia, 
 by the army of Pompey, 64 years before Christ. 
 
 * Nat. Hist. lib. xxvii. f Mem. de Litterat. tome xliii. 
 
 J Robertson’s Disquis. concerning India, second edit. p. 387. 
 
CHAP. I. 
 
 HISTOKICAL NOTICES. 
 
 21 
 
 Little figures covered with a fine deep-blue glaze, whicU 
 are found deposited with Egyptian mummies, cause it to ap¬ 
 pear that porcelain was made in Egypt in very ancient times. 
 It is a curious fact, that the coloring matter wherewith these 
 figures are ornamented, and which has been subjected to va¬ 
 rious chemical tests, affords every indication of its being oxide 
 of cobalt, the identical substance employed for the same pur¬ 
 pose by the European porcelain manufacturers of our day, but 
 the use of which was unknown to us until a comparatively 
 recent period. The ore of cobalt was formerly thrown aside 
 by the miners of Saxony as useless, or was employed only in 
 mending roads.* 
 
 The Portuguese traders were the means of introducing the 
 fine earthenwares of China into more general use in Europe; 
 and the name assigned to the fabric, as distinguishing it from 
 the coarser descriptions of pottery of domestic manufacture, 
 was most probably given by them —porcellana signifying, in 
 the Portuguese language, a cup. It has been attempted to prove 
 a different origin for the name—attributing this to the resem¬ 
 blance which the glazing or varnish, and probably the colors, 
 of porcelain bear to the shells used in some parts of the East 
 instead of money (couries), and which, from the similarity of 
 their shape to that of the back of a little pig, were also called 
 porcella. 
 
 The possession of porcelain vessels afforded but little insight 
 into the nature of their composition or the mode of their man¬ 
 ufacture, as to which many unfounded theories were from 
 time to time proposed. It was long believed, on the authority 
 of Cardan and the elder Scaliger—who, although violently 
 opposed to each other on various and more important subjects, 
 yet agreed in this—that porcelain was made from a mixture of 
 
 * “ About the end of the fifteenth century, cobalt appears to have been 
 dug up in great quantity, in the mines on the borders of Saxony and Bohe¬ 
 mia. As it was not known at first to what purpose it could be applied, it 
 was thrown aside as a useless mineral. The miners had an aversion to it, 
 not only because it gave them much fruitless labor, but because it often 
 proved prejudicial to their health, by the arsenical particles with which it 
 was combined ; and it appears even that the mineralogical name cobalt then 
 first took its rise. Frisch derives it from the Bohemian word kow, which 
 signifies metal; but the conjecture that it was formed from cobalus , which 
 was the name of a spirit that, according to the superstitious notions of 
 the times, haunted mines, destroyed the labors of the miners, and often 
 gave them a great deal of unnecessary trouble, is more probable. The 
 miners perhaps gave this name to the mineral out of joke, because it 
 thwarted them as much as the supposed spirit, by exciting false hopes and 
 rendering their labor often fruitless. It was once customary to introduce 
 into the church service a prayer, that God would preserve miners and their 
 works from Kobolts and spirits."— Beckmann, Hist, of Inventions, vol. ii. 
 pp. 341, 342. 
 
22 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 broken egg and sea shells, which were preparatively buried in 
 the earth for nearly a hundred years. 
 
 It was not until the beginning of the 18th century that any 
 light was thrown upon the subject. At that time, the Jesuit, 
 Francis Xavier d’Entrecolles, who was residing as a missionary 
 in China, contrived to elude the jealous vigilance so generally 
 practised towards strangers in that country; and not only ob¬ 
 tained specimens of the earths used in the composition of their 
 porcelain, but also acquired some knowledge of the processes 
 employed in the manufacture at King-de-ching. A very cir¬ 
 cumstantial letter was written by the learned father on the 
 subject, and published by Grosier in his general description of 
 China: but owing to a want of practical knowledge on the 
 part of D’Entrecolles, his descriptions proved so defective in 
 many particulars, as to afford little or no assistance; besides 
 which, it was not until some time after the publication of his 
 letter that any substances similar to the earths transmitted by 
 him could be discovered in France. 
 
 About the same time, and while the acquisition of these 
 Chinese specimens was exciting the celebrated Reaumur to 
 their examination, and to the institution of a series of experi¬ 
 ments which will be hereafter mentioned, an incidental dis¬ 
 covery made by the baron de Botticher, a German alchemist, 
 occasioned the establishment of the porcelain manufacture in 
 Saxony. While prosecuting his vain experiments in search 
 of the philosopher’s stone, this man prepared some crucibles, 
 which he observed were caused by the action of heat to assume 
 all the characteristics of Oriental porcelain. Blinded by the 
 avarice which prompted their visionary labors, the adepts of 
 that day seem generally to have turned away from the im¬ 
 portant discoveries that courted their notice, and whicli were 
 thus reserved to reward the patient investigations of more phi¬ 
 losophic minds in latter times. From this reproach De Botti¬ 
 cher is free. The importance of the real discovery thus made 
 was sufficiently apparent, and he had the wisdom to abandon 
 immediately his former pursuit, and to give up the energies 
 of his mind to the establishment of a manufacture, which was, 
 in the end, productive of more beneficial results to himself and 
 to his country, than if he had indeed been successful in his 
 alchemical labors. The world at large did not immediately 
 reap the full benefit of this discovery, as, with a jealousy but 
 too common, the processes used in the Dresden works were 
 veiled in impenetrable secrecy. Up to tire period of De Bot- 
 ticher’s death, in 1719, only white porcelain was made in 
 Saxony; yet the success with which this manufacture was 
 accompanied, occasioned attempts at imitation in France; and 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 23 
 
 porcelain works were established at St. Cloud, and in the 
 Fauxbourg St. Antoine at Paris—the fabrics produced in which, 
 although of beautiful external appearance, were wanting in 
 most of the qualities essential to good porcelain. 
 
 The investigations of Reaumur, already alluded to, were 
 undertaken with more rational views, and prosecuted with a 
 more liberal feeling. The result of his researches was com¬ 
 municated by him to the Academy of Sciences, and published 
 by that body in 1727 and 1729. Having procured specimens of 
 Oriental, Saxon, and French porcelains, and broken them, he 
 proceeded to examine their internal structure. The grain in 
 both the Chinese and Saxon pieces appeared compact, smooth, 
 and shining; while that of the French ware was less close and 
 fine, without lustre, and its grain resembled sugar. He next 
 proceeded to ascertain their habitudes on exposure to great 
 heat in a crucible, and reported, that all the European speci¬ 
 mens were melted, while that of China remained unaltered. 
 This most essential difference led Reaumur to discover the 
 true nature of porcelain, which is a semi-vitrified compound, 
 in which one portion remains infusible at the greatest heat to 
 which it can be exposed, while the other portion vitrifies at 
 that heat, and enveloping the infusible part, produces that 
 smooth, compact, and shining texture, as well as transparency, 
 which are distinctive of true porcelain. Macquer, in his 
 Chemical Dictionary, asserts, that Reaumur was wrong in class¬ 
 ing the Saxon manufacture with the other fusible porcelains 
 of European production; since the materials of which it is 
 composed have always been similar to those of which the China 
 ware is made, one portion being absolutely infusible during the 
 baking - . 
 
 In his examination of the two porcelain earths received 
 from China, which are called in that country pe-tun-tse and 
 kao-lin, Reaumur made a small cake of each substance, sepa¬ 
 rately, and exposed both to the heat of a porcelain furnace. 
 One, the pe-tun-tse, was fused by this means, without any ad¬ 
 dition ; while the other, kao-lin, gave no sign of fusion. He 
 next intimately compounded the two earths, and found, when 
 the mixture was baked, that it had acquired all the qualities 
 of the finest Chinese ware. 
 
 All that was then wanting for the perfect imitation of this 
 admired production was the discovery of materials analogous 
 to the specimen furnished by D’Entrecolles. The search for 
 these was very speedily successful; and the manufacture of 
 porcelain having, from this time, been taken under the royal 
 patronage in France, the works of Sevres produced specimens 
 
24 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 of art which vied successfully with those of Dresden and 
 China. 
 
 Mr. Jonas Hanway, in the account of his travels published 
 in 1753, has given a detailed account of the immense collec¬ 
 tion of porcelain deposited in the Chinese palace at Dresden. 
 
 “ The vaults of this palace,” says Mr. Hanway, “ consist of 
 fourteen apartments filled with Chinese and Dresden porce¬ 
 lain. One would imagine there was sufficient to stock a whole 
 country; and yet they say, with an air of importance, that a 
 hundred thousand pieces more are wanted to complete the in¬ 
 tention of furnishing this single palace. 
 
 “ Here are a great number of porcelain figures of wolves, 
 bears, leopards, &c.—some of them as big as the life—a pro¬ 
 digious variety of birds, and a curious collection of different 
 flowers. A clock is preparing for the gallery, whose bells are 
 to be also of porcelain: I heard one of them proved, and think 
 they are sufficient to form any music; but the hammers must 
 be of wood. 
 
 “ Here are forty-eight large China vases, which appear to 
 be of no use, nor any way extraordinary, except for their great 
 size; and yet his Polish majesty purchased them of the late 
 king of Prussia at the price of a whole regiment of dragoons.” 
 
 One part of this collection must have been peculiarly in¬ 
 teresting, as it exhibited, in an orderly arrangement, specimens 
 of Dresden manufacture laid up by this king of Poland, from 
 the first efforts of De Botticher, through every subsequent 
 gradation; “ an idea,” says Mr. Parke, “ truly philosophical, 
 and which reflects more honor on his memory than the barter¬ 
 ing away the liberties of his subjects for pieces of foreign 
 porcelain.” 
 
 Frederick the Great, when he conquered Saxony, forcibly 
 carried away several of the best workmen from the manufac¬ 
 tory at Meissen, near Dresden, and conveyed them to Berlin, 
 where, since that time, a considerable quantity of very good 
 porcelain has been made for the private advantage of the mon¬ 
 arch. As many as 500 men are constantly employed in this 
 establishment; but although much of their material is drawn 
 from Saxony, the Prussian porcelain has never equalled in 
 quality that of Dresden. 
 
 It is generally believed, that since the time when they were 
 first established by the Romans, potteries have always existed 
 in Staffordshire, but it is certain that until the beginning of 
 the eighteenth century the manufacture was confined to a 
 few objects of the commonest and coarsest description. 
 
 The district in this county wherein the great bulk of Eng¬ 
 lish manufactured earthenware is produced, is situated about 
 
CHAP. I. HISTORICAL NOTICES. 25 
 
 a mile from the borders of Cheshire. The potteries commence 
 at a village called Golden Hill, and extend for a distance of 
 more than seven miles, passing through other towns and vil¬ 
 lages to Lane End. The names of the places comprised in 
 this district, intermediate between the two already mentioned, 
 are Newfield, Smithfield, Tunstall, Longport, JBurslem, Co¬ 
 bridge, Etruria, Hanley, Shelton, Stoke, Lower Lane, and 
 Lower Delf. All these have formerly been sufficiently dis¬ 
 tinct from each other; but the increase of the staple manufac¬ 
 ture of the district has called for the erection of so many new 
 potteries and dwelling-houses, that their individuality has been 
 lost, and to a stranger the whole presents very much the ap¬ 
 pearance of one large town. In every part of the kingdom, 
 except the district itself, the whole are ranked under one 
 general name—that of the Potteries. Etruria is the creation 
 of the celebrated Josiah Wedgwood, by whom the place was 
 thus named after one of the ancient Italian states, celebrated 
 for the tasteful forms it gave to its pottery, specimens of which 
 have materially promoted the improvement of our modern 
 English wares. 
 
 In the year 1686, when Dr. Plot published a Natural His¬ 
 tory of Staffordshire, its traffic in earthenware was very unim¬ 
 portant—being carried on only by the workmen themselves, 
 or by pedlars, who conveyed the pieces in baskets on their 
 backs through the adjoining counties. About the time just 
 mentioned (1690), two brothers, named Elers, came from Nu¬ 
 remberg, in Holland, and settled at Bradwell, where they 
 made an improved kind of red ware, and introduced the art 
 of glazing the vessels by throwing common salt into the oven 
 at a certain period of the baking* Every precaution was 
 used by the brothers to keep their processes secret; and it is 
 probable that this circumstance, joined to the success of the 
 strangers, excited the enmity and jealousy of their neighbors 
 to the degree which obliged them to leave the country. The 
 pretext assigned for this persecution was the alarm occasioned 
 by the fumes from their kilns during the time of glazing. These 
 fears subsided, however, when the process was continued by 
 their successor. This man, whose name was Astbury, had, it 
 is said, become master of their secrets by a singular stratagem. 
 Feigning to be of weak intellect, and assuming an appropriate 
 vacuity of countenance, he obtained employment in the Brad- 
 well works, and submitted to all the drudgery and contumely 
 which were drawn upon him by his supposed imbecility. By 
 
 * The salt is decomposed by this means; and, rising in fumes, the alkali 
 which it contains combines with the silica of the ware, and forms a true 
 glass which covers the entire surface. 
 
 c 
 
26 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 this course of proceeding, he was enabled, unsuspected, to 
 acquire a knowledge of all that was done in the manufactory, 
 and to make models for his own use of all the utensils. 
 
 The advantages of this method of glazing with salt were so 
 apparent, that in a short time it was very generally adopted ; 
 and on Saturday, the day appropriated to this process, the 
 thick fumes from nearly sixty potteries filled the towns to a 
 degree which darkened the atmosphere, and covered the hills 
 of the surrounding district.* 
 
 To Astbury is generally ascribed the introduction of white 
 stone-ware, by the adoption of calcined flints in its composition. 
 The popular version of the origin of this improvement states, 
 that “ while travelling to London on horseback, in the year 
 1720, Astbury had occasion, at Dunstable, to seek a remedy 
 for a disorder in his horse’s eyes; when the ostler at the inn, 
 by burning a flint, reduced it to a fine powder, which he blew 
 into them. The potter, observing the beautiful white color 
 of the flint after calcination, instantly conceived the use to 
 which it might be applied in his art.”f 
 
 The merit of this man has been somewhat overlooked, 
 while contemplating the greater claims to admiration possessed 
 by his more philosophic successor in the course of improvement. 
 That could have been no common mind, however, which led 
 Astbury to the long-continued pursuit of his object, by means 
 so humiliating; and which also enabled him, on the occasion 
 just related, to seize upon a fact thus accidentally presented, 
 and which, although of high importance to his art, might have 
 passed unheeded before the eyes of many a common-place 
 manufacturer. 
 
 The step thus made was of consequence in preparing the 
 way for the far greater advances towards perfection, after¬ 
 wards accomplished by Mr. Josiah Wedgwood. This extra¬ 
 ordinary man owed none of his success to fortuitous circum¬ 
 stances. Devoting his mind to patient investigations, and 
 sparing neither pains nor expense in accomplishing his aims, 
 he gathered round him talented artists from different countries, 
 and drew upon the stores of science for aid in pursuing the ob¬ 
 jects of his praiseworthy ambition. The early and signal 
 prosperity whereby his efforts were attended, served only as a 
 motive urging him forward to new exertions, and as the means 
 for calling forth and encouraging talents in others, in a manner 
 calculated to promote the welfare of his country. Previously 
 to his time, the potteries of Staffordshire produced only inferior 
 fabrics, flimsy as to their materials, and void of taste in their 
 
 * Parke, Ohein. Cat. p. 125. 
 
 t Parke, Chem. Cat. p. 126. 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 27 
 
 forms and ornaments—the best among them being only 
 wretched imitations of the grotesque and unmeaning scenes 
 and figures portrayed on the porcelain of China. But such 
 have been the effects resulting from the exertions and exam¬ 
 ple of this one manufacturer, that the wares of that district 
 are now not only brought into general use in this country, to 
 the exclusion of all foreign goods, which had before been 
 largely imported, but English pottery has since been sought 
 for and celebrated throughout the civilized world, and adopted 
 even in places where the art was previously prosecuted. An 
 intelligent foreigner, M. Faujas de Saint Fond, writing on this 
 subject, says, “ its excellent workmanship, its solidity, the ad¬ 
 vantage which it possesses of sustaining the action of fire, its 
 fine glaze impenetrable to acids, the beauty and convenience 
 of its form, and the cheapness of its price, have given rise to 
 a commerce so active and so universal, that in travelling from 
 Paris to Petersburgh, from Amsterdam to the further part of 
 Sweden, and from Dunkirk to the extremity of the south of 
 France, one is served at every inn upon English ware. 
 Spain, Portugal, and Italy, are supplied with it; and vessels 
 are loaded with it for the East Indies, the West Indies, and 
 the continent of America.”* 
 
 It is not among the least of Mr. Wedgwood’s merits, that 
 he overcame the disadvantages of a defective education ; and, 
 amid the calls of an incessantly active life, found time wherein 
 to school his mind in all the discipline necessary for investiga¬ 
 tions purely scientific. The ample fortune which he acquired 
 was ever ready for promoting the spread of knowledge, en¬ 
 couraging the efforts of genius, and lessening, as far as possi¬ 
 ble, the sufferings of his fellow-creatures. His charities, pub¬ 
 lic and private, and especially in his own district, were ex¬ 
 emplary and consistent. He gave life to many objects of 
 public utility. The Trent and Mersey canal was undertaken 
 and accomplished through his influence; and by the benefits 
 it has produced to the district, and to its proprietors, has fully 
 approved his wisdom in its promotion. 
 
 The principal inventions of Mr. Wedgwood were—1. His 
 table ware; the merits of which are, that it has a dense and 
 durable body, and is covered with a brilliant glaze, capable of 
 bearing uninjured sudden and great vicissitudes of heat and 
 cold. This ware, as it was capable of being manufactured 
 with ease and expedition, could be sold at a cheap' rate, and 
 would still yield a handsome profit to the inventor. Its va¬ 
 rious qualities, so superior to any possessed by previous manu- 
 
 * Travels in England and Scotland (English translation,) vol, i. p. 97 
 
28 PORCELAIN MANUFACTURE. CHAP. I. 
 
 factures of either domestic or foreign production, caused this 
 ware to be taken into immediate and universal favor with the 
 public. Among others, the queen bestowed upon it the tribute 
 of her admiration and patronage ; commanded it to be called 
 queen's ware —a name which it continues to bear to the pres¬ 
 ent day; and honored Mr. Wedgwood by appointing him her 
 majesty’s potter. 
 
 2. A terra cotta , which could be made to resemble por¬ 
 phyry, granite, Egyptian pebble, and other beautiful stones of 
 the silicious or chrystalline order. 
 
 3. Basaltes, or black ware. This was a black porcelainous 
 biscuit, having nearly the same properties with the natural 
 stone. It would emit sparks when struck with steel; was 
 capable of taking a high polish; resisted acids; and would 
 bear, without injury, a stronger degree of heat than even the 
 natural basaltes. 
 
 4. White porcelain biscuit. This ware had a smooth, wax¬ 
 like appearance, and was possessed of all the properties ex¬ 
 hibited by the preceding invention, differing from it only in 
 regard to its color. 
 
 5. Bamboo, or cane-colored porcelain biscuit, of the same 
 nature as the preceding. 
 
 6. Jasper. This was also a white porcelainous biscuit, of 
 exquisite delicacy and beauty, having in general all the prop¬ 
 erties of the basaltes, with this in addition,—that it would re¬ 
 ceive through its whole substance, from the admixture of 
 metallic oxides, the same colors as those oxides communi¬ 
 cate to glass or enamel in fusion. This peculiar property, 
 which it shares with no other porcelain or earthenware body 
 of either ancient or modern composition, renders it applicable 
 in a very pleasing manner to the production of cameos, por¬ 
 traits, and all subjects that require to be shown in bas-relief; 
 since the ground can be made of any color that may be pre¬ 
 ferred ; while the raised figures are of the purest white. 
 
 7. A porcelain biscuit, possessing several properties that 
 render it invaluable to the chemist, and which have occasioned 
 this invention to be brought into general use in all laboratories. 
 The ware is exceedingly hard, being little inferior in this re- 
 pect to agate, whence it is peculiarly adapted for forming 
 mortars. It resists the action of the strongest acids and of all 
 corrosive substances, and has the further quality of being per¬ 
 fectly impenetrable by any known liquid. 
 
 The investigations of Reaumur, already detailed, make it 
 evident that the characteristics of porcelain, as far as they de¬ 
 pend upon semi-vitrification, may be obtained when ingre¬ 
 dients wholly fusible are employed, provided the fire be care- 
 
chap. i. 
 
 HISTORICAL NOTICES. 
 
 29 
 
 fully withdrawn from the oven at the precise moment when 
 vitrification has arrived at, and not proceeded beyond, a certain 
 point. Accordingly, this porcelain was, at one time, very com¬ 
 monly produced both in this and other countries. The quality 
 of goods thus composed is always inferior to that of true porce¬ 
 lain ; and, if further or again exposed to the heat of the fur¬ 
 nace, the substance would entirely change its nature, and run 
 into a vitreous and shapeless mass. 
 
 Porcelain of this description, much esteemed for its beauty, 
 was long manufactured at Bow and at Chelsea. It was not 
 until the year 1768, that Mr. Cookworthy discovered certain 
 mineral substances in Cornwall similar in their properties to 
 the porcelain earths of China; and having secured to himself, 
 by patent, the exclusive right of using those materials, was the 
 first person who made true porcelain in England. 
 
 In practising this art, Mr. Cookworthy, and those to whom 
 he afterwards assigned his patent right, attained to considerable 
 success as regarded the quality of their manufactures, although 
 the demand for their goods did not prove proportionate to the 
 money expended in bringing the processes to perfection. One 
 probable cause for the inadequacy of their remuneration, ex¬ 
 isted in the successful efforts of Mr. Wedgwood, which have 
 been already detailed, for improving the quality of common 
 earthenwares made in Staffordshire, whereby foreign porcelain 
 was rendered less an object of desire, and consequently its suc¬ 
 cessful imitation was no longer considered as being of any 
 great importance. 
 
 The extent to which, in the year 1785, this manufacture had 
 arrived, and its importance to the three great interests of the 
 country—landed, maritime, and commercial—may be collected 
 from the evidence then given by Mr. Wedgwood before a com¬ 
 mittee of the privy-council, and at the bars of the two houses 
 of parliament. The question at that time under the considera¬ 
 tion of the legislature, and upon which these examinations 
 were taken, arose out of the proposal of government to abolish 
 the system of commercial restrictions and disabilities then ex¬ 
 isting between Great Britain and Ireland, and to render the 
 intercourse between the two divisions of the empire nearly as 
 free and unrestricted as that between the counties of Durham 
 and Northumberland; a proposition so perfectly natural and 
 reasonable in itself, that, but for the possession of records 
 wherein they have been preserved, we might really be at a 
 loss to conjecture the nature of the arguments whereby it was 
 opposed and defeated. 
 
 In the course of the discussions to which this subject gave 
 rise in the house of lords, the marquess of Lansdowne, remark- 
 
 C 2 
 
30 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 ing upon the evidence given by the respectable merchants and 
 manufacturers at the bar of the house, declared that the result 
 to which he in his own mind had arrived was the very opposite 
 to the conviction which they had adopted. “ Though much 
 valuable information may,” said his lordship, “ doubtless, be de¬ 
 rived from their evidence, it must not be forgotten that they are 
 men peculiarly subject to prejudice and error, in all cases 
 where their personal interests are concerned. Were any one, 
 for instance, to ask a manufacturer of Halifax, what is the 
 greatest crime upon earth 1 Is it felony, is it murder, is it par¬ 
 ricide I No ! he would answer; it is none of these—it is the 
 exporting of wool.” 
 
 In later times, we have seen this measure of justice and 
 sound policy more successfully brought forward ; and it is ac¬ 
 knowledged that each country has since been reaping benefits 
 in consequence, upon the inevitable arrival of which nothing 
 but the strongest commercial prejudices and national jealousy 
 could have thrown even a momentary doubt. 
 
 Mr. Wedgwood, in the course of the evidence already al¬ 
 luded to, thus remarks :—“ Though the manufacturing part 
 alone in the Potteries, and their immediate vicinity, gives bread 
 to 15 or 20,000 people, yet this is but a small object when com¬ 
 pared with the many others which depend on it; namely, 1st, 
 The immense quantity of inland carriage it creates throughout 
 the kingdom, both for its raw materials and finished goods. 
 2d, The great number of people employed in the extensive 
 collieries for its use. 3d, The still greater number employed 
 in raising and preparing its raw materials in several distant 
 parts of England, from near the Land’s End, in Cornwall—one 
 way along different parts of the coast, to Falmouth, Teignmouth, 
 Exeter, Pool, Gravesend, and the Norfolk coast; the other 
 way to Biddeford, Wales, and the Irish coast. 4th, The coast¬ 
 ing vessels, which, after having been employed at the proper 
 season in the Newfoundland fishery, carry these materials 
 coastwise to Liverpool and Hull, to the amount of more than 
 20,000 tons yearly; and at times when, without this employ¬ 
 ment, they would be laid up idle in harbor. 5th, The further 
 conveyance of these materials from those ports, by river and 
 canal navigation, to the Potteries, situated in one of the most 
 inland parts of this kingdom ; and, 6th, The reconveyance of 
 the finished goods to the different parts of this island, where 
 they are shipped for every foreign market that is open to the 
 earthenwares of England.” 
 
 Mr. Wedgwood very justly observed further, that this manu¬ 
 facture is attended with some circumstances of advantage 
 which are almost peculiar to itself; viz. that the value of the 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 31 
 
 finished goods consists almost wholly in the labor bestowed 
 upon them; that every ton of raw materials produces several 
 tons of merchandise for shipping, the freight being paid, not 
 upon the weight, but according to the bulk; that scarcely a 
 vessel leaves any of our ports whose lading is not in part made 
 up of these cheap, bulky, and, for these reasons, valuable articles, 
 to this maritime country; and that fully five parts in six of the 
 aggregate manufactures of the Potteries are exported to foreign 
 markets. 
 
 Important as were the advances which at that time had been 
 made in the art, Mr. Wedgwood was still of opinion that they 
 could be considered but as the beginning of improvements,— 
 that these were still but in their infancy, and but of little mo¬ 
 ment when compared with those to which the art was capable 
 of attaining, through the continued industry and growing in¬ 
 telligence of the manufacturers, in combination with and fostered 
 by the natural facilities and political advantages enjoyed by the 
 country; an opinion fully borne out by the event, and which 
 our progressive experience shows to have been founded on clear 
 and accurate perceptions. 
 
 The manufacture of earthenwares in England is far from 
 being restricted to the district in Staffordshire which has been 
 described already as having acquired the name of “the Pot¬ 
 teries.” Establishments for making the commoner kinds of 
 wares are to be found in many and various parts of the king¬ 
 dom; at Lambeth, especially, several manufactories of stone 
 pottery have been carried on for considerably more than a cen¬ 
 tury, producing articles which have never been surpassed in 
 any country, either for the excellence of their materials and 
 workmanship, or for the magnitude of the vessels and the va¬ 
 riety of uses to which they are adapted. The Lambeth ware 
 may, in fact, be pronounced perfect of its kind. 
 
 Porcelain has long been made at Derby, and at Coalport, 
 near Colebrook Dale, in Shropshire. Establishments have sub¬ 
 sequently risen in the city of Worcester, wherein very beauti¬ 
 ful specimens are produced ; and yet more recently, the 
 manufacture of excellent porcelain has been engrafted upon a 
 long-established pottery for commoner wares, situated at Swin- 
 ton, near Rotherham, in Yorkshire. At the Rockingham 
 works, which have been so named in compliment to their early 
 patron, the celebrated marquess of Rockingham, porcelain is 
 now produced which vies successfully in every kind of excel¬ 
 lence with that of older English establishments. Among many 
 other specimens which attest the proficiency of the Yorkshire 
 manufacturers, two may be more particularly mentioned, which 
 are deserving of more than common attention as denoting the 
 
32 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. I. 
 
 degree of advancement to which the art lias reached in 
 England. 
 
 One of these pieces is a copy in enamel colors, made on a 
 porcelain tablet, from an original painting by Vandyke, and 
 now in the possession of the noble inhabitant of Wentworth 
 Castle. The subject of the picture is, “ The earl of Strafford 
 occupied in dictating his defence to his secretary.” The exe¬ 
 cution of this copy does justice to the masterly original; and, 
 in regard to expression and coloring, has been pronounced equal 
 to the most admired productions of the Sevres works. The 
 other specimen is remarkable not only for elegance of design, 
 and the goodness of the workmanship, but also because it is 
 believed to be the largest piece of porcelain that has hitherto 
 been made in this country. It is a scent-jar, forty-four inches 
 high, made and fired in one entire piece. The base, or plinth, 
 is triangular, having a circular projection at each angle; from 
 these rise lions’ paws, upon which the globular body of the jar 
 is supported. The scent is allowed to escape through hexag¬ 
 onal openings in the neck. The jar is divided into three com¬ 
 partments, by as many rustic handles of knotted oak; while 
 branches of the same tree, wfith their rich foliage rising from 
 the plinth, are spread tastefully over the lions’ paws, and thence 
 entwining with the handles, rise and encircle the base of the 
 neck. The ornaments of the cover are in keeping with those 
 of the jar, it being covered with branches and foliage of the 
 oak: the whole is surmounted by the figure of a rhinoceros. 
 The three compartments into which the jar is divided are en¬ 
 riched with highly finished paintings in enamel colors, executed 
 by one of the proprietors of the works, from designs by Stothard, 
 the subjects of which are drawn from the admirable romance 
 of Cervantes. The circular projections at the base, and the 
 cover, are adorned with paintings from nature, of six subjects 
 of rare botanical plants, the originals of which are in the con¬ 
 servatories of Wentworth Castle. The whole is relieved and 
 enlivened by ornamental work, in burnished and chased gold; 
 and the work, both in its design and execution, is highly honor¬ 
 able to the artists. 
 
 Up to a comparatively recent period, the manufacture of 
 earthenwares formed one of the very few branches of domestic 
 industry which were left free from the evil effects of direct 
 taxation, and, except in one branch, of very minor importance, 
 the art is still in the enjoyment of this immunity; to which fa¬ 
 vorable circumstance may be imputed much of the signal and 
 uniform success whereby it has been attended. In the year 
 1812, when the duty upon glass bottles was doubled, the manu¬ 
 facturers of these represented to the chancellor of the ex- 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 33 
 
 chequer, that unless a countervailing tax was levied upon stone 
 bottles, the latter, being wholly unburthened, would possess an 
 unfair advantage, and might be sold at prices that would drive 
 glass bottles out of use. This was a line of argument in no 
 wise unpalatable to the minister, who readily caught at the 
 suggestion of a new object for taxation; and a duty of five 
 shillings on each hundredweight was immediately imposed upon 
 all stone bottles the content of which should be two quarts and 
 under. 
 
 The levying of this duty calls for the attendance of revenue 
 officers at all hours on the premises of every stoneware manu¬ 
 facturer throughout the kingdom; and it is very much to be 
 doubted whether, in any one year since its first imposition, the 
 expenses of collection have not more than absorbed the whole 
 amount paid by the potters. The total quantity of stoneware 
 made which is chargeable with the duty does not exceed 600 
 tons annually, and a large proportion of this is used for purposes 
 to which glass has never been applied. It is not very likely 
 that stoneware, the utility of which for many purposes is ex¬ 
 ceedingly great, would ever have been brought into competi¬ 
 tion with a material so much lighter, and in many respects so 
 much more convenient, even had the pottery continued free 
 from the domiciliary visits of the exciseman; and now that the 
 experiment has been fairly tried during nearly twenty years, 
 and has been found unproductive of any real revenue, there 
 can be no sufficient reason for continuing the impost. 
 
 CHAP. H. 
 
 GENERAL DESCRIPTION OF INGREDIENTS USED IN THE MANU¬ 
 FACTURE. 
 
 Different branches of the art.—Ingredients used.—Properties of Alumina.— 
 Its infusibility.—Contraction when exposed to heat.—Wedgwood's Pryom- 
 eter.—Composition of Gems.—Great abundance of Clay.—Properties of Si¬ 
 lica.—Its great abundance.—Sea sand.—Incapable of artificial solution in 
 water.—Dissolved naturally.—Springs at Carlsbad.—Boiling fountain in 
 Iceland.—Fusion of Silex.—Kinds of Clay used in Potteries.—Their vari¬ 
 ous merits.—China clay of Cornwall.—Mode of its preparation.—Its anal¬ 
 ysis.—Cornish Felspar.—Its fusibility.—Steatile.—Earth of Baudissero.— 
 Its analysis.—Cornish sopestone.—Spuma maris.—Its employment in por¬ 
 celain works in Spain. * 
 
 The art of manufacturing pottery and porcelain naturally 
 divides itself into four different and distinct branches: the first 
 of these comprehends a knowledge of the nature and peculiar 
 properties of the various materials, whereof the vessels are 
 composed; the second comprises the methods used in combining 
 these materials, and in fashioning the vessels; the third branch 
 
34 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. II. 
 
 includes the choice and management of the colors and enamels 
 employed in painting and ornamenting the wares, together with 
 the operations necessary for their conversion; and the last di¬ 
 vision embraces the means required for completing the manu¬ 
 facture by the aid of fire. In describing, however, the different 
 stages of the manufacture as they occur, the painting and baking 
 processes must unavoidably be intermingled. 
 
 The chief ingredients employed in the composition of all kinds 
 of pottery are clay and flint: these are both classed by chemists 
 among the primitive earths. The first of them, in its state of 
 purity, is denominated alumina, or oxide of aluminum; and the 
 latter is called silica, or oxide of silicium. It is only since the 
 year 1754 that alumina has been acknowledged as a peculiar 
 substance; and the period is much more recent when the re¬ 
 searches of Davy proved it to belong to the class of metallic 
 oxides. 
 
 It is of great importance to make choice of a suitable kind of 
 clay for the manufacture; but, according to the remark of the 
 celebrated Vauquelin, it is much more important to combine 
 this with a due proportion of flint, as good pottery differs from 
 that which is inferior less in the original quality of its elements 
 than in their proportions. 
 
 Clay is an opaque and non-crystallized body, of dull fracture, 
 soft enough in all states to take a mark from iron; when 
 breathed on it exhales an odor which, from its peculiarity, takes 
 its name from the material, and is termed argillaceous. This 
 is owing to the oxide of iron which is mixed with it, as clay, 
 when absolutely pure, does not emit any odor. Clay forms with 
 water a plastic paste, having considerable tenacity, and which, 
 by the action of heat, is brought to a very great degree of hard¬ 
 ness : it is compact, smooth, and almost unctuous to the touch, 
 and when dry, may be easily polished by the finger. It is not 
 soluble in water, but mixes readily with it in all proportions, 
 parting with difficulty from the last portion of that which it has 
 absorbed: it will adhere to the tongue. The description of clay 
 employed by potters is infusible in the heat of a porcelain fur¬ 
 nace, where some kinds, owing to their being combined with 
 oxide of iron, assume a red color, while others become of a pure 
 white. The highest temperature to which clay can be exposed 
 tends only to increase its density,* hardening its substance and 
 diminishing its volume. This diminution of volume produced 
 by increased temperature is an apparent deviation from the 
 general law of expansion by heat; but the deviation is only ap¬ 
 parent, and is probably produced by the vaporization of liquid, 
 combined with the clay. Mr. Wedgwood found that the dimi¬ 
 nution of volume produced by exposing the clay to these ex- 
 
CHAP. XI. 
 
 Wedgwood’s pyrometer. 
 
 35 
 
 treme temperatures, continued the same after the clay was suf¬ 
 fered to cool, and therefore that its amount admitted of delib¬ 
 erate and accurate measurement. He also supposed (though er¬ 
 roneously) that the shrinkage of the clay was always propor¬ 
 tional to the temperature to which it had been exposed. This 
 led to his well-known invention of the pyrometer, an instru¬ 
 ment for measuring degrees of temperature beyond the range 
 of the common thermometer. The instrument consisted of 
 small cylinders, composed of two parts of the porcelain clay of 
 Cornwall, and one part of pure alumina. These, when baked 
 in a low red heat and then cooled, were constructed of such a 
 size as just to enter between the wider extremities of two 
 brass rods, fixed on a plate twenty-four inches long, half an 
 inch asunder at one end, and three-tenths of an inch at the 
 other. These rods were divided to tenths of an inch, and con¬ 
 sequently each division formed the 240th part of the whole 
 length. The clay cylinders, being exposed to the heat which 
 was required to be determined, were subsequently inserted be¬ 
 tween these bars, and by reason of their contraction they ad¬ 
 vanced between them to a point depending on the amount of 
 their shrinkage. 
 
 This pyrometer, however, has been found to be subject to a 
 fatal defect. The shrinkage of the clay does not depend on 
 the temperature alone of the fire to winch it is exposed, but 
 also on the length of time which the fire has acted upon it. 
 Thus a lesser degree of heat will produce the same shrinkage 
 as a greater degree, provided the clay is exposed to the former 
 for a longer portion of time. The instrument has been, conse¬ 
 quently, long since totally laid aside. 
 
 Some of the most valued among the precious stones, such as 
 rubies, sapphires, emeralds, jaspers, and others, are composed 
 of either alumina or silica, or of the two earths in combination, 
 together with different small portions of lime, or oxide of iron, 
 or magnesia, &c. The different kinds of clay are most abun¬ 
 dantly spread over the globe, forming - in many situations entire 
 mountains, in other places existing in vast beds, and elsewhere 
 lying among other mineral substances disposed in strata. It 
 has been generally held that clay results from the slow decom¬ 
 position of silicious and aluminous rocks, which being acted on 
 by water filtrating through them, their constituent parts have, 
 in the course of ages, been separated ; the lighter and finer por¬ 
 tions remaining united at the top, while the grosser but less 
 tenacious parts have been resolved into sandy deposits. 
 
 Silica, or pure flint, which forms the second material in the 
 composition of pottery, has been considered as a primitive earth. 
 It is of very common occurrence in most parts of the world, in 
 
30 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. II. 
 
 primitive mountains. It is frequently found in great abundance 
 embedded in chalk. In Scotland and Ireland it occurs in second¬ 
 ary limestone. Flint abounds in alluvial districts in the form 
 of gravel: an inexhaustible supply of excellent quality might 
 be collected on some parts of the sea-coast of England, and 
 particularly at and near Brighton, where there is enough of 
 this material, known under the name of shingle, to serve the 
 whole manufacturing wants of England for ages to come, while 
 its removal would be attended with advantage to the place 
 whence it should be taken. Flint is silica in a state nearly ap¬ 
 proaching to purity, its constituents being 
 
 Silica.98. 
 
 Lime.0.50 
 
 Alumina .... 0.25 
 Oxide of iron . 0.25 
 Loss.1. 
 
 100 . 
 
 It is usually gray, with occasional striped delineations occur¬ 
 ring in its substance. It it obtained generally in rolled pieces, 
 but often occurs in irregular shapes. It has internally a glim¬ 
 mering lustre; its fracture is conchoidal, and its fragments are 
 sharp-edged. It is translucent. When two pieces are rubbed 
 together in the dark, they emit a phosphorescent light, and 
 give off a peculiar smell. We are unable to dissolve silex in 
 water. This process is, however, constantly performed by na¬ 
 ture. The investigations of Klaproth enabled him to detect 
 25 grains of silex in 1000 ounces of the principal mineral 
 spring at Carlsbad, in Bohemia; and the celebrated boiling 
 fountain at Rykum, in Iceland, deposits so considerable a quan¬ 
 tity of silicious earth, that a solid cup has been formed around 
 it, rising to a considerable height. This solution of silica is 
 probably owing, in both these cases, to the solvent power of soda ; 
 which is also present in the water. The water from the spring 
 at Rykum used formerly to be projected into the air to the per¬ 
 pendicular height of 60 or 70 feet; but the overthrow of a 
 mass of rock having since partially covered its orifice, the 
 stream spouts out laterally to a distance of 50 or 60 feet. The 
 heat of the liquid, after it has reached the surface, is sufficient 
 to raise the thermometer to the boiling point of water; and 
 there is little doubt that the fluid must have parted with some 
 portion of its heat on emerging into the atmosphere. The ca¬ 
 pability of water, in its dense or liquid state, to assume, under 
 these circumstances, a higher degree of heat than that at which 
 it boils under ordinary atmospheric pressure, may be partly at- 
 
CHAP. II. KIA'DS OF CLAY USED IX POTTEKIES. 37 
 
 tributable to the depth from which it is brought, influenced by 
 the same law that occasions fluids to boil at lower temperatures 
 on the tops of high mountains. Silica is also found existing in 
 solution in the Bath waters. 
 
 The best flints are of a dark gray color, approaching to black, 
 and having a considerable degree of transparency. Those 
 which exhibit brown or yellow spots on their interior surfaces 
 should be rejected, on account of the ferruginous particles 
 which they contain, and which would occasion blemishes in the 
 ware. Those larger masses of flint are always most preferred 
 by the potter, which, being dark and clear within, are covered 
 with a white crust externally. The rolled pieces which are 
 taken from chalk pits are mostly of this description. 
 
 De Saussure asserts that pure silex may be fused at a heat 
 equal to 4043 degrees of Wedgwood’s pyrometer; a degree so 
 far beyond any that has yet been observed, that one is at a loss 
 to know upon what data the assertion is founded. 
 
 The clay principally used in the potteries of Staffordshire is 
 brought to them from Dorsetshire and Devonshire. These 
 earths are both of excellent working quality, and, being free 
 from any impregnation of iron, are valuable for the great white¬ 
 ness which they exhibit when burnt. The Dorsetshire clay is 
 brought from the Isle of Purbeck. It is of two kinds, distinguish¬ 
 ed as brown clay and blue clay: that from Devonshire comes 
 from the southern part of the county, and is also of two distinct 
 qualities, which are known as black clay and cracking clay. 
 The clay from Dorsetshire is considered preferable to that from 
 Devonshire for the potter’s use; so that it commands a price 
 in the potteries equal to one eighth more than the latter. 
 
 The good qualities of brown clay are, that it burns of an 
 excellent white, and is not liable to crack during the process 
 of burning. On the other hand, it is subject to the considera¬ 
 ble imperfection of crazing ,—an evil which induces some man¬ 
 ufacturers to discard it altogether from their works. Crazing 
 is a technical phrase, used to denote the cracking of the glaze, 
 which is believed to arise from the imperfect manner in which 
 this is capable of uniting itself with the clay composing the 
 body of the vessel. This defect of crazing is not, however, al¬ 
 ways referable to the cause here assigned, but may be owing 
 equally to the faulty nature of the glaze, which may not be ca¬ 
 pable of perfect fusion in the heat of the kiln; or it may result 
 from the error of the workmen in withdrawing the wares from 
 the kiln at too early a period, and before they are properly 
 cooled; the glaze, which is in fact glass, requiring great care¬ 
 fulness in this respect for its proper annealing, and being, with- 
 
38 
 
 PORCELAIN MANUFACTURE. 
 
 CHAT. II. 
 
 out it, very liable to crack with every material variation of 
 temperature to which it may be suddenly exposed. 
 
 Blue clay combines the greatest number of good qualities, 
 and is the most generally esteemed, of all the four descriptions 
 here mentioned. It burns exceedingly white, forms a very solid 
 quality of ware, and is capable of being advantageously com¬ 
 bined with a greater quantity of silicious earth, or flint, than 
 any of the other kinds; a quality which is desirable, because 
 the greater the proportion of silica that is used, the whiter will 
 prove the ware : the limit to the use of flint being the inability 
 of the clay to bear it in combination beyond a certain propor¬ 
 tion without cracking. Both these descriptions of clay are 
 much used as ingredients in the manufacture of porcelain. 
 
 Black clay owes its distinctive color to the quantity of coaly 
 or bituminous matter which it holds in combination, but which 
 is entirely consumed and dissipated when the clay is submitted 
 to the heat of the oven, leaving the articles of which it is com¬ 
 posed of a very good white ; and which is, indeed, found to be 
 the more perfect in proportion as the clay has originally been 
 blacker. Cracking clay has acquired its name from an evil 
 property of occasioning the ware to crack while undergoing 
 the first application of fire. To compensate in some degree for 
 this evil, the goods in which it is employed prove of an ex¬ 
 treme whiteness. Much judgment and experience must be 
 brought to the employment of this clay, that its tendency to 
 cracking may be as much as possible corrected by a propor¬ 
 tionate admixture. If clay of any description were dried with¬ 
 out the addition of any other body, after being made sufficiently 
 plastic to be modelled on the potter’s wheel, it must inevitably 
 crack, as the evaporation of its water will occasion it to shrink 
 in the proportion of one part in twelve during the drying. 
 
 Another description of clay, much prized for the manufacture 
 of finer kinds of earthenware and porcelain, was found in Corn¬ 
 wall by Mr. Cookworthy, as already mentioned, and is com¬ 
 monly denominated China clay. This is very white and unc¬ 
 tuous to the touch, and is obviously formed by the gradual dis¬ 
 integration of the felspar of granite. There are found in Corn¬ 
 wall large mountains of this mineral, some of which are thus 
 partially decomposed ; this China clay proves, on examination, 
 to be identical with the kao-lin of the Chinese. It was found 
 by Mr. Gerhard in the course of some experiments upon granite 
 (which is a compound of quartz, felspar, and mica,) that the 
 felspar was melted into a transparent glass, that the mica was 
 found lying under it in the form of a black slag, while the 
 quartz remained unaltered. 
 
 The Ciiina clay of Cornwall is prepared by the clay mer- 
 
CHAP. II. KINDS OF CLAY USED IN POTTERIES. 39 
 
 chants on the spot where it is found. The stone is broken up 
 into pieces of a small size, and then cast into a running stream: 
 there the light argillaceous parts are washed oif and held sus¬ 
 pended in the water, while the more ponderous mica and quartz 
 remain at the bottom of the stream. At the end of the rivulet 
 the water is stopped by a dam, and the pure clay gradually sub¬ 
 sides. When this deposit is completed, the clear water is drawn 
 oftj and the solid matter dug out in square blocks, which are 
 placed on shelves, and exposed to a continued current of air 
 until sufficiently dry to be packed in casks for shipment. This 
 clay, which is then in the state of a fine powder, is very 
 smooth, and of an extreme whiteness. Mr. YVedgwood found 
 by analysis that it contains sixty parts of alumina and twenty 
 parts of silica. The manufacturers are required to pay a much 
 higher price for this than for any other of our native earths, 
 but for some finer purposes it is altogether indispensable. 
 
 A portion of undecomposed Cornish felspar is often added to 
 the clay, on account of its fusibility and tenaciousness, by which 
 it binds, as it were, the whole ingredients more closely together. 
 The fusible quality of felspar is owing to the presence of about 
 an eighth part of potass. If this alkaline substance be sepa¬ 
 rated by decomposition, as is the case with the China clay above 
 described, the fusibility no longer exists, and the body remains 
 unaltered in the greatest heat of a porcelain furnace. The use 
 of this material has of late been very much increased in our 
 porcelain works. It is a curious and very useful fact, that al¬ 
 though neither clay, flint, nor lime can be separately melted, 
 yet when mixed together in due proportions, the mass is fused 
 without difficulty, the one mineral acting as a flux to the other. 
 
 Steatite, or soapstone, has of late years been very much em¬ 
 ployed in the composition of porcelain. When present, in even 
 a small proportion, it limits the contraction of the ware in the 
 furnace. Steatite is a sub-species of mica, which is found 
 abundantly in Cornwall, and is met with also in the island of 
 Anglesea. The mineral which forms the porcelain earth of 
 Baudissero, was long considered to be a superior kind of clay, 
 until it was discovered by M. Geobert that it contains not a par¬ 
 ticle of alumina in its composition. This chemist, on endeavor¬ 
 ing to convert the substance into alum, found, to his great sur¬ 
 prise, that he obtained only crystals of sulphate of magnesia 
 (Epsom salts). Proceeding thence to analyze it carefully, he 
 ascertained its composition to be, magnesia 68, carbonic acid 
 12, silica 156, sulphate of lime 1-6, water 2*8. The soapstone 
 of Cornwall differs from this substance, yielding on analysis, 
 magnesia 44, silica 44, alumina 2, iron 7 - 3, magnesia 15, 
 chrome 1-2. It also contains traces of lime and muriatic acid. 
 
40 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. II. 
 
 In a published letter addressed by M. Proust to M. Vauque- 
 lin from Madrid, mention is made of a beautiful kind of porce¬ 
 lain produced in that city, and which is described to be of a 
 texture even harder than the porcelain of France. Instead of 
 employing the kao-lin, the body of the ware is made with spu- 
 mi maris, a species of pot-stone found in the neighborhood of 
 Madrid, and the glaze is composed of felspar brought from Gal- 
 licia. The pot-stone when taken from the quarry is sufficiently 
 soft to admit of its being cut with a knife like soap. Besides 
 magnesia, silex, and some particles of argil and lime, it con¬ 
 tains a portion of potass, the presence of which, in the com¬ 
 petent opinion of M. Proust, contributes not a little to the su¬ 
 perior quality of the manufacture. 
 
 CHAP. III. 
 
 ON THE PREPARATION OF MATERIALS. 
 
 Dilation of Clay.—Chemical Examination of Water necessary.—Rain Wa¬ 
 ter.—Carefulness of German Manufacturers.—Blunging.—Machinery.— 
 Preparing Flints. — Burning. — Breaking. — Grinding. — Dry Grinding.— 
 Brindley’s Improved Mill —Chert.—Care require! in selecting Grinding 
 Stones.—Dilution of Flint-Powder.—Proper Consistence of Dilution.—Ad¬ 
 mixture in due Proportions.—Affinity of Alumina for Silica.—Slip.— 
 Slip-Kiln.—Method of evaporating superfluous Moisture.—Working the 
 Paste.—Time necessary for tempering it —Proportions wherein Clay and 
 Flint are united. — Difficulty of ascertaining this.—Slapping. — French 
 Manufacturers.—Proportions of Ingredients used by them.—Kao-Lin.— 
 Flint.—Gypsum.—Broken Porcelain.—Calcined Bones.—Tender Porcelain. 
 —Its Composition.—Porcelain Earth used in Berlin.—French Potters buy 
 their Materials ready mixed.—Advances on this Plan.—Ineligible in Eng¬ 
 land. 
 
 In preparing the clay, the first operation of the pottery is 
 that of mixing it with water to the consistence of cream. It 
 is well known, that water collected from springs, and from 
 many streams, contains various foreign matters, some of which 
 would be injurious to the composition of porcelain. It is there¬ 
 fore necessary to examine chemically the properties of water 
 before it is employed for this purpose, in order to make choice 
 of that which is purest; and to correct, by some of the well- 
 known means, any bad qualities that may be present. The 
 French manufacturers are accustomed to employ only rain 
 water, whose near approach to purity fits it for the object In 
 Germany, still more precise in his operations, the manufacturer 
 prepares his materials only twice in the year, at the vernal and 
 autumnal equinoxes; persuading himself that at these seasons 
 there is some peculiarity in the rain which better qualifies it for 
 
CHAP. III. PREPARATION OF MATERIALS. 41 
 
 the purpose of his manufacture. Although the grounds for this 
 nicety are not apparent, it would savor of presumption to at¬ 
 tribute the practice entirely to prejudice. The observations of 
 men practically engaged in manual or chemical operations have 
 frequently led to improvements in processes, long before the 
 reasons whereon these should have been founded have been re¬ 
 vealed by scientific researches. 
 
 The mixing of the clay, which is called blunging , is effected 
 in a trough five feet long, three feet wide, and two and a half 
 feet deep. In order fully to break down the clay, and incor¬ 
 porate it with the water, a long wooden instrument, formed 
 with a blade at one end and a cross handle at the other, is 
 moved violently about in the trough in all directions, so that 
 this becomes an operation of great labor. In large establish¬ 
 ments, where machinery is adopted for the abridgement of la¬ 
 bor, the blunging is thus effected:—The clay is thrown into a 
 cast iron cylinder, four feet deep, and twenty inches in diam¬ 
 eter. Through the centre of this cylinder runs an upright 
 • shaft, furnished with knives placed as radii at right angles to 
 the shaft, but so arranged upon it that their flat sides are in 
 the plane of a spiral thread, so that by the revolutions of the 
 shaft, the knives perform the double office of cutting what¬ 
 ever stands in their way, and of forcing downwards the con¬ 
 tents of the cylinder in the manner of a screw. Another set 
 of knives is inserted in the interior surface of the cylinder, 
 and these extend to the shaft in the centre, parallel to, and 
 corresponding with, the revolving knives: thus the two sets, 
 the one active and the other passive, have the effect of shears 
 in cutting the clay into small pieces; while this, in its reduced 
 state, is at the same time forced through an aperture at the 
 bottom of the cylinder, and transferred to a vat for the purpose 
 of being mixed with water; a process which this previous di¬ 
 viding of the clay is found materially to facilitate. 
 
 The vat where this mixture is performed is likewise of a 
 cylindric form, its diameter being equal to four times its depth. 
 In the centre of this vat, also, a perpendicular shaft is inserted, 
 furnished with cross arms or radii, one below the other. These 
 cross arms are connected by upright staves, giving the appear¬ 
 ance of two opposite gates hung upon the central shaft. These 
 revolve within the cylinder; and as they are partially immersed 
 in the pulp, the constant agitation mixes all the finer particles 
 of clay with the water, while stony particles of greater magni¬ 
 tude fall to and remain at the bottom. The pulp, now mixed to 
 the consistence of cream, is passed off from the vat through a 
 series of sieves of increasing degrees of fineness, which are 
 worked to and fro by machinery ; thus a separation is effected 
 
 D 2 
 
42 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. III. 
 
 between the grosser parts and that portion which is fitted to 
 enter into the composition of the ware. 
 
 The next process is that of preparing the flints. These are 
 first burnt in a kiln constructed for the purpose, and which 
 very much resembles an ordinary lime-kiln, being of a conical 
 shape, and about nine feet deep. While the flints are yet red- 
 hot, they are removed from the kiln, and in that state are 
 thrown into cold water ; by means of which their attraction of 
 aggregation is lessened, so as to facilitate greatly the subse¬ 
 quent operation of grinding: they are next broken, either by 
 manual labor, or by machinery. In the latter case they are 
 placed upon a strong iron grating, and there struck by ham¬ 
 mers, until sufficiently reduced in size to fall through the gra¬ 
 ting to a receiver, whence they are conveyed to the flint mill. 
 
 In order to expedite the process, and at the same time to 
 grind the flints finer, a quantity of water is thrown with them 
 into the mill. Another good attending the presence of water 
 in this grinding operation, is the preservation of the health of 
 the workmen. Before the adoption of this method, the atmo¬ 
 sphere of the room became charged with the finer particles of 
 flint, which, adhering to the lungs, frequently occasioned dis¬ 
 tressing and sometimes fatal diseases to the workmen. This 
 great improvement was effected by the illustrious Brindley, 
 who likewise invented the mill now used in the process. This 
 is a large circular vat, about thirty inches deep, having a cen¬ 
 tral step fixed in the bottom to carry the axis of a vertical 
 shaft. The moving power is applied to this shaft by a crown 
 cog wheel placed on the top. At the lower part of the shaft, 
 and at right angles to it, are fixed four arms, upon which the 
 grinding stones are fixed ; large blocks of stone of the same 
 kind being likewise placed in the vat. These stones are a very 
 hard silicious mineral, called chert, which is found in abun¬ 
 dance in the neighborhood of Bakewell, in Derbyshire. The 
 broken flints being then introduced and completely covered 
 with water, the axis is made to revolve with great velocity, 
 when the calcined flints are speedily reduced to an impalpable 
 powder. 
 
 The nature of the grinding stones used in these flint mills is 
 of considerable importance; for should they contain any calca¬ 
 reous carbonate, they will be abraded ; some part of their sub¬ 
 stance will mix with the flint, and consequently with the body 
 of the wares, and thus occasion very serious injury to the man¬ 
 ufacturer. Some years ago, a very heavy loss was sustained by 
 some potters, who had purchased flints ground in a mill the 
 stones of which contained carbonate of lime. 
 
 When the flints are thus sufficiently ground, the semi-fluid 
 
CHAP. in. PREPARATION OF MATERIALS. 43 
 
 is transferred to another vat, also constructed with an upright 
 shaft furnished with arms or vanes for the purpose of agitation ; 
 and a considerable quantity of water being added, the moving 
 power is applied, and the whole violently agitated. The pr<> 
 cess occasions the grosser and weightier particles to take their 
 place at the bottom, while the finer portion remains in suspen¬ 
 sion above; and in this state is passed for subsidence to a reser¬ 
 voir, whence in due time the supernatant water is drawn off 
 through apertures provided for the purpose. 
 
 The dilution of clay is held to be of the proper consistence 
 for mixing, when a quantity that will fill a pint measure 
 weighs twenty-four ounces; and that of the flints is equally 
 considered suitable for use, when the same bulk is brought to 
 weigh thirty-two ounces. It is by their specific gravities, that 
 is, by the comparative densities of these dilutions, as indicated 
 by weighing an equal bulk of each, that the manufacturer is 
 enabled to ascertain the real proportions of the materials, and 
 to combine them in the degrees which his experience leads him 
 to employ for the composition of various kinds of pottery ; and 
 too much nicety can hardly be given to this important part of 
 his labors. 
 
 The dilutions of clay and flint being brought together in 
 suitable proportions, and intimately united by agitation, the 
 mixture is passed, while in a state of semi-fluidity,“through dif¬ 
 ferent sieves, in order to separate any remaining impuritfes, to¬ 
 gether with such portions as have not been sufficiently ground. 
 By these means the mass presents the utmost uniformity and 
 smoothness throughout. The affinity which alumina has for 
 silica, under all circumstances, is so great, that they will unite 
 ewen in the humid way, forming a kind of mortar; and when 
 this becomes hardened by time, it is thereafter incapable of de¬ 
 composition by the action of the atmosphere. 
 
 This fluid mixture ot clay and flint is called slip, and, after 
 passing through the sieves, is pumped to the slip kiln. This is 
 a kind of trough formed of fire-bricks ; its size varies according 
 to the extent of the manufactory, being of the length of forty 
 to sixty feet, from four to six feet wide, and about twelve to 
 eighteen inches deep. Flues from fire-places pass under the 
 whole extent of the troughs, in which the fluid is made to boil, 
 and the process of evaporation is slowly conducted, so as to 
 produce an uniform consistency throughout the mass. This 
 evaporation must be very carefully attended, and the mass fre¬ 
 quently stirred and turned over, otherwise, from the imperfect 
 manner in which it conducts heat, the portion in contact with 
 the bricks would become improperly hardened, while the re¬ 
 mainder would continue fluid; in addition to which, flint being 
 
44 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. III. 
 
 specifically heavier than clay, the former would in the first part 
 of the process, and while the slip is yet fluid, have a natural 
 tendency to subside to the bottom, and thus render the com¬ 
 position of the mass unequal. 
 
 The evaporation is never carried beyond a certain point in 
 the kiln; for should the mass become too dry, it would be im¬ 
 possible to knead it properly, or to mould it on the wheel into 
 any of the forms which it is desired to create. The place 
 where this evaporation is performed is called the slip-house. 
 
 When the clay or paste is removed from the slip-kiln it con¬ 
 tains a great number of air-bubbles, and must be well incorpo¬ 
 rated together or tempered by working or beating it with 
 wooden mallets. It is next cut with a kind of spade into small 
 pieces, which are thrown upon the mass with all the strength 
 of the workmen, and these operations are persisted in until it 
 is supposed that their further continuance would not bring the 
 whole to a more complete state of consistence. 
 
 The mixture, when brought to this state, should be suffered 
 to remain in a mass for a considerable time before it is used; 
 the material by this course becomes much more intimately 
 united than can ever be effected by mechanical means. It is 
 to be feared that, although the English potters are fully aware 
 of this fact, they yet fail to adopt so eligible a practice, which, 
 as it calls for the employment of greater space, time, and capi¬ 
 tal, is neglected for other advantages, which, if not so great in 
 an extended point of view, are certainly more immediate. 
 
 It is not possible to state the precise proportions wherein the 
 clay and flint are brought together in our English potteries. 
 Each manufacturer has in this respect his own practice, which, 
 esteeming it as the best, he endeavors to keep profoundly se¬ 
 cret ; and, besides, the proportions necessarily vary with the 
 quality and properties which it is desired to give to the manu¬ 
 facture. Yauquelin informs us that silex forms at least two 
 thirds of all kinds of pottery; alumine from one fifth to one 
 third; lime from 1-500th to l-2000th part; and iron from the 
 smallest conceivable quantity up to twelve and sometimes even 
 fifteen per cent. The presence of the two latter bodies is ac¬ 
 cidental, arising from the natural composition of the materials, 
 and in particular the oxide of iron, when present in any sen¬ 
 sible degree, renders the clay unfit for all purposes, except that 
 of forming the common red ware. 
 
 Parkes, whose practical essay on the making of earthenware 
 and porcelain is founded on his own personal observations, 
 made during a residence of some years’ continuance at the seat 
 of manufacture, is yet so little able to be precise upon the sub- 
 
CHAP. III. PREPARATION OF MATERIALS. 
 
 45 
 
 ject of proportions, that he tells us flint forms a fourth, a fifth, 
 or a sixth part by weight of the prepared paste. 
 
 ,JT e t - POrt r 0f th f china - cla y of Cornwall enters into the 
 composition of every better kind of earthenware, except only 
 
 thp m ' C °i°m d S ° rt ; ThiS ln - redient is sometimes added to 
 the mass, and blunged with it, and at other times is blunoed 
 
 eparately and mixed in the required proportion with the slip. 
 
 he clay or paste, when taken for use, undergoes the pro- 
 cess of slapping. This labor is assigned to a man of con- 
 
 who P roceed s by placing a lump weighing 
 n fifty to sixty pounds upon a convenient slab or bench, 
 ihe mass is then cut through with a thin brass wire, one end 
 of which is held in either hand, while the part between is 
 forced through the clay, which separates as easily as if it were 
 cut with a knife; then taking up with both hands the piece 
 thus separated, and exerting his utmost strength, he hurls it on 
 _ ? rest of the mass; and this operation is repeated until the 
 ole lump exhibits a perfectly smooth and close appearance 
 herever it is cut. feo complete is the incorporation of the 
 whole mass by this means, that if, at the commencement of the 
 process, two pieces of clay of different colors are taken, the 
 ump, at its completion, will be of one uniform hue, intermedi¬ 
 ate to the two original colors. This laborious operation is one 
 ot ^e very first necessity, in order completely to expel every 
 air-bubble however minute, remaining in the clay, and wdnch 
 could not be so thoroughly driven out by its previous beating in 
 the larger mass when taken from the slip-kiln. If the air 
 were not thus thoroughly expelled, it would become so much 
 ranfied and expanded in the oven, that it would force out a 
 goods^ 6 ° r J ^ Se anc ^ ky blistering, spoil or much injure the 
 
 Some of the more considerable among the potters, who em¬ 
 ploy steam power for blunging the clay and grinding the flints, 
 perform this operation of slapping by the same agency, savin°- 
 thereby both time and labor. In this case the expulsion of the 
 iir is effected by mechanical pressure, and the office is per- 
 ■ormed with perhaps as much efficiency as by hand. 
 
 , saving undergone all these preparations, the clay is now fit 
 or being shaped upon the wheel or fashioned by the aid of 
 noulds into all the diversified forms which fancy may desire. 
 lhis „ branch of the art is divided into three different depart- 
 : nen s—throwing, pressing, and casting—either of which is 
 ismI according to the form of the article manufactured. 
 
 ie manufacturers of porcelain in France do not use so 
 such secrecy as is preserved in our own potteries, with re- 
 pec either to the materials whereof their w ? are is compound- 
 
46 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. III. 
 
 ed, or to the proportions wherein these are employed. The 
 clay which forms five parts in six of the whole mass, is the 
 porcelain earth already mentioned as being identical with the 
 kao-lin of China; to this are added in certain proportions flint 
 and gypsum (plaster of Paris), both calcined and ground; and 
 fragments of broken porcelain, which must be white, also 
 ground to a fine powder. One rule for forming this composi¬ 
 tion assigns nine parts each of flint and broken porcelain, and 
 four parts of calcined gypsum, to each one hundred parts of 
 porcelain clay. Another authority recommends five parts of 
 gypsum and only eight parts of ground porcelain; while the 
 flint and clay are used in the same proportions as in the first 
 rule. If at any time the manufactory should not afford broken 
 porcelain for the purpose, it is recommended that pieces be 
 compounded, about a quarter of an inch thick, of the other 
 three ingredients, wherein the proportions of gypsum and flint 
 are augmented; and these pieces, having been previously con¬ 
 verted into porcelain by baking, are to be ground and mixed in 
 the above-mentioned proportions with the other ingredients. 
 
 It has of late years been the practice of some English manu¬ 
 facturers to use a considerable proportion of calcined bones, to¬ 
 gether with a small quantity of gypsum, in combination with 
 china-clay, flint, Cornish stone and enamel. By this means 
 porcelain of a brilliant and very transparent white is produced, 
 which, however, is deficient in density, and very liable to crack 
 on the application of hot liquids. 
 
 Several among the chemists and scientific manufacturers of 
 porcelain in France have given recipes for the composition of 
 tender porcelain, although this description of ware is no longer 
 made in that country. 
 
 This kind of porcelain will support, without softening, a 
 greater degree of heat than suffices to melt glass. It is semi¬ 
 transparent, has a vitreous fracture, and returns a clear sound 
 when struck by a hard body. It is harder but not so brittle as 
 glass, and bears, without injury, sudden and very considerable 
 alterations of temperature. 
 
 M. Brongniart recommends a mixture of one part of pure 
 white clay, with three parts of a frit compounded of nitre, 
 soda, alum and selenite (sparry gypsum), together with a large 
 proportion of ferruginous sand and a little common salt. The 
 ingredients of this frit are to be calcined together, and the 
 whole intimately kneaded; when cold, the compound is to be 
 reduced to powder, and in that state mixed with the clay. 
 
 This paste is not so cohesive or viscous as that which forms 
 hard porcelain, and greater carefulness is, therefore, called for 
 in fashioning vessels with it. Lime and selenite, or any similar 
 
CHAP. III. PREPARATION OF MATERIALS. 47 
 
 earths which, if fused by themselves, produce a transparent 
 and colorless glass, may answer the same purpose as the frit 
 just mentioned. In making choice, however, of the compound 
 to be thus used, it must be borne in mind, that the paste must 
 not be more stubborn in resisting fire than the seggars , or 
 vessels wherein it is inclosed during the baking, and no greater 
 proportion of any substance that promotes fusion must he used 
 than can be supported by the clay without having its cohesive¬ 
 ness greatly diminished. 
 
 The porcelain earth used in Berlin is compounded with sili- 
 cious sand and sulphate of lime in crystals. The constituents 
 of their flux are varied in the proportions according to the 
 quality of the ware it is intended to produce. In the greater 
 part of the German manufactories felspar is used, and some 
 employ a calcareous sand. 
 
 When tender porcelain was made in the works at Sevres, a 
 small portion of arsenic entered into its composition. This was 
 found very hurtful to the workmen. Few of the turners or 
 moulders, after following their employment for some years, es¬ 
 caped severe pulmonary complaints; and to this disadvantage is 
 ascribed the order of the French government under which this 
 branch of the manufacture has been discontinued in that estab¬ 
 lishment. 
 
 Individual manufacturers of porcelain in France avoid all the 
 labor of preparing their materials, and purchase these in a 
 state of readiness from establishments at Limoges where the 
 best porcelain earth is found. The price of the compound, 
 when delivered in Paris, or at an equal distance from the place 
 of preparation, does not exceed three sous—about one penny 
 halfpenny of our money—per pound. 
 
 This arrangement must considerably simplify the operations 
 of the manufacturers, and lessens the amount of capital which 
 they must employ in the establishment of their works; but it 
 is doubtful whether the accompanying disadvantages are not 
 fully equivalent to these benefits. There are many reasons to 
 render such a plan ineligible in this country. 
 
48 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. IV. 
 
 CHAP. IV. 
 
 ON THE FORMATION OF UTENSILS. 
 
 Throwing.—Potter’s Lathe.—Thrower.—Mode of Proceeding.—Profiles.— 
 Slurry.—Gauges.—Turning Lathe.—Turning and Smoothing.—Moulding 
 Dishes. &c.—Tools.—Steam Machinery.—Engine-Lathe.—Milled Edges.— 
 Handler.—Formation of Handles, Spouts, &c.—Pressing.—Small Orna¬ 
 mental Figures.—Mode of affixing them.—Method of making Moulds.— 
 Boiled Plaster.—Great use of Gypsum in making Moulds.—Stoves.—Mod¬ 
 elling.—Qualifications requisite for a Modeller.—Increasing Skill of Art¬ 
 ists.—Fostered by Mr. Wedgwood.—Mould-Maker.—Method of his Work¬ 
 ing.—Casting.—Carefulness required in Drying. 
 
 The operation of throwing consists in shaping such vessels 
 as have a circular form, and is performed upon a machine call¬ 
 ed a potter’s lathe. 
 
 This consists of an upright shaft, about the height of a com¬ 
 mon table, on the top of which is fixed a circular piece of wood, 
 whose breadth is sufficient to support the widest vessel that is 
 to be made. The bottom of the shaft runs in a step, and the 
 upper part in a socket a little below the circular board, so that 
 
 Fig. 1- 
 
 the shaft and board turn together. The shaft has a pulley fixed 
 upon it by means of which it is turned, an endless band passing 
 round the pulley from a wheel placed at a short distance, and 
 which is ten times the diameter of the pulley; this wheel when 
 turned by a handle sets the lathe in motion. 
 
 The clay to be thrown is first cut and weighed and formed 
 into a ball. It is then placed on the face of the circular board, 
 which being put in motion, the thrower , dipping his hands from 
 time to time into water, or slip, that the clay may not adhere to 
 them, fashions it first into a long thin column, which he forces 
 again down into a lump, and continues these operations until as¬ 
 sured that no air-bubbles can possibly remain in the body of the 
 clay. He then directs that the speed of the wheel shall be mode- 
 
CHAP. IV. 
 
 FORMATION OF UTENSILS. 
 
 49 
 
 rated, and proceeds to give the first form to the vessel. This 
 is done either by his fingers alone, or with the aid of an instru¬ 
 ment shaped according to the desired form. The instruments 
 employed for this purpose are called profiles or ribs. By the 
 assistance of one of these, the inside is smoothed and made to 
 assume the requisite shape, and any inequalities, technically 
 called slurry, are removed. When it is wished to make any 
 number of vessels exactly similar to each other in shape and 
 dimensions, certain pegs are fixed as a gauge without the cir¬ 
 cumference of the revolving board, but placed in such a man¬ 
 ner, that whenever the plastic clay is brought to coincide at 
 the requisite points with the gauge, the thrower knows that 
 the article has attained the proper dimensions. 
 
 In this manner most circular-shaped vessels are formed. 
 When finished to the artist’s satisfaction, he proceeds to re¬ 
 move his work, cutting it from the lathe by passing a thin brass 
 wire through the lowest part of the clay. The vessel is then 
 lifted off and placed on a board or shelf, where it is left to dry 
 partially before it is farther smoothed and shaped in the turn¬ 
 ing-lathe. 
 
 When the vessel is so far dried as to be in that particular 
 state of hardness well known to the workmen, and which is 
 called the green state, it is in the most favorable circumstances 
 for the performance of the remaining operations of turning and 
 smoothing, for being furnished with handles, spouts, and such 
 appendages as cannot be affixed in its first formation. 
 
 For making circular dishes, plates, saucers, or shallow bowls, 
 and other vessels of that class, a plaster mould is used. This 
 is slightly sprinkled with powdered porcelain, sifted through a 
 fine cloth, and placed on the block which surmounts the upright 
 spindle of the lathe. The block being then set in motion, the 
 clay is fashioned in the first place by the hand of the workman, 
 which presses it against the mould, and afterwards with a pro¬ 
 file to give the requisite internal form. If any ledge or foot is 
 required, it is affixed afterwards with slip, in the manner here¬ 
 after described as employed for joining handles and spouts. All 
 superfluous parts are cut away, and the whole is finished by 
 means of a horn tool and a damp sponge. When sufficiently 
 dry to be taken from the moulds, the edges are pared with a 
 sharp knife, and the pieces are slightly polished by the hand. 
 After this, they are placed in piles of four, six, ten, or more, ac¬ 
 cording to their weight and solidity, and are left to harden, 
 preparatory to their being put in the oven. 
 
 The turning-lathe of the potter is similar to that used by the 
 turner in wood. The end of the spindle has a screw thread, 
 upon which are screwed chucks of wood, tapered in their form, 
 
 E 
 
PORCELAIN MANUFACTURE. 
 
 CHAP. IV. 
 
 60 
 
 and differing in their diameters according to the size of the ar¬ 
 ticle to be turned. The tools employed are of different sizes, 
 from a quarter of an inch to two inches broad, and six inches 
 long: they are made of iron, the cutting end being turned up 
 about a quarter of an inch, and ground to a good edge. 
 
 The vessel to be turned being fixed upon the chuck, and mo¬ 
 tion communicated to the lathe, the turner proceeds to reduce 
 the substance of the clay in such parts as are required, to form 
 rings and rims upon the vessel, and generally to attend to those 
 little niceties of shape which are not easily attainable on the 
 throwing-lathe. When this is completed, a contrary motion is 
 given to the spindle, the turner applies the flat part of his tool 
 to the vessel, and using a gentle pressure, produces the requi¬ 
 site smoothness of surface and solidity of texture. 
 
 In those considerable establishments which are furnished 
 with a steam-engine, the throwing and turning lathes are both 
 actuated by it. To the first of these machines motion is then 
 given by means of two upright cones, placed opposite to each 
 other; the apex of the one answering to the base of the other. 
 One of these cones receives motion directly from the engine, 
 and communicates it by means of a leather strap to the other. 
 By this arrangement the horizontal strap has always an equal 
 tension to whichever parts of the cones it is applied, the en¬ 
 largement of the one answering to the diminishing diameter of 
 the other; but the speed given to the lathe will depend upon 
 the position on the driving cone which the strap occupies: if 
 this is at the small part, the driven cone, and consequently the 
 revolving-board of the lathe, will travel more slowly, and its 
 revolutions will, on the other hand, be accelerated in proportion 
 as the strap is made to occupy the larger part of the driving 
 cone. When the strap takes its position on the largest part of 
 this, it will apply to the smallest part of the driven cone, and 
 the speed of the lathe will be at its maximum. The position of 
 the strap upon the cone is regulated at pleasure by a winch, a 
 boy in attendance upon which follows the directions of the 
 thrower. When the article is finished, the strap is thrown off 
 the driving cone, and the motion of the lathe of course ceases. 
 
 The turning lathes, when actuated by the steam-engine, are 
 arranged in a row, the whole length of the room, through 
 which runs a horizontal shaft, and this has fixed upon it, oppo¬ 
 site to each lathe, a drum, straps on which connect the shaft 
 with the lathes. The speed of the lathes is regulated by pro¬ 
 viding pulleys of different sizes, upon any one of which the 
 strap may be guided by the turner during the revolutions of the 
 spindle. When the turning of the vessel is finished, the strap 
 is transferred to another pulley connected by a crossed 6trap 
 
51 
 
 CHAP. IV. FORMATION OF UTENSILS. 
 
 with the spindle, which by that means has a reversed motion 
 communicated to it, and the article under operation is smooth¬ 
 ed and pdished in the manner already described. 
 
 A milled edge is given to earthenware in what is called an 
 engine lathe , where, in addition to the rotary motion communi¬ 
 cated to the article, it has likewise a horizontal movement to 
 and fro, enabling the workman to make the requisite incisions 
 at proper and definite intervals. 
 
 When the vessels are taken from the turning-lathe, they are 
 delivered to the handler, who fixes upon them handles, spouts, 
 and other appendages of that nature. These are affixed to the 
 vessels by means of slip, with which the parts brought into con¬ 
 tact are moistened. Being then left for a short time to dry, the 
 junction is found to be perfectand with a knife the superflu¬ 
 ous clay is removed from about it: the whole vessel is next 
 cleaned with a damp sponge, which moistens the whole equally, 
 and gives uniformity to its appearance. 
 
 Handles, spouts, and objects of that nature are made with, the 
 aid of a press, consisting of a small metallic cylinder, which has 
 an aperture in the centre of its bottom, to which plugs with dif¬ 
 ferently shaped orifices are fitted. It has also a piston, actuated 
 by a screw, which works through an iron bow attached to oppo¬ 
 site sides of the cylinder. The aperture in the bottom being 
 furnished with a plug of the desired form, and the cylinder 
 charged with clay, the piston is inserted, and by the turning of 
 the screw is forced down upon the clay, causing it to protrude 
 through the aperture in the proper shape. This being cut into 
 lengths, and bent into the required form, is, when sufficiently 
 dry, affixed to the vessel as already mentioned. If the clay is 
 required to take a hollow cylindrical form, as it must for spouts, 
 a pin of the same diameter as it is wished to give the tube is 
 fixed above the centre of the plug. It is obvious that some or¬ 
 namented spouts cannot be made by this means. For forming 
 such, two moulds of plaster must be prepared in the manner 
 hereafter described, one half of the figure being impressed in 
 each of the moulds, which must fit together accurately. Clay 
 is then forced into each mould, and the superfluous quantity 
 being cut away, leaving still a small portion above the level of 
 the moulds, the two are brought firmly together to unite the 
 two halves of the article. The mould is then divided, the clay 
 is removed, and finished as to its form with suitable tools by the 
 workman. This is the operation known under the name of 
 pressing. The moulds for the purpose are made with plaster 
 of Paris, (gypsum, or the native sulphate of lime,) the peculiar 
 fitness of which material for the purposes, arises from its prop¬ 
 erty of absorbing water with very great rapidity, so that the 
 
52 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. IV. 
 
 ware inclosed witliin it speedily dries in a sufficient degree to 
 deliver itself (according to the workman’s phrase) easily from 
 the mould. 
 
 Small ornaments, such as figures, animals, foliage, and the 
 like, are more conveniently made by pressing the clay in pias¬ 
 ter moulds, or otherwise these are made of copper, which must 
 previously be slightly smeared with oil, in order to insure the 
 easy delivery of the ornaments. These are then affixed to the 
 vessel by means of slip, according to the method already de¬ 
 scribed. It is in this manner that drinking jugs are so com¬ 
 monly ornamented with figures in relief. 
 
 In order to prepare the plaster for making moulds, it is first 
 ground between a pair of stones, in a mill exactly similar to that 
 employed for grinding wheat; it is next boiled in order to drive 
 off - the water which forms a considerable constituent part of its 
 natural substance. There is an appearance of absurdity in thus 
 speaking of boiling a dry earthy substance; but the workmen 
 who use the term, are not very far wrong in their expression. 
 To all appearance, ebullition goes rapidly on in this operation, 
 and there is a disengagement of steam as in the boiling of watery 
 fluids. When this process is completed, the substance is al¬ 
 ways called boiled plaster. The evaporation is conducted in 
 long brick troughs, having a fire flue running under their en- 
 tire length, in a manner similar to the slip-kiln. The man who 
 superintends the process, is obliged to wear a handkerchief over 
 his mouth and nostrils, to prevent the passage of any particles 
 of the gypsum to his lungs, or stomach, such a circumstance 
 having been found very prejudicial to health. 
 
 The plaster when thus deprived of its water becomes a soft 
 impalpable powder, but when its natural proportion of water is 
 again added, so strong is its affinity for that liquid, and such its 
 capacity for again combining with itself that portion of which it 
 has been deprived, that it attracts and condenses the whole, and 
 will immediately set into a hard and very compact mass, pecu¬ 
 liarly suitable for the purpose here required. 
 
 The consumption of plaster cf Paris, in making moulds for 
 plates and dishes is so considerable, that in the district compre¬ 
 hending the Potteries, in Staffordshire, many tons are annually 
 worn out and thrown away as useless. 
 
 Articles placed in these moulds part with moisture so rapidly, 
 that when put in a very temperate stove, they will become dry 
 enough for removal in two hours, and each individual mould is 
 capable of being used for forming four or five different articles 
 in the course of a working day of twelve hours. The stove 
 wherein these moulds, with their contents, are placed to dry, is 
 a small room built with bricks, and having wooden shelves 
 
CHAP. IV. 
 
 FORMATION OF UTENSILS. 
 
 53 
 
 ranged round it, and over one another from the floor nearly to 
 the ceiling; it is heated by warm air conducted through it in 
 an iron pipe. 
 
 Moulds for producing simple wares, such as plates and dishes, 
 and generally for such objects as are formed by pressing, are 
 simple in their construction; but others, which are used for the 
 third department, that of casting, call for much more art and 
 skill for their invention and execution. For these, the taste of 
 the modeller is put in requisition, calling for the exertion on his 
 part, of a high degree of skill and ingenuity in forming patterns, 
 and adapting to them appropriate ornaments. To be a perfect 
 modeller, in the higher branches of the art, a man should have 
 an acquaintance with the best productions of the classic climes 
 of Greece and Rome; he should be master of a competent 
 knowledge of the art of design; his fancy glowing with ori¬ 
 ginality, tempered and guided by elegance and propriety of 
 feeling, and restrained by correctness of taste and judo-ment. 
 To a man thus gifted, the plastic and well-tempered material 
 wherewith he works offers little of difficulty in the execution 
 of his conceptions. 
 
 In the most considerable works, and where the proprietors 
 are ambitious of excelling, modellers are kept in constant em¬ 
 ployment. Other manufacturers content themselves with buy¬ 
 ing new moulds from artists who compose them on speculation, 
 and who are sometimes so little scrupulous as to dispose of the 
 same pattern to several different purchasers. 
 
 For want of due encouragement, high degrees of excellence 
 in this art were formerly not of frequent occurrence. Mr. 
 Wedgwood, to whom the porcelain manufacture of England 
 owes so many and such various benefits, proved that talent in 
 this branch of art needed only for its development to be fostered 
 and encouraged with liberality. This patriotic individual paid 
 the sum of four hundred pounds to Mr. Webber for modelling 
 the Portland or Barberini vase, although the work called for no 
 original or inventive powers. Since that time, English model¬ 
 lers have attained to such a degree of excellence, that it is said 
 any good modeller, with one qualified assistant, would be able 
 to achieve, in the short space of two weeks, the task which oc¬ 
 cupied Mr. Webber for many months, and which was viewed, 
 at the time, as an honorable proof of both his talent and in¬ 
 dustry. 
 
 The model, when moulded by the hand, must be trimmed, 
 carved, touched, and retouched with suitable tools, constructed 
 of metal or wood, and sometimes even of ivory, for the more 
 perfect finishing of the whole composition. 
 
 When thus completed, the model passes into the hands of the 
 
 E 2 
 
64 PORCELAIN MANUFACTURE. CHAP. IV. 
 
 mould-maker, whose occupation is quite mechanical and distinct 
 from that of the modeller. A strong casting of clay is first 
 formed and securely fixed round the model, leaving sufficient 
 space between for the substance of the mould. Proper propor¬ 
 tions of plaster of Paris and water are then placed in a jug, and 
 the mixture is briskly stirred, so that the water may thoroughly 
 pervade the whole, which is then poured gently upon and 
 around the model, covering it in every part to the requisite de¬ 
 gree of thickness. Upon this some heat is sensibly given out 
 by the plaster, and the whole is very shortly converted into a 
 hard compact mass, easily separable from the model, and found 
 to exhibit a perfect impression of its form, and the minutest 
 niceties of its ornaments. The mould is, after this, placed in a 
 stove to be thoroughly dried, and is then fit for use. 
 
 Many articles were formerly made by casting, which are 
 now produced by the operation of pressing last described. 
 Casting is now employed only for the formation of irregular¬ 
 shaped vessels, where much nicety is required, and which need 
 not have much strength. The casting operation is performed 
 by intimately mixing the united clay and flint with very pure 
 water to the consistence of cream. On pouring this dilution 
 into the mould, the plaster quickly absorbs water from that por¬ 
 tion which lies in contact with its surface, hardening it to such 
 a degree, that on the central and still fluid part being poured off, 
 a coating of clay will remain attached to the mould. This 
 coating having been allowed further to dry during a short time, 
 a second charge of diluted clay, but the consistence of which is 
 much greater than the creamy fluid first used, is poured in, and 
 adds to the substance of the first deposit. Having remained in 
 the mould sufficiently long for this purpose, the remainder of 
 the semi-fluid is poured ofl, and the mould, with its contents, is 
 set in a stove: when sufficiently dry to allow of separation, the 
 article is taken from the mould, and left until it is brought to 
 the green state, when all imperfections are rectified by the 
 workman, whose skill is exerted to render the vessel as smooth 
 and as perfect as possible. 
 
 It is essential to the excellence of all kinds of earthenware, 
 that the means used for drying it previous to the baking should 
 produce an uniform evaporation throughout its entire substance. 
 If too much heat were artificially employed, the surface might 
 be hardened, while the internal part remained moist; and this 
 would be attended with disastrous consequences in the oven, 
 owing to the unequal contraction that would then ensue. It is, for 
 this reason, necessary to allow time for the gradual dispersion 
 of moisture, which, however, may be advantageously expedited, 
 
CHAP. V. OF FIRING AND GLAZING. 55 
 
 by placing the pieces upon plaster shelves, whose absorbent 
 property would occasion the requisite drying in a shorter time, 
 and with increased regularity and uniformity. 
 
 CHAP. V. 
 
 ON THE PROCESSES OF FIRING AND GLAZING. 
 
 Seggars.—Proper Materials for these wanting in England.—Not so in 
 France.—Nungarrow Work.—Why discontinued.—Great Estimation of 
 its Wares.—Cause of Superiority.—Use of Seggars.—Their Forms —Mode 
 of using them.—Sevres Manufactory.—Improved Furnace—Its advan¬ 
 tages.—Description.—Chinese Method of Firing.—Construction of their 
 Kilns.—Care required in Baking.—Duration of Process.—Oven-Man.— 
 Trial Pieces.—Annealing.—Biscuit.—Wine Coolers.—Glazing.—Compo¬ 
 sition of Raw Glazes.—Bad effects of some of thesp to the Public.—To the 
 Workmen.—Pernicious use of Ardent Spirits.—Glazes invented by M. 
 Chaptul.—Bv Mr. Rose.—Porcelain Glazes.—French Glazes.—Palissy.— 
 His Experiments on Enamelling.—His Perseverance and Sufferings.—His 
 Success, and continued Firmness under Persecution.—Inferior Glazes.— 
 Low-priced Wares.—Gloss-Oven.—Regulation of Temperature.—Qualities 
 that determine the Excellence of Porcelain.—Stone-Ware.—Its Compo¬ 
 sition—Lambeth Potteries.—Modes of Glazing. 
 
 In the state whereto the vessels are now brought, they are 
 ready to undergo the first application of fire in the oven. For 
 this purpose they are placed in deep boxes called seggars, 
 made of a mixture of fire clay and old ground seggars, which 
 should be well baked, and capable of sustaining the most in¬ 
 tense degree of heat without being fused. The porcelain 
 manufactures of this country labor under a considerable disad¬ 
 vantage in this respect, being unable to procure materials for 
 the construction of these cases that will sufficiently withstand 
 the direct heat of the furnace. This difficulty does not occur 
 in France, a fact which is assigned by our potters as one prin¬ 
 cipal reason for the better quality of French porcelain. 
 
 A porcelain manufactory was carried on some years since 
 at Nungarrow in Wales, but which is now discontinued. The 
 wares produced in these works were perhaps superior in quality 
 to any porcelain that hitherto has been made in any other part 
 of this country. No expense was spared either in the procure¬ 
 ment of materials, or in conducting the various processes; and 
 the want of success on the part of the spirited proprietors is 
 referrible solely to the deficiency of public patronage, it being 
 found impossible to procure a price for the goods which could 
 adequately meet the cost of their manufacture. Since the dis¬ 
 continuance of this establishment, the excellent quality of its 
 wares has been more justly estimated, and the prices which 
 are now eagerly given by amateurs and collectors for pieces 
 
56 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. V. 
 
 of Nungarrow porcelain, are out of all proportion greater than 
 were originally demanded by the makers. 
 
 The materials of which this porcelain is composed are of the 
 most refractory quality, and it is understood that success in 
 their conversion was only attained through the expensive 
 measure of sacrificing the seggars employed, which, owing to 
 the high degree of heat whereto they were exposed, could 
 never be placed a second time in the furnace. 
 
 The office of the seggars is to protect the wares while being 
 baked from the direct application of flame and from smoke ; 
 the heat is somewhat modified in its transmission through 
 them, and applies itself uniformly to each part of the vessels. 
 The cases are made of various shapes, sizes, and depths, to suit 
 the different pieces they are to contain, and some judgment is 
 required in their composition, to fit them for the several kinds 
 of pottery. 
 
 To prevent any adhesion of the pieces to the seggars, the 
 flat bottom of each is covered with a thin layer of fine white 
 sand. That this even may not adhere to the porcelain, the 
 Chinese strew over the sand some dry kao-lin in powder. 
 Pieces of any considerable size must each be inclosed in a sep¬ 
 arate case, but smaller objects, such as cups or saucers, may be 
 placed together to the number of six or twelve, but in no case 
 must one piece be placed in or on another in the seggar, and 
 all must be so arranged that the heat will be equally applied to 
 every part of each. 
 
 In some instances seggars are made having triangular holes 
 in their sides, for the purpose of admitting prisms of the same 
 form, which are inserted therein, horizontally, in order to sup¬ 
 port a greater number of pieces in a state of isolation within 
 each case than could be accomplished by other means. The 
 prisms thus used must be compounded of the same materials as 
 the cases themselves. This course is not pursued except with 
 common articles, and is adopted with the intention of economiz¬ 
 ing the time, space, and fuel employed for baking them. 
 
 If the clay whereof they are composed be well chosen and 
 carefully managed, the seggars may be placed from fifteen to 
 twenty several times in the furnace before they are rendered 
 useless. 
 
 Some art is required so to dispose the cases within the oven, 
 with reference to their shape, size, and the objects they con¬ 
 tain, that the heat shall be distributed as faithfully as possible, 
 and that the sufficient baking of all the different-sized vessels 
 shall be accomplished during the same time. The largest and 
 coarsest pieces are usually placed on the floor of the oven, 
 which must be previously covered with a layer of sand. If the 
 
CHAP. V. 
 
 OF FIRING AND GLAZING. 
 
 57 
 
 heat be not faithfully distributed through the whole area 
 some pieces would be injured by excessive firing, while others 
 would be inadequately baked. The bottoms of the sepals 
 being flat each as it is placed upon another, forms a cover to 
 that beneath, and the entrance of smoke is further prevented 
 by placing a ring of soft clay on the upper rim of each case. 
 In tms manner the seggars are built one upon another untii 
 they reach nearly to the top of the oven : the upper seggar £ 
 each pfie IS always empty. Each of these piles, as it stahds is 
 caHed a bung; in building them up, intermediate spaces ’of 
 
 throuohout mUSt be lett f ° r the circuJation of heated air 
 
 the privi j e fff s 50 lon §- enjoyed by the royal manu- 
 
 ctoiy at Sevres, and which were accompanied by correspond- 
 
 flTu Ch T pkCed K by tbe French government y upon prwa'e 
 establishments, must have been upon the whole prejudicial to 
 the progress of the art in France, these regulations had yet in 
 some respects a contrary tendency. Being secured in a^reat 
 degree from the effects of competition from without, the di¬ 
 rectors of the royal works were enabled to prosecute experi¬ 
 ments with regard to improvements in their utensils and pro- 
 f sses f Prom ^e adoption of which they might otherwise have 
 
 nea? fn 7 cons;deratl ons of expense. Suggestions ap¬ 
 pear to have been continually made, having such improve¬ 
 ments for their object, by men who enjoyed the highest scien- 
 
 dtJced ° nS ’ and the f U , CCeSS ° f plans thus P r oi i0se d. con¬ 
 duced to the increasing celebrity of the establishment 
 
 formTf 0 lers ’ “*1 d |. Montl P rn y and Macquer contrived a 
 form of furnace, which effected at the time of its adoption a 
 very great advantage. In that previously used (and the con¬ 
 struction of which had been copied from those employed in 
 Saxony,) the heat was so unequally distributed, that it was 
 necessary to vary the composition of the porcelain so as to ren- 
 ler it suitable to different parts of the furnace. The improve¬ 
 ment here noticed occasioned the sufficient equalization of heat 
 iroughout its area, and a great inconvenience was at once and 
 lompfetely remedied. 
 
 The arrangement whereby this important change was ac¬ 
 complished will be understood by a reference to the following 
 igures, which describe the elevation, section, and plan of the 
 
 , ide sam ® letters are employed to denote similar parts 
 o the different figures. " 
 
 . ^ is t} ? e i " ter , ior area of the kiln. This is fourteen feet 
 ight inches high, and eight feet three inches in diameter: 
 
 | he walls should be three feet thick. BBBB are four air-flues 
 hiaced at equal distances m the circumference. CCCC are 
 
58 PORCELAIN MANUFACTURE. CHAP. V. 
 
 hearths one foot below the base of the kiln: the heat from 
 these passes towards its centre. DDDD are openings, eigh¬ 
 teen inches square, for the reception of the fuel. These open¬ 
 ing-. 2. 
 
 ings are provided with mouth pieces of plate iron. E is a 
 door-way in the side of the kiln: its sill is three feet above the 
 
 Fig. 3. 
 
 ground; its width is two feet, and its height five feet sis 
 inches. This door is used for the introduction of the seggan 
 within the kiln, after which it must be securely walled up. f 
 is a square hole, of which there are three in the entire cir¬ 
 cumference. These are designed for the introduction of trial 
 pieces within the kiln: another similar opening is left when 
 
CHAP. V. OP FIRING AND GLAZING. 59 
 
 walling up the door-way E. The whole of these are provided 
 with clay stoppers which exactly fill the holes, and which have 
 projections whereby they can be removed or replaced at plea¬ 
 sure. G is the chimney in the centre of the dome-shaped roof; 
 it is of a conical form, eighteen inches diameter at the base, less¬ 
 ening to twelve inches at the top. HH represent four air- 
 
 Fig. 4. 
 
 a 
 
 loles, placed over the openings F. These air-holes serve to 
 livide the draught, and consequently to equalize the tempera- 
 ure of the kiln. I is a round iron plate, supported on four 
 •illars of the same metal, and placed over the chimney to de¬ 
 end the opening. 
 
 When the firing has been sufficiently performed, no more 
 uel is added, and so soon as the smoke from that already upon 
 he hearths has passed away, the mouth pieces are entirely 
 losed to prevent the passage of air. Shortly after this, the 
 himney G and the air-holes H are also carefully closed, and 
 le kiln is left, that the cooling of its contents may go forward 
 s slowly as possible. 
 
 Previously to the adoption of this improvement, the kiln em- 
 loyed for baking porcelain was always made of a rectangular 
 >rm, having only one fire-place and one air-flue, which stood 
 t the side opposite to that whereon the chimney was placed: 
 a arrangement which rendered quite inevitable the before- 
 lentioned inconvenience, arising from the unequal distribution 
 'heat. 
 
60 PORCELAIN MANUFACTURE. CHAP. V. 
 
 The extension of the art, and the consequent competition 
 among the manufacturers in France since the return of peace, 
 have compelled them to use the utmost economy in their vari¬ 
 ous processes; so that, while the quality of their goods has been 
 fully sustained, the prices have been importantly lowered. 
 These savings have been partly realized through the increased 
 skill of the workmen, but are more referrible to the smaller 
 proportionate quantity of fuel consumed, which has arisen, not 
 from any further improvement in the form of their kilns, but 
 through a better arrangement in filling them, whereby they are 
 now made to contain, at each baking, nearly one third more of 
 pieces than was formerly customary. 
 
 The potter’s oven is now always made of a cylindrical form, 
 and very similar to the common kilns used for burning tiles, 
 with the external appearance of which every one is familiarly 
 acquainted. The furnace mouths of the oven are placed at cer¬ 
 tain intervals around it; from these the fire and heated air pass 
 into horizontal flues in the floor, and thence ascend through all 
 the interstitial spaces between the bungs, until the surplus heat 
 escapes through an aperture in the centre of the roof. 
 
 The Chinese subject the greatest part of their porcelain to 
 only one firing, drying the pieces sufficiently in the air to pre¬ 
 pare them for glazing. This plan they are able to pursue, be¬ 
 cause the nature of their materials is such as to resist the en¬ 
 trance of water. Their glaze, the composition of which will 
 be hereinafter described, is much superior to any used in Euro¬ 
 pean potteries, but requires the most intense degree of heat for 
 its fusion, and considerable art is consequently required for the 
 management of the fire, as well as in the construction of their 
 ovens. These are built in a most substantial manner, so that 
 when the fire is at its greatest height, the hand may be applied 
 to the outside without any fear of burning. The draft is pro¬ 
 moted by placing the oven at the extreme end of a long narrow 
 passage, which acts as a funnel in supplying air for supporting 
 combustion, the intensity of which is regulated by four or more 
 side apertures, or registers, which are opened or shut according 
 as the heat is required to be augmented or moderated. The 
 hearth is placed in front, and occupies the whole breadth of the 
 oven. The pieces which are placed in seggars, are artfully 
 disposed in the oven, in the manner already described as follow¬ 
 ed in England. When the fire is lighted, the furnace door is 
 walled up, leaving only an aperture large enough for the intro¬ 
 duction of fuel. The heat is raised gradually during about 
 thirty hours, after which time fuel is incessantly supplied by 
 two men, who relieve each other at intervals. The wood used 
 for this purpose is very carefully dried and cut into slender bil- 
 
CHAP. V. OF FIRING AND GLAZING. 61 
 
 lets about one foot in length, that their combustion may be ef¬ 
 fected with greater rapidity. 
 
 Great attention is necessary for properly conducting the op¬ 
 eration of baking. Vauquelin observes that the heat must be 
 sufficient to expel all the moisture, and occasion the cohesion 
 of the parts whereof the paste is composed; but that, if carried 
 too far, the texture of the ware becomes too homogeneal, and it 
 is rendered brittle. It requires a degree of heat sufficient to 
 melt silver (4717° Fahrenheit) in order to expel the last portion 
 of water from clay: when this has been effected, it is found 
 that the weight of alumina is diminished forty-six per cent. 
 
 The process of baking usually lasts from forty-eight to fifty 
 hours, during which time the heat is gradually increased; as it 
 would be injurious to apply a very high degree at first. In order 
 to ascertain when the baking has been carried far enough, the 
 oven-man places trial pieces in different parts of the oven, but 
 so disposed that they can readily be taken out for examination. 
 These pieces are rings made of common Staffordshire fire clay, 
 which is found to have the property of changing its color with 
 each accession of temperature. By comparing these rings, 
 therefore, with pieces of the same clay which have previously 
 been sufficiently baked, and which serve as a standard, the ac¬ 
 tual progress of the wares in the oven may at any time be ascer¬ 
 tained precisely, and with less trouble than attends the use of 
 Wedgwood’s pyrometer. When the appearance of these trial 
 pieces is judged satisfactory, the firing is discontinued, the fur¬ 
 nace and ash-pit doors are closed, and the oven, with its con¬ 
 tents, left to cool gradually during twenty-four or thirty hours. 
 It is not necessary to delay the withdrawing of the pieces from 
 the oven, until they have become quite cold; but the sudden 
 alteration of temperature would occasion them to crack, if they 
 were taken out while their heat was greatly above that of the 
 atmosphere. 
 
 Some potters are occasionally tempted, when the furnace 
 contains articles of small value, to risk the damage here men¬ 
 tioned. and to withdraw the seggars with their contents with¬ 
 out delay, their object being to profit by the heat of the furnace 
 either for introducing a new charge, or for drying a fresh set of 
 seggars. No one, however, would be so improvident as to ex¬ 
 pose the finer descriptions of porcelain to this hazard, in order 
 to gain any such immaterial advantage. 
 
 From the similarity of its appearance to well-baked ship 
 bread, the ware is now called biscuit. Its permeability to 
 water when in this state fits it for being employed in cooling 
 liquids. If previously soaked in water, the gradual evaporation 
 from its surface by means of the air, causes an absorption of 
 
 F 
 
62 
 
 PORCELAIN MANUFACTURE. 
 
 CHAR. V* 
 
 heat from the surrounding atmosphere, which is again supplied 
 by neighboring objects, until an equilibrium of temperature is 
 restored. 
 
 The proprietors of potteries are accustomed to furnish vases, 
 urns, and other pieces of ornamental shapes, in the state of bis¬ 
 cuit, to ladies who exercise their taste and ingenuity in embel¬ 
 lishing them by painting and gilding. Being then returned to 
 the manufacturer, the glaze is applied, the baking is finished in 
 the gloss oven, and the gilding is burnished by means that will 
 be described hereafter. 
 
 If it were attempted to apply the glaze to articles of porcelain 
 and earthenware, without their previous conversion into biscuit, 
 their texture and shape would be injured by the absorption of 
 water from the glaze. Neither would it, for the same reason, 
 be possible to ornament the ware by painting, or to transfer pat¬ 
 terns to their surface by printing. There is another reason 
 given for the necessity of this previous baking, in the greater 
 contractibility of the clay than of the glaze, which would crack 
 or peel of!' if the limit of contraction had not been previously 
 attained. It will be remembered that the shrinking- of clay 
 upon the application of heat is permanent, and that no altera¬ 
 tion of its bulk will occur, unless it be subjected to a still higher 
 degree of temperature. By limiting, therefore, the heat of the 
 gloss oven in which the baking is finished, below that applied 
 to the biscuit, the evil of cracking the glaze, through the con¬ 
 traction of the ware, is avoided. 
 
 The glaze usually employed for common kinds of earthen¬ 
 ware is compounded of litharge of lead and ground flints, in 
 the proportion of ten parts by weight of the former to four parts 
 of the latter. Cornish granite is sometimes substituted for 
 flint, and used in the proportion of eight parts to ten of litharge. 
 This method of glazing is objectionable, on account of the injury 
 which, notwithstanding every precaution that can be taken, it 
 occasions, in its application, to the health of the workmen em¬ 
 ployed, who frequently are seized with paralysis; and because 
 the lead, which is soluble by means of acids, and highly pois¬ 
 onous, renders vessels thus glazed improper for preparing or 
 containing many articles of human food. 
 
 The bad effect of raw glazes upon their health, is greatly 
 lessened to the workmen when they can be brought to the fre¬ 
 quent use of ablutions. In every pottery the men employed in 
 glazing should be, and in most establishments they are, plenti¬ 
 fully supplied with soap, which they are enjoined to use on 
 every occasion of quitting their work. Unfortunately, however, 
 the workmen themselves have become erroneously impressed 
 with a belief in the superior efficacy of ardent spirits in ward- 
 
CHAP. V. 
 
 OF FIRING AND GLAZING. 
 
 63 
 
 ing off or counteracting the poisonous effects of lead, and fly to 
 the use of this as a specific, to a degree which too often proves, 
 both physically and morally, worse than the evil which it is in¬ 
 tended to prevent. 
 
 The mixtures just mentioned are called raw glazes; their 
 employment is convenient to the potter because of their cheap¬ 
 ness and extreme fusibility. Flint, which remains unaffected 
 in the focus of the most powerful lens, is, when combined with 
 lead, melted and vitrified at a comparatively low heat. The 
 method of using this glaze is to reduce the ingredients to the 
 state of a fine powder, and throw them into as much water as 
 will make them of the consistence of thin cream. The mixture 
 must be well stirred, that the powders may be always kept uni¬ 
 formly blended throughout the fluid. The pieces are first brush¬ 
 ed to free them from dust, and then merely dipped into the liquid 
 and withdrawn, when they must be turned rapidly about in all 
 directions, that the glaze may flow equally over the whole sur¬ 
 face. The superfluous liquid having been allowed to drain oft' 
 for a few seconds, and the pieces having been set on a board 
 during a few minutes, theyare ready for insertion in the seggars. 
 
 Chaptal, in his “ Chemistry applied to the Arts,” has given a 
 process for forming white enamel, which answers well for gla¬ 
 zing the superior kinds of earthenware and tender porcelain. 
 Equal parts of lead and tin are kept in fusion until completely 
 oxidated. The powder thus formed is ground with water, all 
 impurities are removed by repeated washings, and being dried 
 it is kept for use. The whitest flints are then chosen, and fused 
 with carbonate of potash, the latter being in such proportion to 
 the flint, that the mixture will be soluble in water. To the 
 solution of flint thus made, muriatic acid must, from time to 
 time, be added, until no further precipitation occurs. The 
 precipitate thus obtained is pure silex, which, being washed and 
 dried, is also fit for use. If then one part of this silex, and one 
 part of the metallic oxide, be added to two parts of carbonate of 
 potash, and the whole be fused in a crucible, the mass need only 
 be reduced to a fine powder to prepare it for use in glazing. 
 
 Mr. John Rose, of the porcelain works at Coalport in Shrop¬ 
 shire, speaks in commendation of a glaze for hard porcelain 
 which he has used for some time, and which having been ex¬ 
 amined by competent artists, at the request of the Society of 
 Arts, has been reported on very favorably. Mr. Rose’s glaze 
 is composed of 27 parts of felspar, 18 of borax, 4 of Lynn sand, 
 3 of nitre, 3 of soda, and 3 of the China clay of Cornwall. This 
 mixture is melted together and ground to a fine powder; 3 parts 
 of calcined borax being added previously to the grinding. 
 
 Glazes for porcelain and the finer kinds of earthenware are 
 
64 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. V. 
 
 generally made with white lead, ground flints, ground flint- 
 glass, and common salt; Lynn sand combined with soda, as a 
 flux, being frequently added to the ingredients just mentioned. 
 Almost every manufacturer uses a peculiar glaze, the recipe 
 for which is kept secret by him as much as possible, under the 
 idea of its superiority compared with that employed by his 
 competitors, so that it is not possible to state proportions with 
 accuracy. The French porcelain makers have given the com¬ 
 position of hard glazes made by them, which are all said to be 
 formed of flint, ground porcelain, and crystals of calcined gyp¬ 
 sum, in the following different proportions:— 
 
 No. 1. No. 2. No. 3. 
 
 Calcined flint - -- -- - - 8 parts 17 parts 11 parts. 
 
 Ground porcelain ------ 15 16 18 
 
 Crystals of calcined gypsum - - 9 7 12 
 
 It is necessary to vary the composition of the glaze, in order 
 
 to suit the different materials that form the body of the ware, 
 since that would be a very fine glaze for one mixture of earths, 
 which would be wholly inappropriate to another, proving defi¬ 
 cient in lustre and being liable to crack. Before adopting any 
 glaze in conjunction with a particular kind of ware, it is most 
 prudent to make trial of it upon a small scale, in order to prove 
 the suitableness of the bodies to each other. 
 
 This branch of the potter’s art is greatly indebted to the ex¬ 
 traordinary perseverance of a single man, Bernard de Palissy, 
 a native of France, who was born in Agen at the close of the 
 fifteenth century. His parents occupying an humble station in 
 life, he was entirely indebted to his own unquenchable energy 
 and perseverance for the success which crowned his industry. 
 
 The original occupation of Palissy was that of a draughts¬ 
 man, to which pursuit he added land surveying. Accident 
 having thrown into his hands an enamelled cup, he was imme¬ 
 diately seized with the desire of improving the art, and thence¬ 
 forward relinquishing all other occupations, gave up his whole 
 time, mind, and substance, during several years, to the prosecu¬ 
 tion of experiments on the composition of enamel. He has 
 himself given a narrative of his labors, sacrifices, and suffer¬ 
 ings, during the progress of his pursuit, which is intensely in¬ 
 teresting. 
 
 In this account, Palissy represents himself as alternately 
 planning and building, demolishing and rebuilding his furnace, 
 at every step buoyed up by hope, and as often met, but not sub¬ 
 dued, by disappointment; the object of remonstrance and de¬ 
 rision to his associates, subject to the expostulations of his wife, 
 and witness to the silent but more eloquent reproaches of his 
 children. In other respects Palissy proved himself an amiable 
 
CHAP. V. 
 
 OP FIRING AND GLAZING. 65 
 
 as well as a highly-gifted man; for, notwithstanding that his 
 efforts were ultimately crowned by success,—that standard 
 whereby the judgment of mankind is most easily and therefore 
 most usually formed,—one might hesitate to applaud a degree 
 of perseverance which, for so long a time, materially interfered 
 with the welfare of his family. Amidst all this scene of de¬ 
 privation and disappointment, Palissy bore outwardly a cheer¬ 
 ful countenance, and, throughout the lengthened trial, confined 
 within the dungeon of his own breast those feelings of bitter- 
 ness which he has so forcibly described as being his portion. 
 
 The extremities to which he was at one time reduced were 
 such, that to provide fuel for feeding the furnace, his furniture 
 and afterwards even some of the woodwork of his dwelling 
 was destroyed; and in order to silence the clamor of his assist¬ 
 ant workman for the payment of wages, he stripped himself 
 of a portion of his apparel. At length, however, these efforts 
 were rewarded by complete success; and fame, honors, and in¬ 
 dependence were thenceforward his attendants through a long 
 career of useful occupation. 
 
 Palissy’s after pursuits were of a more general character, 
 embracing the sciences of agriculture, chemistry, and natural 
 history, upon which subjects he both wrote and lectured with 
 ability and success. 
 
 Nor did the firmness of his character forsake him for a mo¬ 
 ment to the end of his life. Being a Protestant, and having 
 ventured, in some of his lectures, to promulgate facts which 
 made against the dogmas of the priests, he was, when in his 
 ninetieth year, dragged by the infuriate zeal of these fanatics 
 to the Bastile, and died, with consistent firmness, within its 
 walls. His heroic reply, while thus imprisoned, to Henry III. 
 is above all praise. “ My good man,” said the king, “ if you 
 cannot conform yourself on the matter of religion, I shall be 
 compelled to leave you in the hands of my enemies.”—“ Sire,” 
 replied the intrepid old man, “ I was already willing to surren¬ 
 der my life, and could any regret have accompanied the action, 
 it must assuredly have vanished upon hearing the great king 
 of France say ‘ I am compelled.’ This, sire, is a condition to 
 which those who force yOu to act contrary to your own good 
 disposition can never reduce me; because I am prepared for 
 death, and because your whole people have not the power to 
 compel a simple potter to bend his knee before images which 
 he has made.” 
 
 So great is the competition among potters in the present day, 
 that means which are injurious to their real quality are fre¬ 
 quently adopted for rendering their wares less costly. Some 
 makers are hence tempted to the employment of materials that 
 
 F 2 
 
66 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. V. 
 
 will enable them, at a moderate price, to furnish articles appa¬ 
 rently good, but which will speedily prove defective when 
 brought into use. The saving which the manufacturer is able 
 to effect, through the adoption of an inferior glaze, consists 
 not so much in the actual cost of its component parts, as in the 
 smaller quantity of fuel required for its vitrification, and in the 
 shorter period of time demanded for its conversion. 
 
 The" earthenwares offered, at low prices, by hawkers and 
 pedlars, and at inferior shops, are mostly composed of clay that 
 will not bear a proper degree of heat in the oven, and are 
 covered by a glaze so tender as to craze after a few cleansings 
 with hot water. If exposed to a high temperature, or if acids 
 be applied, the glaze will be dissolved, and the vessels conse¬ 
 quently rendered useless. The quantity of lead which enters 
 into the composition of the better kinds of glazes is so small, 
 that the deteriorating and pernicious effects which attend upon 
 the use of raw glaze need not be apprehended from their em¬ 
 ployment. 
 
 The seggars used to inclose the wares when baked in the 
 gloss oven, are similar to those employed in the first firing. 
 Previous to their insertion, the pieces must have the glaze 
 wiped from the parts which immediately rest upon the bottoms 
 of the seggars, otherwise they would adhere and might be bro¬ 
 ken in their removal. The cases are piled up in the manner 
 already described, and just that degree of heat must be em¬ 
 ployed which will give perfect fusion to the glaze and cause it 
 to spread regularly over the surface. The temperature, of 
 course, varies according to the quality of the articles and the 
 composition of the glaze; but, for the reason already stated, it 
 must never be carried beyond the degree to which the biscuit 
 has been previously exposed. In practice, the temperature of 
 the gloss oven is generally less by about ten degrees of Wedg¬ 
 wood, or 1300 degrees of Fahrenheit’s scale, than the heat of 
 the biscuit oven. 
 
 As alkaline substances are so powerfully instrumental in 
 promoting the fusion of intractable bodies, it may be thought, 
 that by increasing their proportion when combined with fel¬ 
 spar, glazes might be formed that would fuse at a heat suffi¬ 
 ciently moderate for any description of earthenware, and that, 
 consequently, the use of oxide of lead, which is so pernicious, 
 might be altogether abandoned: but another serious evil which 
 would then be experienced prevents this substitution. The 
 glaze, if it contained beyond a certain portion of alkali, would 
 not undergo the same degree of expansion by heat as the body 
 whereon it is laid, and would, as a consequence, crack to such 
 a degree as, when brought into use, would allow any greasy 
 
CHAP. V. 
 
 OF FiRK AND GLAZING. 
 
 67 
 
 matter to penetrate through to the body of the ware; and this 
 would speedily destroy its coherency. 
 
 . The qualities which it is the object of the manufacturer to 
 give to porcelain of the finest description, are density, white¬ 
 ness, transparency, and fine texture of the glaze. These prop¬ 
 erties are estimated in the order wherein they are here enume¬ 
 rated, compactness of body being the point which it is considered 
 most desirable to attain. The glaze, as seen in the finished 
 porcelain, should not put on a lustrous appearance; but while 
 beautifully smooth to the touch, should present to the eye rather 
 the softness of velvet than the gloss of satin. This peculiar 
 semblance will only be produced with glaze that melts with 
 difficulty, and when the heat has been raised precisely to, and 
 not beyond, the point that is necessary for its fusion. 
 
 Stoneware is a very perfect kind of pottery, and approaches 
 nearer than any other description to the character of porcelain. 
 Its body is exceedingly dense and compact, so much so, indeed, 
 that although vessels formed of it are usually glazed, this cov¬ 
 ering is given to them more with the view of imparting an at¬ 
 tractive appearance than of preserving them from the action of 
 liquids. When properly made and baked, stoneware is suffi¬ 
 ciently hard to strike fire from flint, and is as durable as por¬ 
 celain. 
 
 This kind of earthenware is composed of clay and flint. The 
 proportion in which these ingredients are used is said to vary 
 in different manufactories, and it is difficult to ascertain the 
 precise quantities employed in any. The grinding and dilution 
 of the materials is effected in the manner already described, 
 and when these have separately been thus treated, their union 
 is commonly effected in the proportion of about eighteen mea¬ 
 sures of argillaceous to fourteen measures of siliceous fluid. 
 Any larger proportion of flint would render the compound more 
 lifficult to be worked ; and if much less were used, the baked 
 svare would not present a sufficiently smooth and shining ap- 
 aearance. 
 
 The best descriptions of this ware have very long been made 
 n the potteries at Lambeth, the proprietors of which procure 
 heir supply of clay from Devonshire and Dorsetshire, and pur- 
 :hase flint already ground from Staffordshire, where this ma- 
 erial can be afforded at a cheaper rate than would attend its 
 •reparation so near the metropolis. 
 
 The plan introduced by the two brothers Elers is still pur- 
 ued, of glazing these goods by the decomposition of common 
 alt thrown into the kiln, at or near the conclusion of the baking 
 rocess. Other glazes are likewise employed for many articles, 
 nd, according to the usual system, the particular components of 
 
68 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 these are also veiled in mystery ; ground glass is, however, 
 understood to be the basis of all. 
 
 One of the most considerable of the Lambeth potters has re¬ 
 cently announced the discovery of a glazing compound, which 
 is sufficiently fusible without containing a particle of lead, and 
 which has been proved capable of altogether resisting the ac¬ 
 tion of acids; it is used by him for coating the insides of jars 
 and bottles of all descriptions. 
 
 The different colors observable on the outer surface of drink¬ 
 ing jugs and other articles, are owing to the partial use of a 
 glaze, the part to which this is applied becoming dark in the 
 heat, of the kiln, while the glazing of the light colored portion 
 is caused, as before mentioned, by the introduction of salt. 
 
 The fashioning of stoneware pottery is in all respects con¬ 
 ducted similarly to the processes already fully described. Seg- 
 gars are mostly employed for inclosing the pieces during the 
 baking, which usually occupies about forty-eight hours. 
 
 Vessels of considerable size, some being capable of containing 
 sixty imperial gallons, are made in this manner, and are found 
 highly useful in performing many chemical operations con¬ 
 nected with the arts. 
 
 CHAP. VI. 
 
 ON THE ART OF APPLYING COLORS AND ENGRAVINGS TO 
 EARTHENWARE. 
 
 Antiquity of Enamel Coloring.—Specimens from Ancient Egypt.—From the 
 Royal Works at Sevres.-Painted Ware of Worcester—Of Staffordshire— 
 Of Derby—Of Yorkshire.—Great Services of Mr. Wedgwood in this Branch 
 of the Manufacture.—Mystery in the Preparation of Colors.—Publicatioh 
 of Processes by M. Brongniart.—Metallic Oxides—Addition of Fluxing 
 Bodies necessary—And why.—Colors Employed for tender and for hard 
 Porcelain.—Vehicle used with the Colors.—Mode of their Combination.— 
 Description ofColors—Purple and Violet.—Red.—Yellow.—Blue.—Green. 
 —Brown.—Black.—White.—Compound Colors.—Precautions necessary in 
 Forming those Compounds.—Gilding.—Lustreware.—Preparation of Col¬ 
 ors.—Enamelling Kilns.—Trial Pieces.—Method of Gilding and Burnish¬ 
 ing.—Copperplate Engravings.-—Mode of Transferring Impressions to 
 Earthenwares.—How Performed in France. 
 
 The art of painting on earthenware, although of compara¬ 
 tively recent introduction into England, is by no means a 
 modern invention. It is well known that the ancients manu¬ 
 factured colored enamels; and some specimens of the art, per¬ 
 formed by the Egyptians more than three thousand years ago, 
 have been preserved to the present day, which is an evidence 
 of this fact; showing us, at the same time, that, in so remote an 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 09 
 
 age, the artists of Egypt were possessed of sufficient practical 
 knowledge of chemistry, to avail themselves of processes which 
 have been brought to light anew by scientific investigators of 
 more modern times. 
 
 Recently, the art has been carried to an admirable degree of 
 perfection in Europe. Some specimens are preserved in the 
 porcelain works at Sevres, of which the French artists are 
 justly proud ; while the performances in our own potteries at 
 Worcester, in Staffordshire, at Derby, and yet more recently 
 in Yorkshire, are such as entitle them to be placed in an equal 
 rank with those of our continental neighbors. 
 
 When, about seventy years ago, Mr. Wedgwood commenced 
 the series of improvements, by which his name has been ren¬ 
 dered so deservedly celebrated throughout Europe, no attempts 
 at embellishment had been made in the English potteries; and 
 if ornamented services of porcelain were seen on the tables of 
 the wealthy, tney were always of foreign, and generally of 
 ariental production. So soon, however, as, by the intrinsic 
 aierit of his wares, this enterprising manufacturer had secured 
 lot only the patronage of royalty, but the more solid support of 
 lis countrymen in general, he called into action the crucible of 
 :he chemist, and the pencil of the artist, and led the way in 
 lestowing that degree of outward embellishment on his pro- 
 luctions, which converted them into objects of elegance, and at 
 )nce encouraged and gratified the growing taste for luxury 
 imong the higher classes in this country. 
 
 The system of mystery still preserved in the English pot- 
 ories, in all that respects the composition and glazing of wares, 
 vas likewise long practised with regard to the preparation of 
 :olors. at any time, a manufacturer had found out a prepa- 
 ation more advantageous than that in use before, he always 
 mdeavored to limit the benefit of the discovery to his own 
 vorks; a desire more easy of accomplishment formerly than it 
 las become since the more general diffusion of the light of 
 cience. M. Brongniart, at one time director of the national 
 oanufactory of porcelain at Sevres in France, has the merit of 
 eing the first who published a correct statement of the most 
 pproved plans for preparing and combining the metallic oxides 
 sod in coloring porcelain and glass. The employment of these 
 abstances for such purposes had been long before and com¬ 
 ply practised, and the art was even carried by some of its 
 rofessors to a high degree of perfection; but, as M. Brongniart 
 isarves, no attempt had been made at the time his essay was 
 ritten ( 1801 ), to apply to it the principles of chemical science; 
 id such pretended descriptions as had then been published 
 mtained no theory, and consequently no general principles. 
 
70 PORCELAIN MANUFACTURE. CHAP. VI. 
 
 Where even the authors did offer explanations, these were 
 founded upon the most ridiculous hypotheses; so that all im¬ 
 provements were rather the offspring of chance than the result 
 of systematic inquiry. 
 
 It would afford but little satisfaction, or information, to relate 
 by what steps the art now under consideration was reduced 
 into a system, and thus became, in some measure, deserving of 
 the name of a science. It will be sufficient to state the means 
 by which that art is now rendered available in the best con¬ 
 ducted porcelain works. In a great part of the following de¬ 
 scription, the lucid statements given by M. Brongniart in his 
 essay will be closely followed \ since, with scarcely any varia¬ 
 tion, the same processes have been used in both the French 
 and English establishments to the present day. 
 
 In this branch of the art there are various objects to be con¬ 
 sidered, a proper acquaintance with which is necessary to suc¬ 
 cess. Such are, the composition of colors; the fluxes which 
 are necessary to render these fusible, which unite them to the 
 wares, and in many cases impart brilliancy to their tints; the 
 vehicle employed in laying on the colors, and the course to be 
 pursued in fixing them on "the porcelain by means of heat. 
 
 Metallic oxides form the bases of all vitrifiable colors, but 
 every metallic oxide is not proper for being employed in deco¬ 
 rating porcelain. Some are highly volatile, as the oxides of 
 mercury and of arsenic. Others part so freely with the oxyger 
 they hold in combination, that their color proves uncertain, ant 
 varies with every application of heat j such are the puce-coloret 
 and red oxides of lead, and the yellow oxide of gold. Oxides 
 which are susceptible of great variations are veiy seldom em 
 ployed. Black oxide of iron is not used alone for producing 
 that color on porcelain ; and the green oxide of copper, as for¬ 
 merly prepared, was so uncertain that it was very rarely em 
 ployed; but this evil has, since the time of M. Brongniart 
 been greatly remedied. 
 
 Oxides uncombined with other substances are not susceptibh 
 of fusion; and although they may be attached in thin strata t< 
 vitrifiable bodies by a very violent heat, yet their colors, witl 
 the exception of lead and bismuth, would, in such case, becom< 
 dull, and possibly be even destroyed. In order to promote thei 
 fusion, a flux is therefore added, the composition of which vane 
 according to the means employed for diluting the colors at th< 
 time they are used. Where a volatile oil is chosen for this di 
 lution, a flux composed of glass, nitre, am], borax is most proper 
 but when, as in the Sevres manufactory, gum-water is substi 
 tuted for this volatile oil, the flux must be varied, because bora: 
 cannot be properly diluted in gum-water. A compound of glastj 
 
ClIAl*. VI. APPLYING COLORS A AD ENGRAVINGS. 71 
 
 lead, and silex is therefore preferred by M. Brongniart, who, 
 however, has given no directions regarding the proportions 
 wherein these bodies must be brought together. The other 
 menstruum, which is recommended by M. de Montamy, in his 
 treatise on painting in enamel, is composed of 
 Powdered glass 40 parts. 
 
 Calcined borax * 22 
 Refined nitre - 44 
 
 It is indispensable, not only that the borax and nitre be as pure 
 as they can be rendered, but also that the glass shall not con¬ 
 tain the smallest particle of lead in its composition. These in¬ 
 gredients must first be well triturated together in a glass mor¬ 
 tar, with a pestle of the same material, during an hour, and 
 then exposed in a crucible to the heat of a charcoal fire, until 
 the swelling, which for a time accompanies the fusion of the 
 mass, has ceased. 
 
 By means of this flux the colors are fixed upon the porce¬ 
 lain, and made to assume a resplendent appearance: the metallic 
 oxides, being enveloped by the flux, are preserved from all con¬ 
 tact with the air, and their color is rendered permanent; the 
 fusion having been promoted at a temperature too low for their 
 destruction. 
 
 Trial should be made of the habitudes of different colors in 
 combination with their flux, in order to determine the exact 
 quantity to be employed with each. Various substances vitrify 
 with greater or less facility when thus combined, and the 
 greatest carefulness and skill are consequently required, so to 
 proportion the relative quantities of each, that not more of the 
 flux shall be added than is necessary to cause a perfect vitrifi¬ 
 cation. If too little were used, the colors, although they might 
 attach themselves to the porcelain, would nevertheless be dull; 
 and if too much, the colors would run, their outlines would not 
 be sufficiently decided, and all the finer touches of the artist 
 would disappear. It has been remarked, that colors which re¬ 
 quire for their fusion more than six times their weight of flux, 
 do not flow with sufficient facility ; and, as they cannot be ap¬ 
 plied with a pencil, so as to produce a satisfactory result, should 
 be rejected. 
 
 Such metallic oxides as would have their colors altered by a 
 strong or often repeated heat, are employed after being mixed 
 with their flux, but without having been previously fused with 
 it. In many cases metallic oxides are first fused with the 
 requisite proportion of their flux, and are then ground for use. 
 
 * Mr. Tillnch remarks (Philos. Mag. vol. li.) that borax should be used 
 sparingly, as it causes efflorescence, and promotes the decay of the enamel 
 
72 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 Enamel is glass made opaque by the oxide of tin, and ren¬ 
 dered fusible by the oxide of lead. All glazes that contain lead 
 participate in the properties of enamel. Raw glazes used for 
 covering tender porcelain are of this nature. The colors em¬ 
 ployed in painting this porcelain are those which serve for 
 painting in enamel; they require less flux than others, because 
 the surface to which they are applied becomes soft enough to 
 be penetrated by them. Hard porcelain, whose nature is iden¬ 
 tical with those of China and Saxony, has two kinds of colors 
 applied to it. Those of the first kind, which are used in the 
 representation of different objects, are baked in a heat much 
 below that necessary for baking porcelain; while the other 
 colors, which are few in number, must be exposed to the highest 
 degree required by the porcelain itself. The glaze used for 
 hard porcelain has little or no lead in its composition. The 
 Sevres manufacturers, and some few in England, employ fel¬ 
 spar without any mixture of lead. This glaze, when exposed 
 to the heat of the gloss oven, dilates, and its pores are opened 
 without becoming soft, so that the colors are not absorbed by it, 
 and do not undergo those changes which occur when they are 
 applied to tender porcelain, where, by mixing with the body of 
 the enamel, they become faint and indistinct. This effect is 
 much increased likewise where some particular colors are em¬ 
 ployed, and especially the reds produced from iron, which are 
 exposed to the destructive action of the oxide of lead that is 
 contained in the glaze. Painting on tender porcelain must, for 
 these reasons, be several times retouched with the pencil, in 
 order to give to it the distinctness and brilliancy which follow 
 the use of the same colors on hard porcelain, so that a high de¬ 
 gree of ornament is seldom or never given to any but the latter 
 description. In the embellishment of hard porcelain, these re¬ 
 touchings are not required, except for the most elaborate speci¬ 
 mens of the art, which can by such means, however, be pro¬ 
 duced with the most admirable degree of perfection, so as to 
 render paintings on porcelain not distinguishable from the 
 finest productions of the pictorial art, without reference to the 
 body upon which it is performed, or to the means used for 
 bringing out the colors; natural objects, landscapes, portraits, 
 and even historical pieces being represented with all the truth, 
 as well as with all the brilliancy of coloring, which distinguish 
 the works of the first masters. 
 
 One great inconvenience attends the repeated exposure to 
 the heat of the oven of pieces thus retouched; the colors being 
 liable to peel off*, unless the greatest care has been used in their 
 application. This defect has been remedied in the Sevres 
 works, by introducing a calcareous flux into the felspar glaze, 
 
73 
 
 CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 
 
 which soflens it, without at all affecting the body of the ware. 
 Soda and potash are never used as fluxes, as their introduction 
 causes the colors to scale; the reason for which is, that, becom¬ 
 ing volatile in a great heat, they abandon the color, which then 
 will not adhere to the glaze. 
 
 The liquid matter which serves as a vehicle in laying on the 
 colors, is rubbed with them upon a glass palette until the whole 
 is intimately united. The mixture must be brought to that 
 state of dilution which is most proper and convenient for its 
 application with a hair pencil on the surface of the porcelain. 
 Great care is used in the choice and management of these dilu¬ 
 ent liquids, which must always be sufficiently volatile to be en¬ 
 tirely dissipated in the heat to which the wares are afterwards 
 exposed. In France, the preference is given to oil of lavender 
 as a vehicle; and in order to insure the proper degree of fluid¬ 
 ity, this oil is divided by distillation into two parts: that which 
 first comes over, being the most volatile, and having the least 
 density, is used for diluting the colors when they become too 
 thick; and, on the other hand, the portion that remains in the 
 retort, having the opposite qualities, is reserved for thickening 
 them when they run too freely. Oil of turpentine, which has 
 been some time in store, is more generally used in England, 
 and is said to answer the purpose better than any other volatile 
 fluid. 
 
 It was remarked by Brongniart, whose practical knowledge 
 qualified him to judge correctly on the subject, that of all the 
 processes for painting on glass and porcelain described in works 
 that were in existence at the time his essay was published, 
 there was not one, by strictly following which, the desired co¬ 
 lors could be produced. In describing these processes, one au¬ 
 thor had followed another without knowledge or examination; 
 and even the treatise by Leviel, which forms part of the volu¬ 
 minous work on arts and manufactures, published under the 
 auspices of the Academy of Sciences in Paris, is not free from 
 this reproach. Such want of correctness, from whatever cause 
 it may have arisen, is little honorable to the authors, who if 
 even unable, by penetrating the veil of mystery wherein the 
 manufacturers shrouded their practices, to expose them correct¬ 
 ly to the world, might, without difficulty, have ascertained the 
 truth or falsehood of that to which they were affixing the stamp 
 of their authority. The course which they pursued would as¬ 
 suredly fail of success in the present day, when an acquaintance 
 with chemical phenomena is no longer confined, as it formerly 
 was, to a few among the rarer order of students, and such er¬ 
 rors would be certain of confutation at the moment of their pro¬ 
 mulgation. 
 
74 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 Purple and violet colors are procured by dissolving gold in 
 aqua regia (nitro-muriatic acid), and immersing a bar of pure tin 
 in the solution. The product thus obtained is called, from its in¬ 
 ventor, the purple precipitate of Cassius, and is used very gen¬ 
 erally for giving the above-mentioned colors to porcelain. A 
 preferable way of preparing this precipitate is to dissolve the 
 two metals separately, and by then bringing the solutions to¬ 
 gether in different proportions, various shades of carmine, vio¬ 
 let, and purple are obtained. The first of these three tints is 
 seldom used in porcelain works, for although extremely beauti¬ 
 ful, it is also very transient, and may be easily spoilt by a small 
 excess of heat, or by the contact of carbonaceous vapors, a cir¬ 
 cumstance which is the less important, as its place may be well 
 supplied by a rose color obtained from iron, and which is not 
 liable to the same disadvantage. Carmine color, when used for 
 tender porcelain, is prepared with fulminating gold (made by 
 dissolving the metal with aqua regia and precipitating with am¬ 
 monia), and muriate of silver. This compound is without any 
 addition of tin, which shows that an union of the oxide of tin 
 with that of gold is not necessary—as many have supposed— 
 for the production of purple. 
 
 Violet color is also made with the purple oxide of gold, re¬ 
 quiring the presence of some portion of lead in the flux for the 
 development of this shade. These three colors cannot bear 
 exposure to the full heat of a porcelain furnace, in which they 
 would wholly disappear. In using the precipitate of gold, it is 
 mixed with about six times its own weight of flux, and is em¬ 
 ployed without previously fusing the two bodies together. 
 When first applied on the porcelain, it is of a dirty violet color, 
 but by exposure to heat this passes to a most beautiful purple. 
 It is recommended to employ charcoal as fuel in baking this 
 color. Frequent exposure to the fire will materially impair its 
 beauty. 
 
 Red oxide of iron, prepared by the united action of fire and 
 nitric acid (the aquafortis of commerce) yields a red color, 
 which, although beautiful, is less brilliant than that produced 
 from gold. As already stated, it is, however, preferable on ac¬ 
 count of its less liability to change. Shades of red, deepening 
 from rose color, and passing by the increased application of 
 heat to brown, are obtained from iron. The flux employed with 
 this oxide is composed of vitrified borax, sand, and a small pro¬ 
 portion of red lead, and the color may be used either with or 
 without previous fusion with its flux. By the mixture of black 
 and red oxides of iron, in different proportions, various shades 
 of reddish brown, chestnut, &c. are obtained. Red colors pro¬ 
 duced from iron cannot be used on tender porcelain, since they 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 
 
 75 
 
 disappear, in that case, on exposure to heat. This effect must 
 be ascribed to the presence of lead in the glaze. Several ex¬ 
 periments, conducted by M. Brongniart, have proved this fact 
 beyond all controversy. 
 
 A very permanent red color is procured by calcining the ox¬ 
 ide of iron with double its own weight of common salt (chlo¬ 
 ride of sodium). The processes used for this purpose must be 
 carefully conducted, and the salt purified and decrepitated— 
 that is, subjected to the action of heat until all crackling 
 noise has ceased. The oxide is procured by dissolving iron 
 filings in nitric acid, and precipitating with salt of tartar (sub¬ 
 carbonate of potass). The precipitate must then be placed on 
 a thin sheet of iron, and exposed under a muffle to the heat of 
 a charcoal fire, until it has taken a fine red color. The two 
 substances having been well triturated together in a glass or 
 porcelain mortar, are then calcined in a crucible, and the oper¬ 
 ation should be carried as far as possible, without occasioning 
 the vitrification of the mass. When taken from the fire and 
 cooled, the compound is again triturated; successive portions 
 of hot water are poured upon it, stirred, and then removed, 
 until the water is no longer colored. The fluid thus tinged 
 is allowed to settle, and is, when clear, poured from the sedi¬ 
 ment, which is then washed five or six times in fresh portions 
 of clear water. 
 
 To obtain yellow colors, for both hard and tender porcelain, 
 white oxide of antimony, mixed with sand and oxide of lead, 
 are employed, the latter substance serving as a flux to the 
 others. Great carefulness is required in the preparation, as the 
 lead frequently approaches, by reason of the heat, to a metallic 
 6tate, and, in that case, appears in the form of black spots on 
 the wares. Oxide of tin is sometimes added, and when the co¬ 
 lor is required to be livelier, and approaching to that of saffron, 
 red oxide of iron is added, the too great redness of this being 
 subdued by the action of the lead, in the fusion which the ingre¬ 
 dients undergo, previous to their application on the porcelain. 
 The colors thus produced are not susceptible of change, but if 
 exposed to the full heat of a porcelain furnace would be en¬ 
 tirely dissipated. 
 
 Oxide of uranium, mixed with oxide of lead, produces a 
 straw color. By decomposing chromate of potass, with nitrate 
 of lead, which is a saturated solution of lead in nitric acid, chro¬ 
 mate of lead is precipitated, and this proves a very excellent 
 yellow color. 
 
 Naples yellow is composed of 24 parts of ceruse, 4 parts of 
 oxide of antimony, and one part each of alum and sal ammoniac 
 (muriate of ammonia), calcined together at a moderate heat 
 
76 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 during three hours. The shade is varied by increasing or di¬ 
 minishing the proportion of sal ammoniac. The quantity of flux 
 that must be combined with this color for use is uncertain, and 
 must be matter for experiment with the manufacturer. 
 
 For the production of blue, well prepared and very pure 
 oxide of cobalt is employed, mixed with a flux. Oxides of tin 
 and of zinc, added in different proportions, give different 
 shades, from a deep rich color to a light blue. As the oxide of 
 cobalt is volatilized at a high heat, it is impossible to place in 
 the same case, white pieces, and such as are painted blue; 
 since the former would certainly assume a bluish tint in the 
 operation of baking. This difficulty does not occur with tender 
 porcelain, on which the cobalt is not volatilized as in the other 
 case, owing to the heat being very inferior to that used in ba¬ 
 king hard porcelain. These blue colors, if they have been pre¬ 
 viously fused, do not change at all after their application. The 
 rich smalt, known under the name of azure-blue, is only the 
 glass of cobalt, mixed with sand. This color must be fused in 
 a crucible, and reduced to an impalpable powder in an agate 
 mortar, after which it may be used in combination with flux. 
 
 Prussian blue, which results from the union of hydrocyanic 
 acid with oxide of iron, is very extensively used in the arts; 
 and being prepared on a large scale for sale, in various parts of 
 the kingdom, no manufacturer of porcelain will undergo the 
 trouble, or encounter the unpleasant circumstances attendant 
 upon its preparation, but will rather obtain the comparatively 
 small quantity he may require by purchase. 
 
 Green oxide of copper is usually employed for the production 
 of a green color. On precipitating in different vessels, by means 
 of potass, solutions of copper which are equally pure and con¬ 
 centrated, it is perceptible that the precipitate is formed more 
 quickly in some vessels than in others; and if these different 
 products are separately collected, those which are most prompt¬ 
 ly formed are, when dried, of a fine bright green, and produce 
 a corresponding color on porcelain; while those precipitates 
 which are deposited more slowly, form earthy and less dense 
 particles of a much darker hue, and which, when applied to por¬ 
 celain, yield a less pleasing color, and pass sometimes to black 
 during the baking. If, however, the precipitated oxide is pre¬ 
 viously fused with its flux, this change need not be apprehend¬ 
 ed. Very pure oxide of copper is frequently procured by pla¬ 
 cing sheets of the metal in the oven wherein the ware is glazed. 
 Mixtures of yellow and blue are sometimes used in the compo¬ 
 sition of green colors: some of these will not exist in the heat 
 of a porcelain furnace. Various shades of beautiful green may 
 be obtained, by mixing, in different proportions, Prussian blue 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 77 
 
 with the chromate of lead already described. A mixture of the 
 oxides of cobalt and nickel, will resist a very intense heat, but 
 does not produce a genuine green: it is rather an olive color. 
 
 Oxide of chromium gives a beautiful green color, which is 
 indestructible in the heat of a porcelain furnace. That class of 
 green colors, called celestial blues, can only be applied, accord¬ 
 ing to Brongniart, on tender wares: being partly composed of 
 potass, they scale off from hard porcelain. 
 
 Different shades of light and of deep rich brown are obtained 
 from mixtures of the oxides of iron. These must be fused 
 with thin flux before they are used, after which fusion they do 
 not undergo any change on the application of heat. Russet 
 grounds, known under the designation of tortoise-shell, are pro¬ 
 duced in this manner. Felspar is employed as a flux with these 
 colors. 
 
 There is not any metallic oxide which alone will give a good 
 black. Oxide of manganese approaches the nearest to it. The 
 black oxide of iron yields a very dull color, which sometimes 
 changes to red. The color-makers therefore unite several ox¬ 
 ides together, and thence obtain a very beautiful black. The 
 oxides thus combined are of manganese, the brown oxide of 
 copper, and a small proportion of the oxide of cobalt. A gray 
 color is obtained by omitting the copper, and increasing the 
 proportionate quantity of the flux. 
 
 Cobalt, oxide of copper, and umber, in equal parts, reduced 
 together to an impalpable powder in an agate mortar, prove a 
 very good black. This must be used with three times its 
 weight of flux. Another black is composed of four parts oxide 
 of copper, one part of smalt, and one part of black oxide of iron, 
 which, like the former compound, must be rubbed together to a 
 fine powder, and used with three parts of flux. 
 
 In the “ Annales de Chimie et de Physique,” (Yol. 20.1822), 
 directions are given for the preparation of a beautiful black en¬ 
 amel, the verification of which on the part of our porcelain 
 manufacturers is perhaps desirable. The experiment necessary 
 for this purpose might have been somewhat simplified, if the 
 artist by whom the directions are communicated had stated the 
 proportions wherein the ingredients should be brought together. 
 The formula directs that chloride of platina, dissolved in water, 
 should be mixed with nitrate of mercury. By then subjecting 
 the precipitate which will be formed to a heat just sufficient to 
 volatilize the proto-chloride of mercury, a black powder will be 
 obtained. This is the enamel, which must be applied in the 
 usual manner, in combination with a fluxing material. 
 
 M. de Montamy in his treatise, to which allusion has already 
 been made, gives a recipe for composing a pure white color, 
 
 G 2 
 
78 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 which is found very serviceable by the French artists in form¬ 
 ing their series of shades, as well as in the composition of those 
 parts of their designs which require to be represented in a bril¬ 
 liant white. This color is composed of one part of virgin tin, 
 and two parts of common salt. The latter must be thoroughly 
 purified, by first dissolving it in distilled water, then filtering 
 the solution through paper, and afterwards evaporating it to 
 dryness over the fire in a porcelain capsule. The salt, which is, 
 by this means, made extremely white, must be further exposed 
 to heat in a crucible, until all decrepitating noise has ceased. 
 The purification will be yet more perfect, if, after filtering it, 
 the solution is partially evaporated, and then placed in a cool 
 situation to crystallize slowly. Those artists who are the most 
 particular in their processes, select preferably from the rest 
 such crystals as take the form of cubes. The next part of the 
 process is to place a crucible on the fire, well covered, to pre¬ 
 vent the entrance of smoke or ashes. When this crucible is at 
 a red heat, the tin is introduced, and is left until it is not only 
 fused, but red-hot, at which time the purified salt is added in 
 the proportion already mentioned. Taking then a clean iron 
 spatula, the end of which must be previously heated, the mix¬ 
 ture is stirred until the substances are well incorporated to¬ 
 gether. The crucible being then again covered, is to be sur¬ 
 rounded with burning charcoal, and from time to time, the 
 spatula, which must be always perfectly clean aud hot, should 
 be introduced to agitate the mass. When the end of this spat¬ 
 ula, in being tempered by the heat of the crucible, begins to grow 
 white, it is a sign that the calcination is carried sufficiently far, 
 and that the crucible should be removed from the fire; the cal¬ 
 cination usually occupies an hour for its completion. The com¬ 
 pound should next be bruised in a mortar of glass or of agate, 
 and again placed in a crucible which is set in the midst of 
 burning coals and covered with a muffle. The heat is then 
 raised gradually, and continued during three hours, when, on 
 removing the crucible from the fire, the color is found to be 
 hard, and requires some force to detach it from the vessel. 
 This done, it must be pounded in a mortar, and washed in hot 
 water that has been filtered or distilled, and fresh portions of 
 water added, until the fluid has no longer any taste of salt. 
 The white color is afterwards to be boiled violently with an 
 abundance of water in an earthenware vessel for two hours, 
 supplying hot water during that time to replace the portion that 
 is evaporated. When the supernatant water has become clear 
 by standing, it must be poured off carefully. 
 
 This white may be advantageously employed in painting with 
 oil, as it mixes well with it. When used on porcelain, it must 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 79 
 
 be mixed with three times its weight of flux. The preparation 
 of this color will not succeed unless the tin is extremely pure, 
 and it is essential that the nicest possible degree of cleanliness 
 should be observed throughout the operations. 
 
 By making different mixtures of the various colors here de¬ 
 scribed, every hue that can be desired may be obtained. It is 
 not, however, so easy, as without due consideration it might 
 appear, to produce these various shades. Great judgment in 
 the selection of materials, carefulness in their preparation, and 
 knowledge as to the relative proportions wherein they should be 
 brought together, are essential to success; and an acquaintance 
 with the science of chemistry is highly desirable. There are 
 some colors which, if mixed, would mutually destroy each other, 
 and on the exposure of metallic oxides to heat, changes ensue, 
 which result not from the nature and habitudes of the colors 
 themselves, but rather from the influence of the bodies to which 
 they are applied. 
 
 . It would be scarcely possible to treat satisfactorily upon the 
 inciting causes of all these variations, a full knowledge of which 
 can result alone from the practical experience of the artist and 
 manufacturer. 
 
 Many potters do not prepare their own enamel colors, but 
 purchase what they require from persons who manufacture them 
 for sale. Some of these preparations are exceeding costly, and 
 as the temptation to adulterate them is consequently great, the 
 potter should have good reason to rely on the probity of the 
 color-maker with whom he deals. A fraudulent mixture, the 
 detection of which would be impossible before its use, except 
 by means of a chemical analysis, might be the occasion, in its 
 results, of severe loss and disappointment. With the exception 
 of the great works at Sevres, this system of purchasing their 
 enamel colors has, for many years past, been very general among 
 the potters of France. In a report made to the French govern¬ 
 ment, by a commission appointed in 1819, to examine into the 
 progress of manufacturing industry in that country, occasion 
 was taken for offering congratulations upon this establishment 
 of an independent occupation, as marking the great extension 
 of the porcelain manufacture, and as offering to the artist 
 Deans of obtaining every shade of color, prepared by persons 
 vhose interest is involved in ascertaining their effects when 
 submitted to the heat of the furnace, thus removing all uncer- 
 ainty from the operations of the painter, and rendering it un- 
 lecessary for him to suspend his work that he may prepare his 
 solors. 
 
 The gold used in gilding porcelain is applied in a metallic 
 tate. To prepare it for this purpose, it is dissolved in aqua 
 
80 
 
 Porcelain manufacture. 
 
 chap. VI. 
 
 regia, and the acid being afterwards dissipated by the applica¬ 
 tion of heat, the gold remains in the state of powder at the bot¬ 
 tom of the vessel. This powder must be mixed with borax 
 and gum-water, as a vehicle for causing it to flow from the 
 pencil and fix upon the wares; which being then baked, the 
 gilding appears void of lustre, and requires to be afterwards 
 burnished with either agate or blood-stone. 
 
 Gold and silver lustre-ware is commonly of an inferior quality. 
 The metallic oxides used for covering these vessels are inti¬ 
 mately mixed with some essential oil, and then brushed entirely 
 over their surfaces. The heat of the enamelling oven, which 
 dissipates the oxygen, restores the oxides to their metallic state, 
 but with some diminution of brilliancy. The oxide of plati¬ 
 num is used for making silver-lustre. 
 
 Colors, when they are required for use, should be first 
 pounded quickly in a mortar made of either agate, porcelain, or 
 glass, with a pestle of the same material, and covered to pre¬ 
 vent the access of dust. They must be afterwards ground on a 
 glazed palette, firmly bedded in plaster on a wooden frame, and 
 perfectly level. The artist who decorates porcelain is required 
 to rub his colors with as much nicety as is used by miniature 
 painters, so that there must not remain the least perceptible 
 roughness, either under the muller or between the fingers. The 
 requisite proportions of volatile oil and of flux are added and 
 ground with the colors on the palette, the whole having been 
 carefully weighed before their union. The general rule is to 
 put five parts of flux to two parts of coloring matter: but some 
 colors, as already mentioned, require more, while with others 
 this proportion would be too great. Smalt requires to have 
 combined with it only half the sum of its own weight. 
 
 The artist must be attentive to grind his colors with the 
 smallest quantity of oil that will suffice; if this should be in ex¬ 
 cess, it may in evaporating leave spaces between the particles 
 of color, and the subject would appear very imperfectly exe¬ 
 cuted. The fluidity of the mixture should be kept at that ex¬ 
 act point which enables the artist to produce the finest strokes 
 with clearness and facility. 
 
 Before the pieces which have been painted are baked in the 
 enamelling-kiln, it is necessary to dry the colors by evaporating 
 the oil used with them as the vehicle. 
 
 Every considerable pottery has enamelling-kilns of various 
 sizes. These are in form like a chemist’s muffle, from about 
 six to ten feet long, and from three to five feet wide. The ar¬ 
 ticles are piled in the kiln until it is filled, when the mouth be¬ 
 ing closed, fire is applied, and continued for about eight or ten 
 hours, at the end of which time the colors are found to be burnt 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 81 
 
 into the glaze. In piling the pieces in the kiln, care must be 
 used to avoid the placing of any one piece upon the gilt border 
 of another. The muffle is provided with trial pieces, which 
 can be extracted from time to time during the baking, and 
 which will indicate the general state of the contents of the kiln, 
 so as to govern the continuance of the operation. No delay 
 should occur between the sufficient baking of the colors, and 
 the withdrawing of the fire, as their brilliancy would be injured 
 by its longer continuance. The contents of the kiln are left 
 undisturbed until they are cool, and are then withdrawn. All 
 impure exhalations are prejudicial to the beauty of colors, and 
 every substance whence they can arise should, as far as possi¬ 
 ble, be kept away from the kiln during the process. 
 
 Gilding on porcelain or on glass is performed either with or 
 without the addition of a fluxing material, the gold being made 
 to adhere to the surface by the incipient fusion of either the 
 glazing on the porcelain, or of the surface of the glass, or of the 
 flux employed. 
 
 Gold is used for this purpose sometimes in the form of leaf 
 gold, and at other times in that of powder, prepared either me¬ 
 chanically, or by chemical precipitation. When the first of 
 these two methods is employed, leaf gold must be ground with 
 honey or with gum-water of an equal consistence; the honey 
 or gum being afterwards washed away, the gold may be kept 
 for use in paper or in shells, and the use of these latter recipi¬ 
 ents has occasioned this powder to be known among artists as 
 “ shell gold.” This precious metal is precipitated from its solu¬ 
 tion in aqua regia, by adding to it a watery dilution of green vit¬ 
 riol (proto-sulphate of iron) or strips of metallic copper. Gold 
 powder may likewise be obtained from the same solution by dis¬ 
 tilling it to dryness; but this process is not so convenient as pre¬ 
 cipitation. The powder has also been procured by first forming 
 in amalgam of the metal with mercury, and then evaporating the 
 after; but besides being expensive, the fumes of mercury are 
 bund to be extremely prejudicial to the health of the operators. 
 
 When gold powder is used, it must be mixed with gum-water 
 is a vehicle. Where it is intended to apply leaf gold without 
 my fluxing material to the body of the wares, these should be 
 noistened in the requisite parts with a weak solution of gum- 
 rabic, which must afterwards be allowed to dry. When the 
 [■old is applied, the porcelain or glass may be made sufficiently 
 dhesive by breathing on it. If a flux is employed, it should, 
 fter being rubbed very fine with a muller, be diluted with 
 i'eak gum-water, and very thinly spread over the parts which 
 
 is designed to ornament; when very nearly dry, the leaf gold 
 15 laid upon it. 
 
82 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 Japanners’ gold size, moistened to the requisite degree with 
 oil of turpentine, is sometimes employed. Waiting then until 
 the size is so far dried as to be only clammy to the touch, the 
 gold leaf is laid on with cotton wool. As soon as the gold is 
 applied, the ware is placed in an oven or muffle, that it may be 
 burnt on. 
 
 Some old authors direct the artist to fuse gold with regulus 
 of antimony, to pulverize the mass, and to spread the powder 
 upon the parts to be gilded, exposing the ware afterwards to 
 such a heat as will suffice to evaporate the antimony while the 
 gold remains fixed. This method of proceeding is objectiona¬ 
 ble, from the almost impossibility of spreading the powder in a 
 sufficiently uniform manner, besides which, part of the gold will 
 also be carried off, and some descriptions of glass are even fusi¬ 
 ble with the degree of heat necessary for perfecting the process. 
 
 Circular gold lines are frequently described on small articles, 
 such as cups, saucers, and plates. To assist him in tracing 
 these with accuracy, the artist employs a portable horizontal 
 wheel, the height of which may be adjusted at pleasure, accord¬ 
 ing as the nature of the work requires it to be performed in a 
 standing or a sitting posture. The lower part of this wheel is 
 somewhat similar to the leg and feet of a claw table, the leg 
 being bored out for the reception of a stout metallic wire, the 
 altitude of which is regulated by means of a thumb-screw. 
 
 The upper or movable part of the wheel has a like tubular 
 cavity in its vertical part, by means of which it is dropt on to 
 the upright wire, and is made to rest upon a shoulder fixed on 
 the wire, so that the wheel may be made to turn truly upon 
 this as its axis: the whole is surmounted by a horizontal table. 
 
 In proceeding to use this machine, the artist places his feet 
 firmly upon the base of the wheel, and fixing the article to be 
 ornamented upon the table, he causes the revolution of the 
 wheel with his left hand, and holding his brush steadily in the 
 other, describes the circles with the utmost facility and accu¬ 
 racy. 
 
 Burnishing, which is the last process performed in the manu-! 
 facture of ornamented porcelain, is usually intrusted to female 
 hands. The implements required for this purpose are, a burn-; 
 isher of agate or blood-stone, some white lead, a piece of sheep¬ 
 skin for wiping the ware, and some vinegar. As extreme 
 cleanliness is indispensable, the person engaged in burnishing 
 does not even touch either the porcelain or her implements, 
 but interposes between them and her hands a piece of clean 
 white linen. The agate burnisher should be applied lightly! 
 on the gilding, following all the ornaments, and never rubbing 
 in cross directions, lest the gilding should appear scratched. 
 
CHAP. VI. APPLYING COLORS AND ENGRAVINGS. 83 
 
 After having rubbed the gilding for some time, a little vinegar 
 or white lead should be applied to cleanse the surface. Th^s 
 
 b ™nirT d W , lth a /° ft linen ra £’ the burnishing is recom- 
 
 the thr °^ hout — a 
 
 be r | memb ered, that in the preceding description of 
 
 2 fcSr” US m ? paintln " porcelain, several were mentioned 
 as being unable to support the heat of the gloss-oven. Others 
 
 Jl”’ have not this disadvantage, and will bear the highest 
 emperature without injury. Where colors are applied directly 
 
 mixed wiST 1 ’ ?° 01 i 1S ev , er ." round with them, but they are 
 mixed wuh water only, and the glaze may be added without 
 
 ename kiln 111 ^ appb « ,tlon k of heat The temperature of the 
 enamel-kiln is usually about six degrees of Wedgwood’s 
 
 pyrometer, answering to 1857 degrees of Fahrenheit’s “scale. 
 
 In the year 1817, the Society for the Encouragement of Arts 
 &c., awarded a premium to Mr. R. Wynn, for a list of receipts 
 
 fluxS Un A at c d ^ f °w he P re P aration of enamel colors and 
 
 volume of the 1 ? ° f ^ 1 paper is ™ erted ^ the 35th 
 volume of the Transactions of that Society. 
 
 The fluxes are, No. 1. Red lead.8 parts. 
 
 Calcined borax . . II 
 
 Flint powder ... 2' 
 
 Flint glass.6 
 
 No. 2. Flint glass .... 10 
 
 White arsenic ... 1 
 
 Nitre. 1 
 
 No. 3. Red lead.1 
 
 Flint glass.3 
 
 No. 4. Red lead. 
 
 Borax, not calcined 5j 
 
 Flint glass.8 
 
 No. 5. Flint glass.6 
 
 Flux, No. 2 .4 
 
 Red lead.8 
 
 The ingredients forming each of these fluxes are melted to- 
 ,emer, and the compounds are then finely pounded for use. 
 
 1 he recipes for colors are as follows:— 
 
 YeUow. Red lead . ..8 parts. 
 
 Oxide of antimony .... 1 
 White oxide of tin .... 1 
 * n o red >ents well in a biscuit-ware mortar, and having 
 
 h n i a P !? ce £ f Dutch tile in the make grad- 
 
 suffer * to cool. Take of this mixture 1 part ; 
 ux ’ iNo - Grind them in water for use. By varying 
 
84 
 
 FORCELAIN MANUFACTURE. 
 
 CHAP. VI. 
 
 different shades of 
 
 the proportion of red-lead and antimony, 
 color may be obtained. 
 
 Orange. Red lead.12 parts. 
 
 Red sulphate of iron ... 1 
 
 Oxide of antimony .... 4 
 
 Flint powder. 3 
 
 after calcining these without melting, fuse one part of the com¬ 
 pound with 2| parts of flux. 
 
 Dark-red. Sulphate of iron, calcined dark 
 
 Flux, No. 4. . 6 parts 
 Colcothar . . 1 
 Light-red. Red sulphate of iron, 
 
 of this 
 
 1 part. 
 3 
 
 1 part. 
 
 Flux, No. 1.3 
 
 White lead. 
 
 Brown. Manganese.2^ 
 
 Red lead.8| 
 
 Flint powder.4 
 
 The style of decoration described in the preceding pages of 
 this chapter, is in a great measure confined to the most costly 
 descriptions of porcelain. Wares which are fitted by their 
 price for being brought into more general use, undergo a differ¬ 
 ent kind of embellishment. A great variety of neatly executed 
 patterns are transferred to their surfaces from impressions pre¬ 
 viously printed on paper. Before the introduction of this style 
 of ornament, table services of home manufacture were either 
 composed of plain Queen’s-ware, with occasionally a colored 
 edge ; or at best were furnished with a painted border, which 
 displayed but little taste in its conception, or ability in its exe¬ 
 cution. This modern improvement has added materially to the 
 decent comforts of the middle classes in England, and has more 
 than any other circumstance contributed to the great extension 
 of our trade in earthenware with the continent of Europe. 
 When first invented, and for some time afterwards, the designs 
 employed were only imitations of figures and objects seen on 
 old blue China porcelain; but a better taste has since prevailed, 
 and artists employed in the composition of patterns no longer 
 think it necessary to outrage truth in their representations. 
 Landscapes and figures, in conformity with the simplicity of 
 nature, and exhibiting a considerable degree of taste, are now 
 so common, that this new advantage derived from the printing- 
 press is enjoyed without exciting attention or commanding ac¬ 
 knowledgment. 
 
 The method of transferring printed designs to earthem ves¬ 
 sels is thus pursued. The landscape or pattern is engraved 
 upon copper, and the color, which is mixed with boiled linseed 
 oil, is laid on the plate in the same manner as ink is usually; 
 
CHAr. VI. APPLYING COLORS AND ENGRAVINGS. 85 
 
 applied by copper-plate printers. To increase the fluidity of 
 the oil, the plate is then temporarily placed in a stove, a sheet 
 of damped tissue paper is laid on it, and both are passed in the 
 ordinary manner through the press. The paper, wet with the 
 color, is then delivered to a girl, who reduces its size by cut¬ 
 ting away the blank portion surrounding the pattern, and passes 
 it to another girl, by whom the impression is applied lightly 
 to the ware when in the, state of biscuit. A third girl is next 
 employed, who, with a piece of woollen cloth rolled tightly in 
 the form of a cylinder, rubs the paper closely against the piece, 
 in order to press the color sufficiently into its substance. The 
 paper thus rubbed is left adhering to the article for an hour, 
 when both are placed in a- cistern of water, so that the paper 
 beepmes soft enough to be peeled off without violence, having 
 transferred to the biscuit the impression which it had received 
 from the copper-plate. 
 
 When the pieces thus printed have stood a sufficiently long 
 time to become dry, they are placed in an oven, to which a 
 gentle heat is applied, in order, by dissipating the oil, to pre¬ 
 pare the wares for receiving the glaze. This is, of course, 
 completely transparent, as otherwise the distinctness of the 
 pattern would be impaired. 
 
 For a long time blue, produced from the oxide of cobalt, was 
 the only color employed; but, of late, the potters have extend¬ 
 ed to this pleasing branch of their art all the colors on their 
 palette. 
 
 The glaze on printed goods is vitrified in the gloss-oven in 
 the manner already described. 
 
 The French potters employ a different method for transfer¬ 
 ring engraved patterns. They cast a sheet of fine glue, about 
 a quarter of an inch thick, and diluted while warm to such a 
 degree that when cool it shall be perfectly flexible, and have 
 the consistence of leather. This glue being applied upon the 
 plate, and pressed with the hand, receives the colors according 
 to the pattern, which it gives back to the surface of any vessel 
 to which it may be applied. Two impressions may generally 
 be given in this manner without a fresh application of the glue 
 to the plate. After the second has been impressed, the surface 
 of the glue is cleaned carefully with water applied by a soft 
 brush, and serves again as before. 
 
 The decoration of earthenware by means of engravings is of 
 much more recent adoption in France than in England,—not 
 having been used in the former country until about the year 
 1805. 
 
 In the report made by the Committee appointed to examine 
 into the progress of the arts and manufactures in France, as 
 
 II 
 
86 
 
 TORCELAIN MANUFACTURE. 
 
 CHAP. VII. 
 
 exemplified by specimens exhibited at the Louvre in 1819, and 
 to which report allusion has already been made in this Chapter, 
 attention is drawn to a curious process, whereby a porcelain 
 manufacturer was enabled, on being furnished with an en¬ 
 graved copper-plate, to produce impressions on any scale that 
 might be required, whether larger or smaller than the original. 
 For this purpose no second plate of copper was needed; and 
 the enlarged or diminished copies might be furnished in the 
 course of a very few hours. It is to be regretted that no de¬ 
 scription was given of the means employed for effecting this 
 curious process; but the Committee, who personally witness¬ 
 ed its execution, expressed themselves perfectly satisfied as to 
 its efficiency, and awarded an honorary gold medal to the in¬ 
 ventor.* 
 
 CHAP. YH. 
 
 ON THE MANUFACTURE OF TOBACCO PIPES. 
 
 This Manufacture prosecuted to a great extent.—Description of Material.— 
 Rolling.—Boring.—Moulding.—Polishing.—Baking.—Description of Kiln 
 —Of Crucibles.—Manufacture in Holland.—Originally conveyed there 
 from England. 
 
 The manufacture of tobacco pipes forms a branch of the 
 potter’s art, which has acquired considerable importance from 
 the extent to which it is prosecuted; and it is at the same time 
 interesting from the nature of the processes employed. A short 
 account of these will, therefore, not be thought misplaced in 
 this treatise. 
 
 The clay chiefly employed for the purpose is found in the 
 island of Purbeck, in Dorsetshire, and is preferred on account 
 of its extreme whiteness. Previously to being used, it must 
 be diligently purified from all extraneous matters. The means 
 employed for this latter purpose, being the same as have al¬ 
 ready been described, their recital may be omitted here. 
 
 When the purification is accomplished, and the clay has been 
 formed into cubical masses, weighing each from eighty to one 
 hundred pounds, the workman from time to time cuts off small 
 portions, each sufficient to form one pipe, and, first kneading 
 them thoroughly upon a table, rolls them out to nearly the 
 form and size of pipes, leaving a bulb at the end for the forma¬ 
 tion of the bowl. In this operation, the skill of the man is 
 made apparent by the near approach which this roll makes to 
 the dimensions actually required. Persons who have had a 
 
 * Ann. dc Chim. ct dc Phys. tom. \iii p. 91. 
 
CHAP. VII. MANUFACTURE OF TOBACCO PIPES. 87 
 
 competent experience will succeed in this respect to such a 
 point as completely to fill the mould, to which the rolls must 
 afterwards be transferred, leaving but little surplus clay to clip 
 away. 
 
 Fig. 5. 
 
 When the rolls have been formed for a short time, and by 
 that means have become sufficiently hardened, the workman 
 proceeds to bore the stem by introducing an iron needle. This 
 part of the manufacture calls for a great deal of address, and 
 
 ' Fig. 6. 
 
 can only be satisfactorily accomplished after long practice. In 
 performing it, the roll is taken between two fingers, which fol¬ 
 low the point of the needle in its course through the whole 
 length of the stem. Near to its point the needle has a circular 
 enlargement, the progress of which may be felt through the 
 substance of the clay; and thus the execution of the task is 
 somewhat facilitated. The bore must be made as exactly as 
 possible in the axis of the stem; and, in forming it, the needle 
 must be pushed forward by means of its wooden handle, with 
 a gentle and equable pressure. The part which is to form the 
 head or bowl of the pipe is then bent so as to give it the proper 
 inclination. 
 
 The mould, into which the stem is next placed, is of copper, 
 and divided into two similar parts. On being put to use, the 
 
 Fig. 7. 
 
 whole interior surface of both sections must be slightly touched 
 with a brush containing some very limpid oil, that the stem 
 may be afterwards delivered from it without difficulty. The 
 roll of clay being placed in one section, the other is fitted to it 
 according to marks previously made, so as to insure the perfect 
 correspondence of the two parts. The mould is then subject¬ 
 ed to the action of a small iron press, in which the two parta 
 
88 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VII. 
 
 are forced together by means of nuts and screws; and by this 
 means its exterior form, with all its ornamei ts, is at once given 
 to the pipe. 
 
 The head or bowl has yet to be fashioned. This is in part 
 effected by the fore-finger, and more perfectly thereafter by 
 means of a stamp or form attached to the mould, and which by 
 the action of a lever is introduced within the hollow which the 
 finger has made for the purpose. The bore of the stem is then 
 continued into the bowl, by pushing the needle up to its handle; 
 any excessive quantity of clay that may have been used is next 
 cut away, and the pipe is smoothed by means of an iron or cop¬ 
 per blade. 
 
 The pipes as they are formed are spread out and arranged 
 upon a board, that they may be still further dried; and when 
 they have acquired a certain consistence, any roughnesses that 
 may appear upon the bowl are rubbed away with an appropri¬ 
 ate horn instrument, which is provided with a groove, of which 
 the workman avails himself to perfect the circular form and to 
 smooth the edge of the bowl. 
 
 After this the pipes are placed a second time in the moulds, 
 that any imperfections which they have acquired in their shape 
 may be remedied; and they are then left until sufficiently hard¬ 
 ened to receive the last polish, which is given by rubbing them 
 with flints bored with holes, some of which are of the same di¬ 
 ameter as the stem, wtfile others will admit the head of the 
 pipe. If it should then appear necessary, the workman retouch¬ 
 es the different ornaments on the pipe with a kind of bodkin, 
 and the needle is withdrawn from the stem. 
 
 These various operations, which bear an appearance of com¬ 
 plexity in the narration, are yet so easy of accomplishment, 
 that a clever moulder will furnish 3500 pipes in a week. 
 
 The kiln used for baking the pipes is cylindrical; having a 
 circular fireplace at its bottom. With the exception of the 
 spaces required for the circulation of heated air, the interior 
 of the. kiln is occupied by crucibles, wherein the pipes are 
 placed. These crucibles, which are made very thin, are com¬ 
 posed of the same clay as the pipes, and are strengthened by 
 the insertion of broken pipe-stems. The bottoms are framed 
 of these stems, radiating towards the centre, and having the 
 interstices plastered with pipe clay. The top of each is dome¬ 
 shaped ; and a pillar of clay is placed in the centre through the 
 whole altitude, which serves at once to strengthen the crucible, 
 and to support the stems of the pipes. The side of the cruci¬ 
 ble is provided with six horizontal ledges, proceeding at equal 
 distances all round, and upon these the bowls of the pipes are 
 arranged, while the stems are made to lean against the central 
 
CHAP. VII. MANUFACTURE OF TOBACCO PIPES. 89 
 
 pillar. The crucible is capable of containing in these six di¬ 
 visions fifty gross of pipes; and, if the heat of the furnace is 
 properly managed, these will be sufficiently baked in seven or 
 eight hours. 
 
 Fig. 8 
 
 The property possessed by tobacco pipes of adhesiveness to 
 the tongue, is owing to the great affinity which the clay has 
 for water: this quality is much increased by the baking pro¬ 
 cess. 
 
 The manufacture of tobacco pipes is prosecuted to a very 
 considerable extent in Holland, whence large quantities have 
 long been exported annually. For the introduction of this art 
 the Dutch are indebted to this country; in proof of which as¬ 
 sertion, Mr. Hollis, who passed through the Netherlands in 
 1748, mentions that, having visited very extensive pipe-works 
 at Gouda, he was informed by the master of it, that even to 
 that day their principal working tools bore English names. 
 
 H2 
 
90 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VIII. 
 
 CHAP. VIII. 
 
 ON THE PORCELAIN MANUFACTURE OF CHINA. 
 
 Obscurity wherein its Origin is shrouded—Chiefly practised at King-te- 
 Ching.—Supposed Superiority of Old China Ware.—Materials employed. 
 —Kao-lin—Pe-tun-tse—Their Preparation.—Oils or Varnishes—Their 
 Composition.—Hao-che—Its Superiority to Kao-lin.-—Analysis of Kao¬ 
 lin.—Extent of Factories at King-te-Ching.—Great Number of Workmen 
 employed.—Preparation of Materials.—Method of fashioning Utensils.— 
 Moulds.—Division of Labor.—Deficiency of Chinese in the Art of Design. 
 —Their Excellent Colors.—Numerous Hands employed in Decorating each 
 Piece.—Bad Effect of this System.—Blue long the only Color used for 
 Painting China Ware.—Mode of Preparing various Colors.—Chinese ig¬ 
 norant of Chemical Science.—L T miain.—Tsou-tchi.—Kia-tsing—Method 
 of forming it.—Chinese Furnaces.—Passion for Old Porcelain.—Ku-tong. 
 —Mock Antiquities.—Reasons for Costliness of China Ware in Europe. 
 —High Prices formerly paid in China.—Finest Specimens not brought to 
 Europe.—Porcelain Tower at Nan king.—Chinese Potters prepare Mate¬ 
 rials for the Use of their Descendants.—Common Wares made in China. 
 —Attempt of the Emperor to transfer the Manufacture to Pekin.—His 
 Want of Success. 
 
 No success has attended any efforts that have been made to 
 discover the origin of the art of making porcelain in China, 
 and the date of its invention remains veiled in obscurity. The 
 most that is known on this head is gathered from the written 
 annals of Feou-leang, a city belonging to the same district of 
 the empire as King-te-ching, wherein it is recorded that, from 
 the time answering to the year 442 of the Christian era, the 
 last-mentioned place has enjoyed the honor of supplying the 
 imperial court with porcelain, and that one or two mandarins 
 have usually been deputed from Pekin to inspect this part of 
 the workman’s labors. The invention of the art would assured¬ 
 ly date from a much earlier period than that here mentioned; 
 as it would be long ere the manufacture arrived at such a state 
 of perfection as to render it an object of interest to the court. 
 
 It is a very common opinion in China, that the porcelain 
 ware made by their ancestors was superior in quality to any 
 more recently manufactured. This belief is grounded on the 
 fact, that pieces of porcelain are frequently dug from the earth, 
 which are uniformly found to be of the very finest description. 
 It has been remarked, that this fact is not by any means con¬ 
 clusive evidence upon the subject; the buried pieces were 
 most probably concealed, during periods of civil commotion, on 
 account of their value, and in order to preserve them for their 
 owners, who were without an equal inducement to bury arti¬ 
 cles of more common use. An opinion likewise prevails, and 
 is supported by reference to the same fact, that the quality of 
 porcelain vessels is improved in beauty by a lengthened burying 
 
CHAP. VIII. CHINESE METHOD OF MANUFACTURE. 91 
 
 in the earth ; and the same answer has been applied to this as 
 to the first-mentioned assertion. 
 
 The Chinese employ in the composition of their porcelain 
 two kinds of earths, and two oils or varnishes. Of the earths 
 one, which is called kao-lin, is found intermixed with particles 
 of a shining 1 substance resembling mica; the other is known 
 by the^ name of pe-tun-tse, and is of a brilliant white, exceed¬ 
 ingly fine in its grain, and soft to the touch. Both these de¬ 
 scriptions of earths are found -in mines or quarries situated be¬ 
 tween twenty and thirty leagues from King-te-ching, to which 
 place they are brought in small vessels, which are continually 
 passing up and down the river of Jao-tcheou for that purpose. 
 The hard blocks of pe-tun-tse are cut from the quarry in the 
 form and^ about the size of our bricks, and are brought in this 
 state to King-te-ching. The first preparation which these lumps 
 undergo, is that of breaking and pounding them coarsely with 
 iron mallets, and afterwards more completely in mortars with 
 pestles, wrought either by the hand or by a water-wheel. By 
 this means the blocks of pe-tun-tse are reduced to an almost 
 impalpaple powder, which is thrown into an urn-shaped vessel 
 nearly filled with water, and then stirred briskly about, that the 
 particles may be intimately mixed with the water. When this 
 mixing has been effected, and the fluid has been left during a 
 short time to repose, a white creamy substance forms upon the 
 surface, to the depth of two or three inches: this, being 
 skimmed off, is transferred to another vessel, supplied with 
 clear water. The fluid remaining in the first vessel is then 
 again stirred up; another portion forms upon the surface, which 
 in its turn is removed, and added to the first skimming; and 
 this process is continued as long as any creamy substance can 
 be collected from the surface. What remains in the urn-shaped 
 vessel has not been sufficiently ground ; and, being collected 
 from the bottom, must be again submitted to the process of 
 grinding. 
 
 The skimmings are left to settle in the second vessel, until 
 the solid portion has subsided to the bottom, leaving the super¬ 
 natant water perfectly clear: this is then poured oft’; the sedi¬ 
 ment is transferred to moulds, wherein it remains until nearly 
 dry; and the cakes are then taken out and cut into square 
 pieces of the size most convenient for use. The pe-tun-tse is 
 then in a fit state for combination with kao-lin; and the squares 
 are sold by the hundred to the porcelain makers. It is not often 
 that the manufacturer can venture upon using this material in 
 the state wherein he buys it; the men who have been previ¬ 
 ously employed in preparing the cakes, most generally mix in 
 the squares as large a portion of foreign matter as they expect 
 
92 TORCELAIN MANUFACTURE. CIIAP. VIII. 
 
 will escape detection: a separation of these previously to the 
 employment of the eartli becomes, therefore, needtuh 
 
 A similar process is followed in the preparation ot kao-lin; 
 but this substance being much less hard than pe-tun-tse, less 
 labor is required for its performance. 
 
 The two substances described as oil or varnish are procured, 
 one from a combination of pe-tun-tse with another mineral sub¬ 
 stance, and the other from lime. In the preparation of the first 
 of these, such stones are preferably selected as have the whitest 
 appearance. These undergo the same processes of grinding 
 and washing as have already been described ; except that the 
 creamy substance, when it has subsided in tire second vessel, 
 is not all put into moulds, but only the upper and finer stratum 
 is gathered for the preparation of this varnish. To each one 
 hundred pounds of the substance thus separated one pound of a 
 mineral called she-kao, which is a kind of gypsum, is added. 
 This stone, which resembles alum in its appearance, is first 
 raised in a furnace to a red heat; and then reduced, by pound¬ 
 ing and rubbing in a mortar, to a very fine powder ; in which 
 state its union with the purified pe-tun-tse is effected, the con¬ 
 sistence of the compound being perfectly fluid. 
 
 The preparation of what is called oil of lime , the fourth in¬ 
 gredient required, is thus managed :—Lumps ot quicklime are 
 first sprinkled with water, and reduced to a powder; upon this 
 a bed of dried fern is placed; then another layer of lime, cov¬ 
 ered again by fern ; and so on alternately, until the pile having 
 reached a moderate height, fire is applied: and when the whole 
 of the fern is consumed, the ashes are collected and strewn 
 upon fresh beds of fern, which are again fired ; and this burn¬ 
 ing process is repeated five, six, or more times successively,— 
 it being held that the more frequently the ashes are burnt, the 
 better is the quality of the product. Some ancient Chinese 
 annals affirm that, instead of fern, the wood of a kind of medlar 
 tree was anciently used; and that the quality of the porcelain 
 was in consequence more beautiful. This wood is now become 
 too scarce to be employed for the purpose. The lime and fern 
 ashes are next thrown into a vessel containing fair water, and 
 she-kao is added in the same proportion as to the creamy dilu¬ 
 tion of pe-tun-tse. This she-kao dissolves; and the solid matter 
 being separated from the water by subsidence, and removed in 
 a tolerably fluid state, forms what the Chinese manufacturers 
 call the oil of lime, to the agency of which they attribute all 
 the lustrous appearance of their porcelain. Lime, when un¬ 
 combined, is infusible, except at a very intense degree of heat; 
 and the fern ashes thus added, are essential, acting as a flux, 
 and promoting the fusion of the glaze in the furnace. In mix- 
 
;hap. viii. 
 
 CHINESE METHOD OF MANUFACTURE. 
 
 93 
 
 Inimfit t I? r: n i shes togetller ’ on] y one measure of the oil 
 •r lime is added to ten measures of that of dp tun 1 1 
 
 ng taken that the consistence of both is Lai ThP i f 
 ime is easily, and to tlie seller profitably, adulterated bvthe 
 ddHon of water, combined with such a 
 
 ItT, ETT? US Pr ° P u er degree of consistency ° f ^ 
 
 iSSfr 
 
 'hich can be «dva„tag e M uSr»Sd' intte ^ 
 
 ead of kao lirTth 68 ’ ^lf CaPled bao ' cbe 1 and when used in- 
 ead ot kao-lin, the result is porcelain of very fine Pram ex 
 
 -edingly light, and much better qualified for receiving- colors* 
 
 ■t more brittle and far dearer in its cost, than the Commoner 
 
 r kao „r%h: e price °[ hao " cbe bein g three times that paid 
 kao-lin. I his new substance, when taken from the mine 
 
 idergoes the operation of a careful washing, to separate from’ 
 
 niK i rtn rVi" 1 W , hlch “ is 6u"d aclr 
 
 “ the , n pounded, and treated exactly in a similar 
 
 i?med Th ?? de l Cribed m the Preparation of kao-lin. It is 
 ed that hao-che, thus purified, is capable of beino- made 
 
 o porcelain without any admixture. b 
 
 , Jf tbe k ao-hn which, although much softer than the ne- 
 
 '"porcelain a'nd ^ ^ qU i arry I ! gives stren g tb and body P to 
 IsfnTfi! ’ d ’ c° nse< l uen,1 y, this, or some substitute p OS - 
 ° same quality, forms an indispensable ingredient in 
 
 rSr-5 1113 \ e } at ? d that some Europeans, having prh 
 
 ed y tfemto the 0me bl ° Ck ' S of P e ' tun - tse in Chma, and^on- 
 m ! own country, vainly endeavored to convert 
 
 Inufacturer^thpv 5 becomin g known to some Chinese 
 
 tacturers, they dendmgly remarked, “ that certainlv the 
 
 y p wh"LTl be a T mdeM ^ S° toS 
 
 y whose flesh was to sustain itself without bones” 
 
 s ml, 1 " k f nown ’. from the particles of mica which it con- 
 , ° have its origin in feispar, or graphic granite. It is in- 
 
 ree Tf^ ^ °[ a porceIain f umace even in China, the 
 ,1 f Y hlC ,‘ mU f be most tremendous, as some of the ma- 
 
 ne7» P °H? d m th ? Ir glazes couId not be vitrified at a lower 
 perature than would suffice to fuse Cornish granite The 
 
 WeuTne 68 °T Chlna agr u B Wkh the mines 0 Aiencon and 
 ! ar Eimoges, where a similar earth is found—all 
 
 eTextnT"/ SUpCr ‘ S “ Um of red - friable > micaceous rock, 
 hund tn L gneiss. Tiie constituent ingredients of kao-lin 
 und to be—silica 52, alumina 42, oxide of iron 0.33. 
 
94 
 
 CHAP. VIII 
 
 PORCELAIN MANUFACTURE. 
 
 The factories employed at Kin^chmg 
 as dweUmgs Ae WOTtaa^ ^ ^ as mU st appea| 
 
 S.'Ssssa .■££35;srasji s$sd 
 
 >"Te puriSS ? 1°tStSta has been complete 
 by the processes already descnhed th<inertoption»toun' 
 
 “Sea • “S ver° coatsest descriptions, the kaodm net! 
 
 ^e'SosUrrTon'r^t 5 toe ThSe operations of toe fac 
 
 ry, is that 
 
 gather so as to form , "^h TeSSd ZZ cemented, when 
 
 lhe P " continuaUy^rample^upon the paste bringing 
 
 SSSS=H|S=^ 
 
 lsS=SSi =|»3 
 
 watef or Jobule of air be left remaining in any portion of 
 mass, r the^article which - 
 
 spoiled by the expansion of the Win«•?» woult[ 
 
 SXS&SXMfc ‘»e poroela'e *» ™' - « 
 
 “ffiec^rffSioned by the Chinese workmen in a n 
 ner so similar to that adopted in our own potteries, that 
 
 1)6 The^ moulds ^sed^n The potteries of China for forming ph 
 of multSbrm shape are made in several ?or^s or^, 
 which are brought together when used. 1 hey are ma 
 yeltow Unctuous earth, which occurs abundantly mqnam«. 
 L Kino--te-chin<r; and its preparation by kneading and 
 is veryshnilar to that bestowed on the porcelara earths. W 
 
3HAP. VIII. CHINESE METHOD OF MANUFACTURE. 95 
 
 i uade and used with care, these moulds will last for a long time. 
 The Chinese workmen are not content with the work as deliv¬ 
 ered from the moulds, but uniformly finish the article by the 
 •land, using a variety of chisels and other tools to touch up the 
 various lines and forms given by the mould, as well as to sup¬ 
 ply its probable deficiencies; so that the potter executes, in 
 some sort, the art of a sculptor. • In works where different ob¬ 
 jects appear in relievo, these are made separately, and added 
 n the way commonly used in our own potteries. 
 
 It may give some idea of the number of hands employed in 
 he perfecting of every piece of porcelain to state what D’En- 
 recolles has related to occur with the commonest description 
 if tea-cup. The potter has the management of the wheel; and 
 inder his hands the cup assumes its form, height, and diame¬ 
 ter. It may be well imagined that this workman does not be¬ 
 stow much labor upon his task, when we are told that for fash¬ 
 ioning twenty-six cups he receives a sum equivalent to about 
 jhree farthings of our money: the cup, accordingly, is delivered 
 y him in a very imperfect state to a second workman, who fits 
 t to its base. From him it passes immediately to a third man, 
 i'ho, by means of a mould, placed on a kind of lathe, corrects 
 he imperfections of its shape. A fourth man, by the aid of a 
 hisel, corrects the inequalities and unevennesses of the edges, 
 nd pares the cup to a substance which renders it sufficiently 
 •ansparent. In the course of this operation he has frequently 
 ^course to water, in order by moistening to prevent the crack- 
 lg or breaking of the cup. A fifth workman then smooths the 
 iside by turning it gently on a mould. Considerable care is 
 ?quired in this stage to prevent any warping or the formation 
 f any cavity in the cup. Other men then, according to the 
 escription of cup which it is intended to produce, add either 
 le handle, or some ornaments in relievo, or make sunken im- 
 ressions. The operation that immediately precedes the first 
 iking of the cup, is that of rounding and hollowing the inside 
 ' its foot: this is performed with a chisel. 
 
 By this division of labor, the work is found to proceed with 
 'eater regularity and rapidity. Incessant attention to one op- 
 •ation, and that of a very simple kind, gives to each workman 
 insiderable dexterity and facility in its performance; and no 
 ne is lost in the changing of implements, as must be the case 
 one man had to conduct the manufacture through its several 
 liges. 
 
 Very large pieces of porcelain are made at King-te-ching. 
 hese are sometimes of such magnitude, that they must first 
 Jr formed in two, three, or more sections; each one of which 
 quires to be supported during its formation by three, or more 
 
96 PORCELAIN MANUFACTURE. CHAr. VIII. 
 
 men When the different portions are sufficiently dry, they 
 are united together with slip, in the same manner as handles 
 are attached; and the seams are smoothed and polished with an 
 iron instrument, so that, upon their being afterwards covered 
 with varnish, it is not possible to discern the points of junction. 
 
 The celebrated traveller Marco Polo mentions the vast ex¬ 
 tent to which the manufacture was carried at the tune ot his 
 residence in the Celestial Empire, and states that eight porce¬ 
 lain cups might then be purchased at the low price of a Vene¬ 
 tian groat* , . . 
 
 Among the Chinese, the art of design has never advancer 
 beyond the very first steps. These people appear ignorant of the 
 commonest rules of perspective; and their drawing, especially 
 where attempts are made to describe the human figure, it 
 wretched in the extreme. To make some amends for this, the 
 colors which they employ are exceedingly lively and brillian 
 so that European artists have found it a difficult task to vie witl 
 them in this respect. In examining the painted porcelain ot 
 this singular people, one is almost led to imagine that ther 
 artists have been debarred the sight of the objects which the} 
 attempt to represent, as otherwise some among them mus 
 surely have possessed sufficient innate taste to have led hin 
 from the o-eneral track, and instead of the miserable caricature 
 that disgrace their labors, to have made some approach toward 
 the truth in his delineation of natural objects. 
 
 The system of distributing the work among a great numbe 
 of hands, which is found so successful in the formation of porct 
 lain, is also pursued in the painting department. One artis 
 forms only colored circles about the edges; another trace 
 flowers, which a third paints; a fourth delineates nothing bu 
 mountains; a fifth describes water; a sixth traces the outline o 
 birds, which a seventh fills up with colors. Other artists trac 
 and color animals; others again perform the same tasks wit 
 the human figure, and in this way every object of art and nf 
 ture found upon their porcelain is the work of a particula 
 artist, who does not attempt the delineation of any other sul 
 ject. To this system, so useful in conducting every merely m< 
 chanical operation, may possibly be owing the continued ai 
 herence to old and faulty methods. The celerity which it 
 calculated to produce is unfriendly to the improvements su{ 
 gested by genius; and if even one artist among the crow 
 should be found with taste enough to aim at forming and en 
 bodying juster conceptions, his approaches to nature would or 
 
 * Marsden’s translation, 4to edition, page 560. 
 
CHAP. VIII. CHINESE METHOD OF MANUFACTURE. 
 
 97 
 
 serve to render more glaring the deformities produced by his 
 fellow-laborers, and would, therefore, be wholly inadmissible. 
 
 It is said, that for many ages the Chinese used only white 
 porcelain. Tradition adds, that its whiteness was most bril¬ 
 liant, that the pieces were altogether faultless, and that the 
 only name by which they were known when exported to other 
 kingdoms was that of “ the precious jewels of jao tcheou.” 
 Blue was the first color wherewith they ornamented pottery, 
 but the employment of all other colors very speedily followed 
 upon the introduction of this one. At first, and for a long 
 time, their blue color was prepared from a very fine kind of 
 lapis lazuli, which is native with them ; but they now import 
 smalt from England, at a price so much below that which their 
 own pigment had cost, that they have abandoned its manufac¬ 
 ture, and depend upon their foreign supply. The fine deep-blue 
 sometimes found upon specimens of old Chinese porcelain is 
 much admired and valued by virtuosi , and it is regretted that 
 this color is not used at present. It has been conjectured that 
 the Chinese, who unquestionably possess cobalt, most probably 
 employed its oxide also in the production of this esteemed blue 
 color before they were enabled by their commerce with Euro¬ 
 peans to substitute for it our cheaper pigment; that their 
 method of preparing the ore of cobalt was such, that it retained 
 the arsenic with which it is always found in combination, and 
 that, consequently, its color proved much deeper and richer 
 than the preparation made by us from the same mineral. Our 
 process being performed in a reverberatory furnace, the arsenic 
 is driven off in fumes. There are some kinds of cobalt which 
 are made to yield smalt without this previous roasting, and the 
 superior color which in such case is always produced is attribu¬ 
 ted to the presence of arsenic; since if this mineral be added to 
 smalt while in a state of fusion, the color will be rendered much 
 deeper. The preparation of smalt from cobalt without the aid 
 of fire is more expensive and the produce less in quantity than 
 where the common process is followed. The French manufac- 
 j turers procure their smalt by dissolving cobalt in nitric acid 
 (the aqua fortis of commerce), and then precipitating; and it 
 might be well for our porcelain makers to try the effect of this 
 method. 
 
 The red color used by the Chinese is made from common 
 ! green vitriol or copperas (proto-sulphate of iron), which goes 
 with them by the name of tsa-fari. This material they calcine 
 ; in a crucible, continuing to apply fire for so long a time as 
 thick black fumes are seen to escape from a hole made in the 
 top of the crucible; but when these fumes are succeeded by a 
 
98 
 
 PORCELAIN MANUFACTURE. 
 
 CHAr. VIII 
 
 light and thin cloud, they judge that the process has been car¬ 
 ried sufficiently far, and remove the crucible from the furnace, 
 previously, however, withdrawing a small quantity of the color 
 for inspection, as the test here mentioned is not unerring. 
 When the color proves good, the crucible is left to cool gradu¬ 
 ally, a cake of red matter is then found at the bottom, and a fur¬ 
 ther quantity, in the form of fine powder adhering to its sides. 
 This latter, being the purest and finest color, is kept separate 
 from the cake. Copperas affords about one fourth of its weight 
 of this color, which alone is used for producing all the various 
 shades of red in the porcelain works of King-te-ching. 
 
 White porcelain, made in China, owes much of the fine bril¬ 
 liancy of its color to the oils or varnishes before described; but 
 when a brighter and finer hue than can be thus produced is 
 needed, a mixture of the following kind is prepared. The 
 shores of some of their rivers furnish a species of agate, which 
 is without veins and nearly transparent, so that it approaches 
 to the nature of crystal. This stone is calcined to a white pow¬ 
 der, and then ground as fine as possible. To every ounce of 
 this they add two ounces of white lead (ceruse,) also in fine 
 powder, and these being mixed with the varnish, the whole is 
 laid on the porcelain in the same way as other colors. Accord¬ 
 ing to the descriptions given to us, this compound, besides be¬ 
 ing used for the production of a brilliant white, forms also the 
 ground or basis of several other beautiful colors. Their green, 
 which is prepared from the oxide of copper, is said to be con¬ 
 verted into a fine violet color by admixture with the white just 
 described. Such a change as this must of course be the effect 
 of chemical action promoted by the heat of the furnace. The 
 mere mechanical mixture of white with green would only re¬ 
 duce the depth of its shade. A very small proportion of the 
 white suffices, it is said, to produce a very deep violet, and the 
 hue is rendered lighter in proportion as the quantity of white is 
 increased. Their yellow is said to result from the mixture, in 
 due proportions, of this white with copperas (proto-sulphate of 
 iron). The accounts we have of those processes among the 
 Chinese, which depend upon chemical laws, are given with so 
 little regard to accuracy, and betray so great a want of scien¬ 
 tific acquirement, that these descriptions of their mode of pre¬ 
 paring colors cannot be received with any satisfaction. 
 
 The Chinese painters of porcelain usually mix their colors 
 with gum water, in which a small portion of either saltpetre 
 (nitrate of potass), white lead, or copperas has been first dis¬ 
 solved. Where a red color is used, the porcelain oil or varnish 
 is applied with it. This color is laid on the ware when in the 
 state of biscuit, that is, when it has been once in the oven, but 
 
CHAP. VIII. CHINESE METHOD OF MANUFACTURE. 99 
 
 it requires the heat of the second baking to bring out all its re¬ 
 quisite shades and tints. 
 
 Black porcelain, ornamented with gold, known under the 
 name of umiam, is much esteemed in the East. The black is 
 produced by mixing three drachms of deep blue, with seven 
 drachms of the varnish, which they call oil of stones. The black 
 thus prepared is laid on when the porcelain is first dried, and 
 when the black is also thoroughly dry, the vessel is baked. 
 The gold is then laid on, and the piece is subjected to another 
 baking in a furnace peculiarly constructed for the purpose. 
 The gold is ground in water to a very fine powder; and when 
 this has been very gradually dried in the shade, one tenth of its 
 weight of white lead is added, the mixture is incorporated 
 with gum water, and laid on in the same manner as colors are 
 applied. 
 
 The Chinese have a kind of porcelain, which is in much re¬ 
 pute with them, called tsou-tchi. This has the appearance of 
 having been broken, and of having its fractured edges brought 
 together and cemented, and then covered with the varnish ori¬ 
 ginally used. This effect is produced through the peculiar na¬ 
 ture of the varnish employed, which never spreads evenly, but 
 has a tendency when in fusion to run into veins and ridges of 
 various and uncertain forms. This varnish is made from a sort 
 of agate stones, reduced by calcination to a white powder, 
 which after being long ground in a mortar is carefully washed, 
 and used when of the consistence of cream. It has been sug¬ 
 gested that crystal would probably answer this purpose as well 
 as the coarse agates of the Chinese; and among all the de¬ 
 mands of fashion which is ever seeking for something new, it 
 might perhaps serve the interest of some manufacturer to put 
 this suggestion to the proof. 
 
 Another kind of porcelain, much esteemed by the Chinese, 
 is called by them kia-tsing , which signifies pressed azure. In 
 vessels of this description the colors appear only when the 
 cups are filled with liquid. The manner of making porcelain 
 so as to produce this effect is as follows:—The cup is made 
 very thin, and after having been once baked, the colors are ap¬ 
 plied in the required forms on its inner surface. When dry, a 
 coating of porcelain earth, the same as that already composing 
 the cup, must be laid on the inside; over this, the usual varnish 
 is laid, so that the colored figures are inclosed between two 
 coats or bodies of the ware. The outside, already very thin, is 
 then ground down almost to the painted figures, which are 
 thus made to appear externally, when they must be covered 
 anew with a coat of varnish so as to be scarcely perceptible 
 from the outside, until the vessel being filled with liquid, this 
 
100 
 
 PORCELAIN MANUFACTURE. 
 
 CHAP. VIII. 
 
 acts as a kind of foil behind, and throws ont the figures which 
 before were obscured. So much carefulness is called for in 
 the production of kia-tsing, that the art is very seldom prac¬ 
 tised. 
 
 Another admired art among this people is that of producing 
 the semblance of various figures upon pure white porcelain, 
 whose surfaces are yet entirely smooth. Having fashioned a 
 vessel, with the finest materials and extremely thin, it must be 
 polished inside and out, when a stamp cut with the requisite 
 figures in relief must be pressed upon the inner surface of the 
 unbaked vessel. The finest white varnish must next be applied 
 over its entire surfaces, so that the cavities impressed by the 
 stamp are filled by it, and the smoothness of the inner surface 
 is restored. When the ware is baked, the varying thicknesses 
 of the more opaque varnish will be apparent through the trans¬ 
 parent sides of the cup, and the w T hole of the figures will then 
 be seen as finely and accurately traced as if painted on the out¬ 
 side. 
 
 The methods employed by the manufacturers of King-te- 
 ching in applying the varnish, vary with the different qualities 
 of the wares under operation. For very fine and thin porce¬ 
 lain two exceedingly thin coatings are very carefully applied, 
 and some dexterity is required, both with regard to the quantity 
 laid on, and the equable manner of its application. To pieces 
 of inferior quality, as much varnish is applied in one coating 
 as is comprised in the two layers just mentioned. The foot of 
 the vessel is never properly formed until this stage of the 
 manufacture, and after the painting and varnishing have been 
 completed, when this part is finished on the wheel, and var¬ 
 nished likewise. The work is then fit to be placed in the oven. 
 
 The construction of furnaces and the system followed in 
 baking porcelain in China differ so little from the structure and 
 method pursued in England, that little need be said here con¬ 
 cerning them. It has already been mentioned that the nature 
 of the materials employed calls for a much higher degree of 
 heat than is necessary in our potteries. To insure this, the 
 Chinese are very careful in providing a rapid draught, and in 
 the incessant feeding of their furnaces with small billets of 
 wood, so as to insure its most rapid combustion. The learned 
 Jesuit D’Entrecolles observes, as a thing quite unaccountable, 
 and even inconceivable, if he had not witnessed the fact, that 
 notwithstanding the enormous consumption of wood during so 
 many hours, none of its ashes are ever found upon the hearth 
 of the oven. There would have been greater reason for aston¬ 
 ishment had the contrary fact appeared. The rapid draught 
 excited by the disposition of the oven, and the excessive degree 
 
CHAP. VIII- CHINESE METHOD OF MANUFACTURE. 101 
 
 of its temperature, would serve to carry away completely 
 through the flue so light a substance as wood ashes. 
 
 The taste for old porcelain appears to prevail fully as much 
 in China as it has ever done in this country. It is asserted by 
 some persons, that such as was made in former days was not 
 only composed of finer materials, but was more perfect in the 
 mode of its manufacture. Unfortunately for this assertion, 
 there are workmen at King-te-ching, who make it their occu¬ 
 pation to counterfeit these much-coveted relics of antiquity, 
 which are called ku-tong, and in this they succeed so as to de¬ 
 ceive the most observant connoisseurs. In the preparation of 
 these mock antiques there is but little variation from the meth¬ 
 ods usually practised. They are made thicker than modern 
 porcelain, and are made to undergo the ceremony of burial for 
 one or two months in the most lothesome sink of filth which 
 can be found, by which means every appearance of newness is 
 effaced. 
 
 Several reasons are assigned for the high price at which 
 Chinese porcelain is sold in Europe. One of these is, that owing 
 to their very unscientific manner of conducting the baking 
 process, it rarely happens that some, and sometimes a very con¬ 
 siderable portion, is not spoilt by unequal or excessive heat, and 
 converted to a deformed and shapeless mass. Another reason 
 for dearness is, the constantly diminishing supply of the mate¬ 
 rials used, and more especially of fuel, which becomes very ex¬ 
 pensive. It is added, that as those pieces which are prepared 
 for the markets of Europe, are of patterns unacceptable to the 
 taste of home consumers, and as the factors are exceedingly 
 particular in rejecting every article which exhibits the slightest 
 defect either in form or color, the prices paid to the manufac¬ 
 turers for such as are accepted must be sufficiently high to in¬ 
 clude the cost of those which are rejected. Notwithstanding 
 these circumstances, the prices at which porcelain is now fur¬ 
 nished in China are materially less than those demanded in an¬ 
 cient times, when, we are informed, as much as 100 crowns 
 were given for a single urn at the seat of manufacture. The 
 emperor monopolizes the finest specimens of porcelain manu¬ 
 factured in his dominions, and it lias thence been asserted, that 
 none which has ever found its way to Europe gives an adequate 
 idea of the perfection to which the Chinese have attained in 
 this manufacture. The Porcelain Tower erected at Nan-king 
 offers proof sufficient of the very durable nature of their manu¬ 
 facture. This building is of an octagonal shape, is of nine sto¬ 
 ries, and very nearly 300 feet high, and its entire surface is co¬ 
 vered with porcelain of the finest quality. Although this sin¬ 
 gular and beautiful edifice has been erected more than 400 
 
 12 
 
102 FOUCELAIN MANUFACTURE. CHAP. VIII. 
 
 years, it has hitherto withstood all the alternations of seasons, 
 and every variety of weather, without exhibiting the smallest 
 symptom of deterioration. 
 
 The intimate mixture of the two earthy materials so essen¬ 
 tial to the production of good porcelain is much more perfectly 
 attained, if, after the employment of the mechanical means al¬ 
 ready described, the united mass be left for a considerable time 
 before its employment. The Chinese frequently extend this 
 interval to a space of fifteen or twenty years; and instances are 
 not uncommon, where the provident care of a parent leads him 
 to prepare as much porcelain clay as will suffice for his son’s 
 use, during the whole period of his life. 
 
 The Chinese excel in the manufacture of brown earthen¬ 
 ware, which being sold at a very low price, is used commonly 
 throughout the empire. Porous vessels for cooling water are 
 also made by them of fuller’s earth, which is principally com¬ 
 posed of alumine and very pure silex, in combination with oxide 
 of iron. The name by which porcelain is distinguished in this, 
 the country of its earliest production, is tse-ki. 
 
 An attempt was once made by the government to remove the 
 seat of manufacture to the imperial city of Pekin. This, how¬ 
 ever, although no effort was spared in the business, proved un¬ 
 successful, and the sole prosecution of the art reverted to King- 
 te-ching, where, according to the statement of different travel¬ 
 lers, there are established 500 factories, giving employment to 
 more than a million of artisans. There appears no good reason 
 for believing that the manufacture would not have been prose¬ 
 cuted with equal success at Pekin, if those who directed it had 
 been so disposed; and the different result which has been re¬ 
 corded is supposed to have arisen from the disinclination of the 
 manufacturers to be brought so closely within the control of a 
 government supereminently famed for meddling with the pri¬ 
 vate concerns of its subjects. 
 
MANUFACTURE 
 
 or 
 
 GLASS. 
 

A 
 
 TREATISE 
 
 ON THE 
 
 PROGRESSIVE IMPROVEMENT AND PRESENT STATE 
 
 OF THE 
 
 MANUFACTURE OF GLASS. 
 
 CHAPTER I. 
 
 ON THE NATURE AND PROPERTIES OF GLASS, AND THE HIS¬ 
 TORY OF ITS MANUFACTURE. 
 
 Nature of Glass.—Its various Properties.—Its Utility.—The Assistance it 
 lends to Science.—Excessive Prices formerly paid.—Origin of its English 
 Name.—Aristotle’s Problems.—First Invention ascribed to the Phmni- 
 cians.—Manufactories of Alexandria.—Utensils found in Herculaneum. 
 —Malleable Glass.—Tax on Glass by Alexander Severus.—Portland Vase 
 —Glass employed in forming Windows.—Privileges granted to Manufac¬ 
 turers in France.—Plate-Glass Casting.—Establishment at St.Gobain._Its 
 
 early Failure, and Revival.—Manufacture commenced in England.—Of 
 Flint Glass.—Of Plate Glass.—Chinese unacquainted with Glass-making 
 —Importance of the Manufacture in England.—Glass made a Source of 
 Revenue. 
 
 Many circumstances contribute to render glass one of the 
 aost curious and interesting of manufactured substances. 
 
 . Although perfectly transparent itself, not one of the mate¬ 
 rs of which it is made partakes of that quality. Exceedingly 
 rittle while cold, it becomes, by the application of heat, so re¬ 
 markably flexible and tenacious as to be convertible into every 
 )rm that fancy may dictate or convenience suggest. Its great 
 uctility is shown in a very striking mannerly the slender 
 laments—small as the fibres of spider’s web—into which it is 
 )un for ornamental purposes. Many hundred feet of these 
 laments may be drawn out from a heated mass in the space 
 'one minute. Its pliancy and elasticity are proved by the 
 j cility with which, when in the state just mentioned, it may 
 m bent and retained in various forms, and by the energy 
 herewith its original shape is resumed at the moment of re- 
 ase from its constrained position. 
 
 ! The impermeability of glass to water, even under a consid- 
 able degree of pressure, is well ascertained. A few years 
 1°, the reverend Mr. Campbell, while on a voyage to South- 
 n Africa, among other philosophical experiments wherewith 
 • amused himself, caused two globular glass bottles hermet- 
 illy sealed to be lowered by means of leaden weights to the 
 pth of 1200 feet beneath the surface of the sea. These, 
 
106 MANUFACTURE OF GLASS. CHAP. I. 
 
 through the united and continuous exertions of ten men during 
 fifteen minutes, were again drawn up, and were found to be 
 perfectly empty. 
 
 The continued exposure of glass to the greatest heat where¬ 
 by it is melted, does not produce any sensible diminution in its 
 weight and quantity, or any alteration of its properties. It is 
 capable of receiving colors, and of retaining them in all their 
 lustre for an indefinite period. The strongest acids—with one 
 exception that will be noticed—have no efiect upon it, a cir¬ 
 cumstance that renders glass additionally useful in assisting 
 the researches of chemists. It is capable of receiving the 
 most perfect polish, preserves all its beauty, and does not lose 
 the smallest portion of its substance by the longest and most 
 frequent use. 
 
 The admirable qualities and important uses of glass have 
 been so happily pointed out by one of the most celebrated 
 writers of the last century, that no apology will be needed for 
 the insertion of the passage. 
 
 “ Who, when he saw the first sand or ashes by a casual in¬ 
 tenseness of heat melted into a metalline form, rugged with 
 excrescences, and clouded with impurities, would have im¬ 
 agined that in this shapeless lump lay concealed so many con¬ 
 veniences of life as would in time constitute a great part of the 
 happiness of the world 1 Yet by some such fortuitous liquefac¬ 
 tion was mankind taught to procure a body at once in a high 
 degree solid and transparent, which might admit the light of 
 the sun, and exclude the violence of the wind; which might 
 extend the sight of the philosopher to new ranges of existence 
 and charm him at one time with the unbounded extent of thf 
 material creation, and at another with the endless subordina¬ 
 tion of animal life ; and what is yet of more importance, migh 
 supply the decays of nature, and succor old age with subsidiar) 
 sight. Thus was the first artificer in glass employed, though 
 without his own knowledge or expectation. He was facilitat 
 ing and prolonging the enjoyment of light, enlarging the ave¬ 
 nges of science, and conferring the highest and most lasting 
 pleasures; he was enabling the student to contemplate nature 
 and the beauty to behold herself.” * 
 
 The utility of a substance which is daily and hourly renders 
 serviceable by all classes of persons in almost every humai 
 habitation cannot need to be exemplified. The aids which i 
 offers to scientific researches are almost equally apparent. Ti 
 notice the particular arrangements whereby the chemist, thf 
 naturalist, or the astronomer avails himself of some of the va 
 
 * Rambler, No. U. 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 107 
 
 nous properties of glass in pursuing his investigations, would 
 lead to descriptions which* although interesting in a hioh de- 
 gree, are foreign to the object of this treatise, wherein little 
 more than incidental notices can be given, on points that have 
 relation to improvements in the manufacture. 
 
 It may be useful, however, to notice here an error, not un- 
 frequently made, from observing glass to be the only transpa¬ 
 rent material used in making spectacles, opera glasses, and 
 other optical instruments. Persons are induced, from this cir¬ 
 cumstance, to ascribe to the peculiar quality of glass the ex¬ 
 clusive power of modifying the apparent magnitude, brightness, 
 and distinctness, of objects seen through it. This, however is 
 not an exclusive property of glass, but belongs to every trans¬ 
 parent substance having a density different from that of the air 
 which surrounds the observer. It depends also, not alone on 
 the inherent qualities and density of the transparent substance 
 through which the objects are viewed, but also on the form of 
 the surfaces which bound that substance, and on various other 
 circumstances not necessary to be noticed more particularly 
 here. The reader will, therefore, recollect, that the optical 
 properties of glass are common to the diamond and other trans¬ 
 parent solids, to all transparent liquids, and even to gases 
 Wass is commonly used on account of its cheapness and dura- 
 bility, and for other reasons of convenience. 
 
 It is impossible, however, wholly to dismiss this subject un¬ 
 accompanied by expressions of admiration at the genius of those 
 master spirits, who, by their discoveries and inventions, have 
 rendered glass subservient to purposes that open and enlarge 
 the held of human knowledge in some of those branches of nat¬ 
 ural philosophy which tend most to refine the nature and exalt 
 the character of man. 
 
 Familiarized as we are to the use and appearance of glass, 
 fet no person can ever become indifferent to its advantages, or 
 nsensible to its beauty. Neither can we feel astonishment at 
 he admiration which induced the ancients, while the art of 
 na ing it was little practised, and in those countries where it 
 ■vas not yet established, so greatly to covet the possession of 
 pass vessels as to purchase them at prices which to us appear 
 ‘xorbitant. We are told that the emperor Nero gave for two 
 handles 6000 sestertia, a sum nearly equal to 
 »U,UUUZ. of our money. These vessels were not of any extra- 
 'rdinary size, but were thus highly valued on account of their 
 'ertect transparence, and resemblance to crystal. 
 
 The name whereby this material is known to us is generally 
 ai . 0 derived from the Latin, and to have been suggested 
 y its great similarity in appearance to ice ( glacies .) It has 
 
108 
 
 MANUFACTURE OF GLASS. 
 
 CHAP. I. 
 
 been remarked, however, that the common Latin designation 
 is vitrum; and as the Romans gave this name also to the plant 
 which we call woad, and which our remote ancestors called 
 glastum, it is imagined that glass obtained the same distinctive 
 appellation, because of the bluish tint which it usually exhib¬ 
 ited. There is as little probable foundation for one as for the 
 other conjecture, nor is the question of much importance, since, 
 whichever way it might be determined, no light would be 
 thereby thrown upon any point of interest concerning the origin 
 of the manufacture, which, although involved in the most im¬ 
 penetrable mystery, is yet known to have existed long before 
 its introduction among the Romans. 
 
 The passage in the book of Job (ch. xxxvii. v. 18.) wherein 
 mention is supposed to be made of glass, has been adduced by 
 Neri in proof of its remote origin. Unfortunately for the cor¬ 
 rectness of this opinion it has been found, that in many ancient 
 versions, instead of the glass of the Vulgate and Septuagint, 
 other substances which have diaphanous and shining properties 
 are mentioned. In fact, the word in the original Hebrew lias 
 been frequently used, according to the fancy of translators, to 
 signify different bodies possessing lustre and transparency. 
 
 The two problems of Aristotle—if, indeed, they were pro¬ 
 pounded by that philosopher—“Why do we see through 
 glass 1” and “Why is it not malleable 1” comprise, perhaps, 
 the earliest written mention made of the substance. Theo¬ 
 phrastus, whose writings are not half a century later than the 
 time of Aristotle, mentions the use of sand from the river Belus 
 in making glass; and from that date (300 years b. c.) a know¬ 
 ledge of the material was pretty generally diffused. If reli¬ 
 ance is to be placed upon the statement, that the celebrated 
 sphere of Archimedes was made of glass, the art must in his 
 time (209 years b. c.) have arrived at a considerable degree of 
 perfection. 
 
 Many authorities concur in assigning the merit of the inven¬ 
 tion to the Phoenicians; and the assertion of Pliny is often re¬ 
 peated, which attributes the discovery to accident. Some 
 storm-driven mariners were boiling their food on the sands at 
 the mouth of the river Belus—a small stream running from the 
 foot of Mount Carmel in Galilee—where the herb kali was 
 growing abundantly, and are said to have perceived that the 
 sand, when incorporated with the ashes of this plant, melted 
 and ran into a vitreous substance. It is certain that the sand 
 about this spot was well adapted to the manufacture of glass, 
 and probably the glass-houses of Tyre and Sidon were supplied 
 thence with this material, which may have given rise to the 
 tradition. 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 109 
 
 That the ancient Egyptians were well acquainted with the 
 method of making glass cannot be doubted. The beads where¬ 
 with some mummies are adorned, although composed of earth¬ 
 enware, have an external covering of glaze, which is true 
 glass covered with a metallic oxide; and recent searchers 
 have discovered among the tombs at Thebes some pieces of 
 glass of a blue color, similar in their composition to the glazing 
 on the beads just mentioned. 
 
 The glass-houses of Alexandria were long famed for the 
 skill and ingenuity displayed by their workmen. The Romans 
 were, at one time, supplied with a great part of their glass 
 ware from that city. A coarse and impure manufacture of 
 drinking vessels had been prosecuted at Rome from the time 
 of Nero; but the art could have made only a slow progress 
 notwithstanding the encouragement offered by the high prices 
 at which glass wares of foreign make were sold in the impe¬ 
 rial city. The emperor Hadrian, while at Alexandria, re¬ 
 ceived from a priest some glass cups of various colors, which 
 had been used in the worship of the temple, and transmitted 
 them to Rome as objects of great value and curiosity, with an 
 injunction that they should be used on festivals and other great 
 occasions. 
 
 Utensils of glass have been found among the ruins of Hercu¬ 
 laneum, which city was destroyed in the reign of the empe¬ 
 ror Titus, by the same eruption of Mount Vesuvius which cost 
 the elder Pliny his life. It does not appear that glass was used 
 for admitting light to dwellings in Herculaneum, the largest 
 houses having windows made with a species of transparent tale. 
 
 In the British Museum are four large cinerary urns made of 
 green glass, which have been pronounced by a very competent 
 authority favorable specimens of the proficiency of the ancients 
 in the art of glass-blowing. These are round vases of an ele¬ 
 gant form, furnished with covers and two double handles. The 
 formation of these handles is, it is said, “such as must convince 
 any person capable of appreciating the difficulties which even 
 the modem glass-maker would have to surmount in their exe¬ 
 cution, that the ancients were well acquainted with certain 
 branches of the manufacture.” * 
 
 Several ancient authors (Dion Cassius, Petronius Arbiter, 
 and Isodorus) relate, that in the reign of Tiberius, an archi¬ 
 tect, who had been banished from Rome on account of his great 
 popularity, having, in his retirement, discovered the means of 
 so far altering the nature of glass as to render it malleable, 
 ventured to return to Rome, in the hope of securing both a re- 
 
 * Memoir on Glass Incrustations, by A. Pellatt, Esq. 
 
 K 
 
110 
 
 MANUFACTURE OF GLASS. 
 
 CIIAP. I. 
 
 mission of his sentence and a reward for his invention. This 
 discovery not agreeing, however, with the supposed interests 
 of the tyrant, who feared lest the value of gold might be low¬ 
 ered by its means, the architect was beheaded, and his secret 
 died with him. This is, probably, only another version of the 
 story related by Pliny, of the same important discovery having 
 been made by an artist in Rome, when such of the populace as 
 imagined that their interests would be injuriously affected 
 thereby conspired together and destroyed his dwelling. 
 
 A similar discovery, attended by results as unsatisfactory, and 
 which is said to have occurred in France in the more modern 
 times of Louis XIII., is recorded by Blancourt. He says, that 
 the inventor having presented a bust formed of malleable glass 
 to the cardinal Richelieu, was rewarded for his ingenuity by 
 perpetual imprisonment, lest the “ vested interests” of French 
 glass manufacturers might be injured by the discovery. 
 
 Without venturing altogether to deny the truth of these sto¬ 
 ries, it would be hard to subject to the charge of presumption 
 those persons who entertain doubts upon the matter. It does 
 not, certainly, prove the incorrectness of the statements, that 
 no subsequent examiner into the arcana of nature has been 
 equally fortunate ; and it is assuredly possible that some suc¬ 
 cessful investigator may yet be the means of revealing that 
 which has already been thus ascribed to more than one experi¬ 
 menter. 
 
 Improbable as the achievement of this would seem, it would 
 be scarcely more extraordinary than the transformation of linen 
 rags into sugar, or the conversion of saw-dust into “ wholesome, 
 palatable, and nutritious food.” The purposes both of use and 
 of ornament to which glass would in such a case be applied 
 are almost endless, and their importance can hardly be over¬ 
 rated ; nor should we in these days have occasion to fear, lest 
 the insensate obstructions of some modern Tiberius or Riche¬ 
 lieu should step between the discoverer and the promulgation 
 of his secret. 
 
 According to our present amount of knowledge, the chance 
 of realizing such a discovery is, however, limited within the 
 barest possibility. The quality of malleability is in direct con¬ 
 tradiction to that of vitrification; the existence of the one state 
 seems to be incompatible with that of the other. Some me¬ 
 tallic substances when greatly urged by fire are made to ap¬ 
 proach towards the state of glass, and then lose their mallea¬ 
 bility ; a fact which almost implies the impossibility of impart¬ 
 ing the latter property to glass. Kunkel has indeed observed, 
 that it is possible to produce a composition having an external 
 glassy appearance, which should be pliant and capable of being 
 
CHAP. I. 
 
 HISTORICAL NOTICES. 
 
 Ill 
 
 wrought under the hammer; and Neumann tells us, that in the 
 fusion of muriate of silver a ductile kind of glass is formed, 
 which may be moulded or turned into different figures, and 
 which may be pronounced in some measure malleable; facts 
 to which Henckel has referred in order to account for the tra¬ 
 ditionary stories of the ancients. 
 
 The Latin writers of the Augustan age make frequent men¬ 
 tion of glass. Virgil compares to it the clearness of the water 
 in the Fucine Lake (Ailn. vii. 759.); and Horace speaks of the 
 lustre and transparency of glass in a way which shows that it 
 could then be made with a considerable degree of perfection. 
 In the year 220 a tax was laid by Alexander Severus upon the 
 glass manufacturers of Rome, who at this time existed in such 
 numbers, that a principal quarter was assigned to them in that 
 city, wherein they might carry on their processes. This tax 
 was still levied in the reign of Aurelian. 
 
 The most celebrated specimen of antique glass is the vase, 
 which during more than two centuries ornamented the Barber- 
 ina palace, and which, having been subsequently purchased by 
 the late duchess of Portland, is better known in this country 
 as the Portland vase. This much-admired production was found 
 about the middle of the sixteenth century, inclosed in a mar¬ 
 ble sarcophagus, and deposited in the tomb of Alexander Seve¬ 
 rus, who died in the year 235. The body of this vase, which 
 for a long time was erroneously supposed to be formed of por¬ 
 celain, is made of deep blue glass, and is ornamented with 
 white opaque figures in bas-relief, which are designed and 
 sculptured in the style of cameos with a degree of skill which 
 is truly admirable. 
 
 Glass melted and cast into plates, is said by St. Jerome to 
 have been used in his time (a. d. 422,) to form windows. About 
 a century later, Paulus Silentiarius mentions the windows of 
 the church of St. Sophia at Constantinople which were covered 
 with glass; and from this period frequent allusions to the simi¬ 
 lar use of glass are met with in various authors. 
 
 Long before the establishment of the manufacture within 
 this island, glass was known and used in England. The Vene¬ 
 tians who traded with this country in very remote times fur¬ 
 nished this among other articles of commerce in exchange for 
 tin. The erudite Pennant is of opinion, that glass-making in 
 Britain dates prior to the Roman invasion. The Druids were 
 accustomed to impose upon their more ignorant followers by 
 means of clumsily-formed beads of colored glass, which they 
 pretended were endued with the quality of guarding their pos¬ 
 sessors from evil. 
 
 The venerable Bede, who lived very near the time, and who 
 
112 
 
 MANUFACTURE OF GLASS. 
 
 CHAP. I. 
 
 therefore had good opportunities for ascertaining the fact, has 
 asserted in his history of Weremouth, that in the year 674 the 
 abbot Benedict sent for artists from beyond seas to glaze the 
 windows of the church and monastery of Weremouth in Dur¬ 
 ham, and that these men were our first instructors in the art 
 of making window-glass. This art, however, took root but 
 slowly amotig us; and it was not until the eleventh century 
 that glass windows were at all commonly used, either in pri¬ 
 vate dwellings or in public and religious edifices. Previously 
 to this time, light was imperfectly transmitted through linen 
 cloths or wooden lattices. The houses of the commoner people 
 were not, indeed, furnished with this luxury until the thirteenth 
 and fourteenth centuries, in which respect our ancestors were 
 greatly behind the inhabitants of Italy and France. 
 
 The following curious entry, extracted from the Northum¬ 
 berland household book, makes it apparent that at a much later 
 period than the one just mentioned, the comfort of glazed win¬ 
 dows was not considered as a matter of course even in estab¬ 
 lishments where great state and magnificence were maintained. 
 This entry occurs in the minutes of a survey of Alnwick Cas¬ 
 tle made in the year 1567:— 
 
 “And because throwe extream windes the glasses of the 
 windowes of this and other my lords castels and houses here in 
 the country dooth decay and waste, yt were good the whole 
 leightes of everie windowe at the departure of his lordshippe 
 f om lyinge at anie of his sade castels and houses, and dowring 
 the time of his lordshippes absence or others lyinge in them 
 were taken doune and lade up in safetie; and at sooch tyme as 
 ether his lordshippe or anie other sholde lye at anie of the sade 
 places, the same might then be set uppe of newe with smale 
 charges to his lordshippe; whereas now the decaye thereof 
 shall be verie costlie and chargeable to be repayred.” 
 
 We learn also from Ray’s Itinerary (p. 187), that “in Scot¬ 
 land, as late as 1661, the window’s of the ordinary country 
 houses were not glazed, and only the upper parts of those of 
 even the king’s palaces had glass, the lower ones having only 
 two wooden shutters to open at pleasure and admit the fresh air.” 
 
 When desirous in former times of giving encouragement to 
 some important manufactures, the government of France was 
 induced to declare their prosecution to be nowise incompatible 
 with the dignity of aristocratic blood. Early in the fourteenth 
 century that government made a concession in favor of glass¬ 
 making greatly beyond this point, decreeing, not only that no 
 derogation from nobility should follow the practice of the art, 
 but that none save gentlemen, or the sons of noblemen, should 
 venture to engage in any of its branches, even as working ar- 
 
CHAP. I. HISTORICAL NOTICES. 118 
 
 tisans. This restriction was accompanied by the grant of a royal 
 charter of incorporation conveying various important privileges, 
 under which the occupation became eventually a source of 
 great wealth to several families of distinction, whose descend¬ 
 ants have at times attained to some of the highest dignities of 
 the state. 
 
 The good policy is apparent of thus holding forth induce¬ 
 ments to the only parties then qualified by the possession of 
 capital, and probably also by their intelligence, to establish 
 works upon a scale that could lead either to national advantage 
 or individual profit. A middle class of persons, springing from 
 the lower orders, have since gradually placed themselves at 
 least upon a level in point of intelligence with those of more 
 illustrious descent; and by the exercise of that intelligence, 
 conjointly with prudence, have acquired the means for under¬ 
 taking works of magnitude. This altered state of society 
 would render such exclusive privileges not merely unnecessary, 
 biit would make them absolutely pernicious. 
 
 Notwithstanding the marked encouragement just related on 
 the part of the French government, some time elapsed before 
 the manufactures of France could rival those of Italy. Venice, 
 in particular, long excelled in the quality of its mirrors and 
 drinking-glasses, with which the manufacturers of that city 
 supplied the rest of Europe. The most considerable of their 
 glass-houses were established at Murano, a village situated a 
 short distance from the city. 
 
 During the ministry of the celebrated Colbert, some French 
 artists, who while residing in the Venetian state had acquired 
 a knowledge of the processes used at Murano for the making 
 of plate glass, returned to France in the hope of profitably pur¬ 
 suing the manufacture in their native country. Such an event 
 falling in with the views of Monsieur Colbert, who w T as anxious 
 by every means to extend the useful arts within the kingdom, 
 these artists were in the year 1605 established with privileges 
 at Tourlaville near Cherbourg, and an advance of money was 
 made to them from the public coffers to assist in the formation 
 of their establishment. The plates made by this company were 
 blown, after the system used in the Venetian manufactories. 
 
 It was not until 1688 that the beautiful art of casting plates 
 of glass was invented by a manufacturer named Thevart, who, 
 obtaining a patent for the invention to continue in force during 
 thirty years, established a company and erected works in Paris, 
 where plates were cast of the then extraordinary dimensions 
 of eighty-four inches long by fifty inches wide, a size which 
 excited universal astonishment and admiration. The expense 
 of conducting such a manufactory in the metropolis was, how- 
 
 K 2 
 
114 
 
 MANUFACTURE OF GLASS. 
 
 CHAP. I. 
 
 ever, so great, that the establishment was transferred to St 
 Gobain in Picardy, where the undertaking was prosecuted, not 
 without considerable opposition from the more ancient asso¬ 
 ciation. 
 
 To accommodate the disputes between these rival establish¬ 
 ments, Thevart’s company was bound not to cast any plates 
 whose dimensions should be less than sixty inches in length 
 and forty inches in breadth. The largest piece that had then 
 been produced by blowing did not exceed fifly inches in its 
 largest dimension. This arrangement failed to produce har¬ 
 mony between the rivals ; but in 1695 that end was effectually 
 answered by uniting both companies under the same charter— 
 not however, as the issue proved, to their mutual advantage; 
 —for, possibly owing to the want of the salutary spur of com¬ 
 petition, the company declined in prosperity with such rapidity, 
 that in two years from the junction the united body was in a 
 state of insolvency, obliged to discharge most of its workmen, 
 and to abandon many of its furnaces. 
 
 No blame can be charged upon the French government for 
 the protection and privileges afforded to these companies. It 
 is probable that without some immunities neither of the estab¬ 
 lishments could at that early period have been undertaken. 
 The instances however are rare, and the circumstances whereby 
 they have been attended peculiar, in which joint-stock trading 
 companies have been prosecuted to advantage. The causes of 
 this fact are not difficult of explanation. It is seldom that the 
 personal interest of those to whom the particular management 
 is intrusted is sufficiently strong to insure the requisite amount 
 of attention, or the proper degree of pecuniary watchfulness, 
 if even the still more unfavorable condition does not arise 
 wherein private advantage is opposed to the general prosper¬ 
 ity, and it is sought to conduct the operations rather with a 
 view to individual profit than to the common advantage. 
 
 In the following year a new association was formed out of 
 the ruins of the old company, under the management of An¬ 
 toine d’Agincourt, who re-engaged the discharged workmen, 
 and by the prudence of his arrangements conducted the affairs 
 with considerable profit to the adventurers. 
 
 Blancourt, in his “Art de la Verrerie,” relates as the mode 
 in which the casting of plates of glass was discovered, that a 
 person who was melting some of this material in a crucible ac¬ 
 cidentally spilt it while fluid upon the ground. The metal ran 
 under one of the large flag-stones wherewith the place was 
 paved, which obliged the workman to take up the stone in order 
 to recover the glass. He then found it in the form of a plate, 
 such as could not be produced by the ordinary process of blow- 
 
CHAP. I. 
 
 HISTORICAL NOTICES. H5 
 
 mg. The man’s attention being roused by this fact, he was un- 
 abie to sleep; and conceiving at once the superiority of this 
 method for forming mirrors, he immediately commenced exper- 
 lmentmg ; and before the day appeared had proved the practi¬ 
 cability of the improvement which the purest chance had thus 
 placed within the sphere of his observation. This occurrence 
 is said to have arisen 200 years before it was related by Blan- 
 court, whose treatise is dated in 1698. It cannot therefore have 
 
 Tbevart' renCe t0 ^ ien recent proposals and performance of 
 
 The manufacture of flint glass was first begun in England in 
 the year 1557, at Savoy House in the Strand, and in Crutched 
 P nars. In 1635 Sir Robert Mansell obtained a monopoly for 
 making this kind of glass, in consideration of his being the first 
 person who employed pit-coal instead of wood in his furnaces. 
 1 lie art could not at this time have reached any great decree 
 of perfection, as permission was further conveyed by the patent 
 of importing drinking glasses of fine quality from Venice, and 
 another half century elapsed before this country became inde¬ 
 pendent of foreign supply for such articles. 
 
 The second duke of Buckingham has the merit of much im¬ 
 proving the manufacture of British glass by means of certain 
 \ enetian artists whom he brought to London in 1670. Three 
 years later than this period, the first plates of English glass 
 were made at Lambeth under the auspices of the same noble¬ 
 man. The violence of party spirit which characterized that 
 age should lead us to receive with caution all estimates of char¬ 
 acter which we may find recorded by contemporary biographers. 
 Although there was unquestionably much of vice and profligacy 
 ui the general conduct of this favorite of a vicious and profli¬ 
 gate master, w T e may yet hesitate to believe that the man who 
 could apply himself to the study of letters, and who, in the 
 manner above related, interested himself in promoting the use¬ 
 ful arts of life, could at the same time be so utterly depraved 
 both in mind and in heart as the page of history has repre- 
 sciitcd* 
 
 The first English establishment of magnitude for the casting 
 af plate glass was undertaken in 1773. A respectable body of 
 gentlemen at that time obtained a royal charter of incorpora¬ 
 tion, the privileges of which were confirmed to them by act of 
 3 fjj ameat > un ^ er the style of “ The Governor and Company 
 if British Cast Plate Glass Manufacturers;” and having sub- 
 bribed a capital or joint stock in eighty shares of five hundred 
 xiunds eaeh, constructed works of considerable extent at Ra- 
 /enhead, near Prescot, in Lancashire. This undertaking, the 
 >nly one of the kind existing in this country.vand rivalled by 
 
116 MANUFACTURE OF GLASS. CHAP. I. 
 
 none but that of St. Gobain in France, is still prosecuted with 
 success; and some description of its operations will be found in 
 a future chapter of this volume. 
 
 It is deserving of remark that the Chinese, whose early pro¬ 
 ficiency in the sister art of manufacturing porcelain was so 
 long unrivalled in Europe, have yet no practical knowledge of 
 glass making, and that even now there does not exist, though- 
 out that extensive empire, a single glass-house which is proper¬ 
 ly deserving of that name. Glass working is indeed practised 
 at Canton ; but the art is there wholly confined to the remanu¬ 
 facture of old or broken glass of foreign make, which is melted 
 and either blown or moulded into new forms. 
 
 A similar remark may be applied to the inhabitants of Hin- 
 dostan. Dr. Tennant informs us that “ before the arrival of the 
 Europeans, there was not a house in all India furnished with 
 glass windows,”* although there are not many climates where¬ 
 in such an employment of glass is more conducive to comfort 
 The knowledge which the Hindus then possessed of the art of 
 making this material was limited to the manufacture of trinkets 
 and trifling ornaments; in fact, their inability to construct fur¬ 
 naces of power sufficient to melt together the ingredients of 
 which it should be composed rendered it impossible for that 
 people to apply themselves to the manufacture for any more 
 useful purpose. “ Of its adaptation to optical purposes they 
 were so ignorant, as to be astonished and confounded at the ef¬ 
 fects of a common spy-glass. ”f 
 
 Any more minute inquiries into the origin and progress of 
 the manufacture of glass would not offer much either of inter¬ 
 est or advantage. The investigation would not connect itself 
 with any facts that bear upon the history of commerce, nor 
 throw any light upon questions of international policy. The 
 general abundance of materials needful for making glass, and 
 the facility with which these can be converted—at least into 
 articles fitted for common use—are opposed to its becoming 
 under any circumstances an object of great moment in foreign 
 commerce. The advantage possessed by this country in the 
 superior quality and abundance of its fuel does not offer suffi¬ 
 cient compensation for the heavy charges that would attend the 
 transport of such bulky articles to countries which themselves 
 possess adequate means for prosecuting the manufacture. 
 
 Glass-making, in its various divisions, has long proved a very 
 considerable branch of industry in this kingdom; and although, 
 for reasons that will be noticed, our continually growing pow- 
 
 * Indian Recreations, vol. i. p. 325. 
 
 t Mill’s History of Brit. India, vol. i. p. 361. Quarto edition. 
 
CHAT. I. HISTORICAL NOTICES. 117 
 
 er of attaining comforts has not occasioned a corresponding in¬ 
 crease in the quantity retained for domestic use, our colonial 
 relations have always insured a very considerable export trade 
 to the manufacturers. 
 
 The portion of glass made in Great Britain, and retained for 
 home sale, has long been converted into a source of considerable 
 national revenue. If articles of domestic manufacture are at 
 all legitimate objects of taxation, it does not appear that any 
 peculiar objection can be advanced against the extension of the 
 system to this particular branch of national industry. The prices 
 of such glass utensils as are of most common employment can¬ 
 not be considered great when viewed with reference to their 
 beauty and the extreme convenience which attends upon their 
 use; while upon articles of a more costly description the duty 
 comprises a comparatively small part of the price. It would 
 lierefore seem little likely that any material check to the use 
 d either description would be caused by even a considerable 
 Pigmentation of the rate of duty. The result has, however, 
 ilways disproved the correctness of such an opinion, as every 
 iddition which has been made to the rate of duty has occasion¬ 
 ed a most important falling off in the produce of our glass- 
 louses. 
 
 In the year 1812 an additional duty was imposed upon glass 
 nanufactures generally, which, it was estimated by the then 
 hancellor of the Exchequer, would produce an augmentation 
 if revenue to the extent of 328,000/. The immediate conse¬ 
 quences, however, of this measure, so far disappointed the ex- 
 >ectations of the minister as to occasion a falling off in the 
 inantity manufactured throughout the kingdom of rather more 
 han one third, by which means the anticipated increase of rev¬ 
 alue fell short by the sum of 183,000/. 
 
 The general evil tendency of this system of taxation cannot, 
 perhaps, be better or more clearly exemplified than by the 
 tatement of a few simple facts connected with the manufacture 
 f glass. 
 
 ! The average quantity of all descriptions annually retained 
 )r home use in the three years ending in 1793 was 373,782 
 wt., while the average quantity consumed during the three 
 | ears ending in 1829, amounted to 364,156 cwt.; showing an 
 jnnual decrease in the manufacture of9626 cwt., notwithstanding 
 'ie great increase of population and the still greater strides in 
 Civilization made during the interval by all classes of the com- 
 lunity. 
 
 If the quantities produced during equal periods of three years, 
 nmediately preceding and following the last and most consid- 
 rable advance in the rate of duty, are then contrasted with 
 
118 MANUFACTURE OF GLASS. CHAP. I. 
 
 each other, the effect appears in a yet more striking point of 
 view. The annual average quantity made for home use during 
 the three years ending in 1812 was 413,414 cwt., while the 
 average of the three following years ending in 1815 was 264,931 
 cwt.; showing an immediate falling off of 148,483 cwt., being 
 upwards of 35 per cent, upon the larger quantity; a circum¬ 
 stance which could not fail, among other evils, to bring dis¬ 
 tress and misery upon a considerable number of operative man-' 
 ufacturers. * 
 
 On the other hand, a diminution in the rate of duty on plate 
 glass was effected on the 5th of July, 1819, it being then low¬ 
 ered from 98-s. to 60s. per cwt. As a consequence, the quan¬ 
 tity manufactured has since been steadily and progressively in¬ 
 creasing. During the three years preceding the abatement,, 
 the average quantity annually manufactured was 6209 cwt.,i 
 yielding a gross revenue of 30,424Z., whereas the average quan¬ 
 tity made during the three years ending in 1829 amounted to 
 15,235 cwt., and the revenue produced was 45,705Z., being an 
 increase of more than 50 per cent., derived from a rate of duty 
 diminished to the extent of 40 per cent. 
 
 Could any facts more forcibly point out the pernicious ten¬ 
 dency of heavy duties upon articles of domestic manufacture, of 
 more clearly indicate the course which it were wise to follow 
 in remodelling to as great an extent, and as quickly as is prac¬ 
 ticable, this branch of our financial system 1 
 
 It is much to be regretted that any circumstances should have 
 arisen to delay the execution of the expressed intention of the! 
 government altogether to remove the duties upon glass. When¬ 
 ever this measure shall be accomplished, it can hardly fail tc 
 induce such an extension of the manufacture as will prove gen¬ 
 erally beneficial to the community. The abolition of these du-i 
 ties would be accompanied by the still further advantage of re- ! 
 moving all those vexatious regulations and restrictions under 1 
 which the manufacture is now carried on, and which will cease, 1 
 as a matter of course, when the article is no longer an objectj 
 of revenue. 
 
 It is principally owing to these restrictions that so much for-i 
 eign glass is now brought into this country in the face of what 
 may be considered an amply protecting duty. Foreign manu¬ 
 facturers are allowed to make any and every article out of that 
 quality of glass which will most cheaply and advantageously 
 answer the end, while our own artists are forbidden to form 
 certain objects, except with more costly materials, which pay 
 the higher rates of duty. Nor is this restriction only commer¬ 
 cially wrong, since it forms matter of just complaint on the part 
 of chemists, that they are unable to procure utensils fitted for 
 
ihap. ii. 
 
 INGREDIENTS OF GLASS. 
 
 119 
 
 dfecting many of the nicer operations connected with their 
 cience, because the due protection of the revenue is thought 
 o require that such utensils shall be formed out of that quality 
 f glass alone winch, apart from all considerations of price, is 
 therwise, from its properties, really unfitted for the purpose, 
 relaxations are, indeed, sometimes made on this head in par- 
 icular cases by the commissioners of Excise; but the trouble 
 ecessanly attending applications to a public board is greater 
 ian can be compensated by the trifling money advantage that 
 an result m each case to the manufacturer, and the interests of 
 nence are, consequently, made to suffer. 
 
 CHAP. II. 
 
 N THE VARIOUS INGREDIENTS EMPLOYED IN MAKING 
 
 GLASS. 
 
 ass always ccmp^ed °f Silex with Alkali.-Different Descriptions of 
 Gla»s.—Sea-Sand.—Soda and Potash.—Pearl-Ash.—Barilla.—Kelp.—Wood 
 Chafk ^ ltre ‘ Ijlt ^ lar S e - Minium.—Manganese.—Arsenic.—Borax.— 
 
 Under the general name of glass, chemists comprehend all 
 ineral substances, which, on the application of heat, pass 
 rough a state of fusion into hard and brittle masses, and which, 
 then broken, exhibit a lustrous fracture. Most glasses are 
 insparent also; and the non-existence of this property is gen- 
 ally owing to the presence of some foreign and unessential 
 bstance. 
 
 The glass of commerce—that beautiful manufacture to which 
 3 generic name is most commonly applied—does not include 
 wide a range of bodies ; and is always composed of some si- 
 ious earth, the fusion and vitrification of which has been oc- 
 uoned by certain alkaline earths, or salts, and sometimes with 
 i aid of metallic oxides. 
 
 There are five different and distinct qualities of glass manu- 
 tured for domestic purposes; viz. 
 
 Flint glass, or crystal; 
 
 Crown or German sheet glass; 
 
 Broad or common window glass 
 Bottle or common green glass; and 
 Plate glass; 
 
 materials and the processes used in making which form the 
 )ect of our present inquiry. 
 
 tefbre commencing the description of any of the manipula- 
 is employed in this interesting manufacture, it will be better 
 
GLASS MANUFACTURE. 
 
 CHAP. II. 
 
 120 
 
 to give a general account of the different materials used, and to 
 point out how the particular qualities of glass are influenced by 
 the properties of those various ingredients. 
 
 Each of the five descriptions contains, in common with the 
 others, two ingredients, which, indeed, are essential to theii 
 formation—silex and an alkali. 
 
 The variations of quality, and distinctive differences observ¬ 
 able in glass, principally result from the kind of alkali employ¬ 
 ed, and its degree of purity, as well as from the addition of 
 other accessory materials; such as nitre, oxide of lead or of 
 manganese, white oxide of arsenic, borax, or chalk. 
 
 Silex is not equally proper in all its forms for the composi 
 tion of glass. Sea sand, which consists of spherical grains ol 
 quartz, so minute, as to be qualified for the purpose withou 
 any preparation except careful washing, is the form whereii 
 silex is most commonly used for the purpose in England. A1 
 sea sand is not, indeed, equally applicable to the glass-maker 
 purpose. That used in this country for making the finer de 
 scriptions of ware is usually obtained, either from the port o 
 Lynn, in Norfolk, or from Alum Bay, on the western coast o 
 the Isle of Wight. 
 
 The best glass was formerly made with common flints, ca 
 cined and ground in the manner already described, as used i 
 the manufacture of pottery, and hence the name which it a< 
 quired of flint glass. The employment of silex in this form 
 now wholly discontinued in glass-houses, as it is known th; 
 some qualities of sand answer the purpose equally well, whii 
 the labor and expense of calcining and grinding are saved t 
 the substitution. 
 
 Both soda and potash are well adapted to the purpose of ni: 
 king glass. They are used in the form of carbonates; that ij 
 holding carbonic acid in combination with themselves as base 
 The acid flies off during the progress of the manufacture, ar 
 the result is a compound of silex and alkali. 
 
 As already stated, the quality of glass is influenced by tl 
 degree of purity of the alkali. For making the finest flii 
 glass, pearl-ash, which is potash in a purer form, must be use 
 The alkali must previously be still further purified by solutif 
 and subsidence, and then evaporating the fluid to dryness. I 
 this purification a loss is sustained, amounting to between !i 
 and 40 per cent, in the weight of pearl-ash. Coarser kinds <| 
 alkali, such as barilla, kelp, or wood-ashes, which are combin 
 with many impurities, are employed for the production of inf 
 rior glass. Complete fusion and vitrification are accomplish 
 by these means, the impurities even being of a nature to ass 
 towards the production of these effects. The green color ii 
 parted to glass, is produced by the iron, which is present in 
 
CHAP. II. 
 
 INGREDIENTS OF GLASS. 
 
 121 
 
 greater or less degree in these courser alkaline substances. 
 Barilla, when sufficiently cheap, is always chosen preferably to 
 wood-ashes or kelp. The recent abatement of the import duty 
 levied upon this article of commerce will, therefore, probably 
 tend to the increased consumption of barilla in glass-houses. 
 
 A very small proportion of nitre is used in the composition 
 of glass, to occasion the destruction of any carbonaceous mat¬ 
 ter which may exist in the ingredients. This salt must be 
 added previous to the fusion of the glass. Ata degree of heat 
 much below that of the furnace, nitre will decompose, giving 
 out much oxygen, and maintaining such metallic oxides as 
 may be present in their highest state of oxygenation. It is 
 thus of use in fixing arsenic, the volatile property of which in¬ 
 creases as it approaches the metallic state. 
 
 Oxide of lead, in the form of either litharge or minium, is 
 essential to the making of flint-glass, into the composition of 
 which it enters very largely. This metal acts, in the first 
 place, as a most powerful flux, promoting the fusion of all vit- 
 rifiable substances at comparatively low temperatures. It is 
 also permanently beneficial in imparting highly valuable prop¬ 
 erties to the glass of which it forms a part. This, by its means, 
 is rendered much more dense; has a greater power of refract¬ 
 ing rays of light; possesses more tenacity when red-hot, caus¬ 
 ing it for that reason to be more easily worked; and is render¬ 
 ed more capable of bearing uninjured sudden changes of tem¬ 
 perature. On the other hand, glass, into the composition of 
 which much lead has entered, is so soft as to be easily scratch¬ 
 ed and injured if rubbed against hard bodies. Such glass is 
 also improper as a recipient for many fluids which are of an 
 acrid nature, by which it would be corroded and destroyed. 
 Another great inconvenience attending the use of lead is this, 
 that it does not become intimately enough united with the 
 other components for the whole mass to assume an uniform 
 density. It will almost always happen, that the glass at the 
 bottom of the pot contains a larger proportion of litharge than 
 that above. This inequality of density is continually increas¬ 
 ing as the contents of the pot are diminished by the workman; 
 and it is thence impossible to withdraw from it any two por¬ 
 tions whose densities shall agree.* 
 
 * Mr. Faraday has stated, in his paper on the manufacture of glass for op. 
 tical purposes, which appeared in the Philosophical Transactions for 1830, 
 that he found, on examining “pots containing glass not more than six 
 inches in depth, made from the usual materials, and retained at a full heat 
 for twenty-four hours,” the following differences of specific gravity be¬ 
 tween the glass taken from the bottom and surface of the pots:— 
 
 Top, - 3 38 3 30 328 321 3 15 373 385 381 3 31 330 
 Bottom, 4 04 3 77 385 3 52 3-80 4 63 474 475 399 3 74 
 
 L 
 
122 GLASS MANUFACTURE. CHAP. II. 
 
 Monsieur Guyton Morveau has related a very curious exem¬ 
 plification of this fact, which once occurred to himself when 
 experimenting in conjunction with Monsieur de Buffon in the 
 plate-glass manufactory near Langres.* Remaining in the cru¬ 
 cible was a portion of flint glass in fusion, composed of thirty- 
 two parts powdered crystal, thirty-two parts minium, sixteen 
 of soda, and one part nitre. To this was added the requisite 
 quantity of the ingredients commonly employed for forming 
 plate-glass in the manufactory, and the whole was melted to¬ 
 gether in the furnace. When the mass was sufficiently refined 
 it was laded into the cistern, cast on the copper table in the 
 usual manner, and transferred to the annealing furnace. Its 
 quality being subsequently submitted to examination, the plate 
 was found to be composed of two distinct and perfectly level 
 strata through the whole mass, the lower stratum occupying 
 about one third of its thickness. 
 
 So complete an instance of the precipitation of the denser 
 through the lighter portion is not elsewhere to be met with in 
 the records of glass-making: its occurrence in this particular 
 occasion should probably be referred to the active agency of 
 some cause which escaped the observation of the two philoso¬ 
 phers. 
 
 It is a general effect of this inequality, that the glass, when 
 wrought, appears waved; a defect which is particularly incon¬ 
 venient in that which is intended for the construction of opti¬ 
 cal instruments. Glass is also fusible at lower temperatures 
 according to the proportion of lead which it contains. This 
 quality, which would be mischievous for some purposes, is, on 
 the contrary, beneficial for others. It is often essential to 
 chemists that they shall be able, during the progress of their 
 experiments, to bend the tubes with which they are operating. 
 
 Black oxide of manganese has long been used for clearing 
 glass from any foul color which it might accidentally possess 
 through the impurity of the alkali employed, and in particular 
 from that green tinge which marks the presence of iron. This 
 property of manganese, when in the form of an oxide, occa¬ 
 sioned it to be anciently known as glass soap , a name which 
 very accurately describes its use. The circumstances attend¬ 
 ing the employment of this substance in glass-making are of 
 rather a curious nature. When added in a moderate propor¬ 
 tion to any simple glass, it imparts a purple color; and should 
 its quantity be much increased, this color is deepened until the 
 glass becomes nearly black. If, while the mass thus colored is 
 still in fusion, either white arsenic, or charcoal, or other carbo¬ 
 naceous matter be added, an effervescence is seen to follow, 
 
 * Ann. ile Chim. vol. lxxiii. p. 113. 
 
CHAP. II. 
 
 INGREDIENTS OF GLASS. 
 
 123 
 
 and the color becomes gradually more faint until it altogether 
 disappears, and the glass is rendered clear and transparent. 
 Provided the green hue which it is desired to counteract be 
 considerable, the application of a very small quantity of manga¬ 
 nese is not followed by any sensible tinge of purple; but the 
 moment that the proportion is more than sufficient for the pur¬ 
 pose, this color immediately appears, and must be corrected. 
 This correction is performed in a very simple manner in the 
 glass-house, by thrusting into the pot of melted glass a piece of 
 wood, which, becoming charred by the heat, causes the purple 
 again to vanish; while a slight effervescence as before de¬ 
 scribed, and the escape of numerous bubbles of air, are plainly 
 perceptible. If nitre be then added, the purple color will be 
 restored. 
 
 The reason fos, these changes it is not difficult to explain. 
 The oxide of manganese imparts a purple color, only when in a 
 state of high oxygenation. When brought into contact with 
 carbonaceous matter, it is partially deprived of its oxygen, and 
 loses its coloring property. The air-bubbles which escape con¬ 
 sist of carbonic acid gas, which is disengaged by the action of 
 the charcoal on the oxide of manganese. The effect which 
 follows upon the introduction of nitre is of a contrary nature. 
 When made of a red heat this substance gives out oxygen in 
 great abundance, and the manganese being thus reinvested with 
 the oxygen of which it was deprived by the charcoal, resumes 
 with it the coloring property. 
 
 Another advantage attending the use of oxide of manganese 
 results from its property of powerfully assisting in the fusion of 
 earthy bodies. It also gives considerable density to glass, but 
 the same disadvantage accompanies its use as already has been 
 noticed with regard to litharge. Having from its greater spe¬ 
 cific gravity a tendency to settle towards the bottom of the pot, 
 the glass by this means varies in density throughout its sub¬ 
 stance, in addition to which circumstance the manganese acts 
 injuriously upon the pots by corroding them at the bottom. 
 
 One of the uses of white oxide of arsenic has already been 
 described, that, namely, of correcting the coloring effects of 
 manganese. It is also a very powerful flux, and a great tempt¬ 
 ation to its use is found in its cheapness. It should, however, 
 be employed with moderation. If a considerable time be not 
 allowed for its intimate incorporation with the other ingredients 
 of the glass, this will appear clouded or milky; a fault which 
 will afterwards increase with the lapse of time. An excessive 
 quantity of arsenic likewise occasions the glass to become grad¬ 
 ually soft and to decompose, for which reason the employment 
 of drinking-vessels in this condition is unsafe. 
 
124 GLASS MANUFACTURE. CHAP. II. 
 
 Another, and a harmless, application of arsenic in glass¬ 
 making is, when it is introduced into the fused mass in order to 
 dissipate any carbonaceous matters which result from defects 
 in preparing the alkali. In this case, small lumps of white ar¬ 
 senic are intimately blended with the mass by stirring. The 
 great heat causes it at once to unite with and to carry off the 
 carbon in a volatile form, leaving the glass entirely free from 
 carbonaceous matter, and nearly so from arsenic. 
 
 Borax is used in preparing only the finest descriptions of 
 glass: its employment is, indeed, principally confined to plate 
 glass. It is too expensive to admit of its forming part in the 
 composition of common descriptions, although its use in all 
 cases would be desirable, as its efficacy in promoting the fusion 
 of vitrifiable substances is unrivalled. When the borax has been 
 introduced, the compound is caused by it to flow with great 
 freedom, and to be without specks and bubbles, which would 
 impair both its beauty and utility. Should the alkali employed 
 prove deficient in strength, a small portion of this salt will serve 
 as an effectual remedy. 
 
 Lime in the form of chalk is useful as a very cheap flux. It 
 is also beneficial in facilitating the operations of the workman 
 in fashioning glass, and it has the property of diminishing its 
 liability to crack on exposure to sudden and great variations of 
 temperature. Chalk can only be used sparingly, however, in 
 the glass-house, as the escape of carbonic acid causes the in¬ 
 gredients in the pot to swell considerably during the fusion. 
 The presence of lime in any excessive degree would also occa¬ 
 sion the rapid destruction of the pots, upon the substance of 
 which it acts with considerable energy. Glass wherein lime 
 exists in excess is also rendered cloudy, although the mass while 
 in fusion appears perfectly pellucid. Not more than about six 
 per cent, of lime can be added without risking this defect. 
 
CHAP. III. 
 
 FURNACES. 
 
 125 
 
 CHAP. HI. 
 
 ON THE CONSTRUCTION OF FURNACES, ETC. 
 
 Stability of Furnace Essential.—Fritting Furnace, or Calcar.—Its Use.— 
 Working Furnace.—Double Furnace.—Proportionate Dimensions of Fur- 
 nace and Pots.—Wood-Furnaces.—Comparative Consumption of Fuel in 
 Wood and Coal Furnaces.—Annealing Oven.—Lier-Pans.—Glass-Pots.— 
 Their Formation and Seasoning. 
 
 It is essential to the well conducting of the operations of 
 glass-houses that their furnaces should be well and substantially 
 built of the best materials, and according to the most approved 
 construction. 
 
 Monsieur Loysel was so deeply impressed with the necessity 
 of devoting the greatest degree of attention to this branch of 
 the art, that nearly one half of his clever treatise “ Sur l’Art de 
 la Verrerie” is occupied with its details. This author not only 
 gives instructions for the choice of materials proper for con¬ 
 structing crucibles and furnaces; but also points out the forms 
 which will be found most convenient and advantageous. 
 
 In this country, and since the appearance of the work of M. 
 Loysel, those operations connected with the useful arts which 
 depend upon the agency of heat have become much better un¬ 
 derstood than formerly, so that principles for the right attain¬ 
 ment of which it was then necessary for individuals to search 
 and inquire, and frequently even to experiment, are now be¬ 
 come matters of every-day practice. It cannot, therefore, be 
 necessary to imitate that author in all his lengthened initiatory 
 directions for the digging and purifying of clay—in his descrip¬ 
 tion of the qualities that should determine our selection of this 
 material, or in the detail of mechanical arrangements that will 
 prove most efficacious in giving durability to furnaces.* All 
 these particulars may safely be committed to the skilfulness of 
 the professional builder. 
 
 Some other points there are, however, connected with this 
 subject, wherein a greater degree of knowledge than is at 
 present possessed is indeed desirable. To persons who have be¬ 
 stowed the smallest attention upon the phenomena of heat and 
 combustion it can scarcely fail to appear that science has yet an 
 
 * In stating the degrees of consistence of the clay most proper for the fur¬ 
 naces in different parts and stages of their construction, Mr. Loysel points 
 out a simple method of ascertaining the attainments of these degrees, which 
 has the advantage of being easily accomplished by any workman. It consists 
 in dropping a leaden ball of a given weight from a determinate height upon 
 the mass, which should be of that density which will allow the ball, by the 
 force of gravitation acquired in its descent, exactly to bury itself in the clay. 
 
126 GLASS MANUFACTURE. CHAP. III. 
 
 ample field for research there open to her investigations, and 
 that the arts have still to look for further and most important 
 benefits at the hand of philosophy. 
 
 The whole operations of the glass-house depend upon the sta¬ 
 bility of its furnaces. In their original structure the prudent 
 manufacturer will, therefore, not hesitate to avail himself of the 
 assistance of the ablest builders, and to employ materials which 
 are best qualified by their density and infusibility for resisting 
 the action of violent and long-continued heat. No present sa¬ 
 ving in the cost of construction can at all compensate for the 
 expense and interruptions occasioned by the necessity for fre¬ 
 quent repairs, and still less for the losses of time, labor, and ma¬ 
 terials, that would accompany casualties, the chances of which 
 would be multiplied by want of proper attention to the matters 
 here pointed out. An equal, and perhaps even a greater degree 
 of judgment is required for the selection of materials proper to 
 form glass-pots or crucibles, since these have to withstand the 
 action of heat in as violent a degree as any part of the furnace, 
 and are additionally exposed to injury from the solvent property 
 possessed by some of the materials, for the fusion of which they 
 are employed. These pots are therefore made of the most re¬ 
 fractory, that is, the least fusible, materials, and are fashioned 
 with every possible attention to their strength. 
 
 Three different kinds of furnaces are employed in the manu¬ 
 facture of glass. One, which is called the calcar, a name cor¬ 
 rupted from the French word calquaise, is used for that calci¬ 
 nation of the materials to which they must be subjected previ¬ 
 ously to their complete fusion and vitrification. This process, 
 which is called fritting, a term likewise borrowed from the 
 French, is used for various reasons. In the first place, it expels 
 all moisture from the materials, the presence of which would 
 hazard the destruction of the glass-pots. Next it drives of£ 
 either wholly or in great part, the carbonic acid gas from the 
 chalk and alkalies employed, by which means the swelling of 
 ingredients in the pots is either prevented, or moderated within 
 safe limits. This calcination has the further advantage of de¬ 
 stroying all carbonaceous matters that may be present in the 
 materials. But the principal object of previous calcination is, 
 that a chemical union may be effected, or at least commenced, 
 between the silex, the alkali, and the metallic oxides. Other¬ 
 wise, at the heat of the working furnace, the alkali would fuse, 
 and its comparative levity would cause it to take its station at 
 the surface, while the other ingredients would subside towards 
 the bottom. The uncombined alkali would, in this case, after 
 acting upon and injuring the substance of the crucibles, be, in 
 great part, volatilized and lost; and a portion of the sand would 
 
CHAP. III. 
 
 FURNACES. 
 
 127 
 
 remain unvitrified, while the glass actually produced would 
 contain an excessive quantity of silica. 
 
 These observations do not apply to the preparation of mate¬ 
 rials for making flint glass, the fusibility of which is much 
 greater than that of other descriptions, owing to the presence 
 of its large proportion of lead. For this reason, manufacturers 
 of this kind of glass apply the process of calcination to the sand 
 alone, with the view of separating from it all carbonaceous im¬ 
 purities, previous to its admixture with the remaining materials. 
 
 The name of fixed alkalies has been given to soda and pot¬ 
 ash to denote their property of resisting the destructive influ¬ 
 ence of fire. As they are volatilized freely by subjection to a 
 red heat, this property cannot, however, be strictly ascribed to 
 either of these substances, and the title must be understood only 
 as distinguishing them from other alkaline bodies, which are 
 acted upon by comparatively low additions of temperature. 
 
 The calcar is in the form of an oven about ten feet long, 
 seven feet wide, and two feet high. The coal used in heating 
 it is placed in a sort of trough on one side, and the flame is 
 made to reverberate from the crown of the oven back to the 
 frit. In this operation, care is required to keep the degree of 
 heat at all times within that which would melt the materials, 
 and at first below the point whereat the yet uncombined alkali 
 would be volatilized. 
 
 The process must not be hurried at first; but after two or 
 three hours the temperature may be gradually raised until the 
 mass becomes pasty. Having been kept in this state during 
 three or four hours longer, it is then removed from the calcar 
 and cut quickly, before it has time to harden, into square cakes. 
 These are piled away for future use. It is the opinion of many 
 glass-makers that frit is improved in quality by age; under 
 which impression some among them so manage their operations 
 as not to bring their store successively to use until it has been 
 prepared for at least twelve months. 
 
 The working furnace is that wherein the frit, when placed 
 in the glass-pots or crucibles, is fully melted and converted into 
 glass. These crucibles are deep pots, varying in size according 
 to the objects of the manufacturer, but sometimes large enough 
 for each to contain a ton weight of glass. Twelve of these are 
 usually placed, at regular intervals, in the circumference of 
 each kiln, their only opening being at the side nearest to the 
 wall of the kiln, in which they meet with corresponding open¬ 
 ings, so that the pots can be readily charged, and their contents 
 is readily removed, by the workmen who stand in recesses 
 formed by projections of the masonry. The external form of the 
 furnace is circular, rising conically from its base and termina- 
 
GLASS MANUFACTURE. 
 
 CHAP. III. 
 
 128 
 
 ting in a chimney. The interior is dome-shaped, and supported 
 on arches. Flues are constructed under these for the admis¬ 
 sion of atmospheric air, which, rising through the fire-bars that 
 occupy the centre of the floor of the furnace, the flame and 
 heated air are made to envelop the pots, and thence pass on to 
 the chimney issuing from the centre of the dome. 
 
 A very important saving in the article of fuel has lately been 
 effected in one of the London glass-houses, that of Messrs. Pel- 
 latt and Co., by substituting for one of the large twelve-pot fur¬ 
 naces they had been accustomed to use two similarly construct¬ 
 ed, but having only one half the diameter. The circumference 
 of these two being together equal to that of the large furnace, 
 they are made to contain as great a number of pots, and of the 
 same size, as were formerly employed; while the internal area 
 of the two, being together equal to only one half that of the fur¬ 
 nace for which they are substituted, the pots are necessarily 
 brought more than before within the intensest influence of the 
 fire. The same chimney is made to serve for both furnaces, by 
 which means the expense attending the alteration has been 
 much diminished. 
 
 Fig. 1. 
 
 It is said, that the weekly expenditure of coals has been 
 lessened, by means of this alteration, to the extent of ten chal¬ 
 drons. 
 
 The dimensions of the crucibles and furnace should bear 
 some relation to each other. If the former, from their diminu¬ 
 tive size, are much below the efficiency of the furnace, a very 
 needless expenditure of fuel will be the result; and should the 
 
CHAP. III. FURNACES. 129 
 
 crucibles be too large for the power of the kiln, the heat will 
 not prove sufficient. In this case, an excess of fluxing materi¬ 
 als must be used in order to form glass, which will be imper¬ 
 fect, according as it is fused below the most beneficial degree 
 of temperature. The relative proportions of pots and furnace 
 may be somewhat varied according to the power of promoting 
 combustion, which partly depends upon construction and situa¬ 
 tion. Loysel recommends, that in general the aggregate area 
 of the crucibles should be very little beyond one fourth of the 
 area of the furnace. The experience whereon this recommend¬ 
 ation rested was drawn from the use of wood as a combusti¬ 
 ble, which requires a greater space than coal for the develop¬ 
 ment of a given effect. The difference thus arising would, on 
 the other hand, be lessened by the necessity which we are 
 under for covering the pots; whereas, if the kiln is heated by 
 means of wood, these may remain uncovered, and their con¬ 
 tents will, in consequence, be more efficiently acted on by the 
 heat. Loysel states,* as the result of experiments continued 
 during a whole year, that the weight of dry beach wood con¬ 
 sumed in a glass-house furnace exceeded the weight of coal 
 burnt in the same furnace, and during an equal period, in the 
 proportion of 45 to 28. According to Lavoisier, the heating ef¬ 
 fects of wood and coal are in the proportion of 1089 to 600. 
 
 The result of Loysel’s experiment should consequently have 
 6hown similar effects from the combustion of 45 parts by weight 
 of wood, and 24-8 parts of coal; the difference between this 
 last quantity and 28 being, probably, the loss consequent upon 
 covering the crucibles. 
 
 The openings already mentioned, as serving for the introduc¬ 
 tion of the materials into the crucibles, and for the removal of 
 the melted glass, are called boccas. These may be closed either 
 wholly or partially, according to the need of the workman, by 
 means of movable collars, or, to speak more correctly, by tem¬ 
 porary screens made of fire-clay. On either side of each bocca 
 is a smaller circular opening, sometimes called a boccarella, 
 but more generally by the familiar name of nose-hole, the par¬ 
 ticular use of which will be explained hereafter. 
 
 The annealing oven, or lier, is a long, low, rectangular cham¬ 
 ber, heated at one end, and furnished with numerous shallow 
 iron trays, which can be passed easily along the level bottom 
 of the chamber. These trays are called lier-pans, or fraiches ; 
 which names, together with those of several implements used 
 in glass-houses, are evidently adopted from the French. 
 
 As regards the structure of the annealing chamber, there is 
 nothing that particularly requires notice, or that will not be 
 
 * L’Art de la Verrerie, p. 72. 
 
130 
 
 GLASS MANUFACTURE. 
 
 CHAP. III. 
 
 rendered sufficiently clear by the explanation of its use that 
 will be given in the following chapter, while describing, in 
 their regular course, the consecutive processes of the manufac¬ 
 ture. 
 
 Every glass-house should possess within itself the means of 
 making all the crucibles and other earthen utensils that may 
 be required for its operations. The conveyance of these from 
 any considerable distance would add materially to their cost, 
 not only by the mere expense of carriage, but through the 
 greater liability to fracture, whereto such unwieldy vessels 
 would in that case be subject. 
 
 These crucibles, or glass-pots, should be made with five parts 
 of the best Stourbridge fire-clay and one part of old broken 
 crucibles ground to powder for that purpose. Great nicety is 
 required in mixing these ingredients and in working them to¬ 
 gether, in order to drive out from their substance every particle 
 • of air, the presence of which would, by its expansion in the fur¬ 
 nace, occasion the immediate breaking of the pots. 
 
 The method invariably pursued for kneading the clay is, 
 Fig. 2. that the workman treads on it for a consid¬ 
 erable time with his naked feet, turning it 
 over from time to time, so that every part 
 may, in its turn, be subjected to the required 
 pressure. An attempt was recently made by 
 a glass manufacturer to employ machinery 
 for the purpose; but after having incurred 
 considerable expense, and exerted much in¬ 
 genuity in perfecting his apparatus, this gen¬ 
 tleman has reverted to the old inartificial method, as being deci¬ 
 dedly the best calculated to insure the goodness of his crucibles. 
 This attempt at improvement was not relinquished, until the 
 losses which were sustained in its prosecution became of seri¬ 
 ous moment. 
 
 After the crucibles are formed, they are suffered to remain 
 for a considerable time in the apartment wherein they were 
 made, in order that they may dry equally throughout their sub¬ 
 stance. It is not, indeed, considered prudent to remove them 
 from this situation until they shall have been formed for at least 
 a twelvemonth. 
 
 For some little time before a pot is put to use, it must be 
 placed in an apartment wherein heat can be artificially admit¬ 
 ted, and either raised or lowered at pleasure. It is then re¬ 
 moved for about three days to a furnace particularly appro¬ 
 priated to the baking of pots; and here the temperature, which 
 at first is moderate, is gradually increased, until at last it is 
 
CHAP. IV. 
 
 FLINT GLASS. 
 
 131 
 
 made nearly as intense as that of the working furnace, for in¬ 
 sertion in which the crucible is then sufficiently fitted. 
 
 With all the skill and care that can be employed in their 
 manufacture, these crucibles will frequently break during a 
 very early period of their use, and the loss occasioned by that 
 means to the manufacturer is in many ways one of very seri¬ 
 ous importance. 
 
 CHAPTER IV. 
 
 ON THE MANUFACTURE OF FLINT GLASS. 
 
 The most beautiful and costly Kind of Glass.—Importance of its Quality for 
 Optical Purposes.—Experiments for its Improvement—Undertaken by the 
 Royal Society—Promoted by Government.—Distinguishing Properties of 
 Flint Glass.—To what owing.—Different Compositions.—Process of Melt¬ 
 ing.—Glass-Gall.—Its Use.—Curious Phenomenon.—Implements.—Col¬ 
 lecting Glass on Rod.—Marver.—Paraison.—Blowing.—Re heating.— 
 Elongating.—Pontil.—Fashioning.—Detaching.—Removal to Annealing 
 Oven.—Moulding.—Annealing.—Why indispensable.—Bologna Phials.— 
 Rupert’s Drops. 
 
 Flint glass — known in foreign countries under the name of 
 crystal —retains among us the title originally imparted by its 
 principal ingredient, although the use of flint in its composition 
 has long since been discontinued. 
 
 This glass is the beautiful and peculiarly refulgent com¬ 
 pound whereof the finest articles designed for domestic use 
 or for ornament are made. Of all the vitrified compounds 
 that are manufactured, it is the heaviest and the most brilliant; 
 the one most easily fashioned by the hand of the workman, and 
 that which has the greatest refractive power. It is also, from 
 the nature of its constituent materials, the most costly. 
 
 Vessels of flint glass cannot, however, be properly applied to 
 ill purposes. If| for instance, they are used to contain car¬ 
 bonate of ammonia, they will very soon become so exceedingly 
 brittle, that the very slightest apparent cause will occasion 
 aieces to fall out. Common green bottle glass is not liable to 
 liis objection. 
 
 Were we to judge from the practice of different manufac¬ 
 turers, in bringing together the ingredients that form this com¬ 
 pound, we must believe, that to adhere to any exact proportions 
 s by no means indispensable. In almost every different glass- 
 louse a peculiar recipe is followed, and no two writers upon 
 he subject agree in their statement of the exact doses wherein 
 my of its components should be used. It is by no means be- 
 ieved, however, that these vague proceedings are without in- 
 :onvenience, or that some particular compound might not be 
 
GLASS MANUFACTURE. 
 
 CHAP. IV. 
 
 132 
 
 discovered and adopted, which, for many purposes, would be 
 superior to every other. 
 
 The employment of this species of glass in the construction 
 of optical instruments renders every attempt towards its im¬ 
 provement a matter of universal interest and importance. A 
 committee of scientific men have been for some years engaged, 
 at the expense of government, in a series of experiments, with 
 a view to discover some composition by which glass may be 
 obtained in large pieces, free from those defects which have 
 hitherto circumscribed the power of telescopes within a nar¬ 
 row limit. In such investigations, however, great difficulties 
 are to be encountered; and a long time is as necessary as great 
 talents to overcome them. The progress which has been made 
 by the committee, though not perhaps so great as the lovers 
 of science could have wished, is still as great as the difficulties 
 of the subject—even in the most able hands—would have led 
 us to hope for, and is sufficient to justify sanguine anticipations 
 of future success. 
 
 The properties of flint glass which distinguish it from other 
 vitrified substances are owing to the presence of some metallic 
 oxide. All metals, when oxidated, will combine with silica 
 and alkali to form glass. Few of them are, however, properly 
 qualified for the purpose, in consequence of their imparting 
 colors to the mass. The oxides of lead and of bismuth are the 
 only two which may be used in sufficient quantity without pro¬ 
 ducing this inconvenience ; and as lead is by much the cheap¬ 
 est of these metals, it is always preferably employed in the 
 manufacture. An over dose of lead will, indeed, discolor glass, 
 imparting to it a tinge of yellow. 
 
 It is essential to the goodness of the glass that no impurities 
 or foreign matters should be combined with the lead, and as 
 the adulteration of its various oxides is both easily effected, and 
 difficult of detection, the glass-maker who does not prepare 
 this substance for himself, should make his purchases only from 
 persons on whose probity he can rely. Loysel recommends 
 the use of minium , as being less susceptible of adulteration 
 than the other oxides of lead. English glass-makers more fre¬ 
 quently employ litharge. 
 
 The author just mentioned gives as the composition of crys¬ 
 tal, where coal is employed as fuel,— 
 
 White sand.100 parts. 
 
 Red lead. 80 to 85 
 
 Pearl-ash. 35 to 40 
 
 Nitre.2 to 3 
 
 Oxide of manganese.0-6 
 
 Where wood is used for the reduction of the ingredients, and 
 
CHAP. IV. FLINT GLASS. 133 
 
 where consequently, the crucibles may be left uncovered du¬ 
 ring the process, a different mixture is preferred. In this, a 
 much smaller proportion of metallic oxide is added; and the 
 reason assigned by M. Loysel for this variance is, that the air, 
 having constant and unimpeded access to the surface of the 
 glass, supplies any deficiency of oxygen, while the process is, 
 through the more direct application of heat, more quickly per¬ 
 formed, and the glass when manufactured is harder and more 
 durable. The proportions given for this compound are,— 
 
 White sand.100 parts. 
 
 Red lead . 50 to 60 
 
 Pearl-ash .30 to 40 
 
 Oxide of arsenic. 0-75 to 1 
 
 The specific gravity of this glass will not be so great as that 
 of the former compound in the proportion of 29 to 32, and its 
 refractive power will evidently be smaller also. 
 
 Messrs. Aikin, who, as a matter of scientific research, 
 formerly directed their minds to the consideration of this im¬ 
 portant branch of manufacture, and who then made many ex¬ 
 periments connected with the art of glass-making, state* that a 
 very excellent article may be made from— 
 
 120 parts fine clean white sand ; 
 
 40-well purified pearl-ash; 
 
 35-litharge or minium; 
 
 13-nitre, and a small quantity of the black 
 
 oxide of manganese; 
 
 ■he superior fluxing power of the nitre supplying, in that 
 ■espect, the difference which exists in the proportion of lead 
 tetween this compound and the first formula of Loysel. To 
 ntroduce so large a dose of metallic oxide as is recommended 
 >y the French author produces an inconveniently soft material, 
 fhat the proportion is excessive may well be inferred from the 
 act ascertained by Dr. Priestley, that if a tube of glass so com- 
 'ounded be made red-hot, and a stream of hydrogen gas be 
 iassed through it, the whole inner surface will be covered with 
 half brilliant black substance, which results from a partial 
 eduction of the lead, and moisture will appear at the further 
 nd of the tube. 
 
 The result of many preliminary experiments made on a re- 
 ent occasion by Mr. Faraday, with the object of producing per- 
 ictly homogeneous glass for optical purposes, induced that gen- 
 eman to give the preference to a compound of silica, boracic 
 cid, and oxide of lead, brought together in single proportionals, 
 nd which he therefore designates a silicated borate of lead. 
 
 * Dictionary of Chemistry, vol. i. p. 490. 
 
 M 
 
134 GLAS8 MANUFACTURE. CHAP. IV. 
 
 The important aim of Mr. Faraday’s inquiries induced him 
 to neglect no one particular by which they could be forwarded, 
 and he accordingly employed all those chemical means with 
 which he is so perfectly acquainted to insure the absolute purity 
 of the ingredients which he thus selected. 
 
 The oxide of lead was converted from the state of litharge 
 into a nitrate by first washing it and separating the carbona¬ 
 ceous and ferruginous particles, and then placing it in a clean 
 earthen vessel, and dissolving in dilute nitric acid, so as to form 
 a hot saturated solution. After 18 or 24 hours the crystals 
 which had formed were collected, broken up into small parti¬ 
 cles, and repeatedly washed in fresh clear portions of the 
 mother liquor, in order to remove any insoluble deposited mat¬ 
 ter. When thus perfectly cleaned, the broken crystals were 
 drained, and then dried by being placed in a sand bath and 
 constantly stirred, after which they were preserved m glass 
 bottles for future use. 
 
 Mr. Faraday was enabled to procure pure boracic acid in 
 crystals from the manufacturers, subjecting it in every case, 
 however, to careful examination, and testing it by various 
 agents to ascertain the absence of impurities. 
 
 Sand from the coast of Norfolk needed no other preparation 
 to insure its purity than to be well washed and calcined, and 
 this was the only source whence Mr. Faraday drew his supply 
 of silica. 
 
 The previous fritting described in the last chapter was 
 formerly performed for the manufacture of all kinds of glass; 
 but, as regards the kind under description, is not now 
 adopted. The materials are used in a state of greater purity, 
 and the process is, on that account, as well as for another 
 reason already given, no longer considered advantageous. 
 
 The ingredients having been intimately mixed, are cast, by 
 means of clean iron shovels through the side openings, into the 
 crucibles; which, previously to this, must be brought to a 
 white heat. The pots are filled at once with the mixture; 
 but as the bulk of this decreases materially in melting, a fresh 
 portion must be added when this effect has been produced; and 
 this operation is repeated until, by these successive fillings, the 
 vessels at length become fully charged with melted glass. Be¬ 
 fore any fresh portion of materials is added, that already in the 
 crucible must be completely melted. When this is full, the 
 opening through which the charge was introduced is materially 
 lessened with wet clay, so that only a narrow hole remains, 
 through which the impurities may be removed, and small por¬ 
 tions of the contents may, from time to time, be drawn tor 
 examination. 
 
CHAP. IV. 
 
 FLINT GLASS. 
 
 135 
 
 Immediately upon the materials being placed in the cruci¬ 
 bles, the heat of the furnace is raised to its highest point. The 
 contents are soon observed to sink down in the state of a soft 
 paste, and ere long become perfectly melted. The glass does 
 not, however, immediately thereupon appear transparent, but 
 loses its opacity by slow degrees, as a white porous scum, 
 known by the name of sandiver or glass-gall, rises through 
 the mass and is removed. This scum appears to consist of 
 salts, which more or less exist in alkalies, and which salts, hav¬ 
 ing little or no affinity for silex, and being specifically lighter 
 than glass, rise to the top. Another foreign substance is some¬ 
 times found at the bottom of the pots, and is removed when the 
 glass is worked off. This, which is also called sandiver, is of 
 a nature altogether different from the scum before mentioned, 
 being a vitrified mass of metallic and earthy impurities. In 
 the strong heat of the furnace glass-gall is exceedingly volatile; 
 so that, if not removed as it forms on the surface, it would all 
 be dispersed in the form of a dense vapor, very dark at first, 
 and growing white by degrees, as the glass becomes purer. 
 This vapor is very corrosive, and acts injuriously upon the tops 
 of the crucibles. 
 
 Sandiver is purchased by refiners of metals, who use it as a 
 powerful flux. It is necessary that the whole of this substance 
 should come away before the glass is withdrawn from the pots 
 for use, otherwise articles formed with it will appear cloudy, 
 and filled with bubbles. A very strong and long continued 
 heat is generally required before the whole impurities are dis¬ 
 charged. As the process advances, the glass proves increas¬ 
 ingly flexible, heavier, and less brittle, till at length the glass- 
 gall is altogether thrown off, no more vapors rise, the bubbles 
 expand, rise to the surface and burst, and the whole is seen to 
 be colorless and translucent. 
 
 In this state, vitrification is complete, but the glass is too fluid 
 to be fashioned, and for this purpose its temperature must be 
 lowered by stopping the draught of the furnace in that particu- 
 1 lar part where the crucible is placed; the clay wherewith its 
 ; opening was lessened is then removed, and the operations of 
 1 the glass-blower may be commenced. 
 
 When cooled to the heat most proper for its being wrought, 
 
 ' the glass has lost its perfect fluidity, being of a consistent and 
 tenacious mass, soft enough to yield to the slightest external 
 impression, yet capable of being bent, pulled, and fashioned into 
 all imaginable shapes, without cracking or parting with its te- 
 ! nuity; so that if in this state it be stretched or drawn out, it will 
 preserve the form of a solid fibre, constantly decreasing in its 
 diameter, and will not separate until reduced to the merest fila- 
 
136 
 
 GLASS MANUFACTURE. 
 
 CHAP. IV. 
 
 ment. When no longer heated to redness, glass becomes rigid, 
 brittle, and transparent. During the whole time employed in 
 working a pot of glass, which varies from five to twenty hours, 
 and is sometimes even longer, its consistence should be main¬ 
 tained as nearly as possible at the same point, and to succeed in 
 this calls for considerable attention on the part of the work¬ 
 men. 
 
 The contents of all the crucibles do not come into the work¬ 
 ing state at the same moment; but no injury arises from this 
 cause, as glass may remain for a very considerable period in the 
 melted state without, in any respect, altering its qualities. The 
 fusion and perfect refining of flint glass, as here described, are 
 usually completed in about forty-eight hours from the first 
 charging of the crucibles. 
 
 In the operations of a glass-house it is, indeed, common, pur¬ 
 posely to manage the vitrifying of the materials so that the con¬ 
 tents of the different crucibles shall be brought to the state 
 proper for blowing in succession, that when the glass contained 
 in one is all worked up, that in another shall be in perfect 
 readiness for use. By this arrangement the workmen experi¬ 
 ence no interruption, and the heat of the furnace is constantly 
 maintained, which last is a consideration of some importance; 
 for if through any accident, the temperature be allowed to sink 
 in a material degree, considerable expense of time and fuel are 
 required for its restoration. 
 
 It is by no means advisable to employ in the formation of the 
 same glass vessel materials drawn from more than one cruci¬ 
 ble. Although the original composition may have been alto¬ 
 gether identical, and the fusion of all has been simultaneously 
 carried forward in the same furnace, still a minute difference 
 may, and generally will, exist in the constituent proportions of 
 each mass, arising from an accidental variance of draught, and 
 consequently of heat, in different parts of the furnace, whereby 
 some crucibles may have been made to part with a larger pro¬ 
 portion of their alkali than others. Any circumstances which 
 interfere with the perfect sameness of quality in every part of 
 vessels formed of glass renders them more liable to break on 
 exposure to sudden changes of temperature, by reason of their 
 differing tendencies to expand and contract under such circum¬ 
 stances. 
 
 The implements used by glass-blowers are few in number, 
 and exceedingly inartificial in their form and construction. 
 The principal one is simply a hollow iron rod or tube, about 
 five feet long, upon one end of which the workman collects the 
 quantity of melted glass that will suffice for forming the article 
 intended. In this operation the rod is dipped into the pot and 
 
CHAP. IV. 
 
 FLINT GLASS. 
 
 137 
 
 turned about several times. If the size of the vessel requires a 
 considerable weight of glass for its formation, the rod is taken 
 
 Fig. 3. 
 
 out and exposed momentarily to the current of air, by which 
 means the surface of the glass already collected is sufficiently 
 cooled for a fresh portion to adhere, and this proceeding is re¬ 
 peated until enough is collected for the object. 
 
 When the rod thus loaded is withdrawn from the crucible, it 
 is held for a few seconds in a perpendicular position, the end to 
 which the glass is attached being nearest to the ground, that by 
 its own weight the mass may be lengthened out beyond the rod. 
 The next operation is to roll the glass on the flat surface of a 
 smooth horizontal iron plate called the marver, a name corrupt¬ 
 ed from the French word “ marbre." By this means the par¬ 
 ticles of glass are agglomerated in a cylindrical form, which is 
 then called by the workmen a paraison. The workman then 
 applies his mouth to the other end of the tube, and blows strong¬ 
 ly through it, so that his breath, penetrating the centre of the 
 red-hot glass, causes it to be distended into a hollow globe. The 
 pressure of the breath must be continued upon the tube for a 
 few seconds to prevent the return of any portion of the air 
 
 Fig. 4. 
 
 through the tube, otherwise the external air being more dense 
 than the heated portion confined within, the globe would col¬ 
 lapse : when it has been somewhat stiffened by cooling, this 
 accident is no longer to be apprehended. 
 
 M 2 
 
138 
 
 GLASS MANUFACTURE. 
 
 CHAP. IV. 
 
 The globe, which is not made sufficiently thin by this one 
 blowing, is then heated anew by being held a little within the 
 opening of the furnace; the breath is again employed as before, 
 and so on repeatedly, until the proper size and thickness of the 
 globe are satisfactorily attained. 
 
 If the form of the intended vessel requires the globe to be 
 elongated, this effect is produced by giving to the rod, while 
 the glass attached to it is softened by heat, an alternating mo¬ 
 tion similar to that of a pendulum, or by dexterously making it 
 perform a circle swiftly through the air. The tendency to fly 
 off from the centre which is thus imparted causes the particles 
 to change their relative positions in a degree corresponding with 
 the amount and duration of the force employed. 
 
 At this stage another implement, called a punt , or pontil, is 
 brought into use. This is a solid iron rod of a cylindrical form, 
 
 Fig. 5. 
 
 smaller and lighter than the tube used for blowing, and conse¬ 
 quently more within the power and management of the work¬ 
 man. Upon one end of this rod a small portion of melted glass 
 is collected, by an assistant, from the crucible, and in this state 
 is applied to the surface of the globe on the side opposite to that 
 where it is already attached to the tube. The two heated sub¬ 
 stances speedily uniting, the glass is detached from the hollow 
 
 Fig. 6. 
 
 rod, by touching it near to their point of contact with a small 
 piece of iron wetted with cold water. This occasions the glass 
 
CHAP. IV. 
 
 FLINT GLASS. 
 
 139 
 
 -o crack, so that by giving a smart stroke to the hollow rod, it 
 :s immediately and safely separated, leaving a small hole at the 
 point or rupture. 
 
 The workman now receives from his attendant the pontil 
 vitn the glass vessel attached, and after reheating it at the 
 nrnace mouth as before, seats himself on a sort of stool provided 
 
 Fig. 7. 
 
 mth arms sloping forward, whereon the pontil is supported be- 
 pre him in a horizontal position, the glass being at the man’s 
 lght hand. Thus placed he governs with his left hand the 
 rovements of the pontil by twirling it to and fro along the arms 
 r the stool; and taking in his right hand an iron instrument, 
 ailed a procello, the blades of which are connected too-ether by 
 n elastic bow, in the manner of a pair 
 f sugar-longs, he enlarges or contracts 
 ie vessel in different places until it as- 
 
 nnes the requisite form. Any supera- _ 
 
 undance of material is cut away by the scissors while the 
 ass is red-hot, with as much ease as they could be made to 
 lv ide a piece of soft leather. 
 
 If the article is of a kind, by its size or by the complex na- 
 ire ot its form, to occupy much time in its manufacture, it 
 ust occasionally be reheated, as its increasing rigidity makes 
 more difficult of management. 
 
 To insure the requisite regularity in shape and size, the 
 orkman is provided with compasses and a scale marked off in 
 et and inches. 
 
 The finished article is detached from the pontil in the same 
 anner as it has previously been from the blowing tube, by 
 e ing it at the point where it is attached, and is then dropped 
 ' n y on a bed of ashes kept at the man’s side for the purpose. 
 
 Fig. 8. 
 
140 GLASS MANUFACTURE. CHAP. IV. 
 
 It is then taken up on a pronged stick, or, when from its shape 
 this mode is inconvenient or impracticable, the glass is made 
 to rest during the detaching process on a wooden shovel, 
 wherein it consequently remains when divided. In either case 
 a boy in attendance conveys it without loss of time, and while 
 yet exceedingly hot, to the annealing oven. 
 
 If it be required to give to the article any form or pattern 
 which is unattainable by the simple means narrated, a mould is 
 provided, into which the glass is placed while it is being blown, 
 and where it receives the requisite impression with as much fa¬ 
 cility and faithfulness as wax. 
 
 The process of annealing is one of very great importance; 
 without it, glass would be liable to fly with the smallest change 
 of temperature, and would break with the merest scratch or 
 touch, or even without any apparent external cause of injury. 
 The most reasonable theory which has been proposed in expla¬ 
 nation of this disposition in unannealed glass is, that by its sud¬ 
 den cooling the external particles are forcibly contracted, while 
 the inner substance still remains soft and expanded. The two 
 portions thus take up positions, in relation to each other, very 
 different from those which they would occupy if the contraction 
 of the whole had gone forward equally and gradually. By this 
 means a constant strain is kept up between the different parts, 
 and should a force be applied of a nature to rive any the smallest 
 portion asunder, the equilibrium of resistance is deranged, and 
 the elastic quality of the glass causes the injury to be felt 
 strongly and suddenly, but very unequally, through the whole 
 mass. 
 
 This theory appears to receive confirmation from the well 
 known and often repeated experiments made with the Bologna 
 phial and with Rupert’s drops. The first is a phial of ordinary 
 shape made of any kind of glass, much thicker at its bottom 
 than in its upper portion, and which has been suddenly cooled 
 in the air. This phial, from its thickness, will sustain a con¬ 
 siderable blow from any blunt instrument, or will bear unin¬ 
 jured the sudden concussion caused by the fall of a leaden bul¬ 
 let. But if any hard and angular substance, such as a minute 
 portion of gun flint or even a grain of sand, be dropped into it, 
 the bottom will crack all round and drop off. In performing 
 this experiment, if the glass be very brittle and the substance 
 dropt upon it be very hard and sharp—a cut diamond for in¬ 
 stance—this has been seen to pass through the thick bottom 
 with apparently as little resistance as would be offered by a 
 cobweb. 
 
 The greater comparative thickness of the bottom is an indis¬ 
 pensable quality of these Bologna phials, and the more consid- 
 
CHAP. IV. 
 
 FLINT CLASS. 
 
 141 
 
 erable this disproportion is made, the more easily will the dis¬ 
 ruption be effected. Some of these vessels have been struck 
 by a wooden mallet, and were uninjured, notwithstanding the 
 force applied was sufficient to drive a nail into most kinds of 
 wood ; and yet the glasses broke readily when a small shiver 
 of flmt weighing only two grains was gently dropt within them 
 1 lint being very hard, and its angles when fractured extremely 
 sharp, its points of contact with the glass are exceedinoly 
 smalJ, so that the effect produced by even so very minute a 
 portion of this substance will be comparatively greater than 
 would accompany the blow given by a much larger but softer 
 ind less angular body, and which for these reasons would di¬ 
 vide the shock between a greater comparative number of parti¬ 
 cles of the glass. 
 
 . Another theory has been proposed in order to account for this 
 singular propeity in certain forms of unannealed glass. It has 
 ieen imagined that the sudden cooling of glass may occasion it 
 o be more electric than is consistent with the cohesive attrac- 
 ion of its particles, and that the sudden setting' in motion of 
 he electric fluid which glass contains, may occasion throughout 
 he substance a propagation of the motion of that fluid, which 
 vill go on accumulating within itself a force too great to be at 
 ength resisted. 
 
 This theory is by no means free from difficulties, yet it seems 
 o derive support from a fact which was developed in the course 
 if some experiments made before the Royal Society, in which 
 flass vessels, the thick bottoms of which were only slightly 
 ubbed by the finger, broke after the interval of half anliour 
 pad occurred from the time of rubbing. 
 
 : Rupert’s drops are small solid pieces of common green glass, 
 vhich have been dropped while red-hot into cold water, and’ 
 phich are thus caused to take the form of rounded lumps elon- 
 •ated into a kind of tail. The spherical part will bear very 
 ough treatment without injury; but if the smallest portion of 
 be tail be broken offj the whole article instantly bursts into a 
 ountless number of fragments, so minute as to produce only a 
 light stinging sensation in the hand by the sudden disruption, 
 r one of these drops is immersed in a phial or tall glass filled 
 nth water, and its end be broken off with a pair of pincers, the 
 ulb will be rent so suddenly and with so great a force as will 
 ifallibly break the vessel wherein it is contained. The stoutest 
 ine or beer bottle would not be strong enough to withstand 
 ie shock. 
 
 Messrs. Aikin completely destroyed this property in drops of 
 iis kind and in Bologna phials, by heating them to redness and 
 len allowing them to cool gradually as in the annealing oven. 
 
142 GLASS MANUFACTURE. CHAP. IV. 
 
 Not only was their quality of bursting corrected by this treat¬ 
 ment, but the particles of glass were made to assume a closer 
 union among themselves, which fact was proved by the acquire¬ 
 ment of a sensible increase in their specific gravity. 
 
 The internal form of an annealing oven has been already de¬ 
 scribed. Articles newly made are placed on the shallow trays 
 
 Fig. 9. 
 
 previously mentioned, in the part of the oven most exposed to 
 the heat of the fire, which, it will be remembered, is kindled 
 under one end only. Each one of these lier pans or fraiches, as 
 it is filled, is pushed forward in the oven, towards the colder 
 end, to make place for a fresh tray, until the articles, at length 1 
 and in succession, reach the farthest extremity of the oven, 
 whence they are taken, but little warmer than the temperature 
 of the atmosphere. 
 
 By the gradual manner in which they have parted with their 
 heat, time lias been allowed for the regular contraction of the 
 whole into an uniform and consistent substance. 
 
 In glass-houses where objects of various magnitudes and de¬ 
 scriptions are made, two or more of these annealing ovens are 
 usually attached to each working furnace. Pieces which are 
 large, and of considerable substance, require that the oven in 
 which they are annealed should be made much hotter than is 
 necessary for thinner and smaller pieces. Glass which is after¬ 
 wards to pass through the hands of the cutter is always made 
 of considerable thickness, and requires not only that the heat 
 ot the oven should be very considerable when it is first inserted, 
 but that it should be withdrawn from this heat very gradually j 
 while, on the contrary, such articles as are very thin may be 
 placed at first in a much more moderate temperature, and may 
 be removed altogether at the expiration of a few hours. 
 
CHAP. IV. FLINT GLASS. 143 
 
 It is impossible by written explanations to impart beyond a 
 very faint idea of the truly curious and interesting operations 
 of the glass-blower. This difficulty does not arise from any 
 complexity in the manipulations. Although, in common with 
 nearly all the manual arts, these call for long practice to insure 
 proficiency, they are yet exceedingly simple in their nature. 
 But there is something more than ordinarily striking—perhaps, 
 even, it may be said fascinating—in watching the progress 
 through which a substance, in its usual state rigid and brittle to 
 a proverb, passes, by rapid conversion, from a glowing and 
 shapeless lump to a perfect article of most elegant manufac¬ 
 ture. The absolute control which the workman exercises over 
 its form and substance; the perfect ease and security where¬ 
 with he pulls, and twirls, and divides, and joins, a matter which 
 we are accustomed to handle with only gentleness and care; 
 never fail to excite a high degree of admiration even in those 
 who have had frequent opportunities for witnessing the pro¬ 
 cesses. 
 
 The amusement to be derived from watching the operations 
 employed in many branches of manufacture is probably much 
 greater than would be imagined by persons who have not so in¬ 
 dulged their curiosity; and among these manufactures, al¬ 
 though there are doubtless many that call in a higher degree 
 for our admiration as proofs of the genius and perseverance of 
 man, there is not one calculated to afford, for the time, more 
 gratification than the operations of a glass-house. 
 
 CHAP. V. 
 
 ON THE MANUFACTURE OF CROWN GLASS, BROAD GLASS, AND 
 BOTTLE GLASS. 
 
 Description of Crown Glass.—Harder than Flint Glass.—More difficult to 
 Fashion.—Its Composition.—In France.—In England.—Fritting.—Cullet. 
 —Refining.—Sulphate of Soda.—Vegetable Charcoal.—Gathering.—Blow¬ 
 ing.—Reheating.—Flattening.—Transferring to Pontil.—Twirling.—Ex¬ 
 panding.—Opening.—Annealing.—Nice Regulation of Temperature re¬ 
 quired in this Process.—dualities of Crown Glass.—German Glass.— 
 Broad Glass.—Inferior to Crown Glass.—Its Composition.—Preparation. 
 —Working.—Bursting.—Opening.—Annealing.—Bottle Glass.—Manufac¬ 
 ture checked by Increase of Duty.—Composition.—Restrictions as to Ma¬ 
 terials.—Their bad Tendency.—Superiority of Bottle Glass for certain 
 Purposes.—Materials employed in France.—At Newcastle.—Fashioning. 
 —Moulding.—Experiments suggested by Count Chaptal.—Klingstein.— 
 Volcanic Granite. 
 
 The name of crown glass is given to the best kind of glass 
 commonly used in making windows, and for like purposes. In 
 the composition of this material, no lead or metallic oxide en- 
 
144 
 
 GLASS MANUFACTURE. 
 
 CHAP. V. 
 
 ters as a fluxing agent. A small quantity of manganese is fre¬ 
 quently used, and sometimes also a minute portion of oxide of 
 cobalt; but the object of these additions is the correction of a 
 faulty color in the glass, arising from impurities in the sand and 
 alkali. This kind is, therefore, much harder than flint glass, 
 and would consequently be more difficult to fashion, if it were 
 desired to give it any other form than that of a plane surface. 
 
 The composition of crown glass varies considerably. Loysel 
 has given several different recipes for its formation. That 
 which he most recommends, stating that it is employed at the 
 extensive works of St. Gobain, consists of 
 
 Fine white sand.100 parts. 
 
 Carbonate of lime.12 
 
 Carbonate of soda, calcined, 45 to 48 
 Clippings of crown glass . . 100; 
 with such additions of manganese and oxide of cobalt, as may 
 be required to correct impurities and remove the color which 
 they occasion. By proper carefulness in selecting and purify¬ 
 ing the ingredients, the employment of these metallic bodies is 
 rendered unnecessary. 
 
 Crown glass is generally made in France of 100 parts of 
 fine white sand, 50 to 65 parts potash, 6 to 12 parts dry slaked 
 lime in powder, and from 10 to 100 parts of broken glass of 
 similar quality : this composition is frequently employed in 
 that country for the manufacture of common drinking vessels, 
 as well as of window panes. 
 
 In England, this material has usually been composed of fine 
 Lynn sand, kelp, and slaked lime ; the proportions of these in¬ 
 gredients varying according to the quality of the kelp, some 
 kinds of which contain a greater amount of alkali than others. 
 That from Orkney is considered to be the best, not only on this 
 account, but also because the glass which is made of it proves 
 of a better color than where Scotch or Irish kelp is employed. 
 The proportions when the kelp is of the best quality are, 
 
 Fine sand .... 5 bushels or 200 pounds’ weight, 
 
 Ground kelp . 11.330 
 
 Slaked lime.15; 
 
 which ingredients are fritted in the calcar as already described, 
 preparatory to their fusion. When put into the crucible, about 
 half its weight of broken glass, or, as it is called in the manu¬ 
 factory, cullet, is added to the frit. This compound requires to 
 be kept in fusion at a high degree of heat during thirty-five to 
 forty hours, in which time an intimate union of all the parts 
 takes place; the glass refines itself by throwing off all its san- 
 diver, and becomes perfectly transparent. It is not advisable to 
 use a larger proportion of broken and refuse glass than that 
 
CHAr. V. 
 
 CROWN GLASS. 
 
 145 
 
 just mentioned, because, by its long exposure to heat when in 
 fusion, glass is made to give up a portion of its alkali, becoming 
 harsher and less fusible. The quantity of glass usually em¬ 
 ployed is serviceable by sooner bringing the pot to a working 
 state ; but any larger quantity would, for the reason just stated, 
 sensibly alter the quality of the whole contents of the crucible. 
 The fragments, before they are used, are first heated, and then 
 suddenly plunged into cold water, which renders it easy to re¬ 
 duce them to powder. 
 
 A very superior quality of crown glass is made by the mix¬ 
 ture of 
 
 120 parts by weight of White sand. 
 
 60.Purified pearl-ash, 
 
 30.Saltpetre, 
 
 2.Borax, 
 
 1.Arsenic. 
 
 If the color should prove yellow, this is corrected by the ad¬ 
 dition of a small quantity of manganese. 
 
 Another composition, cheaper than the foregoing, consists of 
 120 pounds of White sand, 
 
 50.Unpurified pearl-ash, 
 
 20.Common salt, 
 
 10.Saltpetre, 
 
 4.Arsenic, 
 
 and 3 ounces of Manganese. 
 
 This produces glass of a good and useful description, much em¬ 
 ployed in the manufacture of apothecaries’ vials. 
 
 The late M. Gehlen, who was well experienced in the art 
 of glass-making, composed crown glass of the following ma¬ 
 terials*:— 
 
 Sand.100 parts. 
 
 Dry sulphate of soda . . 50 
 
 Quick-lime in powder . 17 to 20 
 
 Charcoal. 4. 
 
 In this case the sulphuric acid in combination with the soda is 
 decomposed by the charcoal, and driven off during the fusion, 
 leaving the soda to unite with the sand. M. Gehlen made 
 many experiments to ascertain the effects of various combina¬ 
 tions with sulphate of soda, and found that this salt could be 
 used without the addition of any other saline flux. If mixed 
 with only sand, the vitrification was very imperfect even after 
 long-continued heat. The addition of lime caused it to suc¬ 
 ceed better, but the time and fuel required were still excessive. 
 When, however, by the addition of vegetable charcoal, the sul- 
 
 * Annates de Cliimie et de Physique. Fevrier, 1816. 
 
 N 
 
146 
 
 GLASS MANUFACTURE. 
 
 CHAP. V. 
 
 phuric acid was decomposed, and the powerful affinity de¬ 
 stroyed, which prevented the soda from acting on the sand, vit¬ 
 rification was produced both perfectly and quickly. If used in 
 any other proportions than those above mentioned, M. Gehlen 
 found that the fusion was accompanied by disagreeable sulphur¬ 
 ous odors, and by an extraordinary swelling over of the mate¬ 
 rials. The decomposition of the sulphate of soda may be 
 effected with equal advantage, either during or before vitrifica¬ 
 tion, according as the choice of the manufacturer may be influ¬ 
 enced by local circumstances. 
 
 When the materials are properly fused and refined by the 
 removal of all the glass gall, the workman commences his 
 blowing operations in exactly the same manner as has already 
 been described in the process for making flint glass. By re¬ 
 peated dippings of the iron tube into the crucible, he gathers 
 as much glass upon its end as experience teaches him will suf¬ 
 fice for the formation of a sheet of glass of the usual size, and 
 which generally weighs from ten to eleven pounds. This lump 
 he allows to project beyond the extreme end of the tube ; and 
 first rolling it on the iron plane before described, to give the 
 glass a cylindrical form, he commences blowing, when, it as¬ 
 sumes the shape of a pear. A fresh heating and a second blow¬ 
 ing enlarge its dimensions, and render its shape more globular. 
 A third operation of heating and blowing still further enlarges 
 the size of the glass, and reduces its substance. The side op¬ 
 posite to the tube is then flattened by pressure against a plane 
 
 Fig. 10. 
 
 surface ; a small portion of melted glass is collected on the end 
 of a punt, and is applied to the centre of this flattened side, 
 forming an union with it exactly opposite to the hollow tube, 
 
CHAP. V. CROWN GLASS. - 147 
 
 which is then removed by wetting the glass near to their point 
 of union, leaving a circular hole in the glass about two inches 
 in diameter. 
 
 At this period the glass must be again held to one of the 
 openings ot the furnace until it has become sufficiently hot and 
 ductile for the further alteration of its shape. The workman 
 then dexterously twirls the punt in his hand, slowly at first, 
 and then more and more quickly, when the glass yields to the 
 centrifugal impulse; its diameter becomes greater and greater; 
 the hole just mentioned expands proportionally; and when in 
 this continued progression the doubled portion opposite to the 
 iron rod, and between the periphery of the glass and the ori¬ 
 fice, is diminished to an annulus or ring only a few inches 
 wide, this in an unaccountable manner instantly flies com¬ 
 pletely open, and the glass is converted into a plane disc of 
 fifty to sixty inches diameter, having an uniform thickness 
 throughout the entire plate, with the exception of the spot 
 where it is attached to the iron rod, and where there is a knot 
 
 Fig. 11. 
 
 or lump which is called a bull's eye. Twelve of these plates 
 make up what is called a crate or side of glass. 
 
 The effect of this operation upon persons who witness it for 
 the first time is both pleasing and surprising in a high degree. 
 The force wherewith the glass flies open at the close of the 
 process would be sufficient, if its brittleness were not removed 
 by heat, to break it into innumerable fragments. 
 
 The plate, when thus finished, is detached from the iron rod 
 by the usual method, and placed resting on its edge in the an- 
 
148 
 
 GLASS MANUFACTURE. 
 
 CHAP. V. 
 
 nealing oven. Some considerable care is necessary for regula¬ 
 ting the temperature at this stage; for if the heat be too great, 
 the softened glass will bend, and for that reason will be lessen¬ 
 ed in value, while, if the oven be not sufficiently hot, the plates 
 are very likely to crack; and if even this disaster should not 
 happen, the glass will prove of inferior quality, and so brittle, 
 that the glazier will be unable to cut it with any degree of cer¬ 
 tainty in the wished-for direction. 
 
 Crown glass is sold, according to its quality, under four dif¬ 
 ferent denominations—firsts, seconds, thirds, and fourths—at 
 considerable difference of price; that of the fourth quality not 
 yielding to the manufacturer nearly one half of the price of 
 the first. These variations arise principally from the want of 
 sufficient care on the part of the attendants, in maintaining the 
 necessary degree of heat in the furnace. If this is once suffer¬ 
 ed to fall, the property of glass in being a very imperfect con¬ 
 ductor of heat renders it difficult again to raise it to the former 
 degree. In the operations of a large glass-house, it does not 
 often happen that beyond one third of the quantity made is of 
 the first quality; seconds and thirds compose the largest propor¬ 
 tion of the produce; and it seldom occurs that the quality 
 sinks below the latter of these two denominations. 
 
 Large plates ofcrown glass, such as are required for glazing 
 engraved prints, used formerly to be imported from Germany. 
 This country has, however, for a long time, been not only in¬ 
 dependent in this respect of all foreign manufacturers, but 
 similar plates of English make are exported to a considerable 
 extent. 
 
 Broad glass is a common coarse description of window glass, 
 made of inferior ingredients, and by a somewhat different pro¬ 
 cess of manufacture than that last described. The material 
 principally employed for the purpose is soap-boiler’s waste. 
 This compound is a pasty mass, consisting of the insoluble mat¬ 
 ter of the kelp or barilla, and of the lime which has been used 
 to render the alkali caustic, together with a quantity of salt 
 and water. This substance is united with kelp and sand, and 
 the mixture is dried and fritted. The proportions wherein the 
 ingredients are used necessarily vary according to the quality 
 of the principal constituents, and the manufacturer must be 
 guided by practical knowledge in apportioning the quantities. 
 
 A very usual mixture is six measures of soap-boiler’s waste, 
 three of kelp, and three to four measures of sand. The quality 
 of the last of these ingredients is of greater moment to the 
 manufacturer than would seem to be generally imagined. 
 Coarse sand is known to require a greater quantity of alkali 
 for its fusion than that which is fine; and as, notwithstanding 
 
CHAP. V. 
 
 BROAD GLASS. 
 
 149 
 
 this, the glass when made does not contain the alkali m a 
 larger proportion, it follows, that the difference has been dissi¬ 
 pated and lost during the process. The carbonaceous matter, 
 which would injure the color of the glass, is principally burned 
 out, and the carbonic acid gas separated during the fritting; 
 after the completion of which, the mass, still red-hot, is re¬ 
 moved with iron shovels to the melting furnace, the crucibles 
 are entirely filled, and after twelve or sixteen hours’ exposure 
 to the proper degree of heat, the whole is perfectly vitrified. 
 
 The formation of this glass into sheets is thus performed:— 
 The necessary quantity being collected upon the end of the 
 iron tube, as already described, is expanded by the workman’s 
 breath into a globular, or rather into an elliptical shape, of about 
 twelve inches diameter, and of the requisite thickness. This 
 done, the glass is carried to the mouth of the oven; and the end 
 of the tube through which the workman has blown being 
 closed, the further expansion by heat of the confined air causes 
 the glass to burst in its weakest part. While still hot and duc¬ 
 tile, it is then opened by a pair of shears through its entire 
 length into a flat plate, which is then conveyed to the anneal¬ 
 ing oven. 
 
 More than one half of the entire manufacture of glass in 
 Great Britain is composed of common green bottle glass. The 
 quantity of this material upon which duty has been levied, on 
 an average of the last six years, exceeds 11,000 tons annually. 
 However considerable this amount may appear, it is not greater 
 than the annual average manufacture of a similar period com¬ 
 mencing in the year 1790,—a fact which may be thought ex¬ 
 traordinary, when it is considered that during the intervening 
 years our population has been importantly augmented ; that the 
 comforts, and even the luxuries of life, have been brought with¬ 
 in the reach of a much larger proportion of our fellow-country¬ 
 men ; and that our colonial markets have, in the same time, 
 been very considerably extended. The circumstance of the 
 rate of duty having been doubled would hardly appear cause 
 sufficient for thus arresting the progress of consumption in an 
 article so generally required; since this duty, at its highest 
 rate, has never exceeded eight shillings per himdred weight. 
 A more minute examination into the case leaves us, however, 
 without any reason for doubting that to the increase of the 
 rate of duty, and to it alone, is to be ascribed the check given 
 to this branch of manufacture. In the year 1812, when the 
 duty was 4s. 0-ty. per hundred weight, upwards of 13,000 tons 
 of common bottle glass contributed towards the revenue. In 
 the succeeding year, when an additional tax of 4s. 0§<Z. was 
 imposed, the consumption immediately fell to somewhere below 
 
 N 2 
 
150 
 
 GLASS MANUFACTURE. 
 
 CHAP. V. 
 
 8000 tons. From this extreme depression it has since gradu¬ 
 ally risen, through the increasing numbers and improved con¬ 
 dition of the community, and aided by a diminution of price, 
 independent of the duty; but even now the manufacture has 
 not reached within 2500 tons of the point which it had attain¬ 
 ed in the year 1812; thus in a very striking manner verifying 
 the remark so often made as to the variance between common 
 and legislative arithmetic, and proving the pernicious tendency 
 of taxes levied upon articles of domestic manufacture. It is to 
 be hoped that the improvement of the national revenue conse¬ 
 quent upon the progressive state of our manufacturing inte¬ 
 rests, and the constantly ameliorating circumstances of many 
 classes of the community, will enable the government to carry 
 speedily into effect a measure already announced for abolishing 
 entirely the duties upon glass of home fabric, when this branch 
 of the manufacture will assuredly receive an impulse that will 
 carry it far beyond the highest point to which it has ever yet 
 attained. 
 
 The composition of bottle glass is as little uniform as that of 
 any other description of the material; varying greatly in differ¬ 
 ent parts of the kingdom, and indeed in almost every individ¬ 
 ual manufactory. It is usually made of sand, lime, and some¬ 
 times clay, any kind of alkali or alkaline ashes which may hap¬ 
 pen to offer the greatest inducement in point of price, and some¬ 
 times the vitreous slag produced from the fusion of iron ore. 
 Soap-makers’ waste is frequently used in the proportion of three 
 measures to one measure of sand. 
 
 The rate of duty upon this description of glass being only 
 one eighth of that levied upon flint glass, the manufacturers 
 are restricted to the use of the commonest kind of sea or river 
 sand, lest the revenue should suffer by the superior quality of 
 this less burdened ware. This is unfortunate, since, for the 
 reason already given, the employment of such coarse sand oc¬ 
 casions the necessity for using a large portion of alkaline mat¬ 
 ter, and, in that respect, increases the charges to the glass- 
 blower. The impurity of the alkali, and the abundance of flux¬ 
 ing materials of an earthy nature, joined to the very high degree 
 of heat at which they are fused, occasion the glass to contain a 
 very small proportion of real saline matter; for which reason it 
 is better qualified than flint glass to be employed as the recipi¬ 
 ent of fluids which have any corrosive action. Chemical re¬ 
 torts and subliming vessels, and carboys for containing aqua¬ 
 fortis, should, for this reason, be always made with this common 
 glass, which has this further advantage over flint glass—that it 
 will bear a much stronger heat without being softened or un¬ 
 dergoing any alteration of its shape. 
 
CHAP. V. 
 
 BOTTLE GLASS. 
 
 151 
 
 . ®?, ttIe £ las . 3 13 a very hard and well vitrified substance, and 
 is of less specific gravity than other descriptions. Loysel erives 
 as the composition usually employed in France for the produc¬ 
 tion of this material,— ^ 
 
 Common white or yellow sand . . 100 parts. 
 
 Coarse kelp. 30 to 40 
 
 Lixiviated earth of ashes.160 to 170 
 
 Fresh wood or other ashes .... 30 to 40 
 Yellow clay, or brick earth ... 80 to 100 
 Broken glass ad libitum, usually 100; 
 which composition does not produce any glass gall. 
 
 At Newcastle upon Tyne, where the manufacture of bottle 
 glass is much encouraged by the excessive cheapness of small 
 coal, or slack, the manufacturers employ a mixture of lime and 
 feea sand. This must be frequently wetted with sea water, 
 which, on evaporating, deposits its salt; the soda contained in 
 this being the only alkali employed. When combined with 
 silica, and exposed to a high degree of heat, lime appears to be 
 endued vvitii the property of decomposing common salt; its 
 presence is, therefore, essential to the success of this operation. 
 
 Articles made of bottle glass are fashioned by the same pro¬ 
 cess as those of flint glass, with the exception of wine and beer 
 Dottles, the containing parts of which are blown in metallic 
 moulds, m order to keep them nearly of an uniform size. The 
 ?reen color of this glass is owing to the presence of a portion 
 31 iron in the sea sand, and, probably also, in the vegetable ashes 
 3f which it is composed. 
 
 Ifj*during the time when the workmen are employed in 
 moulding and blowing bottles, the melted glass should—as bl¬ 
 eed it frequently will—become cooler than is desirable for the 
 lurpose, so that it is found necessary to replenish the fire, so 
 much dust will be thus occasioned, owing to the description of 
 :oal employed, that the surface of the melted glass will be cov¬ 
 ered with carbonaceous matter. The effect of this upon the 
 contents of the crucible is very curious. The glass, which had 
 ietore remained perfectly quiet, becomes suddenly so disturbed 
 nroughout as to present the appearance of violent ebullition, 
 nd the whole mass is immediately crowded with an infinite 
 mmber of minute air-bubbles, which, so long as they are suffer- 
 d to remain, render the glass wholly unfit for use. 
 
 he time that would be required for burning away this car- 
 onaceous deposit, and to restore the glass to its former working 
 rate, would be so considerable, that it would be highly incon- 
 ement to wait for the production of this effect; and it is there- 
 )re fortunate that a simple remedy has been discovered, which 
 
GLASS MANUFACTURE. 
 
 CHAP. V. 
 
 152 
 
 immediately and perfectly restores every thing to its former 
 state. 
 
 Whenever the accident here mentioned occurs, the work¬ 
 man has only to throw a small quantity of water into the cruci¬ 
 ble, when the whole mass will be immediately stilled, and the 
 bubbles will as instantly disappear, so that the workman may 
 proceed without further delay. This curious effect has been 
 referred to the decomposition by heat of the water, which, giv¬ 
 ing up its oxygen to the coal-dust, converts it into carbonic acid 
 gas; in which form it is instantly driven off by the excessive 
 heat of the furnace, and is dissipated in the atmosphere. 
 
 In 1780, the celebrated M. Chaptal recommended M. Ducros, 
 a manufacturer of bottle glass, to make trial of a new material 
 for his purpose. This gentleman entered in consequence upon 
 various experiments, which were, many of them, to a certain 
 extent, successful. The substance thus recommended, and 
 which formed the basis of these experiments, was decomposed, 
 pulverulent, basaltic earth. This is found in great abundance 
 in many parts of France, and is equally obtainable in the valleys 
 of all basaltic countries. 
 
 In the first trial made of this earth by M. Ducros, it was fused 
 in a glass pot without admixture with any other substance; and 
 the result obtained was glass of an exceedingly deep yellow 
 color, and lustrous. In subsequent experiments, various pro¬ 
 portions of sand were used in conjunction with the basaltic 
 earth. The mixture that was found to answer the purpose best 
 was where equal parts of each ingredient were employed. This 
 produced glass of an olive green color. .• 
 
 There was tor some time a considerable demand for bottles 
 thus composed; but owing to a difficulty which the manufac¬ 
 turer experienced in procuring materials having the requisite 
 uniformity in their constituent parts, the manufacture was, after 
 a time, abandoned. 
 
 M. Alliot has published the results of a course of experiments 
 made by him with basaltic earth, with a view to the composi¬ 
 tion of glass. Not being able to have recourse to the furnace 
 of a glass-house, M. Alliot was obliged to content himself with 
 the less intense heat of a potter’s kiln, wherein the different 
 mixtures which he employed were severally heated during 
 eighteen hours. It is probable that the results which he has 
 detailed would have proved more satisfactory, could recourse 
 have been had to a more efficient mode of heating. The ex¬ 
 periments were all conducted in crucibles. 
 
 No. 1. was filled with the pure basaltic earth. This, in fusing, 
 was converted into a black glass, which was opaque, and tol¬ 
 erably well melted. 
 
HAP. V. BOTTLE GLASS. 153 
 
 o. 2. contained a mixture composed in equal parts of basalt, 
 ashes, and white quartz in powder. This produced a coffee- 
 colored glass, which was lustrous, and somewhat resembled 
 porcelain in appearance. 
 
 o. 3. was charged with half basalt and half common sand. 
 The glass produced from this compound appeared, when in 
 the mass, of a blue-black color; but when small thin portions 
 were examined, these proved of a yellowish green. This 
 glass was tolerably well melted. 
 
 o. 4. consisted of one third each basaltic earth, sand, and re¬ 
 fuse soda. The result was a transparent glass of a greenish 
 yellow color, and of good quality ; it was very smooth and 
 shining, well melted, and would have formed excellent bot¬ 
 tles. 
 
 ). 5. consisted wholly of sand taken from the river Orb, in 
 the immediate neighborhood of which there is found a con¬ 
 siderable quantity of basaltic earth. The glass from this sand 
 was well melted, and appeared to be every way adapted for 
 the manufacture of very good and serviceable glass bottles. 
 
 This basaltic earth is exceedingly well qualified both for fU- 
 n by itself, and for employment as a fluxing material where 
 ier substances are used. It is found, by analysis, to contain 
 )ut 45 parts of silex, 16 of alumine, 20 of oxide of iron, 9 of 
 ie, and from 2% to 4 parts of pure soda; three of these sub- 
 nces being very powerful fluxes. 
 
 Some other minerals have been proposed, on account of the 
 a which they contain, as well qualified for making glass: 
 ; h, for instance, is klingstein, which contains nearly one 
 slflh part of its weight of that alkali; but as the other flux- 
 ' materials present in basaltic earth are wanting in those 
 er minerals, they prove far less fusible. 
 
 Whenever basaltic earth is largely employed in the compo- 
 on of glass, it usually proves of a dark olive green color, 
 ying sometimes to a very deep yellow 7 ; and it does not ap- 
 r at all probable that this color could in any material degree 
 corrected. The glass produced is specifically lighter than 
 common green bottle glass; and at the same time is con- 
 ;rably harder and tougher, so as to bear, without injury, 
 vs which would infallibly break ordinary glass. The quan- 
 of alkali which it contains is small—much smaller, in fact, 
 i is required to bring glass of every other description to a 
 kable state. For this reason basaltic glass is peculiarly well 
 iified for chemical purposes; as vessels made with it will 
 3t the destructive action of corrosive liquids. 
 i addition to the experiments already detailed as having 
 
154 GLASS MANUFACTURE. CHAP. V 
 
 been made by him with basaltic earth, M. Alliot made trial c 
 various other combinations for the production of bottle glas 
 He succeeded with the two following : 
 
 The first was a mixture in equal parts of ashes and a vole 
 nic granite. This fused perfectly, and produced a very fii 
 dark and lustrous glass, exceedingly well qualified for the cor 
 position of bottles. The second was composed of 1 part ore 
 nary soda, 12 parts ashes, and 6 parts common sand. The gla 
 thus formed was of a yellowish black color, interspersed wi 
 veins of bluish white, which were opaque. 
 
 When the duty shall be removed, and the manufacturer fin 
 himself without restriction in regard to the materials which i 
 may employ, we may expect to witness some considerable ii 
 provements in this branch of the glass-maker s art. 
 
 CHAP. VI. 
 
 OF THE MANUFACTURE OF PLATE GLASS. 
 
 Different Descriptions of Plate Glass.-Blown Plates limited in Size-C 
 Plate Works at Ravenhead.—Difficulties of the Process.—Materials, 
 nous Compositions.- Borax.- Mixing Mahals.-^tting.-Furaa 
 ami Crucibles at St. Gobain.—Pots.—Cuvettes.--Regulation of Firin^. 
 Castin" Tables.—Arrangement of Foundery at Ravenhead. Anneal 
 Ovens-Process of Casting Plates.—Annealing.—Squaring.—Gnndine 
 Economical Improvement.—Smoothing.—Emery Powder.—Comparat 
 Value of Large and Small Plates.—Polishing.—Si vering.—Preparation 
 Amalgam.—Mode of its Application.—Blowing Plate Glass.—Punching 
 Partial Cutting.—Transfer to Pontil.—Completion of Cutting.—Openi 
 —Sizes of Plates.—Effect of Sun’s Rays in Discoloring Plate Glass. 
 
 Two descriptions of plate glass are made: one by blowi 
 and opening, in the manner of broad glass, as already describe 
 the other by casting the melted materials upon a plane meto. 
 surface, somewhat in the manner pursued for makmg sh 
 
 lea piates of glass which are blown are necessarily limited 
 their size, although some of considerable dimensions are p 
 duced in this way. When cast, the extent of the plates n 
 be much greater; and, indeed, is limited only by the very he; 
 expense attending the erection of machinery, and the prose 
 tion of the manufacture in its various parts. Different ma 
 factories have been established at various times in this krngt 
 for the production of plate glass by blowing, but these, one at 
 another, have mostly been discontinued. The last estabh 
 ment of this kind in London existed a very few years since 
 East Smithfield; but being a private establishment, and 
 proprietors finding it impossible to continue a successful com 
 
HAI*. VI. 
 
 PLATE GLASS. 155 
 
 ition with the powerful corporate body alluded to in the first 
 hapter of this treatise, the works have been discontinued ; and 
 tie only place in England where plate glass of any great mag¬ 
 nitude is now manufactured, is on the premises of the British 
 ate Glass Company in Ravenhead, in Lancashire, where 
 lates are cast which equal, in every respect, the produce of 
 1 e French manufactory at St. Gobain. The office of this cor- 
 oration is at the foot of Blackfriars Bridge, in London; and 
 ere plates of glass of the most perfect quality, and of all di- 
 lensions up to the prodigious length of 160 inches, may at all 
 mes be procured. 
 
 j Great reluctance has always been evinced by the proprietors 
 j; P ‘ lte glass works to permit their examination by visitors, 
 ersons are, indeed, occasionally admitted to view the myste- 
 es; but, either by their habits and rank in life, such individ- 
 ils are unqualified or unlikely to describe what they witness: 
 ■’ tJie re jaxation is made in their favor under a seal of confi- 
 P“ce, which renders it impossible that they should impart the 
 formation they have acquired. The late Mr. Parkes appears 
 1 have been fortunate in this respect; and having obtained 
 emission to visit the works at Ravenhead, was not restrained 
 om publishing a short, but interesting, account of the pro- 
 P ses which he witnessed. From this source the following 
 ascription is drawn, as far, at least, as relates to the buildings 
 id arrangements particularly used at Ravenhead. 
 
 IMore care in the choice of materials, and greater nicety in 
 inducting the processes, are required for the preparation of 
 ate glass than are needed in any other branch of the manu- 
 oture. ihe materials employed are sand, soda, and lime, to 
 bich are added manganese and oxide of cobalt as decoloring 
 bsiances. The sand must be of the finest and whitest kind : 
 e grains should be sharp, and of a moderate size; if very 
 lall, they are likely to clot together, and consequently will 
 t mix intimately with the alkali; and if the grains are large, 
 3 y are on thls account longer in being fused. The sand 
 ist be passed through a wire sieve of the proper closeness 
 o water, and should be well agitated to separate all dirt and 
 purities. The alkali used is always soda: this is preferred 
 potash: as glass made with the former substance is thinner, 
 
 1 flows better while hot, and yet is equally durable when 
 a. Ihe quality of flowing freely is of the very first import- 
 :e m casting large plates, which, to be perfect, require to be 
 -bout streak or bubble. Another advantage attending the use 
 s a. is this, that the neutral salts of which it is the base, 
 b as muriate and sulphate of soda, and which, in this in- 
 ice, constitute the glass gall, are dissipated more readily by 
 
GLASS MANUFACTURE. 
 
 CHAP. VI. 
 
 156 
 
 the heat of the furnace, than are the salts of which potash is 
 the base. The soda must be used in a state of considerable pu¬ 
 rity ; and is generally either that which is separated from the 
 ashes of barilla, and other soda plants, by lixiviation, or is pro¬ 
 duced by the decomposition of common salt. 
 
 Lime acts in promoting the fusibility of the silex and alkali, 
 fulfilling thus the same office as is performed by litharge in the 
 manufacture of flint glass. From one fifteenth to one twenty- 
 fourth part of the whole materials is the largest proportion thal 
 can properly be used of lime; any greater quantity would im¬ 
 pair both the color and solidity of the glass. 
 
 Manganese would have the effect of giving a slight tinge of 
 red; but when mixed in a proper proportion with the blue of 
 the cobalt, and both together are met by the natural slight yel¬ 
 low of the other materials, each neutralizes the other, so tha 
 scarcely any definable tint remains. 
 
 In addition to these ingredients, a considerable quantity of 
 fragments of glass, or, as it is called, cullet, is used in combina 
 tion with the fresh materials. Of these fragments there is al 
 ways an abundant supply in the glass-house, produced fron 
 what is spilt in casting, and from the ends and edges that ar- 
 cut off in shaping the plates. This broken glass, or cullet, i 
 previously made friable, by throwing it, while hot, into col 
 
 water. . 
 
 It is considered that the addition of one pound of pure soda i 
 sufficient for four pounds of sand. But it is not enough, in th< 
 preparation of glass for casting, to apply the alkali only in th< 
 proportion necessary to produce good glass; much more thai 
 this must be used, in order to procure the requisite degree o: 
 fluidity. 
 
 The composition given by Loysel as being used in the grea 
 works at St. Gobain is this:— 
 
 White sand,.160 parts 
 
 Carbonate of lime, . 12 
 
 Soda,... 45 to 48 
 
 Fragments of glass of like quality, .... 100 
 
 Oxide of manganese,. 0£ 
 
 Parkes recommends the following proportions, as qualified t- 
 produce plates of glass of the best description:— 
 
 Lynn sand, previously well washed and dried, . . 720 parts 
 Alkaline salt, containing 40 per cent, of soda, . . 450 
 
 Lime, slaked and sifted,. 80 
 
 Nitre,. 25 
 
 Cullet, or broken plate glass, .425 
 
 1700 
 
HAP. VI. PLATE GLASS. 157 
 
 ^hese quantities are required to produce one pot of metal , which 
 » r ill yield 1200 pounds of good plate glass. 
 
 Another author states the following proportions as being 
 Hind to produce very fine glass:— 
 
 Fine white sand,. 300 pounds 
 
 Soda,.200 
 
 Lime, . .. 30 
 
 Oxide of manganese, ...... 32 ounces 
 
 Oxide of cobalt,. 3 
 
 Fragments of glass,. 300 pounds 
 
 The well-known property of borax, as a powerful flux, has 
 ccasioned the suggestion that, by its means, glass made with 
 otash might be caused to flow in fusion as freely as that where- 
 l soda is employed. It has been asserted that small quantities 
 f borax have always been used in the works at St. Gobain; 
 ut the secrecy observed in regard to all the operations canned 
 n in that establishment renders it impossible to say what de- 
 ree of truth there is in the assertion. 
 
 Great care is required in mixing the materials; much more, 
 ideed, than is called for in regard to other kinds of glass. The 
 ind, lime, soda, and manganese, being properly intermingled, 
 re fritted in small furnaces, wherein the temperature is grad- 
 ally raised to a full red, or even to a white, heat, at which 
 oint it is maintained, and the materials are carefully stirred 
 ntil vapor is no longer given off, and no further change is un- 
 ergone by the materials. This process of fritting lasts about 
 x hours; and when it is nearly completed, the remaining part 
 f the ingredients, consisting of the cobalt and broken glass, are 
 Ided. The latter, having already been perfectly vitrified, does 
 ot, consequently, require any lengthened exposure to the fire. 
 
 The furnaces at St. Gobain, in which the perfect fusion and 
 itrification are accomplished, are eighteen feet long and fifteen 
 r ide. They contain two kinds of crucibles. The larger ones, 
 herein the glass is melted, are called pots, and are formed 
 ke inverted truncated cones; the other crucibles, which are 
 nailer, are called cuvettes: these last are kept empty in the 
 irnaces, exposed to the frill degree of its heat, that when the 
 lass is ready for casting, and is transferred to them, they may 
 it injuriously lower its temperature. The comparative size 
 ’ these cuvettes varies according to the dimensions of the 
 :ates which it is intended to cast: when these are very large, 
 le cuvette will contain one third of the charge of the pot; but 
 i other cases its capacity is not greater than a fourth, a fifth, 
 
 ’ a sixth part, of the contents of the crucible. 
 
 The method used for regulating the supply of fuel to the fur- 
 
 O 
 
158 
 
 GLASS MANUFACTURE. 
 
 CHAP. VI. 
 
 nace in the great works of St. Gobain, is at once so rude and 
 so absurd, that one would hesitate to believe in the correctness 
 of the narration, if it did not rest upon good authority. It is 
 said tiiat two persons are employed, who, being disencumbered 
 of all superfluous clothing, incessantly run round the furnace 
 with a speed “ equal to seven leagues in six hours.” These 
 men on their circuit take up each two small billets of wood, cut 
 to a certain size, and heaped together; these they deposit as 
 they run, first one and then the other, in the openings of the 
 furnace, which by such means is fed at regularly recurring in¬ 
 tervals of time. Having continued this intellectual employ¬ 
 ment, without ceasing, during six hours, the men then surren¬ 
 der their “ seven league boots” to others, whose heels and hands 
 are similarly employed during an equal period of time; after 
 which they are in turn relieved by the first set of couriers. 
 
 From the time of filling the pots, it requires nearly forty 
 hours’ exposure to strong heat, ere the materials are properly 
 vitrified and in a state fit for casting. The processes of filling 
 the pots, and of removing the glass gall, and the various ap¬ 
 pearances that ensue in the refining, are precisely similar to 
 what has already been described in a former chapter. 
 
 When the glass is thoroughly refined, the cuvette—which 
 must be perfectly clean, and, as already mentioned, of a tem¬ 
 perature equal with that of the glass—is filled in the following 
 manner: A copper ladle, ten to twelve inches in diameter, 
 fixed to an iron handle seven feet long, is plunged into the glass 
 pot, and brought up filled with metal glass, which is transfer¬ 
 red to the cuvette; the ladle, during this transference, is 
 supported upon a strong iron rest, placed under its bottom, 
 and held by two other workmen. This precaution is neces¬ 
 sary to prevent the bending and giving way of the red-hot 
 copper under the weight of fluid glass which it contains. When 
 by successive ladings the cuvette is filled, it is suffered to re¬ 
 main during some hours in the furnace, that the air-bubbles 
 formed by this disturbance may have time to rise and disperse; 
 an effect which is ascertained to have ensued by the inspection 
 of samples withdrawn from time to time for the purpose. 
 
 Another essential part of the apparatus consists in flat tables 
 whereon the plates of glass are cast. These tables have per¬ 
 fectly smooth and level metallic surfaces, of suitable dimen¬ 
 sions and solidity, supported by masonry. At St. Gobain, and 
 formerly also at Ravenhead, these tables were made of copper; 
 the reason assigned for preferring this metal being, that it does 
 not discolor the hot melted glass, while the use of iron was 
 thought to be accompanied by this disadvantage. These copper 
 tables were very costly, both from the nature of their material, 
 and the labor bestowed in grinding and polishing their surfaces; 
 
;hap. vi. 
 
 PLATE GLASS. 
 
 159 
 
 md as the sudden access of heat that accompanied the pouring 
 >ver them of such a torrent of melted glass occasioned the 
 netal frequently to crack, the tables were by such an accident 
 •endered useless. The British Plate Glass Company having 
 experienced several disasters of this nature, its directors detdV- 
 nined upon making trial of iron; and they accordingly pro¬ 
 cured a plate to be cast, fifteen feet long, nine feet wide, and 
 cix inches thick, which has fully answered the intended purpose 
 —having, during several years of constant use, stood uninjured 
 hrough all the sudden and violent alternations of temperature 
 ,o which it has been exposed. This table is so massive, weigh- 
 ng nearly fourteen tons, that it became necessary to construct 
 i carriage purposely for its conveyance from the iron foundery 
 ,o the glass-house. It is supported on casters, for the conveni¬ 
 ence of readily removing it towards the mouths of the different 
 innealing ovens. 
 
 The foundery at Ravenhead wherein this table is used is said 
 ,o be the largest room under one roof that has ever yet been 
 erected in this kingdom; it is 339 feet long, 155 wide, and pro¬ 
 portionately lofty. Westminster Hall, to which the superiority 
 n this respect is so commonly ascribed, is smaller—its length 
 peing 300, and its breadth only 100 feet. The melting fiir- 
 paces, which are ranged down the centre, occupy about one 
 bird of the whole area of this apartment. The annealing ovens 
 ire placed in two rows, one on each side of the foundery, and 
 pccupy the greatest proportion of the side walls. Each of these 
 pvens is sixteen feet wide and forty feet deep. Their floors 
 peing level with the surface of the casting table, the plates of 
 2 [lass may be deposited in them immediately after they are cast, 
 ivith little difficulty and without delay. 
 
 When the melted glass in the cuvette is found to be in the 
 2xact state that experience has pointed out as being most fa¬ 
 vorable for its flowing readily and equably, this vessel is with- 
 Irawn from the furnace by means of a crane, and is placed 
 upon a low carriage, in order to its removal to the casting table, 
 which, as it is previously placed contiguous to the annealing 
 pven that is to be filled, may therefore be at a considerable dis¬ 
 tance from the melting furnace. Measures are then taken for 
 cleaning the exterior of the crucible, and for carefully removing 
 with a broad copper sabre any scum that may have formed upon 
 the surface of the glass, as the mixture of any of these foreign 
 natters would infallibly spoil the beauty of the plate. These 
 lone, the cuvette is wound up to a sufficient height by a crane; 
 md then, by means of another simple piece of mechanism, is 
 swung over the upper end of the casting table; and being 
 thrown into an inclined position, a torrent of melted glass is 
 
160 
 
 GLASS MANUFACTURE. 
 
 CHAT. VI. 
 
 The glass is prevented from running off the sides of the tabic 
 by ribs of metal, one of which is placed along the whole lenoth 
 of each side, their depth being the exact measure which it is 
 desired to give to the thickness of the glass. A similar rib, at¬ 
 tached to a cross piece, is temporarily held, during the casting, 
 at the lower end of the table. When the whole contents of 
 the crucible have been delivered, a large hollow copper cylin¬ 
 der, which has been made perfectly true and smooth in a turn¬ 
 ing-lathe, and which extends entirely across the table, resting 
 on the side ribs, is set in motion; and the glass, during its pro¬ 
 gress, is spread out into a sheet of uniform breadth and thick¬ 
 ness. Its length depends upon the quantity of melted glass 
 contained in the cuvette: should this be more than is needed 
 for the formation of a plate having the full dimensions of the 
 table, the metal rib is removed from its lower part, and the sur¬ 
 plus glass is received in a vessel of water placed under the ex¬ 
 treme end for the purpose. 
 
 Mr. Parkes, in speaking of this operation, remarks—“ The 
 spectacle ot such a vast body of melted glass poured at once 
 from an immense crucible, on a metallic table of great magni¬ 
 tude, is truly grand; and the variety of colors which the plate 
 exhibits immediately after the roller has passed over it, renders 
 this an operation far more splendid and interesting than can 
 possibly be described.” 
 
 suddenly poured out on the surface of the table, which must 
 previously have been heated, and wiped perfectly clean. 
 
 Fig. 12. 
 
PLATE GLASS. 
 
 161 
 
 CIIAP. VI. 
 
 At least twenty workmen are busily employed during this 
 process of casting. From the time that the cuvette is removed 
 from the furnace, to the completion of the casting by the hard¬ 
 ening of the glass, the apartment must be kept as free as pos¬ 
 sible from disturbance; even the opening and shutting of a door 
 might, by setting the air in motion, disturb the surface of the 
 i glass, and thus impair the value of the plate. So soon as it is 
 completely set, the plate is carefully inspected; and should any 
 flaws or bubbles appear upon any part of its surface, it is im¬ 
 mediately divided by cutting through them. 
 
 When the plate of glass thus formed has been sufficiently 
 fixed by cooling, it is slipped from the table gradually and care¬ 
 fully into one of the annealing ovens, where it remains in a 
 horizontal position; its treatment differing in this respect from 
 that pursued with crown and broad glass, which stand on edge 
 during the annealing process. As each oven in this manner 
 becomes filled, it is closed up by an iron door, the crevices of 
 -which are carefully stopped with mortar or clay, to prevent 
 any access of external air to the oven; and thus to provide as 
 far as possible for the gradual cooling of the plates, the neces¬ 
 sity for which has already been sufficiently explained. When 
 'the glass has remained during about fifteen days in these ovens, 
 they are opened, and the contents withdrawn. 
 
 The plates have then to undergo all the operations of squa¬ 
 ring, grinding, polishing, and silvering, in order to fit them for 
 sale. 
 
 The first process—that of squaring and smoothing the edges 
 !—is performed by passing a rough diamond along the surface 
 of the glass, guided by a square rule; the diamond cuts to a 
 certain depth "into the substance, when, by gently striking the 
 glass with a small hammer underneath the part which is cut, 
 the piece comes away ; and the roughnesses of the edge thus 
 left are removed by pincers. The plate is then taken to the 
 [ grinding apartment. 
 
 The next step is to embed each of the plates upon a table or 
 frame adjusted horizontally, and made of either freestone or 
 wood, cementing the glass securely thereto by plaster of Paris. 
 One plate being then reversed and suspended over another, the 
 material employed in grinding their surfaces is introduced be¬ 
 tween the two, and they are made to rub steadily and evenly 
 upon each other by means of machinery set in motion by a 
 ! steam-engine. It was formerly usual to employ river sand and 
 water, for the purpose of abrading the surfaces; a circumstance 
 which entailed considerable waste and loss upon the manufac¬ 
 turers. The glass which was ground oft, and which usually 
 amounts to one half the weight of the plates as they are cast, 
 
 O 2 
 
162 GLASS MANUFACTURE. CHAP. VI. 
 
 being thus mixed with a material which contained a portion of 
 iron, was sold at a low rate for making bottle glass, or for 
 scouring pewter. Mr. Parkes has calculated that the loss of 
 glass by this means to one establishment—that which was car¬ 
 ried on in East Smithfield—amounted to two tons weekly ; and 
 that the expenditure of sand in the same period was at least 
 sixteen to twenty tons. 
 
 A method has, however, been devised for saving the whole 
 of this glass, so as to render it available for the manufacture 
 of the better descriptions. This plan consists in substituting, 
 for the river sand before mentioned, ground flints, which con¬ 
 tain no portion of iron. A further great advantage attending 
 this method is, that one ton of ground flints is equally effective 
 with five tons of sand, and that the operation is completed in a 
 shorter time than formerly. 
 
 When one side of each plate has been sufficiently ground, it 
 is loosened from the frame, and turned over, so as to present 
 the other surface to be ground in the same manner. Some de¬ 
 gree of pressure is employed, by loading the upper plate with 
 weights as the grinding of each side approaches to completion. 
 The process thus described used formerly to last during three 
 entire days, but this time is now much abridged. The greatest 
 attention is required, in order to finish with the surfaces per¬ 
 fectly level and parallel, for which end a rule and plumb line 
 are employed. 
 
 By means of this grinding, the plates will have been made 
 level, and all inequalities in the surface will have been re¬ 
 moved ; but they are too rough to receive a polish: to fit them 
 for this, they must again be ground with emery powder of in¬ 
 creasing degrees of fineness. The preparation and sorting of 
 this powder are effected in the following simple and ingenious 
 manner:— 
 
 A considerable quantity of emery is put into a vessel con¬ 
 taining water, and is stirred about violently until the whole is 
 mechanically mixed with the water. Emery is absolutely in¬ 
 soluble by such means; and if the mixture were left at l'est 
 during a sufficient time, the whole would subside in layers; 
 the coarsest and heaviest particles sinking first, and so on suc¬ 
 cessively, until the very finest particles would range themselves 
 as the upper stratum. Previously to this, however, and while 
 these finest grains are still suspended in the water, it is poured 
 off into a separate vessel, and the emery is there allowed to 
 settle. A fresh supply of water is poured into the first vessel, 
 the contents of which are again violently agitated, and allowed 
 partially to subside as before. A shorter interval is allowed for 
 this than in the first case; and then the liquor is poured off into 
 
CHAP. VI. 
 
 PLATE GLASS. 
 
 163 
 
 a third vessel, by which means emery of the second degree of 
 fineness is separated. This operation is repeated, in order to 
 obtain powders having four different degrees of fineness: the 
 deposits are then separately dried upon a stove to a consistence 
 proper for making them up into small balls, in which form they 
 are delivered to the workman. 
 
 In this further rubbing together, or, as it is called, smoothing 
 of the glass plates, it must be understood that the coarsest 
 emery is first used, and so on, substituting powders having in¬ 
 creasing degrees of fineness as the work proceeds. ° 
 
 This operation completed, the glass is perfectly even; and 
 although the surfaces appear opaque or deadened, they are so 
 smooth that no scratchiness is at all perceptible. The plates 
 are now again subjected to a rigid examination; and should any 
 flaws or defects be perceptible in them, which had before es¬ 
 caped detection, they are cut up with a diamond into smaller 
 plates, so that the blemishes are left at their edges; regard be¬ 
 ing had to economy in dividing the glass, so as to produce the 
 smallest possible number of pieces. Attention to this circum¬ 
 stance is of the greatest importance to the profitable working 
 rf the establishment, since the value of smaller plates bears no 
 comparison with that of glasses having more considerable di- 
 nensions. This may be seen at once in referring to the fol- 
 owing table, which has been calculated upon some of the pub- 
 ished prices of the British Plate Glass Company. 
 
 Dimensions. 
 
 
 Surface in Square 
 Inches. 
 
 Price. 
 
 Price per 
 Sq. Inch. 
 
 60 inches by 30 inches. 
 
 1,800 
 
 £ 
 
 10 
 
 5. 
 
 10 
 
 d. 
 
 1 
 
 d. 
 
 1-400 
 
 60 - - 
 
 - 
 
 40 - 
 
 - 
 
 2,400 
 
 16 
 
 3 
 
 5 
 
 1-617 
 
 60 - - 
 
 - 
 
 50 - 
 
 - 
 
 3,000 
 
 22 
 
 10 
 
 5 
 
 1-800 
 
 70 - - 
 
 - 
 
 50 - 
 
 - 
 
 3,500 
 
 28 
 
 7 
 
 8 
 
 1-946 
 
 80 - - 
 
 - 
 
 50 - 
 
 - 
 
 4,000 
 
 34 
 
 14 
 
 10 
 
 2-085 
 
 100 - - 
 
 - 
 
 50 - 
 
 - 
 
 5,000 
 
 48 
 
 9 
 
 8 
 
 1-327 
 
 100 - - 
 
 - 
 
 60 - 
 
 - 
 
 6,000 
 
 63 
 
 15 
 
 1 
 
 2-550 
 
 100 - - 
 
 - 
 
 70 - 
 
 - 
 
 7,000 
 
 80 
 
 8 
 
 2 
 
 2-757 
 
 100 - - 
 
 - 
 
 80 - 
 
 - 
 
 8,000 
 
 98 
 
 4 
 
 10 
 
 2-947 
 
 132 - - 
 
 - 
 
 84 - 
 
 - 
 
 11,088 
 
 200 
 
 8 
 
 0 
 
 4-337 
 
 160 - - 
 
 - 
 
 80 - 
 
 - 
 
 12,800 
 
 246 
 
 15 
 
 4 
 
 4-705 
 
 The largest of the plates here mentioned is capable by reduc- 
 ion of being converted into 7| plates having the dimensions of 
 lie smallest in the Table ; whereas the price of the former is 
 !3-| times greater than that of each of the small plates, and 
 
GLASS MANUFACTURE. 
 
 CHAP. VI.! 
 
 164 
 
 more than 3^ times the aggregate value of those into which it 
 would be divided. 
 
 The reason for this progressional rate in the prices is suffi¬ 
 ciently obvious. Could such a degree of perfection be attained 
 in the different processes of manufacture, that a certainty ex¬ 
 isted of producing plates of every requisite dimension, there: 
 would no longer be any pretence for thus enhancing the prices' 
 of the larger pieces; and plates might be sold indiscriminately 
 at«o much per superficial foot in the manner usual with linen; 
 or woollen fabrics, making perhaps some allowance for the 
 greater expensiveness of machinery required for large than for 1 
 small operations. But such a degree of certainty is so far from, 
 accompanying the labors of the glass-founder, that it is but very 
 rarely he is enabled to finish and produce for sale any plates of j 
 extra dimensions; while it most frequently happens that the 
 presence of numerous flaws and bubbles compels the division 
 and subdivision of the glass into portions bearing, for the very 
 reason of their abundance, only a small relative value. . i 
 
 It is represented as being an interesting sight to witness the; 
 grinding and smoothing of a great number of plates of large 
 dimensions, which by means of machinery are thus made to 
 move with great velocity, and in all directions. 
 
 The next process is that of polishmg. For this purpose a' 
 substance is used, known in commerce and the arts as colcothar 
 or crocus martis. This is the brown red oxide of iron, which 
 remains in the retorts after the distillation of the acid from 
 sulphate of iron. 
 
 The instrument used in polishing is a piece of wood covered 
 with many folds of woollen cloth, each fold having between it 
 some carded wool, so that the whole forms a tolerably hard but 
 elastic cushion; and this is furnished with a handle for the con¬ 
 venience of the workman. 
 
 The plate is embedded in plaster upon the table in the man¬ 
 ner already described, and the polishing instrument being wet¬ 
 ted by means of a brush, and covered with colcothar, the work¬ 
 man commences his operation by rubbing the cushion backward 
 and forward over the surface of the plate; not, indeed, attempt¬ 
 ing to polish the entire surface at the same time, but operating 
 upon separate portions, beginning at each corner, and proceed¬ 
 ing regularly towards the centre, so as to leave no part unvis¬ 
 ited by its due degree of attention and labor. 
 
 Considerable dexterity and practical skill are needed, not 
 only to produce a high polish upon the plate, but also to give 
 this in an uniform degree over its whole surface; and the 
 finishing touches require, therefore, to be given with great care 
 and judgment. 
 
CHAP. VI. PLATE GLASS. 165 
 
 When one side is polished, the plate is turned on the table, 
 as it has before been in grinding and smoothing; but as the 
 white plaster would appear through the glass and hinder the 
 workman from forming an accurate judgment upon his progress 
 in this second operation, the previously polished side is provided 
 with a coating of red colcothar. When the workman is satis¬ 
 fied with the result of his labor upon this second surface, the 
 plate is taken from the table, and being cleaned, is laid, each 
 side in its turn, upon a dark biue or black cloth, which, as it 
 admits only a moderate light, show's by inspection any parts 
 which may be less elaborately polished than the rest: these 
 must be retouched by a small polishing cushion, in the same 
 manner as before. 
 
 It would be a tedious operation, if every small fragment of 
 glass, such pieces, for instance, as are used in swing frames on 
 toilet-tables, must be polished separately. The edges of several 
 of these pieces are therefore brought together for the purpose ; 
 but as all these are not of one uniform thickness, it is necessary 
 to remedy this inconvenience ; and, in order to bring their sur¬ 
 faces to a perfect level, they are arranged, with the side to be 
 polished downwards, on a large smooth level plate ; plaster of 
 Paris is then poured upon their upper surfaces, which are thus 
 embedded together, and on being turned over, the whole num¬ 
 ber of pieces is found to be so level, that the polishing may be 
 performed as easily and as effectually as it could be with one 
 entire plate. 
 
 When the polishing of the plates has been satisfactorily com¬ 
 pleted, they are washed with water, and are either removed to 
 the ware-room for sale, or, in case of their being intended for 
 mirrors, to the silvering apartment. 
 
 The last process used in a plate-glass manufactory is that 
 which is called silvering. This, in common with the greater 
 part of the operation connected with this branch of the art, is 
 simple, but requires practice and dexterous management for its 
 proper performance. The application to the posterior surface 
 ff mirrors of some substance that will accurately reflect the 
 rays of light falling upon them, is absolutely necessary to ren- 
 ler them useful. The substance which has been found to an¬ 
 swer this purpose best is mercury; which, as it cannot be aj> 
 alied alone in its fluid state, is, by a partial amalgamation, pre¬ 
 viously made to adhere to the surface, and afterwards to incor¬ 
 porate itself with the substance of a very thin leaf of tinfoil. 
 
 The operation is thus conducted:—A perfectly flat and 
 smooth slab of thick wood, or of stone, somewhat larger than 
 my plate which it may be required to silver, must be inclosed 
 within a wooden frame open at the top, and having a ledge a 
 
166 
 
 GLASS MANUFACTURE. 
 
 CHAP. VI. 
 
 few inches deep round three of its sides. The bottom of this 
 frame is provided with a channel to collect the surplus mer¬ 
 cury, and to convey it to a vessel placed underneath. The slab 
 is fixed on a pivot, so that one end may be raised and the other 
 depressed at pleasure. 
 
 When it is used, the slab must first he adjusted horizontally, 
 and covered with gray paper stretched tightly over it. A sheet 
 of very thin tinfoil, a little larger than the plate to be silvered, 
 is then laid smooth upon the paper, and as much mercury is 
 poured steadily upon it as will remain upon its flat surface. 
 That end of the slab which is unprovided with a ledge is then 
 covered with parchment, and the plate of glass is carefully slid- 
 den into the frame, resting the while upon the parchment. 
 
 The art of properly effecting this deposit of the glass upon 
 the foil consists in holding it, during its sliding, in such a posi¬ 
 tion that it will dip into the mercury, carrying a portion of the 
 metal before it, but without once touching the tin in its pas¬ 
 sage. By this means any dust or oxide which may rest upon 
 the mercury will be removed, and no air-bubbles will remain 
 between the glass and the foil; while, if the tin were touched, 
 however slightly, it would certainly be torn. 
 
 When the entire surface of the glass plate has thus passed, 
 it is allowed gently to drop on the tinfoil, and to squeeze out 
 the superfluous mercury from between, and which is collected 
 in the channel already mentioned. The plate being then cov¬ 
 ered with a thick flannel, is loaded at regular intervals of space 
 with considerable weights, and the end of the slab is a little 
 raised, which assists the escape of the superabundant mercury. 
 The whole remains in this situation during the entire day, tire 
 slope of the slab being gradually increased to facilitate the 
 dropping of the mercury. At the end of this time, the plate 
 is cautiously taken from the frame, carefully avoiding to touch 
 the under side, then covered uniformly with a soft amalgam of 
 tin and mercury. The plate is then placed in a wooden frame, 
 and left during several days until the amalgam is found to be 
 so far hardened as to adhere with a great degree of firmness 
 to the glass : in this state not even a slight scratch would suf¬ 
 fice for its removal. The plate is then in a finished state, and 
 fit for being framed. 
 
 The amalgam does not, however, acquire its greatest degree 
 of hardness until some time has elapsed; and globules of Mer¬ 
 cury will occasionally drop from mirrors for some time even 
 after they have been framed. Portions of the amalgam are at 
 times detached while in this state, by violent concussions of the 
 air, such as a thunder storm, or the firing of artillery. No 
 patching can ever be applied in such a case that will be suffi' 
 
CHAP. VI. PLATE GLASS. 1G7 
 
 Gently perfect to escape detection; but a white seam will in¬ 
 variably be perceptible at the points of junction. 
 
 Although the processes followed in blowing plate glass are, 
 n most respects, similar to those used in fashioning broad glass, 
 some difference is yet observed; which, indeed, is occasioned 
 is much through the increased bulk and weight of the mass 
 rnder operation, as on account of any real difference in the 
 composition of the fabrics; only a very short account of the 
 irocess can therefore be required. 
 
 The first instrument used is a hollow rod, agreeing in every 
 articular, except its size, with that used for forming flint and 
 crown glass. This rod is full six feet in length, and two inches 
 n diameter; made smaller at the end to which the breath is 
 applied, and widened at the extremity upon which the glass is 
 gathered. It is necessary to take up a considerable weight of 
 flass upon this tube; and some management is required in 
 irder to effect this. When the workman has gathered all 
 hat will adhere by turning the end continually round in the 
 'ot, he then withdraws it from the furnace; and holding it 
 ver a bucket of water, sprinkles the glass on the end of "the 
 ube, turning it constantly round in his hand. When cooled in 
 his manner, the glass adheres firmly to the tube, and is rendered 
 ■y that means capable of sustaining a greater weight than it 
 vould otherwise support. The tube is then dipped again into 
 he pot, and the same process is repeated. 
 
 Fig. 13. 
 
 After the third dipping it will have gathered a mass of glass 
 n the shape of a pear, ten inches in diameter, and about 
 welve inches long. This must again be cooled with sprink- 
 ing as before; and while the workman is at the same time 
 ilowing into the tube, so as to give a hollow form to the glass, 
 aid to reduce it to the requisite thickness, the rod must be 
 cwung to and fro with an alternating motion, in order to length¬ 
 en the shape of the material; and this proceeding being several 
 imes repeated, the glass assumes the form of a cylinder, the 
 ower end of which is hemispherical. 
 
 Fig. 14. 
 
168 GLASS MANUFACTURE. CHAP. VI. 
 
 The assistant is then placed three feet and a half from the 
 ground, upon a stool, whereon are fixed two upright pieces of 
 wood, with a cross piece of the same material, for the purpose 
 of supporting the tube with the glass. These are held by the 
 assistant in an oblique position, the end with the glass inclin¬ 
 ing downwards, that the workman may be able, with an iron 
 punching instrument and a mallet, to drive a hole through the 
 centre of the hemispherical end of the cylinder. 
 
 Fig. 15. 
 
 The glass now is subjected to examination; and if found 
 sufficiently free from imperfections, is held at the aperture of 
 the furnace during seven or eight minutes to heat it again 
 thoroughly. While thus held, the rod is supported in its hori¬ 
 zontal position by a small iron trestle placed before the orifice 
 of the furnace conveniently for that purpose. The glass being 
 thus sufficiently softened by heat, the assistant is again mount¬ 
 ed upon the stool; and resting the tube upon the wooden cross¬ 
 piece, twirls it round, while the workman insinuates a pair of 
 large broad shears which are pointed at the end, into the hole 
 
 Fig. 16. 
 
 previously punched. This is gradually enlarged, until the 
 glass, through its whole length, and except at the part where 
 it is attached to the tube, has a cylindrical form. 
 
 Fig. 17. 
 
 The tube is then again rested on the trestle, and the glass is 
 reheated at the furnace, when the shears are used to cut the cyl¬ 
 inder through half its length, beginning at the open end, and 
 proceeding towards the point where it is attached to the tube. 
 
 Fig. 18. 
 
CHAP. VI. 
 
 PLATE GLASS. 
 
 169 
 
 The next proceeding is to take a pontil, an instrument al¬ 
 ready described as being a solid rod of iron of smaller diameter 
 than the tube, from which last the glass is now to be transferred 
 to the pontil. This differs from the instrument used for the 
 like purpose in making flint glass, by having an iron cross¬ 
 piece, twelve inches in length, placed across its extreme end, 
 and forming with it the letter T. The pontil being thoroughly 
 heated at the end, a quantity of melted glass is gathered from 
 the pot upon the cross-piece, which being presented to the diam¬ 
 eter of the cylinder, the two cohere speedily and firmly to¬ 
 gether : the hollow tube is then disconnected from the glass in 
 the manner already described. 
 
 Fig. 19. 
 
 The pontil with the cylinder is now rested on the trestle, 
 and presented to the furnace, that the end which has hitherto 
 been attached to the tube may in turn be heated and subjected 
 to the same processes as have just been effected with the other 
 end : the extremity is opened by introducing the shears so as 
 to complete the cylinder {jig. 20.); and then after a fresh 
 
 Fig. 20. 
 
 heating the workman cuts through the remaining half of the 
 length of the cylinder in a line with and joining to the cut 
 already mentioned, so that the cylinder is divided on one of 
 its sides through its entire length. 
 
 Fig. 21. 
 
 The glass is then placed with the cut side upwards upon an 
 iron shovel; it is separated from the pontil, and immediately 
 removed to the hottest part of the annealing oven, where it 
 gradually becomes again heated to redness. Advantage is 
 then taken of the softened state of the cylinder to open it, by 
 the help of an appropriate iron instrument, lifting up and turn¬ 
 ing back the cut edges of the glass, until the whole is flattened 
 upon the hearth of the annealing oven. A small iron rake is 
 then employed to push the plate along the floor to the end of 
 
 P 
 
GLASS MANUFACTURE. 
 
 CHAP. VI. 
 
 170 
 
 the oven; and when this lias been filled through a succession 
 of operations such as are here described, the door is stopped 
 
 Fig. 22. 
 
 and cemented. All further processes are in every respect the' 
 same as are followed with plates that have been cast. 
 
 The great size and weight of the glass render these opera¬ 
 tions exceedingly laborious, so that a man and his assistant can 
 hardly do more than make one plate in an hour, nor can they 
 continue their labor longer than six hours, resting during an 
 equal space before they resume their toil. 
 
 Plates which are blown cannot properly be made above forty- 
 five, or at most fifty, inches in length, and with a proportionate 
 breadth. They have sometimes been made larger, but are 
 then too thin to admit of their properly bearing the processes 
 of grinding and polishing, and are besides liable to warp, which 
 of course destroys their value when employed as mirrors. 
 
 It was long since observed, that by exposing plate glass to 
 the solar rays, it is made to acquire a violet or purple tinge, 
 and this so rapidly, that the alteration is clearly discernible at 
 the end of one or two years. Some plates, originally colorless, 
 which had thus become tinged, having been brought under the 
 notice of Mr. Faraday, he was induced to experiment upon the 
 subject For this purpose, he procured three different pieces 
 of plate glass, which were tinged so slightly as to appear alto¬ 
 gether colorless, unless when viewed through their edges. 
 Each of these pieces was broken into two portions, one of 
 which was wrapped in paper, and set aside in a dark place \ 
 while the portion from which it had been separated was ex¬ 
 posed to the air and the light of the sun. This exposure was 
 commenced in the month of January; and in the following Sep¬ 
 tember a comparative examination was made. The pieces 
 from which the light had been excluded exhibited no sign of 
 change, while those which had been exposed had, in this short 
 space of eight months, acquired so considerable a degree of 
 color as would, under other circumstances, have created a 
 doubt regarding their original identity. 
 
CHAP. VII. 
 
 ARTIFICIAL GEMS. 
 
 171 
 
 CHAPTER VII. 
 
 ON THE COMPOSITION OF ARTIFICIAL GEMS. 
 
 Great interest formerly attached to this subject.—Different Compositions 
 for Artificial Gems.—Mode of Preparation.—Rock Crystal formerly em¬ 
 ployed.—Not superior to Sand.—Diamond Pastes.—Selection of various 
 Pastes for Imitating different Gems.—Reasons for such selection. 
 
 A very considerable portion of every treatise on glass-ma¬ 
 king, which was in existence a century ago, and which com¬ 
 prises nearly the whole of what has ever been published on the 
 subject, was devoted to the art of composing factitious gems. 
 A great deal of mystery would seem to have been affected 
 upon this subject on the part of the manufacturers, each one of 
 whom was, or pretended to be, possessed of some secret recipe , 
 which he thought superior to all others for the composition of 
 these ornaments. 
 
 A corresponding anxiety to acquire a knowledge of these 
 mysteries being evinced on the part of the public, the authors 
 above alluded to, so far acquiesced in this feeling as to load 
 their writings with one receipt after another, in almost endless 
 succession, and in following which the artist was assured, that 
 he might successfully rival nature in the production of these 
 much-admired objects. 
 
 The greater part of the compositions thus recommended, if 
 indeed they were ever used, has long since passed into neg¬ 
 lect ; and it will not be necessary, in the present day, to insert 
 more than a very few directions on the subject, which are given 
 upon the authority of M. Fontanieu, as being well qualified, 
 with the addition of various coloring matters, for counterfeiting 
 precious stones. 
 
 No. 1. is composed of 20 parts of litharge, 12 of silex, 4 of 
 nitre, 4 of borax, and 2 parts of white arsenic. These ingre¬ 
 dients should be fritted together in a crucible, and afterwards 
 melted, in which state the whole must be poured suddenly into 
 cold water. Any portion of lead which may have been revived 
 in the metallic state will then be apparent and must be separa¬ 
 ted. The glass may then be remelted for use. 
 
 No. 2. For this composition, mix together 20 parts of ceruse, 
 8 of silex in powder, 4 of carbonate of potash, and 2 of borax. 
 When these are perfectly melted, the whole should be poured 
 into water, and then remelted in a clean crucible, in the same 
 manner as No. 1. 
 
 No. 3. consists of 16 parts of minium, 8 of rock crystal in 
 powder, 4 of nitre, and 4 of carbonate of potash. These ingl'e- 
 
172 
 
 GLASS MANUFACTURE. 
 
 CHAP. VII. 
 
 dients must be melted and remelted in the manner already de¬ 
 scribed as necessary with the preceding mixtures. 
 
 No. 4 differs essentially from the three foregoing combina¬ 
 tions in being without any portion of lead. It is made with 24 
 parts of borax, 8 parts of rock crystal, and 8 of carbonate of 
 potash. The rock crystal, previous to its use for this purpose, 
 must be reduced to a state of great purity, by fusing it with an 
 excess of alkali, and then precipitating it by an excess of acid, 
 in the form of an impalpable powder. 
 
 No. 5. The processes necessary for the production of this 
 species of glass are much more complex than the preceding. In 
 the first place, 3 parts of alkali are to be fritted with 1 part of 
 rock crystal, which mixture must then be dissolved in water 
 and saturated with dilute nitric acid. The silex which is pre¬ 
 cipitated by this means must then be edulcorated and dried, 
 when it will appear in the form of a very fine impalpable pow¬ 
 der. Two parts of this must be melted in a crucible with 3 
 parts, by weight, of the best ceruse, and the glass which re¬ 
 sults must be poured into water. Break this down and remelt 
 it with one twelfth of its weight of borax, and pour it again into 
 water. If this last product is once more melted with one twelfth 
 of its weight of nitre, the result will be a very fine hard glass, 
 having an extremely beautiful lustre. 
 
 The length of time required for fusing hard glasses or pastes 
 is at the least twenty-four hours. The process herein directed, 
 of pouring the melted glass into water, and then remelting, is 
 found to be of considerable use in thoroughly and intimately 
 mixing the ingredients together. 
 
 Of the foregoing compositions, No. 1. will be found extreme¬ 
 ly fusible, on account of its considerable proportion of fluxing 
 materials. It calls for the employment of the very best descrip¬ 
 tion of crucibles, in order to withstand, for the requisite time, 
 the corroding effects of the mixture. If any kind of glass into 
 the composition of which lead has not entered, is applied to and 
 melted on the interior surface of the crucible, so as to line it 
 with a perfect glaze previous to use, the evil just mentioned 
 will be materially remedied. 
 
 In order to make a perfect glass, which at the same time 
 shall be sufficiently workable, 2 parts of silex require from 3 to 
 4 parts, by weight, of oxide of lead; but a somewhat smaller 
 quantity of the latter may be used, if the deficiency is made up 
 by the addition of some other fluxing material: the glass in 
 this case will prove both hard and brilliant; and, when proper¬ 
 ly set, will exhibit a much nearer imitation of the diamond than 
 most other vitreous compositions. 
 
 It was formerly imagined by artists who wrought these arti- 
 
CHAP. VII. 
 
 ARTIFICIAL GEMS. 
 
 173 
 
 ficial gems, that if the glass employed by them had for its basis 
 rock crystal, rather than sand, flint, or any other mineral of the 
 like character, the result was a much harder glass than ordi¬ 
 nary. This idea is, however, wholly without foundation; for 
 when the crystal has once been fused through the admixture 
 of any kind of flux, the hardness of the mineral will be irrecov¬ 
 erably lost, as this quality depends altogether upon its natural 
 aggregation, which, in such case, is necessarily destroyed. 
 
 Rock crystal is, perhaps, somewhat purer than most other 
 siliceous substances, some of which contain minute traces of 
 iron, and which may possibly impair the beauty of some colors 
 which are imparted to glass. The same means as are used to 
 render flint friable, are employed for that purpose with rock 
 crystal: this should on no account be ground in metallic 
 vessels. 
 
 Some artists have succeeded, to a certain extent, in produ¬ 
 cing a very fine, hard, brilliant, and colorless glass paste, in im¬ 
 itation of the diamond, and have even given to this a very con¬ 
 siderable play of light, or, as it is technically termed, water; 
 but it has not been found practicable to compound any vitreous 
 substance which could for a moment deceive the eye of any 
 person accustomed to witness the superior brilliancy of real 
 gems. The best of these mock diamonds require, indeed, the 
 aid of artifice in the mode of their setting, to render them in 
 any great degree ornamental. M. Fontanieu recommends his 
 glass, No. 1, described in this Chapter, as being better quali¬ 
 fied than any other for making artificial diamonds. To bring 
 this glass to such a degree of brilliancy and clearness as will 
 prove at all satisfactory, it must be retained in a state of per¬ 
 fect fusion for a considerable space of time. 
 
 Loysel recommends, for the same purpose, the employment 
 of a different composition, the result of which will be a glass, 
 having the same specific gravity as the white oriental diamond, 
 and for this reason better imitating that resplendent substance 
 in its refractive and dispersive powers. His recipe is as fol¬ 
 lows :— 
 
 White sand purified by being washed first 
 in muriatic acid, and afterwards in pure 
 water, until all traces of the acid are 
 
 removed.100 parts. 
 
 Red oxide of lead (minium).150 
 
 Calcined potash. 30 to 35 
 
 Calcined borax. 10 
 
 Oxide of arsenic. 1 
 
 This composition is easily fusible at a moderate heat; but like 
 that proposed by Fontanieu, requires to be kept in a melted 
 
 P 2 
 
174 
 
 GLASS MANUFACTURE. 
 
 CHAP. VII. 
 
 state for two or three days, to perfect the refining, and to cause 
 the dissipation of the superabundant alkali. 
 
 The same author has furnished the following receipts for the 
 formation of pastes, qualified, upon the addition of appropriate 
 coloring materials, for the imitation of various gems. The re¬ 
 marks already made as to the length of time required for the 
 due preparation of the diamond paste equally apply to these 
 compositions:— 
 
 White sand, purified in the manner point¬ 
 ed out in the preceding receipt, .... 100 parts. 
 
 Red oxide of lead.200 
 
 Calcined potash, and nitre, of each .... 20 to 25. 
 
 The specific gravity of this glass, water being 1, will be 3.9 
 to 4. 
 
 White sand, prepared in the manner be¬ 
 
 fore mentioned,.100 parts. 
 
 Red oxide of lead,.300 
 
 Calcined potash,. 5 to 10 
 
 Calcined borax,. 200 to 300 
 
 The specific gravity of this compound will vary from 3-3 to 4. 
 
 White sand, prepared as above,.100 parts. 
 
 Red oxide of lead,.250 
 
 Calcined potash,. 15 to 20 
 
 Calcined borax,. 25 to 30. 
 
 This will have a greater specific gravity varying from 4 to 
 4.5. 
 
 In making his selection between one or other of these pastes, 
 the artist should be guided by their various specific gravities, 
 choosing preferably that glass which is nearest in this respect 
 to the particular gem which he is desirous of imitating; and 
 this, not witli the view of providing himself with an additional 
 means of deception, but because, the refractive and dispersive 
 powers of different transparent bodies being determined by 
 their comparative weights, the resemblance will, by such a 
 selection, be rendered more perfect to the eye. To one simple 
 test, that of their hardness, recourse can be had so easily, that 
 every one may, with very little previous instruction, ascertain 
 for himself the genuineness of any gem that is offered to his 
 notice, without any apprehension of being deceived. 
 
CHAP. VIII. 
 
 PHOSPHORIC GLASS. 
 
 175 
 
 CHAP. VIII. 
 
 ON THE MANUFACTURE OF GLASS FROM CALCINED BONES. 
 
 Preparation of Bones.—Their Vitrification.—Process known to Becher_ 
 
 Concealed by him.—Curious Suggestion as to its Employment—This 
 Glass highly electric when newly made. 
 
 Glass may be made from calcined bones by digesting- them 
 during two or three days with half their weight of sulphuric 
 acid, evaporating to dryness, and washing the residue in many 
 different waters, until all the soluble matter is exhausted. The 
 production of this effect is known by the water having no 
 longer a yellow tinge. 
 
 The different waters thus used must then be brought to¬ 
 gether and evaporated to afford a solid extract. To separate 
 the sulphate of lime contained in this, the extract must be dis¬ 
 solved in the least possible quantity of water, and filtered: the 
 salt will then remain on the filter. This extract may be mixed 
 with powdered charcoal, and distilled for the production of 
 phosphorus; but if, instead of this, it be placed in a large cru¬ 
 cible, and the fire is urged, it will at first swell considerably, 
 but ere long will again settle, and at that instant the glass is 
 made. This is white, and of a milky color. 
 
 These directions are taken from the System of Chemistry of 
 M. Chaptal; who tells us that before his time Becher was per¬ 
 fectly well acquainted with the use to which bones could thus 
 be applied, but that he concealed the process, on account of the 
 abuse which, according to his apprehensions, might be made of 
 t, and to which he plainly enough alludes in the words—“ IIo- 
 no vitrum est, et in vitrum redigi potest; sicut et omnia ani- 
 nalia.” This author was, nevertheless, led to express his re¬ 
 gret that the Scythians, who drank from disgusting skulls, were 
 lot acquainted with the art of converting them into so cleanly 
 ■ substance as glass;—and he also showed the possibility of 
 orming a gallery of family effigies, moulded from glass, the 
 •roduce of the identical bones of the originals, in which the 
 ikenesses might be preserved as truly as they now are by the 
 mner. M. Chaptal adds, that a skeleton of nineteen pounds 1 
 might may be made to yield five pounds of this phosphoric 
 lass. 
 
 Newly made glass of this description will emit very strong 
 metric sparks, which will fly to the hand at the distance of two 
 iches: but this property ceases after one or two days, however 
 j irefully the glass may be preserved from contact with the at- 
 ' osphere. The substance is in fact phosphoric acid which has 
 
GLASS MANUFACTURE. 
 
 CHAP. IX. 
 
 176 
 
 been deprived of its water, and which if not carefully preserved 
 from the atmosphere it will again imbibe, becoming deliques¬ 
 cent. It has an acid taste, and is soluble in water. 
 
 CHAP. IX. 
 
 ON THE USE MADE OF THE BLOWPIPE, AND ON VARIOUS SMALL 
 MANUFACTURES OF GLASS. 
 
 Thermometer Tubes.—Mode of giving to them an Elliptical Bore.—Blowpipe 
 and Apparatus described.—Materials used.—Method of Working.—Seal¬ 
 in'* Tubes.—Bending and Joining Tubes.—Bulbs.—Spun Glass.—Watch- 
 Glasses.—Lunette Glasses.—Glass Beads.—Manufactory at Murano.— 
 Striped Tubes.—Mode of forming Beads.—Sorting them.—Numerous Kinds 
 of Beads.—Mock Pearls.—Manner of their Invention and formation.—Dial 
 Plates.—How formed.—Lettering and Figuring. 
 
 A considerable number of articles are made of glass with 
 the aid of a lamp and blowpipe. The principal of these articles, 
 such as thermometers and barometers, are formed from tubes 
 which are made at the glass-houses, of different bores and sub¬ 
 stances, by drawing out quickly, and while soft with heat, a 
 thick and short tube into one that is thin and long. 
 
 The method of performing this process is, to gather the ne¬ 
 cessary weight of glass upon the rod; and this glass having: 
 been elongated and hollowed by the workman’s breath in the; 
 usual manner, a punt is attached to the end of the cylinder op¬ 
 posite to the rod. The workman then holding the rod and his; 
 assistant the punt, each proceeds in a direction opposite to that 
 taken by the other, by which means the tube is elongated in 
 the necessary degree; and being then made to rest upon billets 
 of wood placed horizontally and parallel to each other at equal 
 distances on the ground, it speedily cools, and may in that state: 
 be readily cut into convenient lengths. 
 
 Fig. 23, 
 
 Whatever may be the original form of this tube and of its 
 perforation, it is found that the same form will be relatively 
 continued throughout the entire length to which it is drawn 
 out If its perforation be at first cylindrical, it will so continue] 
 
UP. IX. BLOWPIPE. 177 
 
 rntever degree of length and minuteness it may be made to 
 sume ; and an equal sameness will be found to accompany 
 ^ prolongation, if any other form be originally given to the 
 
 A method has been suggested by Mr. Wilson, of Glasgow, to 
 nder the mercury in a thermometer tube easily observable, 
 thout incurring the inconveniencies which attend a laro-e 
 re. 1 his method is founded on the property above mcntion- 
 ’ w-, whlch ls indeed common to all ductile substances* 
 r. Wilson proposes to form the tubes witli an elliptical per- 
 ation, which when drawn out will form a mere slit, the flat 
 e ot which is to be turned towards the observer. It does not 
 rear, however, that these tubes have come into any extensive 
 
 rhis elliptical bore is caused by flattening, in the necessary 
 free, and before it is drawn out, the short thick tube already 
 cubed ; restoring then its external cylindric form by coatino- 
 ver with a further portion of melted glass, and rolling it on 
 iron slab, mentioned in page 137, in our descriptionof the 
 cesses pursued in blowing flint glass. 
 
 [’he apparatus usually employed by those who undertake this 
 uch of glass-working is extremely simple. The table is 
 stantially made, and has fixed at its bottom a small double- 
 ; t bellows, worked with a foot-board, that the artist may- 
 self govern its action, and at the same time have both his 
 as at liberty for the other operations which he has to con- 
 t. A pipe, proceeding from the bellows, conducts the blast 
 •ir to the lamp, which is usually nothing but a bundle of 
 •se cotton thread, placed in a common tin vessel of a horse- 
 : shape, the flame being fed with lumps of tallow heaped up 
 intermixed with the cotton. A small chimney is hung over 
 lamp, and at a short distance from the flame, to carry off 
 ;moke, which otherwise would be inconvenient to the work- 
 • The blast pipe is so placed and directed that it throws 
 ie jet of flame from the lamp in a direction contrary to that 
 pied by the workman, so that all annoyance from this source 
 ually avoided. 
 
 wo or three very simple iron tools, such as files, forceps, 
 ors, &c., make up the rest of the glass-worker’s apparatus; 
 
 - his materials are mostly confined to an assortment of 
 i having various bores, and composed of different thick- 
 :s of glass. When employed in making toys or ornaments 
 iss, tubes of various colors are provided by the workman: 
 are easily procurable at any glass-house, a good stock of 
 
 ? 0 r If, beautiful scientific application of this principle, see Lardner’s Me- 
 s, Cab. Cyc. p. 9. art. (12.) 
 
178 GLASS MANUFACTURE. CHAP. J 
 
 all kinds of tubing being generally kept by the makers. T 
 flame, when most strongly urged by the blowpipe, is about fi 
 inches long, having its end of a blunt round form; its col 
 in the part nearest to the wick, is of clear light blue, and 
 yond this of a pale yellow, the blue portion having by far 
 greatest heating power. 
 
 In proceeding to work, care must be taken to remove 
 moisture from the tubes, both within and on the outside ; tl 
 must be heated gradually, to prevent their cracking; and 
 greater the thickness of the glass, the more necessity there is 
 caution on this head. Glass is so imperfect a conductor of he 
 that where utensils made with it of any considerable thickn 
 have fire applied to them, it is difficult to prevent an unequal 
 gree of expansion, which induces that corresponding inequa 
 of pressure among the different parts under which some \ 
 inevitably give way and fly asunder. It is for this reason t 
 glasses intended for use in chemical laboratories can hardly 
 made too thin, or with too great attention to the equality of tl 
 substance, so that heat may be quickly and uniformly transmit 
 through the mass. 
 
 Glass tubes should be first heated by being held in the fla 
 of the lamp, without employing the blast of air; they she 
 next be brought to the yellow outer edge of the flame wl 
 urged by the blowpipe; and, lastly, the fusion must be complc 
 through bringing the glass by slow degrees within the hoti 
 part of the flame. 
 
 The power of a blowpipe, such as is usually employed 
 these purposes, is sufficient for bringing to a white heat a s< 
 lump of glass large enough to form a bulb which will cont 
 three fluid ounces; a size much larger than can be required 
 purposes to which the lamp is usually applied. 
 
 It may be well to describe briefly one or two operations, s 
 as are usually effected by means of the lamp and blovvpi 
 from which will be made apparent the great facility wherev 
 this seemingly refractory substance can be moulded, throi 
 the agency of heat, according to the will of the workman. 
 
 If it be wished to seal a tube hermetically, that is, to clos 
 effectually at the end by causing the intimate union of its j 
 tides, it will suffice that the part be held during a short t 
 in the flame, turning the tube round with the fingers so a 
 occasion an equal action upon every part: by this means 
 end will presently be so far softened, or partially fused, that 
 particles will fall in and run together; thus effectually do 4 
 the orifice, and producing the appearance of a small butto 
 the extremity. This operation may be hastened, if, when 
 glass is rendered soft by heat, and before any fusion has ensi 
 
iAP. IX. BINDING TUBES. 179 
 
 e parts are brought into contact towards their common centre 
 ' means of a stout iron needle. In some cases, and partieular- 
 wheu the tube is of any considerable substance, the button 
 us formed on the end would be inconveniently large, and 
 ight besides either fly in cooling - , or be accidentally broken. 
 !iis can be remedied by lessening, in the following manner, 
 e quantity of glass whereof it is composed. 
 
 The end being softened in the flame of the lamp, and another 
 3ce of tube of the same size having been equally acted upon, 
 e two ends are to be brought together, and may, by a very 
 tie management, be firmly united. If then the tube which is 
 be sealed is softened a little higher up than the point of 
 ion, and the two tubes are pulled gently in opposite directions 
 itil they separate, that which is heated will be drawn out with 
 liminished substance, and may be easily sealed in the part 
 it is required, the joined ends and a portion of the sealed tube 
 maining attached to the waste piece. 
 
 In making some kinds of thermometers, and for various pur¬ 
 ses connected with experimental chemistry, it is often requir- 
 to bend tubes of glass: when these are of small bore, and 
 eir substance is tolerably thick, it is only requisite to hold the 
 be in the weaker part of the flame, in order to soften it 
 rough about one or two inches of its length, when it may be 
 iwly and gently brought to the shape required. 
 
 Something more than this is needed if the tube be wide and 
 substance thin. In order to preserve in sucli case the particu- 
 • form of the bore, and to prevent its being much straightened, 
 perhaps closed at the bend, as it most probably would be if no 
 ecaution were taken against it, one end of the tube should be 
 rmetically sealed ; and during the time the workman employs 
 nself in bending it at the required part, he should also blow 
 sadily but very gently into the open end. The pressure of 
 ! breath employed in this manner, will keep the softened 
 rt of the tube distended in the proper degree, so that it can- 
 t collapse during the bending, and the perforation will be 
 tintained in its original form. The closed end of the tube 
 ly be readily cut off by first scratching with a file and then 
 jaking it suddenly; an operation which, with a very little 
 •e, may be performed without risk of dividing the tube in any 
 ler part of its length. 
 
 Two tubes may be joined together with tolerable accuracy 
 heating their ends in the flame, and then bringing them 
 o contact; turning them round in opposite directions with a 
 ewing motion, in order to complete their junction. If it be 
 sired to remove the thickened ring of glass which will thus 
 produced, one end of the tube must then be previously seal- 
 
180 
 
 GLASS MANUFACTURE. 
 
 CHAP. IX 
 
 ed ; and when the union has been fully completed in the wa 
 described, and while the glass is yet soft, the workman mm 
 blow into the open end, and gently pull the tube at the point o 
 junction, until the ring disappears, and the whole tube become 
 equally cylindrical. 
 
 In forming hollow bulbs at the end of tubes, such, for ir 
 stance, as are required in making thermometers, the followin 
 process must be used:—The end whereat the bulb is to be forn: 
 ed must be sealed; and in order to collect at this extremity th 
 needful quantity of glass, it must be pressed while yet quite he 
 upon some hard surface, by which means that part is somewha 
 shortened and consolidated into a lump. This must then b 
 held in the most intense flame of the blowpipe until it is quit 
 white hot; being then removed, and the breath applied model 
 ately and steadily to the open end, and keeping the tube in th 
 meanwhile with the heated end hanging downwards, th 
 lump will be enlarged into a spherical bulb, the diameter, an' 
 consequently the substance, of which can be regulated accord 
 ing to the pleasure of the workman. 
 
 It has been already mentioned that glass may be spun int 
 very long and minute threads, with great velocity, when th' 
 mass from which it is drawn has been previously heated. Fo 
 this operation the use of the blowpipe is required, and the man 
 ner of its performance is very simple. 
 
 The lump of glass being sufficiently softened by the flame 
 another piece of glass is applied to it, when the two, coherin' 
 together, and being then drawn apart, are seen to be connects 
 by minute filaments. A fine thread being thus obtained, its en< 
 is applied to a wheel or reel, and the heat of the glass bein' 
 maintained, while the wheel is turned with considerable velo 
 city, a thread may be drawn continuously out as long as tin 
 workman pleases, or until the store of glass is wholly expended 
 
 The thread thus made is extremely flexible and delicate!) 
 fine. Its firmness depends in a great measure upon the hea 
 whereat the glass is maintained, and upon the velocity where 
 with the wheel is turned: the greater these are, the firmer wil 
 be the thread. 
 
 Glass is only treated in this manner in order to afford a pleas' 
 ing exemplification of some of its properties, or for purposes of 
 ornament. When it is desired to produce colored threads, the 
 material employed should be embued with a very deep tint, as 
 when drawn out in such minute filaments, it would otherwise 
 appear nearly colorless. 
 
 The preparation of watch-glasses involves a series of simple 
 but interesting processes. Only a part of these is performed al 
 
CIIAP. IX. 
 
 WATCH-GLASSES. 
 
 181 
 
 the glass-house; the remainder being the objects of a separate, 
 and, when viewed with reference to its extent, by no means 
 unimportant branch of trade and manufacture. 
 
 All that is effected by the glass-blower is the production of 
 regular hollow spheres, each being eight inches in diameter, 
 and weighing twelve ounces. 
 
 It is a circumstance, perhaps, not the least deserving of notice, 
 in detailing the operations of the glass-house, that the men em¬ 
 ployed to gather glass from the pots for this and similar pur¬ 
 poses, upon the end of the hollow rods, attain through constant 
 practice so much proficiency as to bring away with the great¬ 
 est accuracy exactly the quantity that is needed for the forma¬ 
 tion of the required object. To such a degree is this correct¬ 
 ness ca rried, that, on weighing many dozens of spheres such as 
 have just been described, not one has been found that varies 
 half an ounce from the proper weight. 
 
 The blowing of these hollow globes is performed with great 
 celerity. Owing to the circumstance that the glass of which 
 they are composed is exceedingly thin, so that their cooling, 
 although rapid, is also effected with considerable regularity 
 through their substance; and because in the further progress 
 towards their ultimate form they are again to be softened by 
 heat, these globes are delivered to the watch-glass maker as 
 soon as they are blown, and without passing through the 
 annealing oven. 
 
 The first operation performed by the last-mentioned artist is 
 to divide each sphere into the largest possible number of sec¬ 
 tions of the requisite size; it being manifest that any errors 
 committed at this stage of the proceeding would, by wasting 
 his material, place the manufacturer at a disadvantage. 
 
 In proceeding to effect this division, the workman seats him¬ 
 self ; and taking the globe in his lap, with a piece of heated 
 wire or tobacco-pipe, (which last is perhaps chosen preferably, 
 because it longer retains a sufficient degree of heat,) he traces 
 a line upon the globe, and quickly thereafter wetting the line 
 thus traced, the glass will crack and divide along the line with 
 the most admirable precision. The sections thus obtained will 
 necessarily have many angular irregularities: these are dexter¬ 
 ously clipped away by means of scissors. 
 
 The segments into which the individual pieces have now 
 been cut, will be wanting in the requisite degree of convexity. 
 Before this can be imparted to them, they must have their brit¬ 
 tleness removed, and be considerably softened by heat. When 
 this has been effected, taking an appropriate instrument in each 
 hand, and using them much in the same manner as the dairy¬ 
 maid employs her wooden spoons in raising a pat of butter, 
 
 Q 
 
182 GLASS MANUFACTURE. CHAP. IX. 
 
 the workman presses the edges of the glass regularly in to¬ 
 wards the centre, which is by this means made to rise in a cor¬ 
 responding proportion. The edges are then ground evenly off, 
 and the watch-glass is ready for sale. 
 
 Lunette glasses are differently made. These are not seg¬ 
 ments of spheres, but have their edges abruptly raised, and 
 their interior areas or faces flattened. In forming these lu¬ 
 nettes, a much smaller quantity of glass is gathered from the 
 pot than is required in blowing globes for ordinary watch- 
 glasses. A hollow pear-shaped figure is then blown, having 
 the larger end, which is farthest from the extremity of the rod, 
 of the size required for a watch-glass, and the requisite flat¬ 
 ness is occasioned by pressing this end, while soft, upon any 
 smooth level surface. 
 
 These glasses are necessarily much higher in price than 
 those more commonly used for watches; both because they are 
 made to contain a greater weight of glass, and because, only 
 one form being cut from each hollow pear-shaped figure, the 
 labor expended in the manufacture is proportionally greater. 
 
 A very considerable manufacture of glass for the formation 
 of beads is carried on at a place called Murano, situated near 
 the city of Venice. There is nothing peculiar in the composi¬ 
 tion of the glass made use of for this purpose, nor in the meth¬ 
 ods employed for its preparation; and although the manufactu¬ 
 rers affect great secrecy as to the coloring substances which 
 they mix with the glass, it is not likely that they possess any 
 real advantage over others in this respect, or that they have 
 made any useful discovery of materials different from those 
 commonly employed in coloring glass. 
 
 When upon inspection the colored glass is found to be in a 
 fit state for working, the necessary quantity is gathered in the 
 usual manner upon the rod, and is blown into a hollow form. 
 A second workman then provides himself with an appropriate 
 instrument, with which he takes hold of the glass at the end 
 which is farthest from the extremity of the rod, and the two 
 men running thereupon expeditiously in exactly opposite direc¬ 
 tions, the glass is drawn out into a pipe or tube, in the manner 
 of those used for constructing thermometers, the thickness of 
 which depends upon the distance by which the men separate 
 themselves. Whatever this thickness may be, the perforation 
 of the tube is preserved, and bears the same proportion rela¬ 
 tively to the substance of the glass as was originally given to 
 it by the blower. In these particulars the workmen of course 
 govern themselves according to the size and description of the 
 beads which are to be made. The glass-house at Murano is 
 
CHAP. IX. 
 
 GLASS BEADS. 
 
 183 
 
 provided with a kind of gallery 150 feet in length, and which 
 much resembles a rope-walk, wherein the tubes are drawn out 
 in the manner here described. 
 
 Tubes striped witli different colors are made by gathering 
 from two or more pots lumps of different colored glass, which 
 are united by twisting them together before they are drawn 
 out to the requisite length. 
 
 As soon as they are sufficiently cool for the purpose, the 
 tubes are divided into equal lengths, sorted according to their 
 colors and sizes, packed in chests, and then dispatched to the 
 city of Venice, within which the actual manufacture of the 
 beads is conducted. 
 
 When they arrive at the bead manufactory, the tubes are 
 again very carefully inspected, and sorted according to their 
 different diameters, preparatory to their being cut into pieces 
 sufficiently small for making beads. 
 
 For performing this latter operation, a sharp iron instrument 
 is provided, shaped like a chisel, and securely fixed in a block 
 of wood. Placing the glass tube upon the edge of this tool 
 at the part to be separated; the workman then, with another 
 sharp instrument in his hand, cuts, or rather chips, the pipe 
 into pieces of the requisite size; the skill of the man being 
 shown by the uniformity of size preserved between the differ¬ 
 ent fragments. 
 
 The minute pieces thus obtained are in the next process 
 thrown into a bowl containing a mixture of sand and wood- 
 ashes, in which they are continually stirred about until the 
 perforations in the pieces are all filled by the sand and ashes. 
 This provision is indispensable, in order to prevent the sides 
 from falling together when softened by heat in the next opera¬ 
 tion. 
 
 A metallic vessel with a long handle is then provided, 
 wherein the' pieces of glass are placed, together with a further 
 quantity of wood-ashes and sand; and the whole being subject¬ 
 ed to heat over a charcoal fire, are continually stirred with a 
 'hatchet-shaped spatula. By this simple means the beads ac¬ 
 quire their globular form. 
 
 When this has been imparted, and the beads are again cool, 
 they are agitated in sieves, in order to separate the sand and 
 ashes; this done, thev are transferred to other sieves of differ¬ 
 ent degrees of fineness, in order to divide the beads according 
 to their various sizes. Those of each size are then, after being 
 strung by children upon separate threads, made up into bun¬ 
 dles, and packed in casks for exportation. 
 
 In this manner, not fewer than sixty different kinds of glass 
 beads are prepared in vast quantities. The principal trade in 
 
GLASS MANUFACTURE. 
 
 CHAP. IX, 
 
 184 
 
 these is carried on with Spain and the coast of Africa; but 
 some portions find their way to nearly all parts of the world. 
 
 Another and a more costly description of glass beads, made 
 in imitation of pearls, has long been produced in France. Al¬ 
 though the name of the inventor of these ornaments has been 
 faithfully preserved, the period of their invention is not pre¬ 
 cisely known. Reaumur, on whose assertions the greatest re¬ 
 liance may generally be placed, states this to have occurred in 
 1856. An anecdote related by Beckmann* of a cheat success¬ 
 fully played off upon a lady by a French nobleman, leads to the 
 conclusion that thirty years later than the period here mention¬ 
 ed, these mock pearls were far from being generally introduced 
 or even known. 
 
 The manner of their invention was this:—M. Jaquin having 
 observed that upon washing a small fish, the Cyprinus albur- 
 nus, or bleak, the water contained numerous fine particles, 
 having the color of silver, and a pearly lustre, he suffered the 
 water to stand for some time, and, collecting the sediment, 
 covered with it some beads made of plaster of Paris, the fa¬ 
 vorable appearance of which induced him to manufacture more 
 of the same kind for sale. These were at first eagerly adopt¬ 
 ed ; but the ladies soon finding that when they were exposed 
 to heat, the lustrous coating transferred itself from the beads 
 to their skin, they were as quickly discarded. 
 
 The next attempt of M. Jaquin was more successful. He 
 procured some glass tubes of a quality easily fusible, and, by 
 means of a blowpipe, converted these into numerous hollow 
 globules. He then proceeded to line the interior surface of 
 these with the powdered fish-scales, which he called essence 
 of pearl, or essence <T Orient. This was rendered adhesive by 
 being mixed with a solution of isinglass, when it was intro¬ 
 duced in a heated state inside the globules, and spread over the 
 whole interior surface, by shaking the beads which, for that 
 purpose, were placed in a bowl upon the table. These hollow 
 beads being blown exceedingly thin, in order to produce a bet¬ 
 ter effect, were consequently very tender. To remedy this 
 evil, as soon as the pearly varnish was sufficiently dry, they 
 were filled with white wax, and being then bored through with 
 a needle, were threaded for sale. 
 
 An expert workman can blow from five to six thousand small 
 glass globules in a day; but, as some attention is called for in 
 regard to the shape and appearance of these beads, the produce 
 of a man’s daily labor will not much exceed one fourth of that 
 quantity. The closer to counterfeit nature in their manufacture, 
 
 * Hist, of Inventions, vol. ii. art. Artificial Pearls. 
 
MOCK PEARLS. 
 
 CHAP. IX. 
 
 1 
 
 185 
 
 these beads are sometimes purposely made with blemishes, and 
 of somewhat irregular forms. Some are made pear-shaped; 
 others are elongated like olives; and others again are flattened 
 on one side, in imitation of natural pearls, which are set in a 
 manner to show only one side. 
 
 The fish whose scales are put to this use are about four 
 inches in length. They are found in great abundance in some 
 rivers; and, being exceedingly voracious, suffer themselves to 
 be taken without difficulty. The scales furnished by 250 of 
 these fish will not weigh more than an ounce, and this will not 
 yield more than a fourth of that quantity of the pearly powder 
 applicable to the preparation of beads; so that 16,000 fish are re¬ 
 quired in order to obtain only one pound of the essence of pearl. 
 
 Up to a recent period, the heirs of Jaquin, the first inventor, 
 carried on a considerable manufactory of these mock pearls in 
 Paris. The fish are tolerably abundant in the river Seine; but 
 their scales are conveyed from distant parts in much larger 
 quantities than can be procured on the spot, for which purpose 
 they are preserved in volatile alkali. 
 
 The dial-plates of clocks and watches are made of opaque 
 white glass, which has acquired the name of enamel. The pe¬ 
 culiarly delicate appearance of these, as well as their opaque¬ 
 ness, result from the presence of oxide of tin. 
 
 These plates, which are not of greater diameter than twelve 
 inches, are made in one piece; but any which are required to 
 be larger than this, must be formed in separate segments, and 
 afterwards joined together. 
 
 In the preparation of dial-plates, the first process is that of 
 hammering a thin plate of copper of the requisite size upon a 
 slightly concave anvil constructed of hard wood; for which 
 operation a convex hammer is employed, and in this manner 
 the proper state of convexity is imparted to the plate, without 
 impairing in any degree the smoothness of its surface. 
 
 The centre hole for the hour and minute hands, as well as 
 that whereby the key must be introduced for the purpose of 
 winding up the clock or watch, together with other smaller 
 holes, for the screws by which the dial is to be attached to the 
 works, are all made by passing tools of appropriate forms and 
 sizes through the copper, from the concave side, in such a man¬ 
 ner that the metal displaced in the act may form ridges round 
 the holes on the convex side, and be instrumental in retaining 
 the enamel to the requisite thickness upon the surface, when 
 in its state of fusion. For this same purpose, the outside edge 
 of the plate is hammered up all round, so as to form a ridge of 
 the requisite depth; and provision must be made for this rim 
 
 Q 2 
 
18G 
 
 GLASS MANUFACTURE. 
 
 CHAP. IX. 
 
 in the size originally given to the copper. The metallic plate 
 thus formed is thoroughly cleansed by being immersed in a 
 weak dilution of nitric acid, after which it is dipped in pure 
 water, and rubbed smartly over with a brush formed of brass 
 wires. 
 
 The white enamel is then broken in a hardened steel mor¬ 
 tar, until it is reduced to fragments about the size of fine 
 sand ; and the whole should be brought as nearly as possible to 
 the same state as regards the size of the particles. The pounded 
 glass is then washed in very clear water, and the heavier parts 
 having subsided, the remaining milky-looking liquid is poured 
 off and left to settle in a separate vessel. This operation is 
 several times repeated; so that the powder may be divided into 
 separate portions, having different degrees of fineness. 
 
 The enamel being thus sorted and well washed, the separate 
 portions are placed in glass vessels, and nitric acid is poured 
 over, so as completely to cover the powders. The acid must 
 be left on the enamel during the space of twelve hours, the 
 whole being occasionally stirred with a glass spatula, in order 
 to dissolve away any metallic particles which may have been 
 abraded from the steel mortar, and which would greatly impair 
 the whiteness of the enamel when subsequently applied on the 
 face of the plate. The acid is then poured off, and the enamel 
 washed in successive waters, until it no longer contains any 
 acidity; after which, it is again covered with pure water, and 
 in this state it must remain until used, that its perfect white¬ 
 ness and purity may be preserved. 
 
 It is necessary to operate upon both sides of the plate, lest 
 the heat of the enamel, when in a state of fusion on the con¬ 
 vex side, should alter the curvature of the copper, and deform 
 its shape. 
 
 The enamel, when prepared in the manner described, is first 
 applied to the concave or under face; in which process the 
 artist spreads over it with a spatula, as thin and as evenly as 
 possible, a portion of the finer settlings. A tool which had pre¬ 
 viously been i nserted in the centre hole is then withdrawn, and 
 its place sup](lied with a rag of clean linen, which absorbs all 
 the superfluous water from the enamel, bringing it to such a 
 state of consistency, that this, which is called the counter-en¬ 
 amelling, will adhere sufficiently to the copper when the posi¬ 
 tion of the plate shall be reversed. In then proceeding to op¬ 
 erate upon the convex surface, the plate must be turned over, 
 a tool being again placed in the centre hole, and a layer of the 
 coarser part of the pounded glass thereafter applied with every 
 possible care as to the evenness of its distribution. It is par¬ 
 ticularly requisite to cover well the edges of the dial-plate, as 
 
CHAP. IX. DIAL PLATES. JQ7 
 
 well as those of the different holes, lest the heat should after¬ 
 wards act too powerfully upon the metal. To draw off the su¬ 
 perfluous moisture from this layer of enamel, a fine linen cloth 
 is applied round the entire edge, which, in this altered position 
 of the dial, is now its lowest part, and has in that respect taken 
 1 the place of the centre hole in the counter-enamelling process 
 hist mentioned. In order that the particles mav arrano-e them¬ 
 selves properly and closely together, the tool still remaining in 
 the centre hole is then subjected to two or three slight concus¬ 
 sions, and much of the beautiful appearance of the finished 
 dial-plate depends upon the neatness with which this operation 
 is performed. If the enamel is evenly spread and well packed 
 together, no hollows will be left below the surface when it has 
 ibeen melted, and the requisite degree of smoothness will be at¬ 
 tained. To dissipate any moisture which may now be retained 
 iy the enamel, the plate is dried on a sheet of iron over a 
 chafing-dish. 
 
 The dial-plate, thus prepared, is introduced cautiously and 
 by degrees under a muffle placed in a furnace, it beino- neces¬ 
 sary to heat it gradually: in this situation it must remain until 
 it is perceived that the enamel begins to melt; the sheet of 
 ;ron on which the dial is placed should then be turned o-ently 
 round, in order that every part may be equally exposed*to the 
 leat of the muffle. So soon as the enamel is seen to be per¬ 
 fectly melted over the whole surface, the plate must be with¬ 
 drawn with as much caution and deliberateness as was used 
 lpon its introduction; and, in order to prevent the cracking 1 
 md scaling off to which the glass would otherwise be liable 
 i he plate must remain for some time cooling very gradually at 
 he mouth of the muffle. The necessity for this delay in the 
 irocess arises from the same physical law which obliges the 
 | Manufacturer to have recourse in larger operations to the 
 I annealing oven. 
 
 When this first firing has been completed, the plate must be 
 leaned,-as before, with a very weak dilution of nitric acid 1 
 nd a layer of the finer settlings of the enamel is to be spread,’ 
 
 I a the manner already described, over the convex side It is 
 ot necessary to apply any further coating to the inner or con- 
 : ave surface, unless upon examination any part of the former 
 iyer shall appear defective ; in which case such part must be 
 mde good with a further portion of the same division of the 
 namel as was used before. 
 
 The same precautions that were observed in the first firino- 
 >r placing the dial-plate within, and for removing it from the 
 iuffle, must be repeated now ; and must equally be practised 
 ben a third layer, which must be of the finest and whitest 
 
188 GLASS MANUFACTURE. CHAP. IX. 
 
 portion of the enamel, is subsequently spread over the convex 
 side. When this third layer has in its turn been fused and 
 gradually cooled, the dial-plate is complete, with the exception 
 of the figures or lettering, which must he placed upon the con¬ 
 vex side to mark the divisions of the hours and minutes, and 
 which are thus applied :— 
 
 A black enamel, which is so composed that it will fuse at a 
 lower degree of heat than the white opaque glass already em¬ 
 ployed, is to be ground exceedingly fine in an agate mortar 
 with a pestle of the same substance, and in combination with 
 oil of lavender; which, as it would of itself be too thick, must 
 have its consistence reduced by the addition of oil of turpentine. 
 To such an exceeding degree of fineness is it considered ne¬ 
 cessary to reduce this black enamel for the purpose, that the 
 labor of half a day is usually employed in thus grinding a drachm 
 weight. A further quantity of the mixed essential oils must 
 afterwards be added, that the enamel may be sufficiently thin 
 to flow readily from the pencil. 
 
 The dial-plate is then placed upon some level surface, and 
 by means of a pair of compasses, having one of the legs blunt 
 at the end and rounded, so that it will freely turn in the centre 
 hole where it is placed, and the other leg provided with a black- 
 lead pencil, two circular lines are slightly traced at unequal 
 distances from the centre, between which the numerals are to 
 be inserted. The exact position of these is determined by 
 means of a sector furnished with a movable limb; and the dif¬ 
 ferent figures being drawn with a camel’s hair pencil charged 
 with the prepared black enamel, this is left to become pefectly 
 dry in the air; and its fusion having afterwards been effected 
 in the muffle, the dial-plate is completed, and in a fit state to 
 be placed in the hands of the clockmaker. 
 
CHAP. X. 
 
 FORMATION OF LENSES. 
 
 189 
 
 CHAP. X. 
 
 ON THE FORMATION OF LENSES. 
 
 Preparations of the necessary Tools.—Choice of Glass.—Grinding.—Polish¬ 
 ing.—Curdled Lenses.—Means used for avoiding this Defect. 
 
 In grinding glass for spectacles, or preparing them as lenses 
 for optical instruments, the first thing to be attended to is to de¬ 
 termine the proper focal distance of the glass. Taking then a 
 pair of compasses, which, on the supposition that the glass is 
 intended to be convex or concave on both sides, must be opened 
 to the full focal distance; two arches or segments of circles, 
 each extended somewhat beyond the breadth which it is in¬ 
 tended to give to the glass, must be described upon a piece of 
 sheet copper, which must then be filed away from the out¬ 
 side of one and from the inside of the other arch. By this 
 means two gauges are formed, the one convex and the other 
 concave, and each perfectly answering to the other. 
 
 If it is intended that the glass shall be what the opticians call 
 plano-convex or plano-concave, that is, having one of its sides 
 flat, while the other has received the requisite curvature, the 
 compasses wherewith the arches are described should be opened 
 to only one half the focal distance. 
 
 Two circular plates of brass, about one-tenth of an inch in 
 thickness, and each being of a little larger diameter than the 
 intended lenses, are then securely soldered upon a cylindrical 
 piece of lead of an equal diameter with the brass discs, and one 
 inch in thickness; these, which are called tools, are then fixed 
 in the lathe, and turned so as to correspond with the copper 
 gauges, the surface of one being made convex, and of the other 
 2 oncave. 
 
 The two brass discs are then to be ground together with 
 emery, or with pounded Turkey-stone, until their surfaces ex¬ 
 actly coincide in every point. 
 
 If the focal distance is very short, so that the convexity and 
 ■oncavity require to be very considerable, the brass discs should 
 he hammered as nearly as possible to their intended form be- 
 bre they are soldered to the leaden cylinders, and turned; 
 therwise either the thickness of the brasses would require to 
 >e inconveniently increased, or the more considerable portion of 
 heir substance, which must in such case be cut away, would 
 ccasion the discs to be too thin and yielding. 
 
 The glass of which a lens is composed is chosen with refer- 
 nce to the purpose to which it is to be applied, and according 
 jits refraetive and dispersive powers: its selection must be 
 
GLASS MANUFACTURE. 
 
 CHAP. X. 
 
 190 
 
 left to the discretion of the optician. Its two surfaces should 
 originally be perfectly parallel. Being cut or clipped into a 
 circular form by means of scissors or pincers, the edge must be 
 smoothed on a common grindstone, and the glass fixed by seat¬ 
 ing one of its surfaces in softened pitch on the flat end of a solid, 
 cylindrical, wooden handle of smaller diameter than the glass. 
 The centre of the axis of this handle must coincide exactly with 
 the centre of the glass. 
 
 If, to suit a short focal distance, the curvature of the lens re¬ 
 quires to be great, it will simplify the labor of the artist, if, pre¬ 
 viously to its being thus fitted to its handle, the glass is reduced 
 upon the grindstone as nearly as possible to the shape of the 
 gauge. Some judgment is, however, necessary in this process, 
 lest the abrasion should be carried too far, even in any one mi¬ 
 nute point, which would render the glass wholly unserviceable. 
 
 The convex form is that which is most commonly given to 
 lenses; and in describing the process for effecting this, the 
 mode of producing concave glasses will equally be understood; 
 the only difference between the two methods being this,—that 
 in the first operation, the concave tool and gauge are brought 
 into use ; while for the other, those having a convex form are 
 employed. 
 
 The whole being thus prepared, the concave tool is fixed 
 firmly on the working bench; and having some fine emery 
 sprinkled on its surface, the glass is worked upon it with circu¬ 
 lar and cross strokes alternately; the artist being careful that 
 the centre of the glass shall never pass beyond the edge of the 
 tool. 
 
 When by these means the glass has been so far ground that 
 its surface coincides with that of the tool at every point, the 
 emery is to be washed away, and some of the finer kind substi¬ 
 tuted ; and so on through three or four different degrees of fine¬ 
 ness, until all the roughnesses and apparent scratches on the 
 glass are worn down, and it has become perfectly smooth to the 
 touch, although dull and opaque to the eye: after this it is 
 sometimes further ground with finely pounded pumice-stone. 
 
 At the expiration of every five or six minutes, during this 
 grinding process, the surface of the tool is rubbed for a short 
 time within the concave tool, that its proper curvature may be 
 perfectly preserved. When the operation has been completed, 
 the glass is easily separated from its wooden handle by means 
 of a thin knife, and the pitch is removed by rubbing it with oil. 
 The side which has been ground is, in its turn, fixed upon the 
 wooden handle, and the other side is then ground in the same 
 manner as the first. 
 
 Convex glasses are frequently prepared for common purposes, 
 
CHAP. X. 
 
 POLISHING LENSES. 191 
 
 in another manner. The concave tool is fixed upon the lathe 
 and the glass being held steadily in the hand, and sprinkled 
 with emery, is applied to the tool during its revolutions. For 
 concave glasses, the convex tool is fitted to the lathe, and the 
 glass is in like manner presented to it; but this method, although 
 easier and more expeditious, is greatly inferior in its result to 
 hand-grinding, and cannot be resorted to when any thin" like 
 perfectness in the intended instrument is desired. 
 
 The same brass tool which is used for grinding, serves also 
 for polishing lenses; but before it is thus employed, a smooth 
 tlnck piece of felt must be stretched over and cemented to it 
 and the outer surface being then covered with washed putty 
 powder, which is a combination of the oxides of tin and lead 
 the tool is worked upon the lens with the same motions as are 
 employed m grinding it. The consistency of the powder is a 
 point retiring attention; for if it be too moist, it will cause 
 the fibres of the felt to rise up and polish, not only the surface, 
 aroperly speaking, but likewise the innumerable hollows, which, 
 lot withstanding all appearances to the contrary, are actually 
 eft m the surface from the grinding. If the lens be subjected 
 ■o examination in a microscope, this effect will be rendered 
 tiny apparent. The evil consequence resulting from this de- 
 ect is, that the cavities being polished, admit the rays of light 
 und disperse, instead of collecting them, as would be the case 
 t the surface were uniform. When this fault exists in a de¬ 
 cree so exaggerated as to be visible to the naked eye, the lens 
 s said to be curdled. 
 
 An excellent method has lately been adopted by an eminent 
 ptician in London, whereby this defect is avoided. Bees’ 
 rax is hardened to a proper degree by admixture with dry red 
 ulphate of iron, which has previously been carefully washed; 
 nd instead of the covering of felt, this compound is melted 
 ver the brass tool. When cold, the casing thus formed is suf- 
 ciently hardened to be turned to the required curvature, and 
 1 tt! 00 ’ waen this ^ as been done, is in a fit state for use. 
 
 riie peculiar advantage of this compound, as a polishing 
 lbstance, consists in its perfect uniformity; besides which, it 
 as this further recommendation, that if any hard particles 
 lould accidentally insinuate themselves between the tool and 
 ie lens, and which m other circumstances would scratch the 
 lass, the wax is sufficiently yielding to allow them to bury 
 lemselves in its substance, so that all injury of this kind is 
 raided. 
 
 Lenses which have been thus treated, will bear examination 
 ^ a ^ microsco P e ) their polish appearing uniformly clear and 
 
X92 GLASS MANUFACTURE. CHAP. X. 
 
 Convex lenses in their simple state have been used for col- 
 lectin" the heating rays of the sun, or for forming what are 
 called”burning-glasses. One of the largest lenses ever appfied 
 to this purpose was made of flint glass by Mr. Parker. I he 
 diameter of this glass was 3 feet; its focal distance was 45 
 inches; and the circular spot of light which it cast at the focal 
 point w T as 1 inch in diameter. Still farther, and as much as 
 possible to condense the rays, Mr. Parker employed a smaller 
 lens, 13 inches in diameter, in conjunction with the larger one, 
 and by means of this the heating rays were concentrated at 
 the focal point to f of an inch. The effects produced by this 
 arrangement were surprising: 20 grains of pure gold were 
 fused in 4 seconds; the same effect was produced on 10 grains 
 of platina in 3 seconds; and a diamond, whose weight was 10 
 grains, was found to have lost 4 grains after having been placed 
 within the focus during 30 minutes. 
 
 This lens, which cost 700/., has since passed into the posses¬ 
 sion of the emperor of China. 
 
 CHAP. XI. 
 
 ON THE PRINCIPAL DEFECTS OBSERVABLE IN GLASS. 
 
 Stria:— Render Glass unfit for Optical Purposes.—Threads—Render Glass 
 fragile.—Cause of this.—Tears—One of the greatest Defects.—Render 
 Glass useless.— Knots.—Bubbles.—Whence they proceed.—Do not much 
 affect the duality of Glass.—Objects to be attained for avoiding these De¬ 
 fects.—M. Guinand.—His humble Origin.—Energy of Character.—Exam 
 ines Telescopes, and constructs others.—Unable to procure Glass of good 
 Quality.—Is incited to examine into the Causes of Inferiority.—His ex 
 traordinary Perseverance amidst Accidents and Difficulties.—His ultimate 
 Success.—Accident leading to further Improvement—Prosecutes Ins art 
 in Bavaria.—Returns to Switzerland, and further pursues his favorite Ob¬ 
 ject._Dies.—Frauenhofer.—Rises from Obscurity by his Talents.—His 
 
 Scientific Acquirements.—Produces Specimens of perfect Glass.—Dies at 
 an early Age.—Respect paid to his Memory. 
 
 The principal defects observable in manufactured glass, are 
 strife, threads, tears, and knots. These, when they occur to 
 any extent, all impair its beauty, and some of them injure itSi 
 actual quality. Although it is not difticult to attain such an 
 amount of proficiency in the manufacture as will preserve the 
 materials from these evils in their extreme degree, yet, alto-i 
 gether to avoid their occurrence, and to obtain glass of a per-; 
 feet quality, is a task that long, and with only doubtful success,! 
 has engaged the thoughts and labors of men devoted to scien-j 
 tific pursuits. The difficulties that attend the attainment of 
 this object arc sufficiently proved by the fact that, during ten 
 years, one of the most considerable and most scientific opticians 
 
CHAP. XI. 
 
 DEFECTS IN GLASS. 
 
 193 
 
 in London has been disappointed in his efforts to procure a disc 
 of flint glass only five inches in diameter, sufficiently fitted, by 
 the absence of defects, to be employed in the construction of a 
 telescope. 
 
 Striae are undulating appearances, perfectly vitrified, and 
 equally transparent with any other part of the glass: they do 
 not occasion any roughness or inequality in the surface, but re¬ 
 sult from a want of congruity in the composition of the parti¬ 
 cles which make up the substance: in other words, the struc¬ 
 ture is not perfectly homogeneous; and although each different 
 portion may be altogether good in itself, and the whole mass, 
 if made up of any one of these portions, would be equally per¬ 
 fect in itself, yet, the whole acting without any uniformity, the 
 rays of light in passing through them are bent or refracted 
 differently, and the objects beyond appear distorted. 
 
 This condition must exist to a considerable extent to be easi¬ 
 ly discernible by the naked eye, or detrimental to the quality 
 of the glass, when applied to the more ordinary purposes of 
 use or ornament; but glass striated in a scarcely perceptible 
 degree, is yet wholly inapplicable to the construction of optical 
 instruments, where the objects they are intended to present to 
 the eye will be many times magnified; and where, consequent¬ 
 ly, every defect or distortion that accompanies their transmis¬ 
 sion through the glass will be equally enlarged. The end pro¬ 
 posed in the employment of these philosophical instruments, is 
 the minutely accurate examination of distant or very diminu¬ 
 tive objects; and this purpose it is evident must be completely 
 frustrated, by the defect here described. 
 
 The name of threads is usually given to fibrous appearances 
 in the body of the glass, which result from the vitrification of 
 clay. Their color is greener than that of the rest of the glass. 
 Threads, if existing in great numbers, render the material ex¬ 
 tremely fragile; and the same effect is produced, if, although 
 fewer in number, the threads are individually larger. The 
 cause of this increased brittleness is, that the dilation and con¬ 
 traction, at different temperatures, of glass, which results from 
 tire fusion of clay, differ from those of glass made with silice¬ 
 ous sand; for which reason, each in turn exerts a hurtful influ¬ 
 ence upon the other. 
 
 Tears are, perhaps, the greatest defect that can be found in 
 glass. They are in fact an exaggeration of the imperfection 
 last described, and usually proceed from the fusion and vitrifi¬ 
 cation of portions of the clay that forms the arch of the fur¬ 
 nace, and which are suffered to drop into the pots, and to float 
 in the glass while in its state of fusion. Wherever these tears 
 exist, the material is brittle in a very high degree, so as fre- 
 
194 
 
 GLASS MANUFACTURE. 
 
 CHAP. XI. 
 
 quently to crack, without any apparent cause, by the mere ef¬ 
 fect of the unequal expansion just described, which accident is 
 more likely to occur in proportion as the drops are nearer to 
 the surface. This defect is one of so serious a nature, that it 
 is usual, on discovering its existence, at once to throw aside 
 the glass as useless. In places where, as is frequently the case 
 in England, covered crucibles are employed, this accident is in 
 a great degree avoided. 
 
 Three kinds of knots are observable in glass; one of these 
 arises from the aggregation of several imperfectly vitrified 
 grains of sand. Another is owing to some portions of glass 
 gall not having been removed during the refining; and the 
 third kind is produced by any small parts of the crucible or of 
 the furnace which, having been abraded by the rubbing of the 
 tools or other accidental circumstance, have fallen into the 
 glass. 
 
 Small bubbles are frequently seen abundantly spread through¬ 
 out the substance of the glass. These indicate an imperfect 
 degree of refining, and proceed from the disengagement of 
 gas which occurs during the process of vitrification. Their 
 presence announces that the glass has not been sufficiently fluid 
 in the course of its refining to allow of their dispersion. This 
 may happen through one of two causes, either that a sufficient 
 amount of fluxing material has not been used with the sand, 
 or that the fire has not been sufficiently intense for the due 
 liquefaction of the compound. These bubbles are chiefly ob¬ 
 jectionable on account of their unsightly appearance, and do 
 not really deteriorate the quality of the glass even for optical 
 purposes. In this case each bubble acts as a small convex lens, 
 rapidly turning aside the rays which strike against it, and oc¬ 
 casioning a diminution of light in proportion to its area. But 
 when these bubbles are even numerous, the sum of their 
 united areas will amount to only a small proportion of the 
 whole surface of the glass; and the loss of light will be incon¬ 
 siderable.* 
 
 It thus appears that the principal object to be sought after in 
 the manufacture of perfectly homogeneous glass is, to avoid 
 those variations in the composition and specific gravity of its 
 different parts, which occasion the striated appearance de¬ 
 scribed above. To enter minutely, and at length, into a con¬ 
 sideration of the means that have been proposed and adopted 
 with a view to remedy this considerable evil, would present 
 little that is amusing to the general reader; while those per¬ 
 sons who feel any particular interest in the subject, or whose 
 
 * R * r Faraday, Bakerian Lect.; Phil. Trans. 1830, p. 
 
CHAP. XI. 
 
 M. GUINAND. 
 
 195 
 
 taste for scientific research leads them to admire the detail of 
 well considered and ably conducted plans for the mastery of a 
 difficult operation, may gratify themselves by consulting Mr. 
 Faraday’s truly valuable paper already referred to, and which 
 will be found comprised in the Philosophical Transactions for 
 the year 1830. 
 
 Some exceedingly favorable specimens of glass for optical 
 purposes have lately been prepared by Mr. Green, the proprie¬ 
 tor of the Stangate Glass-house; a gentleman whose personal 
 attention has been unintermittingly given during many years 
 to all the practical operations and details of an extensive es¬ 
 tablishment. Mr. Green is far from asserting that in what has 
 been accomplished he has arrived at any certainty in the solu¬ 
 tion of this difficult problem, and feels that at most he has 
 hitherto made only an approach to it; while, however, it is 
 such an approach as justifies the hope, that, through continued 
 thought and exertion, a still greater and more important de¬ 
 gree of perfection may be attained. 
 
 The circumstances which attended the long-continued and 
 laborious investigations on this subject of another and a very 
 extraordinary man, are, in themselves, so curious and interest¬ 
 ing, and seem likely to be followed by such important conse¬ 
 quences, to at least one branch of the art, that a treatise on the 
 manufacture of glass might be justly charged with incomplete¬ 
 ness, if it did not furnish at least a sketch of those circum¬ 
 stances. 
 
 The following account is condensed from a memoir, read at 
 a sitting of the Society of Physics and Natural History of Ge¬ 
 neva, on the 19th of February, 1823, as given in the nineteenth 
 volume of the Quarterly Journal of Science, published in Lon¬ 
 don in the year 1825. 
 
 The late M. Guinand was born in an inconsiderable village, 
 among the mountains of Neufchatel in Switzerland. His father 
 was by trade a joiner, and must have been in very indifferent 
 circumstances, as his son was called upon to assist him when 
 only ten years old, and without having acquired more than a 
 very imperfect knowledge of the first rudiments of learning ; 
 a deficiency which was never afterwards supplied, as M. Gui¬ 
 nand always read with difficulty, and wrote very imperfectly. 
 He must, even at this early period, have been a lad of consid¬ 
 erable talent, and of a disposition that urged him to the exer¬ 
 tion requisite for raising his condition in society. We find 
 him, when between thirteen and fourteen years old, having 
 quitted the employment of a joiner for that of a cabinet-maker, 
 chiefly engaged in making cases for clocks. At this period he 
 acquired from an acquaintance some knowledge of the art of 
 
196 
 
 GLASS MANUFACTURE. 
 
 CHAP. XI. 
 
 casting and working in metals, of which knowledge lie after¬ 
 wards availed himself by adopting, when twenty years of age, 
 the occupation of a watch-case maker, the manufacture of 
 watches forming a very considerable branch of industry in that 
 part of the country. 
 
 At the house of a person for whom he then worked, M. J. 
 Droz, the constructor of several automaton figures, which forty 
 years ago made the tour of Europe, young Guinand enjoyed 
 an opportunity of seeing for the first time a very fine reflecting 
 telescope which had been made in England, and which at once 
 appeared to him so curious and interesting an object, that he 
 petitioned for and obtained leave to take it in pieces, the more 
 minutely to examine its construction. The use made of this 
 permission was soon rendered apparent by the production of a 
 similar telescope; and this, which he had constructed with his 
 own hands, on being examined by many competent persons, 
 was pronounced by them to be equal in excellence to that 
 which had served him as a pattern. 
 
 Surprised at this success, the gentleman to whose kindness 
 he owed this opportunity questioned the artist as to his ac¬ 
 quaintance with the science of optics, and in particular to what 
 treatise he was indebted for his proficiency. The surprise of 
 M. Droz was naturally increased on learning that the instru¬ 
 ment had been produced without any knowledge whatever of 
 the theory of optics, and with no more acquaintance with the 
 practice of the art than had been acquired through the exam¬ 
 ination of the English instrument. M. Droz immediately placed 
 a treatise on the subject in the hands of the young man, which 
 he rather deciphered than read; but the substance of which 
 was imbibed by him so completely, that he was enabled, after 
 witnessing the making of one pair of spectacles, to form and 
 polish lenses, and to make spectacles for himself and others, 
 which were pronounced to be excellent. His principal amuse¬ 
 ment at this time was found in manufacturing telescopes, which 
 he got up at a cheap rate, forming the tubes of pasteboard. 
 
 When the important discovery of achromatic glasses reached 
 < Switzerland, Guinand’s mind was very strongly excited by it; 
 and M. Droz having obtained a telescope of the new construc¬ 
 tion, again permitted the young man to examine its various 
 parts and structure. The very imperfect state of the arts at 
 that time in Switzerland, and the deficient means of Guinand, 
 prevented his achieving the construction of a similar instru¬ 
 ment. He was unable to produce glasses of different refractive 
 power; and it was not until several years after that an ac¬ 
 quaintance, making a visit to England, conveyed to him a piece 
 of flint glass, with which, although it was by no means void of 
 
CHAP. XI. M. GUINAND. 197 
 
 imperfections, being considerably striated, he succeeded in 
 making some tolerably good achromatic glasses. Finding that 
 not only the glass which lie had himself worked, but that every 
 other specimen which he examined was thus imperfect, he was 
 incited to a more particular scrutiny into the subject, and bring¬ 
 ing into action all the knowledge he had acquired in the art of 
 fusion, he melted in his furnace the fragments of his flint glass. 
 All the satisfaction derived from this experiment was the ac¬ 
 quirement of some degree of knowledge as to the composition 
 of flint glass, some particles of lead being revived in the metal¬ 
 lic state during the process. Guinand was thirty-five years old 
 at the time when this fresh incitement led to his seeking after 
 such chemical knowledge as might assist him in experiments 
 on vitrification, and his evenings’ employment during six or 
 seven years was to melt in his blast furnace a few pounds’ 
 weight of glass, carefully noting down every circumstance at¬ 
 tending each experiment, that he might be enabled to continue 
 such as afforded any prospect of advantage, and to avoid others 
 which had a contrary tendency. 
 
 • These small experiments led to no decisive results; and he 
 was upwards of forty years old when, having undertaken a 
 new and more profitable trade, that of making bells for repeat¬ 
 ing-watches, he was enabled to devote more of his earnings to 
 the prosecution of experiments, which he thenceforth under¬ 
 took upon a scale more likely by their results to reward his 
 perseverance. 
 
 In this pursuit he was still exposed to numerous accidents 
 and difficulties, which would have deterred most persons from 
 continuing the research. His furnace, which lie had con¬ 
 structed with his own hands, out of such materials as he could 
 procure, and which was capable of melting at once 200 lbs. 
 weight of glass, proved defective. He was then obliged to pro¬ 
 cure materials for the purpose from abroad ; and having once 
 more completed its erection, and consumed much fuel in heat¬ 
 ing it, had the mortification to find that it still required altera¬ 
 tion. Then his crucibles, which he was equally obliged to form 
 with materials ill-qualified for the object, cracked during the 
 process, and the vitreous matter was lost among the ashes of 
 his furnace. Although during all this time his family arrange¬ 
 ments were formed upon a plan of the most rigid economy, he 
 was compelled to employ an interval between each one of his 
 experiments in earning at his regular employment sufficient 
 means for subsistence, and for providing the apparatus, mate¬ 
 rials* and fuel needful for renewing them. 
 
 All this time the pursuit had laid hold so completely of his 
 mind, that he was deprived of his natural rest while considering 
 
 R 2 
 
198 GLASS MANUFACTURE. CHAP. XI. 
 
 upon the causes of his various failures, and endeavoring to rea¬ 
 son out the means for their prevention. 
 
 Having at length succeeded in obtaining a block of glass 
 weighing about 2(J0 pounds, and having sawn it into two verti¬ 
 cal sections, he polished one of the faces, in order, as far as 
 possible, to examine the circumstances produced by the fusion. 
 
 To account for the numerous and various defects exhibited 
 by this specimen, M. Guinand formed a theory which he made 
 the groundwork of his future operations. A more intimate 
 knowledge of those defects, and a conviction thus attained of 
 the great difficulties opposed to their removal, instead of damp¬ 
 ing his ardor in the pursuit, served to infuse new energy into 
 his mind. Nor was he mistaken in his estimate of the obstacles 
 to be surmounted; “ so that,” as he himself declared, “ the 
 sacrifices and exertions which he had previously made were 
 trifling when compared with those which he afterwards under¬ 
 went for the purpose of removing these various defects, and of 
 rendering his glass homogeneous.” 
 
 The steps through which he pursued this arduous under¬ 
 taking, and the methods by which its success was accomplished, 
 it is not possible to detail. All‘that is publicly known upon the 
 subject is, that he succeeded in discovering a mode of proceed¬ 
 ing which gave the almost certainty of producing in the fusion 
 of a pot containing from 200 to 400 pounds of glass, one half 
 at least of its substance entirely homogeneous, and therefore 
 fitted for the construction of perfect optical instruments. With 
 this result, satisfactory as it would have been to most men, 
 Guinand expressed himself by no means contented, and con¬ 
 tinued his researches, without, however, ever arriving much 
 nearer to perfection in the art. 
 
 He was now enabled to make for use discs of glass perfectly 
 homogeneous, with a diameter of twelve inches; a great 
 achievement, when compared with what had been at any time 
 accomplished by others. 
 
 On one occasion the artist had succeeded, through much 
 carefulness and exertion, in obtaining a disc eighteen inches in 
 diameter, and of a quality perfectly satisfactory. This was al¬ 
 ready finished and placed in the annealing oven to cool gradu¬ 
 ally, when, through some unaccountable accident, the fire 
 caught the roof of his humble dwelling. With some trouble 
 the flames were extinguished ; but the water used for this pur¬ 
 pose had found its way into the oven, and the precious deposit 
 was destroyed. It is said that the discouragement caused by 
 this accident prevented M. Guinand from afterwards attempting 
 any similarly extensive experiment. He entertained no doubt, 
 however, that, with means for operating on a larger scale than 
 
M. GUINAND. 
 
 CHAP. XI. 
 
 199 
 
 he could accomplish, lensc9 of double or even triple the diame¬ 
 ter here mentioned might be produced. 
 
 For some time after he had thus far succeeded in his object, 
 M. Guinand was accustomed to divide his blocks of glass by 
 that which appeared the only fitting method, sawing them into 
 sections perpendicular to their axis, polishing the sections, and 
 then selecting such parts as were adapted to his purpose, re¬ 
 turning the remaining portions to the crucible for future opera¬ 
 tions. By this means he had frequently the mortification of per¬ 
 ceiving that the glass was divided, so as to present a less ex¬ 
 tended surface of perfect material than the state of the block 
 would, if previously known, have rendered possible; and he 
 was frequently able to procure discs of only small diameter, 
 when, could he have been fully aware of the particular circum¬ 
 stances of the glass throughout its substance, he might, by cut¬ 
 ting in another direction, have obtained a more satisfactory re¬ 
 sult. 
 
 This disadvantage was remedied in a way apparently as un¬ 
 toward as it was singular and unexpected. While his men 
 were one day carrying a block of glass on a hand-barrow to a 
 water saw-mill, which he had constructed at the fall of the 
 river Doubs, a short distance from his dwelling, the mass acci¬ 
 dently slipped, and, rolling to the bottom of a rocky declivity, 
 was broken into several pieces. Endeavoring to make the best 
 of this seeming misfortune, such fragments of glass were se¬ 
 lected for operation as appeared to be fitted by their homoge¬ 
 neity for the purpose; and these were softened in circular 
 moulds, in such a manner that they furnished discs of a very 
 satisfactory quality. Further examination enabled Guinand to 
 perceive that the fracture had in a great measure followed the 
 variations of density in the glass; and, pursuing the idea thus 
 obtained, the artist thenceforth adhered to a method so singu¬ 
 larly in the first instance forced upon him. 
 
 After this, M. Guinand contrived a mode of cleaving the 
 glass while cooling, so that the fracture accompanied the direc¬ 
 tion of the more faulty parts; by which course he frequently 
 obtained masses of glass which were absolutely homogeneous, 
 weighing from forty to fifty pounds. These masses, cleft again 
 by means of wedges into pieces of convenient shape, were re¬ 
 melted in moulds which gave them the form of discs; an ope¬ 
 ration which differs essentially from that used by other glass- 
 makers. 
 
 Several years of his life were thus employed by this extraor¬ 
 dinary man in making bells for repeating-watches, and con¬ 
 structing achromatic telescopes with glass of his own prepar¬ 
 ing. The retired spot wherein he resided, offered only very 
 
200 
 
 GLASS MANUFACTURE. 
 
 CHAP. XI. 
 
 limited opportunities for acquiring a reputation in the world; 
 yet, by degrees, the superior value of his labors became appre¬ 
 ciated, and he was visited by such men of science as travelled 
 into the neighborhood of his dwelling. By one of these, a 
 knowledge of his merits was conveyed to M. Frauenhofer, the 
 chief of a celebrated manufactory for optical instruments, es¬ 
 tablished at Benedictbeurn in Bavaria. This gentleman having 
 in consequence obtained some discs of glass made by Guinand, 
 found their quality so satisfactory, that he repaired in person to 
 Brenets, where the artist resided, and engaged him to settle in 
 Bavaria. This was in 1805, when Guinand was upwards of 
 sixty years of age. He continued at Benedictbeurn during nine 
 years, occupied solely in the manufacture of glass, to the great 
 increase of M. Frauenhofer’s reputation. 
 
 Being desirous, at the end of this time, to return to his native 
 land, a pension was granted to him by the establishment, on 
 condition that he should no longer employ himself in making 
 glass, nor disclose his process to any person whatever ; a con¬ 
 dition which did not long agree with the still active energies 
 of his mind. Believing that by new experiments he could raise 
 his discovery to a yet higher degree of improvement, he obtain¬ 
 ed the consent of M. Frauenhofer to cancel their subsisting 
 agreement; and relinquishing his pension, once again devoted 
 himself with ardor to his favorite pursuit. 
 
 M. Guinand lived for several years after this time (1816,) 
 and produced several telescopes of great magnitude, and re¬ 
 markable for their excellence; it being perhaps not the least 
 extraordinary among the circumstances attending them, that, 
 to use the words of the memoir, whence the foregoing account 
 is drawn, “ they have been constructed by an old man upwards 
 of seventy, who himself manufactures the flint and crown glass 
 which he uses in their construction, after having made with his 
 own hands the vitrifying furnace and his crucibles; who, with¬ 
 out any mathematical knowledge, devises a graphic method of 
 ascertaining the proportions of the curves that must be given 
 to the lenses, afterwards works and polishes them by means pe¬ 
 culiar to himself; and lastly, constructs all the parts of the dif¬ 
 ferent mountings, either with joints or on stands, melts and 
 turns the plates, solders the tubes, prepares the wood, and com¬ 
 pounds the varnish.” 
 
 Arrangements had been made by the French government 
 for purchasing his secret, when the artist, verging on his eigh¬ 
 tieth year, died, after a short illness. That secret did not, how¬ 
 ever, die with him, but is possessed by his son, who continues 
 to labor in the employment so singularly commenced, and so 
 successfully and energetically followed by his father. 
 
CHAP. XI. 
 
 M. GUINAND. 
 
 201 
 
 The name of Frauenhofer, which has been introduced in the 
 foregoing narrative, is one intimately connected with inquiries 
 in the art of making perfect glass. It would be wrong to leave 
 the reader under an impression that the merit of this artist was 
 limited to the single act of patronage extended towards Gui- 
 nand, and which, although indicative of his discernment as a 
 tradesman, would afford no reason for investing him with any 
 part of the extraordinary merit which truly belonged to his 
 character. 
 
 Like Guinand, his beginning in life was humble; being in¬ 
 debted solely to the powers of his own mind for the eminence 
 to which he attained. Having occupied the lowest station as an 
 ordinary workman in a great manufacturing establishment, he, 
 by the force of his transcendent talents, and in the course of a 
 few years, raised himself to the chief direction of its business. 
 During the intervals of labor he acquired a competent know¬ 
 ledge of mathematical science; and devoting himself to the per¬ 
 fection of the refracting telescope, proved that he possessed a 
 truly philosophical and scientific mind. Having soon mastered 
 the theoretical difficulties which presented themselves, he still, 
 however, found all his labors unavailing, through the imperfec¬ 
 tion of the material employed; and set himself to remedy this 
 evil, by a series of admirable experiments. 
 
 It might be thought invidious to inquire in what degree his 
 success in these was owing to the previous labors and assist¬ 
 ance of Guinand, or how far his discoveries were personal and 
 original. Both produced and left behind them specimens of 
 perfect glass in large pieces; but the public has equally in 
 either case to regret the want of knowledge as to the processes 
 employed for the attainment of an object so desirable. 
 
 Frauenhofer died in the year 1826, at an early age; a victim, 
 it is said, to unremitting attention bestowed upon an unhealthy 
 employment. Had his life been continued to the same length¬ 
 ened period as was allotted to his fellow-laborer, what might 
 not the world have expected from one, who so early had burst 
 tbe chains of ignorance, and overcome the paralyzing difficul¬ 
 ties of birth and adverse fortune; taking his station during 
 life among the genuine philosophers of the age, and falling, 
 admired, and lamented, and eulogized by the most scientific 
 societies of Europe ! 
 
 Tbe great value of flint glass, from which all perceptible 
 defects are absent, may be imagined from the sketch which 
 has here been given of the efforts made for its production. 
 Very high prices are, in fact, paid for object glasses of a satis¬ 
 factory quality, which are of any magnitude; while even small 
 fragments of such glass are sought after by opticians with 
 
GLASS MANUFACTURE. 
 
 CIIAP. XI. 
 
 202 
 
 great avidity. A few years ago the director of one of the 
 London glass-houses having made a pot of flint glass for optical 
 purposes, sold this, in the regular course of his business, to a 
 commission merchant, who transmitted it to his correspondent 
 on the Continent. Some months having elapsed thereafter, 
 during which time its possessor had ascertained the true value 
 of his purchase, the manufacturer was surprised at receiving 
 numerous inquiries on the subject of this lump of glass, on the 
 part of several English opticians. These were anxious to pro¬ 
 cure portions of a material, the fame of which had reached 
 them from abroad. Upon this, the maker instituted a search, 
 and having succeeded in identifying some fragments, as having 
 formed part of the same melting, was enabled to procure very 
 considerable prices for that upon which he had previously set 
 little or no value, and which had been preserved only through 
 accident. 
 
 On a yet more recent occasion, information having reached 
 London that a large and superior object glass was on sale in 
 the metropolis of a neighboring kingdom, one of our most cele¬ 
 brated astronomers hastened across the channel, and while 
 others were chaffering with its possessor about the price, our 
 countryman stept in, and paying at once the full amount de¬ 
 manded, brought off the prize, to the great mortification of his 
 competitors. 
 
 CHAP. xn. 
 
 ON THE SPECIFIC GRAVITY OF GLASS. 
 
 Importance of this duality.—Experiments of Loysel.—His Reasonings and 
 Formulae.—Specific weight augmented by Lime.—Mixed Glasses.—Their 
 Specific weight.—Method of Determining this.—Influence ofTemperature 
 on the Specific weight of Glass. 
 
 The specific gravity of glass is a quality of considerable im¬ 
 portance, when the material is required for conversion into the 
 object-glasses of achromatic telescopes, or for the composition 
 of counterfeit gems, although any very minute attention to this 
 point is not considered essential in conducting the commoner 
 processes of the glass-house. 
 
 Loysel, to whose justly esteemed work on the art of glass¬ 
 making allusion has been so frequently made in these pages, 
 went through a series of experiments upon the specific gravi¬ 
 ties of various vitreous bodies, with the view of giving such 
 instructions for the composition of the nicer qualities of glass, 
 
CHAP. XII. 
 
 SPECIFIC GRAVITY OF GLASS. 
 
 203 
 
 as should absolve manufacturers from the necessity of making 
 those preliminary trials upon every occasion, which are attended 
 by much inconvenient delay in the prosecution of extensive 
 operations. 
 
 Adopting the practical aim of this French author, some of 
 his ingenious formula; will be here given, together with a state* 
 rnent of the premises whereupon they w T ere founded. 
 
 The specific gravity of water being expressed by the num¬ 
 ber 100, that of sand is 263; while soda deprived of all car¬ 
 bonic acid by fusion in the furnace of a glass-house, is of the 
 specific weight 199, and the same substance, when brought 
 again by cooling to a concrete state, is not heavier than 222. 
 It might, therefore, be supposed that the specific weight of 
 glass, considered as a compound of sand and alkali, would be 
 diminished in proportion as its dose of silica was lessened and 
 that of its alkali was augmented. The contrary of this fact 
 results, however, from the combination of these two substances 
 through the agency of fire. 
 
 “ Sand,” says M. Loysel, “ contains, in addition to silica, 
 some other substance, the nature of which has not been investi¬ 
 gated, and which is sensibly disengaged from the silica by the 
 alkali, in the form of an elastic fluid, in the act of their com¬ 
 bination to form glass. 
 
 “We are ignorant of the degree wherein caloric adheres 
 more or less strongly to one or other of these substances; in 
 other words, their capacity for heat is not known; but, in 
 order to avoid errors, it will suffice, that we know the results 
 of several similar combinations. If we ascertain carefully the 
 doses of silica and alkali, which compose glasses formed of 
 these substances at different degrees of heat, together with 
 their various specific gravities, we perceive that the differences 
 between their doses of alkali are obviously proportional to the 
 differences of their weights. Knowing then how far these 
 proportions vary in respect of two descriptions of glass, we 
 have it in our power to compute, with respect to a third com¬ 
 position, either its quantity of alkali from its specific gravity, 
 or, on the other hand, its weight from its dose of alkali.” 
 
 From actual experiments made on different glasses, the fol¬ 
 lowing results have been obtained, the weight of water being 
 expressed by 100 :— 
 
 Glass, No. 1. contained 80 parts silica, 20 parts alkali, its specific gravity 236 
 No. 2 —— 54 — silica, 46 — alkali, its specific gravity 254 
 
 Difference 
 
 26 
 
 18 
 
 If it be then required to know what proportions of the same 
 materials must be used for the production of another glass, 
 
204 GLASS MANUFACTURE. CIIAr. XII. 
 
 No. 3., the specific gravity of which will be 242, the solution 
 of the question may be found by the following formulae:—As 
 the difference between the specific weights of the compounds 1. 
 and 2., which is 18, is to the difference between the weights 
 of 1. and 3., which is 6 : so is the difference between the doses 
 of alkali employed in Nos. L and 2., which is 26, to the differ¬ 
 ence between the doses of Nos. 1. and 3., and which difference 
 is thus found to be 9. Adding then this number to that which 
 represents the alkali of No. 1., we may conclude that the glass 
 of No. 3. must contain 29 parts of alkali and 71 parts of silica. 
 It has been proved by experiment that glass of the specific 
 gravity proposed, 242, is composed by the union of 70 of silica 
 with 30 of alkali. 
 
 When a manufacturer has thus two well-established results 
 to serve as general means of comparison, the simple ascertain¬ 
 ment of specific gravities will suffice for determining if any 
 variation lias taken place in the manufacture, as well as for 
 discovering, and in general remedying, its cause. 
 
 If any lime enters into its composition, as is the case with 
 glass of common quality, its weight is rapidly augmented, and 
 it is therefore useful to determine, from time to time, the 
 weight of the glass produced, comparing it with that of some 
 other sample which is known to have been well and carefully 
 made. If it is seen that the weight increases, it may be con¬ 
 cluded, either that a larger proportion than usual of lime is 
 present, or that the fire has not been sufficienty urged, and that 
 too large a proportion of alkali has been allowed to remain in 
 combination with the glass. 
 
 The rule already stated is said by M. Loysel to apply with 
 equal certainty to the heavy glasses composed of silica and 
 oxide of lead, the differences between the weights of various 
 specimens of flint-glass being also proportional to the differ¬ 
 ences in their quantities of metallic oxide :— 
 
 Glass, No. 1. composed of 27 sand 73 minium, has a specific gravity of 520 
 
 No. 2. -- 11 — 89 - - 657 
 
 Difference.16 137 
 
 From these data, the specific gravity of another composition, 
 No. 3.—made up of 20 parts sand and 80 parts minium, may 
 thus be ascertained :—As the difference between the quantities 
 of minium contained in Nos. 1. and 2. is to the difference be¬ 
 tween the proportional quantities of minium in Nos. 1. and 3.; ; 
 so is the difference between the weights of 1. and 2. to the 
 difference between the specific gravities of 1. and ?, and which 
 is thus found to amount to 59 ; which number, the quantity of 
 
CHAP. XII. SPECIFIC GRAVITY OF GLASS. 205 
 
 oxide being greater in No. 3., must be added to 520, the weight 
 of No. 1., and we thus have 579 as the weight of the proposed 
 composition. 
 
 In forming flint glass, it is proper, in addition to the sand 
 and minium above supposed, to employ alkaline substances; 
 and it is desirable that the manufacturer should have it in his 
 power to predict, within a trifling amount, the specific weight 
 of every compound that he may determine to employ. The 
 means to be employed by him for the attainment of this end 
 are founded on the following considerations:— 
 
 The manufacture of flint glass requires the employment of a 
 lower degree of heat than is necessary for the formation of 
 other descriptions, which do not contain an equal abundance 
 of fluxing materials for vitrifying the sand. The temperature 
 of the furnace is commonly such, that if glass be made in it 
 composed of silica and alkali in such proportions that the one 
 will saturate the other, it will usually contain about 75 parts 
 of silica, and 25 parts of alkali; and this glass will have a spe¬ 
 cific gravity of about 24. The same means of heating being 
 employed, 73 parts of minium will be saturated by 27 parts of 
 sand, producing glass the specific weight of which is 52. In 
 practice, it is, however, probable, that 75 parts of minium will 
 combine with 25 of sand, and the result will have the specific 
 gravity of 54. 
 
 On the other hand, if two glasses of different character, one 
 of which is composed of silica and alkali, and the other of silica 
 and lead, are melted together, the specific gravity of each being 
 known, the weight of the compound resulting from their union 
 will depart in only a very trifling degree from that which 
 would be given by calculation, according to the usual rules for 
 determining the specific gravities of alloys. The same result 
 will equally ensue, if, instead of thus previously forming two 
 different kinds of glass, the materials of which they should be 
 composed are themselves brought together for the purpose of 
 their original vitrification. 
 
 If, then, we consider the sand of the composition as divided 
 into two portions, one of which must necessarily combine with 
 the minium for its vitrification, while the other is required for 
 the saturation of the alkali—the surplus quantity, if any, of the 
 latter constituent being dissipated by heat during the process 
 of vitrification, the calculation necessary for determining the 
 weight of the compound will proceed according to the follow¬ 
 ing example:— 
 
 Let it be supposed that the manufacturer wishes to form flint 
 glass by the union of 100 parts of sand, 50 parts of minium, 
 and 40 of potash. These materials might be divided into the 
 
 S 
 
206 
 
 GLASS MANUFACTURE. 
 
 CHAP. XII. 
 
 following proportions for producing two very different descrip¬ 
 tions of glass:—Thus, the 50 parts of minium, which would 
 be reduced in the process of vitrification to 48 parts, would be 
 completely vitrified by the addition of 16 parts of sand ; the ab¬ 
 solute weight of glass thus formed would be 64, and its specific 
 weight (that of water being 10) would, as before stated, be 54. 
 The quantity of sand remaining (84 parts) might be combined 
 with the whole of the potash; but as, in the process of vitrifi¬ 
 cation, all the surplus quantity of the alkali would be dissi¬ 
 pated, glass would be formed containing 84 parts of sand and 28 
 of potash, having 112 as its absolute, and 24 as its specific 
 weight. If, then, the whole materials are placed together in 
 the crucible for their original vitrification, we shall have, after 
 the reduction of the minium by 2 parts, and the dissipation by 
 heat of 12 parts of potash, a glass, the absolute weight of 
 which is 176, and whereof we desire to know the specific 
 gravity. For ascertaining this, the specific weights of the two 
 kinds of glass that might be separately formed, must be multi¬ 
 plied into each other, and their sum again multiplied by the ab¬ 
 solute weight of both, in order to find a dividend. Proceeding, 
 then, with the absolute weights of the two descriptions of 
 glass which might be formed, and multiplying each separately 
 by the specific weight of the other, adding the two products 
 together, another sum will be obtained, by employing which as 
 a divisor, the quotient will be equal to the specific gravity of 
 the compound. 
 
 Thus, in the above example, the specific weights, 54 and 24, 
 of the two descriptions, being multiplied into each other, and 
 their sum multiplied by 176, the absolute weight of both, a 
 product will be obtained of 228,096 for the dividend. Multi¬ 
 plying, then, 64, the absolute weight of one glass, by 24, the 
 specific weight of the other; and again, 112, the absolute 
 weight of the remaining glass, by the remaining specific weight 
 54, we have two sums, 1536 and 6048, which, added together, 
 and employed as a divisor, gives, as its quotient, a very minute 
 fraction over 30, which is known to be the specific gravity of 
 glass composed of sand, minium, and potash, in the proportions 
 first stated. 
 
 With respect to heavy glasses, results are obtained by calcu¬ 
 lation, which are rather greater than the reality; a circum¬ 
 stance for which it is not difficult to account The great abun¬ 
 dance of oxide of lead used in their composition, attacks the 
 body of the crucible, so as partially to dissolve it; and being 
 thus provided with a somewhat larger proportion of the lighter 
 material, the weight of the compound will be necessarily and 
 proportionally diminished. This difference between the com- 
 
CHAP. XII. 
 
 SPECIFIC GRAVITY OF GLASS. 
 
 207 
 
 puted and the real weights will, of course, be greater, according 
 as the proportion of minium is augmented; its action upon the 
 crucible being, by such means, rendered more destructive. 
 
 Notwithstanding the degree of uncertainty thus occasioned, 
 it must still be useful to know how, by a very simple calcula¬ 
 tion, to make a near approximation to the truth, and thus, as 
 already said, to avoid the necessity of conducting long and un¬ 
 certain preliminary experiments. 
 
 The specific gravity of glass is influenced by the degree of 
 heat to which it has been exposed during its vitrification; be¬ 
 ing always least when the temperature has been greatest. The 
 cause of this variation is to be found in the different quantities 
 of alkali that have been dissipated, the silica appearing to de¬ 
 part from the completeness of its aggregation, in proportion as 
 it is deprived of alkali.* 
 
 Flint glass is not entitled to any drawback upon its exporta¬ 
 tion, unless its specific gravity be at least three times that of 
 water. The duty drawn back on the shipment of flint glass is 
 considerably greater than the rate originally paid on other de¬ 
 scriptions ; and but for the resort which is had to its gravity as 
 a test, those other descriptions might in many cases be substi¬ 
 tuted, and a considerable profit be thereby fraudulently obtain¬ 
 ed by the exporter at the expense of the revenue. 
 
 * The rule for ascertaining the mean specific gravity of different bodies 
 should never be relied on until verified by experiment. The condensation of 
 volume which some substances undergo when brought into combination 
 with others, is such as to render all calculations concerning them, under 
 such circumstances, vague and erroneous. From the experiments of M. 
 Loysel it would appear, however, that except in the case which he has no¬ 
 ticed, that of employing different degrees of heat, this condensation does not 
 occur with the various compositions of which glass is formed, and recourse 
 may therefore be had to the formula usually employed for ascertaining mean 
 specific gravities, when we desire to determine those of different vitreous 
 combinations. The rule is as follows: 
 
 The specific gravity of one body is to that of another, as the weight of 
 the first divided by its volume is to the weight of the second divided by its 
 volume ; and the mean specific gravity of the two is found by dividing the 
 sum of the weights by the sum of the volumes. 
 
 Let W, to, be the two weights; V, v, the two volumes; P, p , the two spe¬ 
 cific gravities ; and M, the calculated mean specific gravity. 
 
 W -\-W W id W p -f- w>P 
 
 Then, M = --; andV -{- v= -1-=-; hence 
 
 V + tJ P p P p 
 
 W -f w W -}- w (W -f- w) P p 
 
 - — - — -;- = M. 
 
 V-f» W p 4- w¥ Pto -(- pW 
 
208 
 
 GLA6S MANUFACTURE. 
 
 CHAP. XIII. 
 
 CHAP. Xffl. 
 
 ON THE ART OF COLORING GLASS. 
 
 Antiauity of this Art.—Specimens of Roman Mosaic.—Analysis of these 
 by Klaproth—Metallic Oxides.—Gold-Purple.—Its great Coloring Power. 
 —Kunckel.—His Proficiency in Coloring Glass.—Yellow Color—From Sil¬ 
 ver—From Lead—From Tartar—From Beechwood Charcoal—From Oxide 
 of Iron.—Green.—Black Glass.—Blue.—Directions found in old Authors. 
 —Imitation of the Garnet—Of the Amethyst—Of the Emerald—Of Sap¬ 
 phires.—Opaque Glasses—Black—White—Opal.—Ancient Pictures form¬ 
 ed of Colored Glass—How executed.—Description of Ancient Mosaics.— 
 More recent Prosecution of this Art.—Accidental Coloring of Plate Glass 
 at St. Gobain.—Ineffectual Attempts to reproduce this Effect. 
 
 It appears probable that the art of coloring 1 glass was disco¬ 
 vered and prosecuted at a period very little subsequent to that 
 of the manufacture of the article itself. The most ancient au¬ 
 thors who have mentioned the existence of the material, have 
 also recorded the fact of its being tinged with various colors, 
 in imitation of gems. Strabo, Seneca, and Pliny, all make 
 mention of this use, as being one to which glass was applied 
 by artists in very early times. 
 
 The fact has already been mentioned of colored figures hav¬ 
 ing been found with Egyptian mummies, and which are, there¬ 
 fore, known to have been in existence for upwards of 3000 
 years. These curious relics of ancient times have also been 
 discovered decorated with colored glass beads; and a mummy 
 thus ornamented is to be seen in the British Museum. 
 
 In the reign of Augustus, the Romans began the use of co¬ 
 lored glass in the composition of mosaic decorations. Several 
 specimens of this kind have been found at a late period, among 
 the ruins of a villa built by Tiberius in the island of Capri; 
 and some of these specimens having been subjected to analysis 
 by the accurate and ingenious Klaproth, it is known that in 
 that early time recourse was had to the same class of coloring 
 ingredients as is employed by the moderns. Some difference 
 must, indeed, have been observed in their processes, as the an¬ 
 cients were unacquainted with the use of the mineral acids, 
 which are now found to be so convenient in the preparation of 
 metallic oxides. 
 
 Klaproth has given the following as the result of his exami¬ 
 nation of some of the Roman specimens above mentioned:— 
 
 One which was a lively copper red, opaque, and very bright 
 where recently fractured, contained, in 200 grains,— 
 
CHAP. XIII. 
 
 COLORING OF GLASS. 
 
 209 
 
 SiJex.142 
 
 Oxide of lead. 28 
 
 copper. 15 
 
 iron. 2 
 
 A1 amine. 5 
 
 Lime. 3 
 
 195 
 
 Another, a light verdigris green, also opaque, with a splendent 
 fracture and scoriaceous, contained in a similar quantity,— 
 
 Silex.130 
 
 Oxide of copper. 20 
 
 lead. 15 
 
 iron. 7 
 
 Lime. 13 
 
 Alumine. 11 
 
 196 
 
 It is remarkable that the constituent ingredients of both these 
 specimens should prove to be the same. The difference be¬ 
 tween them exists only in their relative proportions; and the 
 colors depend upon the different degrees of oxidation off the 
 copper. Sub-oxide of copper,—that is, copper which has com¬ 
 bined with itself only half the quantity of oxygen required for 
 the production of the perfect oxide—produces a red enamel; 
 while that which has received its full proportion of oxygen 
 yields a green enamel color. 
 
 The specimen of ancient blue glass which was analyzed by 
 Klaproth contained,— 
 
 Silex.163 parts. 
 
 Oxide of iron. 19 
 
 copper.. 1 
 
 Alumine. 3 
 
 Lime. 0* 
 
 186* 
 
 It appears, therefore, to have been indebted to the oxide of iron 
 for its blue color, as no trace was detected of any other ingre¬ 
 dient to which this could be referred. Since the discovery of 
 the certain and commodious method of producing blue enamel 
 by means of cobalt, the art of obtaining this color from iron has 
 been lost. 
 
210 
 
 GLASS MANUFACTURE. 
 
 CHAP. XIII. 
 
 The causes which influence the employment of metallic ox¬ 
 ides for the embellishment of porcelain have been sufficiently 
 detailed in the preceding treatise. The same reasons also 
 oblige the artist to have recourse to the same class of sub¬ 
 stances for imparting colors to glass. The mode of application 
 of coloring materials to these two branches of manufacture dif¬ 
 fers, however, in this,—that while, in ornamenting porcelain, 
 they are applied superficially, in the manner of pigments, they 
 enter more intimately into the composition of glass, being 
 transfused through the whole mass, and equally incorporated 
 with its entire substance. 
 
 The preparation of metallic oxides as coloring materials is 
 nearly similar in all cases; it will not, therefore, be necessary 
 here to repeat directions, or to give many explanations upon 
 that head. 
 
 Gold, in a state of great division and oxidated, has long been 
 celebrated as a means for imparting to glass a most exquisite 
 purple-red color resembling the ruby, and nearly equalling that 
 gem in the richness of its hue. It is not by any means easy to 
 prepare glass of this color with any certainty of a successful 
 result. The great tendency which is shown by gold to assume 
 the reguline state, when exposed to excessive heat, to carbona¬ 
 ceous vapors, or to the action of hydrogen, renders necessary a 
 great degree of careful management in the various processes. 
 
 The manner has already been given of preparing the purple 
 precipitate of Cassius; the form wherein gold has been used 
 with so much celebrity in imparting red and purple colors. It 
 lias been very generally imagined, that the tin used in the pre¬ 
 paration of this precipitate is essential to the production of the 
 requisite color; an opinion which has been shown to be void of 
 foundation, as preparations of gold have been made without the 
 agency of tin, and which have equally possessed the power of 
 imparting the finest purple color to glass. The coloring proper¬ 
 ty of any of the simple oxides of gold is found to be mate¬ 
 rially greater than that of Cassius’s precipitate; which circum¬ 
 stance has been brought forward as another argument to prove 
 that the presence of tin is far from adding any thing to the 
 body of the color. It is probable, however, that, although not 
 indispensable, tin is yet useful, as enabling the gold to bear 
 without reduction a higher degree and a longer continuance of 
 heat. With this same object, it has been recommended to add 
 to the precipitate, before using it, a small quantity of nitre, by 
 which the gold will be preserved at its due degree of oxidation. 
 
 It is not essential that gold used for this preparation should 
 be absolutely pure or unalloyed; since neither copper nor sil- 
 
CHAP. XIII. COLORING OF GLASS. 211 
 
 ver, when present in small quantities, appears to alter or di¬ 
 minish its coloring power. 
 
 Fulminating gold, prepared by precipitating the metal from 
 its nitro-muriatic solution by means of ammonia, is also used in 
 coloring glass; but as this preparation would explode violently 
 when exposed to a heat even very much below that to which 
 it must be subjected in use, this explosive property must be 
 previously removed by mixing it with a fixed alkali, and re¬ 
 taining it for some time at a comparatively low temperature. 
 A more manageable preparation results from the precipitation 
 of the nitro-muriate of gold by means of carbonate of potash. 
 This is not fulminating, as it is from the presence of ammonia 
 that the explosive property is derived. 
 
 A very ingenious process has been used for producing an in¬ 
 timate union between the oxide of gold and silex. This con¬ 
 sists of adding to the solution of the metal in nitro-muriatic 
 acid, a proportion of silica dissolved in an alkaline lixivium, 
 and pouring therein any acid in sufficient quantity to saturate 
 the alkali. In this case, the silex and gold are precipitated in 
 very intimate combination; and if then washed with clear 
 water, dried, and mixed with nitre, borax, or any other suitable 
 fluxing substance, will be fit for use as a coloring material. 
 
 When the precipitate of Cassius is employed, about one 
 sixth part of its weight is added of perfect white oxide ot anti¬ 
 mony. This, from imparting a yellowish tinge, is considered 
 to be an important ingredient in fine ruby-colored glass. 
 
 The proper management of the heat employed in the pro¬ 
 duction of this much-admired preparation is a difficult acquire¬ 
 ment, known only to clever and experienced artists. II the 
 temperature be allowed to rise too high, the color will be much 
 injured, and probably even altogether destroyed. The contact 
 of every kind of smoke and vapor should also be carefully 
 avoided in the fusion of ruby-colored glass, which is said to be 
 apparently colorless when it leaves the crucible, and only to 
 put on its exquisite tint as it becomes cool. 
 
 Kunckel and other old w’riters upon the art of manufacturing 
 glass have stated, that the coloring powers of the purple pre¬ 
 cipitate of Cassius are so considerable, as that one part, if added 
 to one thousand parts of glass, will impart to the whole a full 
 and rich body of color. 
 
 The artist just mentioned, who was greatly celebrated for 
 his attainments in this ornamental branch of the art, was in 
 consequence ennobled by Charles XI. king of Sweden, and as¬ 
 sumed the name of Lowenstiern. He made artificial rubies, 
 which were highly esteemed, and which he sold, in the man¬ 
 ner of real gems, according to their weight, and at very consid- 
 
GLASS MANUFACTURE. 
 
 CHAP. XIII. 
 
 212 
 
 erable prices. The achievement upon which he most prided 
 himself! was the production of a cup of ruby glass, which was 
 of the thickness of an inch, and weighed twenty-four pounds: 
 this cup went into the possession of the elector of Cologne. 
 
 Kunckel directed, in 1679, the operations of the glass-houses 
 at Potsdam, where he met with the greatest encouragement, 
 and was liberally assisted in his researches by the elector of 
 Brandenburg, who expended the sum of 1600 ducats to assist 
 the efforts of the artist towards attaining perfection in the art 
 of making ruby glass. A cup, with a cover of this material, 
 which was made by him, and is still in existence at Berlin, 
 continues to be an object of much admiration. 
 
 Silver, in all its forms of oxidation, imparts a very pure and 
 beautiful yellow color to vitreous bodies; but this color is easi¬ 
 ly destroyed, through the accidental employment of too high a 
 degree of heat; an evil against the occurrence of which it is so 
 exceedingly difficult to provide, that silver is very seldom re¬ 
 sorted to as a coloring material by glass-workers. The incon¬ 
 venience here mentioned may in some degree be avoided 
 when oxides of silver are used in combination with alumirxe, as 
 in the ornamenting of porcelain; but this remedy is manifestly 
 inapplicable to glass. Other bodies can, however, be used with 
 the best effect in imparting a yellow color to this substance. 
 
 Oxide of lead employed alone, if in very considerable quanti¬ 
 ty, would give a very good yellow color; but as it would re¬ 
 quire that at least three fourths of the weight of the glass 
 should be made up of this oxide, in order to give sufficient in¬ 
 tensity to the color, it is very seldom used for the purpose. 
 Glass thus formed would be inconveniently soft, and from its 
 powerful fluxing quality would act injuriously upon the cruci¬ 
 bles in which it was made. 
 
 Chromate of lead, which is not liable to the objections just 
 mentioned, is on that account used preferably. Before the com¬ 
 paratively recent discoveries in chemical science had shown to 
 artists in what manner to procure this valuable coloring ingre¬ 
 dient with sufficient facility and at a moderate cost, the makers 
 of colored glass employed the oxides of lead, silver, and anti¬ 
 mony in combination, for the production of yellow colors; vary¬ 
 ing the proportions wherein each substance was used according 
 to the hue which it was desired to impart. 
 
 Colors varying in their shades from brown to a fine transpa¬ 
 rent yellow may be given to common glass by simply adding to 
 it, while in a state of perfect fusion, some vegetable carbonace¬ 
 ous matter. This must always be supplied in excess, since 
 part of it, rising to the top of the crucible, will be burnt away; 
 but some portion will also continue uniformly diffused through- 
 
CHAP. XIII. COLORING OF GLASS. 213 
 
 out the glass, and, without at all impairing its transparent qual¬ 
 ity, will give to it a very fine yellow. The substance which 
 most commonly has been employed for this purpose is tartar; 
 but almost any solid and inflammable vegetable matter will 
 probably answer equally well. Charcoal made from beechwood 
 is found to be altogether efficacious. The addition of a small 
 quantity of nitre is sometimes useful in clearing the color and 
 removing any cloudiness which it may have contracted; but if 
 great discretion be not shown in the addition of this substance, 
 the color will be altogether destroyed. During the time of its 
 preparation, the glass swells very much in the crucible, owing 
 to the escape of part of the carbonaceous matter in the form of 
 gas; and when tartar is employed, this effect is experienced in 
 an exaggerated degree. It is said that this effervescence might 
 be avoided, if freshly burnt and perfectly dried charcoal were 
 heated strongly in a close vessel, and added in that state to the 
 contents of the crucible. 
 
 The oxides of iron give many and very different shades of 
 enamel colors. It has already been mentioned, that the green 
 color of common bottle-glass is owing to the presence of iron 
 in the unpurified sea-sand and ashes of which it is composed. 
 An increased quantity of this oxide, if applied to glass when in 
 a state of perfect vitrification, will give a yellow color to the 
 mass. A still larger quantity will impart a brownish black hue, 
 which, however, appears to be nothing more than a yellow very 
 highly concentrated, as the latter color may be again produced 
 by simply diluting the contents of the crucible with an addi¬ 
 tional quantity of uncolored glass. 
 
 The red color which is imparted by the oxides of iron to por¬ 
 celain, is owing to its state of imperfect vitrification, whereby 
 the metal is held suspended in a state of minute division 
 throughout the mass, which same effect is indeed apparent in 
 the treatment of glass up to a certain point; but when in the 
 advancing stages of vitrification the heat is raised so that a per¬ 
 fect fusion of the glassy substance as well as of the oxide is 
 produced, the color is immediately converted to yellow. 
 
 The use of the black oxide of manganese in correcting the 
 impurities of the alkali employed in the original composition of 
 glass, as well as in removing the green tinge resulting from 
 the presence of iron in the sand, has already been explained. 
 Where these imperfections do not exist in the original ingre¬ 
 dients, if manganese be added to the glass, it will impart a pur¬ 
 plish red color. This oxide also forms a principal constituent 
 in the production of black glasses: it is most commonly used in 
 combination with nitre. If any portion of arsenical salts should 
 j be present in the glass, it is altogether useless to attempt the 
 
GLASS MANUFACTURE. 
 
 CHAP. XIII. 
 
 214 
 
 employment of manganese as a coloring ingredient, since its 
 efficacy would be wholly destroyed. 
 
 All the simple as well as the carbonated oxides of copper,; 
 when perfectly vitrified in conjunction with any kind of glass 
 or fluxing material, will yield a very fine green, and the chan¬ 
 ces of complete success in the attainment of this are greater 
 than attend the production of most other colors. It appears to; 
 be nearly a matter of indifference which of the combinations of 
 copper with oxygen are employed for the purpose. The pre¬ 
 parations most usually chosen are either the carbonated oxide 
 resulting from the addition of sulphate of copper to some car-j 
 bonated alkali, or that which is known as the as ustum, which 
 is copper oxidated and calcined simply by means of heat and 
 the access of air. 
 
 Copper may be made to yield a carmine red color, and if mix-! 
 ed with iron, a full deep red, by adding to the glass with which; 
 it has already been combined a quantity of tartar. This addi-j 
 tion must not be made until the glass is in a state of perfect fu-| 
 sion, and the mixture should be worked off without delay. Itj 
 should be mentioned that when used for the production of these 
 colors, the oxide of copper must be reduced to nearly the regu- 
 line state. If the heat is continued long after the tartar has 
 been added, the effect will be lost, and the green color re¬ 
 stored. 
 
 When the oxides of copper and iron are thus united for de¬ 
 veloping a full deep red color, the iron must be to the copper 
 in the proportion of three parts to one; and according as this 
 proportionate difference is lessened, so will the color be found 
 to approach to the carmine tint. 
 
 The time for stirring in the tartar should be chosen when 
 the melted glass appears of a faint greenish yellow ; the whole 
 mass will then immediately swell up prodigiously; and upon 
 again subsiding will appear, as before stated, of a clear red co¬ 
 lor, and fit for being immediately used. It is probable that char¬ 
 coal or other carbonaceous matters might be substituted for tar¬ 
 tar in this process with equal success. 
 
 Copper in a state of oxidation is often used when combiner 
 with the oxides of manganese and iron for the production of 
 black glass. 
 
 The protoxide of chromium may be used for producing r 
 green color in glass, with as much advantage as attends its em¬ 
 ployment in the embellishment of porcelain, that substance be¬ 
 ing capable of sustaining without injury the highest heat of the 
 crucible. Chrome is the natural coloring matter of the preciou: 
 emerald, and is found to be a very valuable substance in the 
 composition of artificial gems. 
 
CHAP. XIII. 
 
 COLORING OF GLASS. 
 
 215 
 
 Oxide of cobalt is universally employed for the production of 
 blue colors in vitrifiable bodies. The fine deep shade which it 
 imparts is unalterable by fire of any degree of intensity, and suc¬ 
 ceeds equally well with every different composition of glass. 
 
 This metallic oxide is also employed towards the composition 
 of other colors: combined with the oxides of lead and antimony, 
 it furnishes a green; and if mixed with those of manganese and 
 iron, produces a very fine black. 
 
 Neri, Kunckel, and Fontanieu have left in their writings 
 many recipes for the preparation of artificial gems through the 
 employment of different coloring materials. The directions, as 
 given in the works of these authors, differ so importantly the one 
 from the other as regards the proportions best fitted for the 
 composition of the same article, that we are forced to believe 
 either that some great errors have been committed on the part 
 of their subsequent editors, or that the writers themselves were 
 wanting in the kind and degree of knowledge to which they 
 pretended, and which were required to fit them for the task 
 they undertook. 
 
 . A few of these recipes, and such as appear most free from 
 this objection, may be here given. 
 
 The basis of each of these compositions is most frequently 
 either one of the colorless glasses or pastes described in Chap¬ 
 ter VII., or some other very similar vitreous compound; but it 
 sometimes happens that the constituent materials of the glass, 
 and the proportions wherein they are to be brought together, 
 are indicated as well as the coloring substances. 
 
 The following is recommended by Neri, as furnishing a very 
 excellent imitation of the garnet:—Rock crystal 2 ounces, min¬ 
 ium 6 ounces, manganese 16 grains, zaffre 2 grains. This must 
 be a very inconvenient composition, both on account of the ex¬ 
 ceeding softness of the glass, and the destructive effect it would 
 have upon the crucible during the time of its preparation. We 
 learn from the analysis of Berzelius, that the coloring matter 
 of the “ precious garnet,” that being the variety which it is 
 wished thus to imitate, consists of the black oxide of iron and 
 oxide of manganese. A more modern recipe than the fore¬ 
 going for the successful imitation of this gem, consists of purest 
 white glass 2 ounces, glass of antimony 1 ounce, Cassius’s pre¬ 
 cipitate 1 grain, oxide of manganese 1 grain; which composi¬ 
 tion is free from the objections to which that of Neri is so justly 
 exposed. 
 
 The directions of Fontanieu for imitating the color of the 
 amethyst are, that to 24 ounces of the glass composed according 
 to instructions given in Chap. VII. under the number 5, are to 
 be added half an ounce of the oxide of manganese, 4 grains of 
 
216 
 
 MANUFACTURE OF GLASS. 
 
 CHAP. XIII. 
 
 the purple precipitate of gold, and l|oz. of nitre, but it is im¬ 
 possible to believe that the recipe of Fontanieu has been cor¬ 
 rectly given. The quantity of coloring matter here indicated 
 would be better proportioned to 24 pounds of glass, than to the 
 same number of ounces as directed. 
 
 Many, and greatly varying instructions have been given for 
 imitating the emerald. Fontanieu recommends 160 parts of 
 any glass basis which contains a large proportion of lead, 4 parts 
 of oxide of copper prepared by simple calcination, and y 8 th of a 
 part of any oxide of iron; which last ingredient is added for 
 the purpose of giving something like a richness of tint, and for 
 correcting the coldness of hue that would result from the em¬ 
 ployment of the oxide of copper alone. The presence of lead in 
 the glass would also conduce to the same end. 
 
 Another rule given from the same authority directs the use 
 of 576 parts of glass, similarly constituted to that pointed out in 
 the last receipt, 6 parts of the same oxide of copper, and only 
 jijth of a part of oxide of iron; thus differing from the former 
 compound, only as to the proportions wherein the coloring in¬ 
 gredients are employed. 
 
 A third receipt for the attainment of the same object is very 
 different from the two preceding. It recommends the employ¬ 
 ment of 200 parts of fine sand, 400 parts of minium, 8 of cal¬ 
 cined verdigris, and as much as 1 part of oxide of iron. A fourth 
 method for the composition of glass of an emerald green is, to 
 mix, in due proportions, some blue glass colored by means 
 of oxide of cobalt, with yellow glass prepared with oxide of an¬ 
 timony. A great many other prescriptions are offered for the 
 imitations of emeralds, but these vary more in the relative pro¬ 
 portions of their ingredients than in the principle of their com¬ 
 position ; and it cannot, therefore, be necessary to insert them 
 here. 
 
 The imitation of sapphires is always effected through the 
 coloring agency of the oxides of cobalt and manganese. There 
 is, however, a material difference as regards tire basis of the 
 glass in the various directions which are found for the purpose; 
 one recommending that this shall be composed without lead, 
 and another directing that this mineral shall enter largely into 
 the composition of the paste. To 100 parts of glass of the first 
 kind it is directed that 1 part of zaffre, and y^th of a part of ox¬ 
 ide of manganese, shall be added. Where the second descrip¬ 
 tion of paste is recommended as the basis, the artist is directed 
 to prepare this by adding to 240 parts of glass frit made with 
 only soda and silica, 192 parts of minium, 2 of zaffre, and jd of 
 a part of manganese. This compound must be fused together, 
 
CHAP. XIII. COLORING OF GLASS. 217 
 
 poured into water, and then remelted as directed by Fontanieu, 
 for the formation of the pastes described in Chapter VII. 
 
 The oxide of cobalt is, in the present day, a necessary ingre¬ 
 dient in every imitation of the sapphire, so that it is never at¬ 
 tempted to act without it. We have seen, however, that a 
 very fine blue glass was formerly made having the oxide of iron 
 for its coloring ingredient, and as it is known that the coloring 
 property of real gems having that hue, resides in this metal 
 when in some particular state of oxidation, we must own to 
 having lost, in this respect, one means of imitating nature which 
 was known and exercised by our predecessors. 
 
 The colored glasses comprised in the foregoing descriptions, 
 are all translucent. The preparation of others, which have the 
 opposite quality of opacity, is effected either by means of apply¬ 
 ing excessive doses of the same metallic oxides which, in small¬ 
 er quantities, are used for imparting colors; or by the addition 
 to those oxides of some other substance which has the property 
 of obstructing the rays of light in their passage through the 
 glass. 
 
 In general, the first method is used only for the production 
 of black glass, while the second plan is pursued with all other 
 descriptions, as well those which are designed to retain a per¬ 
 manent white color, as with yellow, blue, green, or any other 
 colored opaque glasses. 
 
 The most approved method of preparing black glass, of good 
 quality, which shall be of a full deep black and perfectly opaque, 
 is by mixing together equal parts of black oxide of manganese, 
 zaffre, and protoxide of iron ; adding one part of this mixture to 
 fifteen or twenty parts of colorless transparent glass, and fusing 
 the whole together. 
 
 Some large and beautiful slabs of perfectly black glass have 
 lately been imported into London from St. Petersburgh, and ap¬ 
 pear well fitted to be used as substitutes for marble in the con¬ 
 struction of certain articles of household furniture. 
 
 White opaque glass, which has this quality imparted to it by 
 means of the oxide of tin, is called enamel; and it is this sub¬ 
 stance of which the dial-plates of watches and of table clocks 
 are commonly made. This compound is, however, too expen¬ 
 sive for more ordinary uses, and a very good white glass is made 
 for such purposes by substituting for the oxide of tin, a consid¬ 
 erable proportion of phosphate of lime in the state of a very fine 
 powder. This substance is procurable in great abundance, and 
 at a moderate cost, in almost every situation. Phosphate of lime 
 is extremely infusible, so that the opaqueness of the glass with 
 which it is united, arises from its holding in intimate mixture 
 an unvitrescible earthy salt. 
 
218 
 
 GLASS MANUFACTURE. 
 
 CHAT. XIII. 
 
 One receipt given by Neri for producing white opaque glass 
 is as follows:—Mix together 60 parts of fine white sand, and 40 
 parts of potash, with 10 of finely pounded bone-ash, and melt 
 the compound during the same length of time as is usually em¬ 
 ployed in ordinary glass-making. It is said that this glass is 
 transparent for as long as it continues at a full red heat; and 
 that, as it gradually cools, it first puts on a milky appearance, 
 and afterwards becomes wholly opaque. If this change does in 
 reality take place, and is not rather the result of a deception 
 which prevents the proper distinguishing of its degree of opacity 
 while red-hot, it may probably arise from the circumstance that 
 the excessive heat of the melted glass enables it to take up a 
 greater quantity—in other words—to supersaturate itself with 
 the phosphate of lime, which it parts with again in cooling. 
 
 Another receipt of the same artist is 130 parts of calcined 
 flint or fine sand, 70 parts of nitre, 12 of borax, 12 of tartrate of 
 potash, 5 of arsenic, and 15 of bone-ash. 
 
 Fontanieu has given directions for imitating the peculiar 
 lustre of the semi-transparent opal, by mixing 576 parts of his 
 glass No. 3. (Chap. VII.,) with 10 parts of muriate of silver, 2 
 parts of magnetic iron ore, and 26 parts of bone-ash. The 
 beautiful play of colors exhibited by the “ precious opal ” is de¬ 
 servedly an object of much admiration, and it has always been 
 a subject of interest to imitate successfully so pleasing an effect 
 Ornamental pieces of opal glass have usually been obtained 
 from France; but their production, of a quality fully equal to 
 these importations, may now be witnessed in the London glass¬ 
 works. 
 
 The peculiar delicacy and beauty of this glass do not appear 
 while it remains in a. state of fusion or at a red heat, and are 
 not fully developed until it is sufficiently cooled to have acquir¬ 
 ed its quality of brittleness. 
 
 Other colored glasses which are opaque, are made by the 
 same processes as are followed with transparent glasses of the 
 like colors, substituting for the common vitreous base, one of the 
 above described, opaque-white glasses. 
 
 The ancients employed methods of converting colored glasses 
 into representations of natural objects, which were extremely 
 beautiful, and the manner of producing which is now lost. The 
 existence even of this art is only known in these modern days 
 from specimens which have been accidentally discovered ; and 
 our knowledge of the peculiar nature of their formation is 
 wholly derived from the examination to which these specimens 
 have been subjected. 
 
 The first mention made of these works of art is to be found 
 
CHAP. XIII. 
 
 COLORING OF GLASS. 
 
 219 
 
 in the Collection of Antiquities,” by count Caylus, who de¬ 
 scribed them as composed of delicate different-colored fibres of 
 glass joined with the greatest nicety, and conglutinated into a 
 compact homogeneous mass by fusion. Winkelmann, in his 
 “ Annotations on the History of the Arts among the Ancients,” 
 describes these same specimens as pictures made of glass tubes, 
 and introduces them to further observation by these words:— 
 “ The works of the ancients in glass which are not noticed in 
 the history of the arts, deserve particularly to be mentioned in 
 this place, more especially because the ancients carried the art 
 of working in glass to a much higher degree than we have ar¬ 
 rived at; a fact which, to those who have not seen their works 
 of this kind, might have the appearance of a groundless asser¬ 
 tion.” 
 
 The author just quoted particularly describes two small 
 pieces of glass thus constructed which were brought to Rome 
 in the year 1765, and which, indeed, appear to have been well 
 deserving of his careful examination, as confirming the opinion 
 he had given respecting the superior proficiency of the an¬ 
 cients. The account of these curiosities cannot be better given 
 than in Winkelmann’s own words:—“Each of them is not 
 quite one inch long, and one third of an inch broad. One plate 
 exhibits, on a dark ground of variegated colors, a bird repre¬ 
 senting a duck of various very lively colors, more suitable to 
 the Chinese arbitrary taste, than adapted to show the true tints 
 of nature. The outlines are well decided and sharp; the colors 
 beautiful and pure, and have a very striking and brilliant effect, 
 because the artist, according to the nature of the parts, has in 
 some employed an opaque and in others a transparent glass. 
 The most delicate pencil of the miniature painter could not 
 have traced more accurately and distinctly either the circle of 
 the pupil of the eye, or the apparently scaly feathers on the 
 breast and wings, behind the beginning of which this piece had 
 been broken. But the admiration of the beholder is at the high¬ 
 est pitch when, by turning the glass, he sees the same bird on 
 the reverse, without perceiving any difference in the smallest 
 points; whence we could not but conclude that this picture is 
 continued through the whole thickness of the specimen, and 
 that if the glass were cut transversely, the same picture of the 
 duck would be found repeated in the several slabs; a conclu¬ 
 sion which was still further confirmed by the transparent places 
 of some beautiful colors upon the eye and breast that were ob¬ 
 served. The painting has on both sides a granular appearance, 
 and seems to have been formed in the manner of mosaic works, 
 of single pieces, but so accurately united, that a powerful mag¬ 
 nifying-glass was unable to discover any junctures. This cir- 
 
220 
 
 GLASS MANUFACTURE. 
 
 CHAP. XIII. 
 
 cumstance, and the continuation of the picture throughout the 
 whole substance, rendered it extremely difficult to form any 
 direct notion of the process or manner of forming such a work ; 
 and the conception of it might have long continued enigmatical, 
 were it not that, in the section of the fracture mentioned, lines 
 are observable of the same colors which appear on the upper 
 surface that pervade the whole mass from one side to the other; 
 whence it became a rational conclusion, that this- kind of paint¬ 
 ing must have been executed by joining variously colored fila¬ 
 ments of glass, and subsequently fusing the same into one co¬ 
 herent body. The other specimen is of almost the same size, 
 and made in the same manner. It exhibits ornamental draw¬ 
 ings of green, white, and yellow colors, which are traced on a 
 blue ground, and represent volutes, beads, and flowers, resting 
 on pyramidally converging lines. All these are very distinct 
 and separate, but so extremely small, that even a keen eye 
 finds it difficult to perceive the subtle endings; those, in par¬ 
 ticular, in which the volutes terminate ; notwithstanding which, 
 these ornaments pass uninterruptedly through the whole thick¬ 
 ness of the piece.” 
 
 Klaproth, who had in his possession some specimens of these 
 antique compositions in colored glass, compiled a paper upon the 
 subject, which was read before the Royal Academy of Sciences 
 at Berlin, in October, 1798; and the collection of antiquities 
 formed by Mr. Townley, comprised a ring which contained a 
 singular antique glass paste, which represented a bird of so 
 small a delineation, as not to be distinctly visible without the 
 aid of a magnifying lens, and which yet had every appearance 
 of having been produced in the manner described by Winkel- 
 mann. Numerous antique specimens, similarly composed, are 
 deposited in the British Museum. They are for the most part 
 fragments, and it is to be regretted that we are without any 
 records of their origin. 
 
 Keysler, the account of whose travels to different parts of 
 Europe in the early part of the last century contains a great 
 variety of entertaining and instructive matter, has given the 
 following description of a mode of composing pictures in col¬ 
 ored glass, which was at that time employed in decorating some 
 of the churches in Rome. It will be seen that the methcxl pur¬ 
 sued by the Roman artists in some respects resembled that used 
 for the composition of antique pastes, as described by Winkel- 
 mann. Recourse appears to have been had to this mode of pro¬ 
 ducing pictures, in cases where the original paintings on wood 
 or canvas were perishing through the dampness of the walls, 
 and where it was wished to supply their places with copies 
 composed of an imperishable substance. 
 
CHAP. XIII. ROMAN MOSAICS. 221 
 
 “ The materials used are little pieces of glass, of all the dif¬ 
 ferent shades in every tint or color like those of the fine Eng¬ 
 lish worsted used in needle-work. The glass is first cast into 
 thin cakes, which are afterwards cut into long pieces of differ¬ 
 ent thickness. Many of the pieces used in the works on roofs 
 and ceilings, which are, consequently, seen only at a great dis¬ 
 tance, appear to be a finger’s breadth; but the finer works con¬ 
 sist only of glass pins, if I may call them so, not thicker than 
 a common sewing-needle, so that a prtrait of four feet square 
 shall take up two millions of such pins or studs. These are so 
 closely joined together, that, after the piece is polished, it can 
 hardly be discerned to be glass, but rather looks like a picture 
 painted with the finest colors. The ground on which these 
 vitreous pieces are inlaid is a paste compounded of calcined 
 marble, fine sand, gum tragacanth, white of eggs, and oil: it is 
 at first so soft that the pieces are easily inserted, and upon any 
 oversight may be taken out again, and the paste new moulded 
 for the admission of other pins; but by degrees it grows as hard 
 as a stone, so that no impression can be made on the work. 
 
 “ This paste is spread within a wooden frame, which for the 
 larger pieces must not be less than a foot in breadth and thick¬ 
 ness. A piece of about eighty square feet, if performed with 
 tolerable care and delicacy, will employ eight artists for two 
 years. 
 
 “ The pins of the several colors lie ready before the artists 
 in cases, as the letters are laid before the compositors in a 
 printing-house; and such is their accuracy in imitating the 
 finest strokes of the pencil, that the only apparent difference 
 betwixt the original painting and such a copy is, that the latter 
 has a much finer lustre, and the colors are more vivid.” 
 
 An accident occurred many years ago in the plate-glass 
 works at St. Gobain, which seemed to offer the means of ob¬ 
 taining a bright red color for glass by the employment of cop¬ 
 per, at a much less expense than has hitherto attended the pro¬ 
 duction of that tint from gold. 
 
 It will be remembered that, in the manufacture of plate 
 glass, when the refining is completed, and it is wished to trans¬ 
 fer a portion of its contents from the melting-pot to the cu¬ 
 vette, a copper ladle is employed. It is necessary, while using 
 this implement, to dip it occasionally into water, lest it should 
 become too hot and warp, or possibly melt. On the occasion 
 referred to, the workman having omitted this necessary pre¬ 
 caution, the last of these misfortunes ensued ; dipping the 
 heated ladle once too often in the melted glass, only part was 
 brought out attached to its iron handle. 
 
 It was imagined that the copper thus melted would sink, by 
 
 T 2 
 
222 
 
 GLASS MANUFACTURE. 
 
 CHAP. XIII. 
 
 reason of its greater gravity, to the bottom, and would be found 
 there in the metallic state on the emptying of the pot The 
 casting and annealing of the plates were proceeded with ac¬ 
 cordingly ; and, on their completion, the workmen were sur¬ 
 prised to find that not only were grains of metallic copper em¬ 
 bedded in the substance of the glass, but bands uniformly col¬ 
 ored of a fine bright red were distributed throughout the plates. 
 
 The color must, in this case, have been produced by the cop¬ 
 per, which was suddenly carried to the degree of oxidation 
 necessary for its development. M. Guyton-Morveau, when in¬ 
 formed of this circumstance, was desirous of ascertaining, by 
 direct experiment, what means would be most efficacious in 
 producing the same effect. The result of his endeavors has 
 been published.* 
 
 The first attempt was made -with plate glass. In order to 
 bring the glass and copper into more intimate union, the first 
 was reduced to powder, and the other was used in the form of 
 filings. The metal was used in the proportion of 3 parts to 
 100 parts of glass: this mixture was brought to a state of com¬ 
 plete fusion before the glass was poured out. No success at¬ 
 tended this experiment, the glass appearing uncolored, and the 
 copper remaining mixed with it mechanically in the form of 
 metallic globules. 
 
 The next trial was made with common white glass, mixed 
 with twice the proportional weight of copper filings that had 
 been employed in the first experiment. The compound having 
 been completely melted, was found to have assumed a red color, 
 which was uniformly diffused throughout the mass; but this 
 color was so deep as to render the glass nearly opaque. 
 
 A trial made with copper, already in the form of an oxide, 
 imparted a greenish color to the glass. 
 
 It is impossible not to remark that the circumstances under 
 which these experiments were conducted, as detailed by M. 
 Guyton-Morveau, differ in some essential particulars from those 
 which accompanied the accident by which they were suggested. 
 In that case, the glass was already in the state of fusion, and 
 probably also in a high state of incandescence, before the addi¬ 
 tion of the copper. The proportion of metal used in the second 
 experiment was evidently excessive; and it is surprising that 
 t he effect produced did not lead M. Guyton-Morveau to try the 
 effect of a smaller proportion. 
 
 Attempts have been made to color glass by subjecting it to 
 the action of heat, while surrounded by some cementing sub¬ 
 stances already impregnated with metallic oxides as coloring in- 
 
 * An. de Chim. vol. lxxiii. p. 132. 
 
CHAP. XIII. 
 
 COLORING OF GLASS. 
 
 223 
 
 gredients. In most of these cases the glass remained perfectly 
 colorless, unless the heat had been carried sufficiently far to in¬ 
 duce devitrification; which state, as it renders the material 
 opaque, furnishes sufficient objection to the use of this method 
 of coloring. Even in those cases where transparency is not re¬ 
 quired, the same effect can be attained by easier means, and 
 free from a very serious inconvenience, that of the adhesion 
 of the cementing substance to the glass. Some curious facts 
 connected with this subject will be detailed in the concluding 
 chapter of this volume, which treats of the devitrification of 
 glass. 
 
 CHAP. XIV. 
 
 ON THE ART OF STAINING AND PAINTING GLASS. 
 
 This Art more recent than that of Coloring.—Encouraged by the Monks.— 
 Early Specimen at St. Denis.—Art never much cultivated in England.— 
 Splendid Paintings at Gouda.—Directions given by old Authors for com¬ 
 posing Colors.—Fluxes.—Vehicles for diluting Colors.—Description of va¬ 
 rious Stains.—Method of floating these.—Of painting on Glass.—Imitation 
 of ground Glass with transparent Patterns.—Description of Kiln employed. 
 —Method of firing.—Second and third firing.—Ancient method of fixing 
 different colored Glasses on each other. 
 
 The invention of the art of painting on and staining glass, 
 although probably recent as compared with that of coloring the 
 body of the metal when in fusion, is yet known to have existed 
 for many centuries. 
 
 The exact period of its adoption is, indeed, involved in much 
 obscurity ; and it can, at best, be regarded as only a reasonable 
 conjecture, which assigns its principal excellence, if not its ori¬ 
 gin, to the fostering care of those religious communities which, 
 upon the breaking up of the great western empire of Rome, 
 became, and for so long a period thereafter continued, the sole 
 depositaries of learning and the arts in Europe. 
 
 Endowed by the piety or superstition of their unenlightened 
 followers with revenues far beyond their personal wants, the 
 clergy of that time expended a portion of their superfluous wealth 
 in the construction of those splendid temples which attest to the 
 present day the architectural skill and genius of their founders, 
 remaining unsurpassed and almost unrivalled in their kind as 
 objects of admiration through a great portion of Europe. The 
 ministers of a religion which addressed itself to the imagina¬ 
 tions and the feelings of its votaries, thdy could not, perhaps, 
 have adopted more effectual means for obtaining and perpetu¬ 
 ating their influence over the multitude. Some idea of the ex- 
 
224 
 
 GLASS MANUFACTURE. 
 
 CHAIN XIV. 
 
 tent to which these means must have operated may be formed 
 by every one who recalls to mind the sensations of solemnity 
 amounting to awe wherewith he has himself been struck as he 
 has stood beneath the lofty sculptured arches of a cathedral, or 
 walked through its lengthened aisles, radiant with tints glow¬ 
 ing through emblazoned windows. 
 
 The earliest specimens of these embellishments differ from 
 those of more recent date in having been formed of small pieces 
 of glass colored throughout during the process of its original 
 manufacture, and which, to distinguish it from glass colored or 
 stained by the methods that will be hereafter described, has 
 been called by artists pot metal. Pieces of this, cut to the shapes 
 required, were joined together in the manner of mosaic by the 
 interposition of lead, in a way which has since fallen greatly 
 into disuse; the method of staining and burning in metallic 
 colors on the surface of the glass having been found far more 
 beautiful, admitting of greater variety of tints, as well as of 
 those delicate shadings which were manifestly unattainable by 
 even the most laborious composition in mosaic work. 
 
 Perhaps the oldest existing specimen of this later-discovered 
 art of painting on glass is to be seen on the windows of the ab¬ 
 bey of St. Denis, whereon were recorded, in 1194, various 
 events which occurred during the first crusade. 
 
 This art has never flourished to any great degree in England, 
 where at no time have men of genius been much encouraged to 
 apply their talents to its advancement: many among the most 
 admired specimens of painted glass which ornament our re¬ 
 ligious edifices, are the productions of foreign artists. 
 
 The great church at Gouda, in Holland, is splendidly embel¬ 
 lished with painted windows, which, about the year 1555, were 
 executed by various artists, the most celebrated among whom 
 were Dirk and Walter Crabeth. The one among the windows 
 which is the most highly esteemed was painted by the first 
 mentioned of these two brothers; and Mr. Hollis mentions, as 
 evidence of the value placed upon this work of art, that for the 
 lower part of this window,—about twenty feet square,—Mr. 
 Trevor, some time English resident at the Hague, had in vain 
 offered to give a solid plate of gold of the same surface, and of 
 the thickness of three Dutch guilders. 
 
 This particular division of the fine arts differs from other 
 branches in containing within itself fewer incentives to its pros¬ 
 ecution. Its practice is accompanied by various laborious and 
 differing processes. The range of subjects which it admits is 
 far more circumscribed, and the opportunities which it offers for 
 the display of excellence are far less frequent. The artist is 
 even without the gratification of witnessing the satisfactory 
 
CHAP. XIV. STAINING AND PAINTING GLASS. 225 
 
 progress of his own work, the appearance of which is compara¬ 
 tively dull and uninteresting until after it has passed from his 
 own hands into those of “ red Lemnos’ artisan.” The sculptor 
 and the painter in oil colors can seldom fail in procuring means 
 for exhibiting their works; so that, according to the degree of 
 talent evinced by them will generally be their encouragement 
 and reward; while the man who has conquered every disad¬ 
 vantage attending the processes of staining glass, and who may 
 have produced a piece, the conception and execution of which 
 are alike honorable to his genius and assiduity, might look in 
 vain for the opportunity of bringing its merits before the world. 
 These works have, therefore, seldom if ever been undertaken, 
 unless at the requirement of others, who, dictating both the 
 subject and its details according to their own peculiar tastes 
 and wishes, leave nothing wherein the superior talents of the 
 artist can be displayed, save the correctness of drawing and the 
 elaborateness of execution. A man of genius will not consent 
 to be thus trammelled, or follow, for the attainment of a precari¬ 
 ous recompense, one profession, when, by bringing to the exer¬ 
 cise of another the same amount of talent, and far less labor, he 
 may at once give scope to his conceptions and advance his 
 worldly interests. 
 
 A much wider field than presents itself for the exercise of 
 this art in England, is certainly offered in Catholic countries, 
 where not only is it more in accordance with the feelings of 
 the people to ornament their religious edifices, but where a 
 much freer scope is given to the artist in the choice of subjects 
 for embellishment. Popular legends of the saints in honor of 
 whom their churches are named, which are shut out by our 
 simpler form of worship and severer religious discipline, afford 
 a never-failing source whence these subjects may be drawn; 
 while he whcTlabors for the adornment of a Protestant church, 
 is restricted to subjects founded upon mere scriptural authority. 
 England has, indeed, within the last half century, produced 
 some few proficients in this art, whose productions would do 
 honor to any country : but the encouragement extended towards 
 these talented individuals has been too limited to raise up, as in 
 other pursuits, a succession of masters; while some, by whom 
 it has at first been embraced, have been allured from it by the 
 more general and liberal patronage accorded to the professors 
 of oil painting. 
 
 Staining and painting on glass differ in some respects from 
 all other styles of pictorial embellishment. They agree, how¬ 
 ever, generally with the processes used in painting porcelain, 
 not only in the nature of the substances to be embellished, and 
 in the materials whence the colors are derived, but likewise for 
 
226 
 
 GLASS MANUFACTURE. 
 
 CHAP. XIV. 
 
 the most part in the methods used for the application of those 
 colors, and in the necessity which exists for fixing them by ex¬ 
 posure to a high degree of heat. The art is, indeed, in most 
 particulars, so extremely analagous to the methods employed 
 for painting porcelain, and which have already been treated of 
 in this volume, that it will not be necessary to occupy much 
 space in its description. 
 
 The colors are drawn from the same class of natural sub¬ 
 stances as afford enamel colors; they are prepared, and for the 
 most part are applied, in the same manner; while any difference 
 which may be found to exist in the mode of fixing and bringing 
 out the effect of colors by the aid of fire, are more referrible to 
 the varied forms of the articles than to any actual difference 
 observable between the habitudes of glass and porcelain. 
 
 Boyle, in one of his letters on the subject of imbuing glass 
 with metallic colors, wherein are detailed some experiments 
 which he himself made in order to obtain a ruby color, relates 
 also an anecdote of an artist, who wished, for some purpose, to 
 prepare an amalgam of gold and mercury. With this view he 
 kept the two metals for some time together in a state of fusion 
 in a glass retort, when this at length burst with a tremendous 
 explosion. Mr. Boyle adds, that he saw some of the fragments, 
 and he declares them to be of the finest ruby color he ever be¬ 
 held. 
 
 Many directions are to be found in the works of old writers 
 for the composition of stains and colors. Some of these agree 
 very closely with recipes in use at present, while others are 
 evidently incorrect or incomplete ; it being impossible, by fol¬ 
 lowing them, to obtain the colors which they are said to fur¬ 
 nish. There appears to have always existed a spirit of exclu¬ 
 sion on the part of professors of this art; and it has been said 
 that this jealousy has even weighed with those among them 
 who have written on the subject, so far as purposely to give 
 false directions, that students might be deterred from the fur¬ 
 ther prosecution of their attempts. It is more charitable, and 
 at the same time more consonant with probability, to imagine, 
 that the errors which abound in these works are owing rather 
 to the carelessness of transcribers and editors, than to wilful 
 misstatements on the part of the authors. Let this be as it may, 
 it still is certain that until the period when M. Brongniart pub¬ 
 lished the results of his experiments and practice in regard to 
 enamel colors, the public was not in possession of any informa¬ 
 tion whereon reliance could safely be placed for their produc¬ 
 tion. 
 
 Various compositions are recommended to be used with the 
 colors as fluxes, in order to promote their fusion when exposed 
 
CHAP. XIV. STAINING AND PAINTING GLASS. 22? 
 
 to the heat of the furnace: these compositions are termed hard 
 or soft fluxes, in proportion as they require a greater or less 
 amount of heat for their perfect fusion, and for the production 
 of their full effect upon the metallic oxides with which they are 
 joined. In choosing between them, regard must be had to the 
 peculiar nature of the individual substance or compound where¬ 
 with they are combined, that the flowing of all in fusion may 
 take place as nearly as possible together. With this view, it is 
 evident that a waste both of time and labor would be experi¬ 
 enced, if any hard flux were used with an oxide which could 
 be brought to melt at a low heat; and, on the other hand, that 
 it would be still more improper to use a soft flux with oxides 
 which are more refractory, seeing that the proper incorporation 
 of the two substances could not possibly in that case be occa¬ 
 sioned. 
 
 Oxide of lead forms a principal ingredient in many fluxes. 
 It is necessary, however, to be sparing in its use where it is re¬ 
 quired to produce pink colors, as these would be injuriously 
 acted upon by any excessive quantity of lead. Its place may in 
 such case be advantageously supplied by borax. 
 
 A fluxing compound, very generally used, is made by the 
 union of thirty-two parts of flint glass with twelve parts of 
 pearl-ash, and two parts of borax; which composition will fuse 
 at a medium heat. If it should be required to render this more 
 fusible, such an effect may be gained either by substituting for 
 the pearl-ash four parts of red oxide of lead, or by increasing 
 proportionally the dose of borax; and if, on the other hand, it is 
 desired to produce a hard flux, this end may be attained by 
 omitting the borax altogether, and adding an equal quantity of 
 common table salt. 
 
 The directions for the preparation of fluxes for porcelain, 
 which will be found in another part of this volume, apply equal¬ 
 ly to those which are to be used with glass, and it would be 
 therefore useless to repeat them here. 
 
 When enamel colors are applied to glass, they are, besides 
 their union with a fluxing material, mixed in the same manner 
 as for painting on porcelain, with some substance as a vehicle 
 for causing them to flow readily from the brush, and at the same 
 time to prevent the colors from blending themselves one with 
 the other during the operation. Oil of lavender, balsam of 
 capivi, oil of turpentine or of amber, or sometimes gum-water, 
 are employed as this vehicle. The choice of any particular 
 substance must depend, as in the painting on porcelain bodies, 
 upon the nature of the coloring matters employed, and is of no 
 real consequence to the ultimate appearance of the glass, since 
 
GLASS MANUFACTURE. 
 
 CHAT. XIV. 
 
 228 
 
 the whole will be entirely evaporated when submitted to the 
 intense heat of the furnace. 
 
 The coloring compounds having been previously ground with 
 an appropriate flux upon either a porphyry or strong plate- 
 glass palette, by means of a muller of the same material, must 
 again be ground in the same manner, and reduced to a proper 
 consistency with the vehicle just mentioned. The artist will 
 do well to prepare at first a sufficient quantity of every color 
 required for the completion of the object which he has in hand ; 
 it being extremely difficult, if not impossible, to produce tints 
 identically the same at any subsequent time, although the 
 greatest attention be paid to the proportions of their ingredients. 
 The injury which may be thus occasioned to the beauty of the 
 piece need not be insisted upon. 
 
 Many objects may be painted on glass by persons who have 
 not acquired any previous knowledge of the art of design. The 
 transparent nature of the material enables the artist to see dis¬ 
 tinctly both the outline and the shading of any pattern which 
 may be fixed upon its under side. The outlines of every such 
 pattern should be decidedly given; and the whole contour anc 
 shading must be at once obvious when looking on its uppei 
 surface. When the pattern paper is laid horizontally upon th( 
 glass, it must be secured by wafers at each of its four corners 
 to prevent its shifting ; the glass must then be placed upon ar 
 easel similar in form to a music-stand, and fixed steadily upoi 
 the table. Means should also be taken to prevent the slipping 
 of the glass upon the easel, by passing a string across its fact 
 in any position that will secure this object, without interfering 
 with the subject intended to be drawn. 
 
 To support the arm of the artist while he is employed ii 
 painting, as it would be improper for him to touch the glass, i 
 will be necessary to use a rest stick, in the manner observe' 
 by artists who paint with oil colors. 
 
 It is considered advisable to trace the outline, in the firs 
 instance, with common Indian ink much diluted, before usinj 
 for the purpose the pencil color, about to be described: th> 
 reasons for which are, that the strokes will admit of easier cor 
 rection, and that a rough line will be thus formed upon the sin 
 face of the plate, which, drying immediately after the applies 
 tion, serves to direct the point of the brush when charged wit 
 the color, and to occasion the delivery of the latter with greate 
 ease and regularity than would be otherwise attainable : b 
 this means the artist may avoid any patching or altering of th 
 outline, which would seldom fail to render the work roug 
 and unsightly, but which must be resorted to if the line 
 prove unequal or imperfect. Faults of this kind may, indeet 
 
CHAP. XIV. STAINING AND PAINTING GLASS. 
 
 229 
 
 be partially corrected at any period of the process; but as the 
 glass must be fired anew after each application of color, and 
 as the firings constitute the principal part of the expense, it is 
 of course advisable to exercise all possible carefulness, in order 
 to avoid, as far as possible, the necessity for their repetition. 
 
 The color most usually employed for drawing the outlines 
 and for shading different subjects, and which is therefore called 
 by artists outline or pencil color, is made of the saflfon-colored 
 oxide of iron commonly known in the shops by the name of 
 crocus martis. This oxide must be well ground in combina¬ 
 tion with an equal weight of soft flux upon a porphyry or 
 plate-glass palette, as before directed, and subsequently also 
 with oil of amber as its vehicle. To provide for the preserva¬ 
 tion of its proper degree of consistency, the addition of one or 
 two drops of balsam of capivi may be needed ; it is desirable, 
 however, to make as sparing use as possible of this substance, 
 which sometimes, when evaporated in the intense heat of the 
 kiln, will, through its greasiness, indispose the glass from 
 taking the color properly; and little vacancies may in conse¬ 
 quence be left unoccupied, and requiring to be subsequently 
 supplied. The pencil color thus prepared is a dark-reddish 
 brown, and remains unaltered by the heat of the furnace. In 
 order that the outline, while it is sufficiently decided, may at 
 the same time be fine and clear, the pencil color must be used 
 as little moistened as will admit of its flowing from the brush; 
 and until it has become perfectly dry and hard upon the glass, 
 no subsequent part of the coloring process should be commenced. 
 
 If when the pattern is wafered on the glass, and the outline 
 has been completely traced, it is desired to make one or more 
 copies of the figure upon other plates of glass, this may be done 
 without removing the paper from the first, by simply placing 
 the second and other plates in succession upon that to which 
 the pattern is attached, the transparency of which will admit 
 of the outlines being traced with the same facility as if the 
 pattern had been transferred to each individual plate. 
 
 The best crown-glass is generally chosen for painting or 
 staining as being most transparent and free from color. 
 
 The~colors must be laid on with a long-haired sable pencil; 
 its handle must be of a length which will allow the artist to use 
 his hand with freedom, and should be securely attached to the 
 brush, so that the two cannot become disunited. If such an 
 accident were to occur as the falling of this brush charged 
 with color, it would be impossible adequately to repair the mis¬ 
 chief by any means short of obliterating the whole, and begin¬ 
 ning the work anew. 
 
 The shading and coloring are very frequently performed 
 
232 
 
 GLASS MANUFACTURE. 
 
 CHAT. XIV. 
 
 will considerably heighten and bring out the colors. Should 
 there, however, be any imperfections either in the stain, or 
 painting, or pencil shading, these must be repaired by the artist 
 previous to consigning the glass again to the kiln. 
 
 It is sometimes wished to give to glass the appearance of 
 having been ground, leaving at the same time transparent lines 
 or patterns upon its surface, the effect of which is very pleasing 
 to the eye. In preparing for the production of this appearance, 
 the artist uses a large camel-hair pencil, the end of which is 
 dipped into oil of amber, so as to take up only a small quantity 
 at any one time ; and with this, holding the brush perpendicu¬ 
 lar to the glass, every part of the latter must be dabbed so that 
 the surface will be dimmed by the oil. This must not lie 
 thicker on one part than on another, and should by no means 
 be applied in sufficient quantity to give it a fluid appearance. 
 Taking then a mixture, composed of one part of white oxide 
 of tin, with three parts of flux, previously well ground together, 
 this must be sifted from a lawn sieve very gently over the 
 glass, until the whole surface is evenly covered. The requi¬ 
 site quantity of this powder will adhere slightly to the glass 
 through the means of the oil; and when, in the course of six 
 or eight hours, this has become sufficiently dry, the superfluous 
 powder must be lightly removed with a soft brush made of 
 badgers’ hair. The appearance of the glass will now perfectly 
 resemble that which has been ground. 
 
 In order to produce lines or patterns upon its surface, that 
 shall have the usual polish and transparent quality of glass, a 
 pattern must be drawn upon paper, having its lines sufficiently 
 strong to be visible through the powder; and this being fixed 
 upon the reverse side, the artist with a blunt wooden instru¬ 
 ment scrapes off the composition in lines accordant with those 
 of the pattern. The plate of glass having then been subjected 
 to burning in the kiln, it will be found that the powder has 
 been partially melted by the heat, and is so firmly united to the 
 glass, that its removal will be extremely difficult. 
 
 It now remains to describe the particular apparatus and pro¬ 
 cess used for burning-in the colors which have been applied to 
 the surface of the glass. The size of the kiln is of course de¬ 
 pendent on the magnitude and number of the pieces of glass 
 upon which it may be desired to operate at any one time. It 
 would be unwise to construct one of larger dimensions than 
 are likely to be needed in use, as the due heating of the glass 
 is more difficult and expensive, in proportion as the relative 
 size of the furnace is increased. 
 
 The glass is placed during the firing in a close iron box or 
 oven, which is called a muffle, and which is provided with hori- 
 
CHAP. XIV. STAINING AND PAINTING GLASS. 233 
 
 zontal iron shelves placed at regular distances apart, whereon 
 the plates are deposited. The relative sizes of the muffle and 
 furnace are such, that a space not less than four inches remains 
 between the two on every side, by which means the fire may 
 be made wholly to envelop the muffle. This receptacle is pro¬ 
 vided with a tube proceeding from its front, and narrowing to¬ 
 wards its extremity, without-side the furnace wall, the use of 
 which tube is to examine the state of the glass from time to 
 time during the process of firing. The iron plates for support¬ 
 ing and separating the glass, and which are fitted to the shape 
 of the muffle, are kept at their proper distances, usually about 
 one inch asunder, by legs of the requisite length placed at their 
 four corners. The shape of the muffle is usually wider at the 
 top than at the bottom, so that pieces of various dimensions 
 may be contained in its different compartments. The number 
 of these bears reference to the size of the apparatus, some 
 small muffles having no more than five or six, while others of 
 greater dimensions are provided with double that number of 
 shelves. 
 
 If the plates of glass were placed in immediate contact with 
 the iron shelves within the muffle, the metal would have an 
 injurious effect upon some colors. The iron is, besides, liable 
 to be warped ; and, when the glass was brought into a softened 
 state by heat, would communicate its own distorted shape. 
 Another and a greater evil than even these would arise from 
 the too sudden variations of temperature whereunto the glass 
 would be subjected, owing to the strong conducting power of 
 the iron, and which would imminently endanger the cracking 
 of the glass. 
 
 A perfect remedy for all these evils is found in previously 
 preparing a smooth and even bed for the glass, by sifting 
 pounded whiting to the depth of a quarter or three eighths of 
 an inch over the entire surface of the iron shelves. Upon this 
 bed the glass must be deposited with every possible care, so as 
 to avoid rubbing the colors. 
 
 If more than one piece is committed to each shelf, they must 
 on no account be brought into contact, nor must they be al¬ 
 lowed to touch or even to approach within half an inch of the 
 side of the muffle. When, after proceeding in this manner, 
 the muffle has been filled, or all the glass that is ready for 
 burning has been deposited, the cover must be put on to the 
 muffle, and the fire lighted. It is usual to employ coke and 
 charcoal as fuel for burning glass, both because they afford a 
 steadier and more effective heat than coal, and because the sul¬ 
 phur which the latter so commonly contains might have an evil 
 effect upon the colors. 
 
 U 2 
 
236 
 
 GLASS MANUFACTURE. 
 
 CHAP. XV. 
 
 they are of necessity numerous, yet partake of the simplicity 
 observable throughout the various processes of the manufacture. 
 
 In some principal establishments, steam power is used for 
 giving motion to a shaft which causes the revolution of numer¬ 
 ous large wheels or drums fixed thereon, and each of these being 
 connected by a band with a pulley on the axle of a smaller 
 wheel, occasions the latter to revolve with great celerity: these 
 small wheels are the cutting instruments. The occupation is 
 frequently carried on in the apartment of an individual work¬ 
 man, and in this case, only one large wheel, similarly connected 
 with the axle of one of smaller diameter, is turned by means of 
 a winch, a boy being employed for the purpose. In all other 
 respects the process is identical, whether prosecuted in the attic 
 of the artisan, or in the spacious factory of the manufacturer. 
 
 The small wheels are so arranged, that each can be unfixed 
 without difficulty, and another substituted of a form better suited 
 to the work in hand, or of a material more adapted to the stage 
 of the process. 
 
 As regards their forms, these cutting wheels are either nar¬ 
 row or broad—flat-edged—mitre-edged, that is, with two faces 
 forming a sharp angle at their point of meeting—convex or con¬ 
 cave. In fact, so various are the wants of the workman, that 
 as many as forty or fifty wheels having differently shaped edges, 
 are to be found in the workshop. 
 
 The materials employed in the formation of these cutting im¬ 
 plements are, iron, both cast and wrought; Yorkshire stone; 
 and willow wood. Wrought iron is, indeed, only used for cut¬ 
 ters of the narrowest dimensions, and which it would therefore 
 not be possible to make sufficiently tough of cast metal. Iron 
 wheels are used only for the first or roughest part of the opera¬ 
 tion, and their employment is even dispensed with altogether, 
 where it is intended that the pattern shall be at all minute; as 
 the metal and the sand, which must be used in conjunction with 
 it, would act too roughly, and frequently chip away portions of 
 the glass. For such minute works, and for smoothing down the 
 asperities which will always be occasioned where iron cutters 
 have been applied, a wheel of Yorkshire stone, moistened with 
 water, must be used. The further smoothing and subsequent 
 polishing of the cut surfaces are effected with wooden wheels: 
 for the first of these objects, the edge is dressed with either 
 pumice-stone or rotten-stone ; and for imparting the high de¬ 
 gree of polish that is requisite for properly finishing the process, 
 putty-powder is employed. 
 
 Beneath each one of the cutting wheels, a small cistern is 
 fixed to receive the sand, water, or powder which has been 
 used; and over the wheel, a small keg or a conical vessel is 
 
CHAP. XV. 
 
 GLASS CUTTING. 
 
 237 
 
 placed, the cock or opening at the bottom of which is so situated 
 and regulated, as that the requisite quantity of moisture will be 
 imparted from it to the wheel. The vessel which is placed 
 over the iron wheel is furnished with fine sand, and into this 
 water is admitted in such quantity as will insure the constant 
 delivery of the moistened sand upon the face of the wheel in 
 such proportion as the workman finds most desirable. The 
 emery powder, rotten-stone, or putty-powder, are applied from 
 time to time as required by the workman, on the edge of the 
 smoothing or polishing wheel. 
 
 From this short description of the implements, the manner of 
 their employment will be readily comprehended. The glass- 
 cutter seats himself on a stool in front of the wheel; and taking 
 in his hand the glass to be ornamented, applies this to the face 
 of the cutter, the correctness of his eye and the steadiness of his 
 hand being called into requisition, in the successive applications 
 to the wheel, of those parts of the glass that are to be cut. 
 Placed at his right hand each workman has a small tub con¬ 
 taining water, wherewith from time to time he washes away 
 the particles of sand or powder which may adhere to the glass, 
 that he may the better judge as to the progress of his work. 
 
 It may readily be supposed that, in conducting a process of 
 this nature, with so exceedingly brittle a substance, accidents 
 will often occur through the breaking of the material. The 
 frequency of these casualties will of course depend, in a great 
 measure, upon the original quality of the material; and this 
 forms one reason why the best description of glass is generally 
 chosen for the purpose of being cut. 
 
 In fitting up the machinery, it is plain that the utmost accu¬ 
 racy must be exercised. If the cutting-wheels were allowed 
 to turn upon their centres with the smallest degree of eccen¬ 
 tricity, it would be quite impossible for the operator to proceed 
 with any regularity in his work, or to produce a satisfactory 
 effect. 
 
 The wages of glass-cutters, in common with those of men 
 employed in the different manufacturing processes of a glass¬ 
 house, are paid according to the work which they deliver in a 
 finished and perfect state; so that if any accident should occur 
 to the glass while in their hands, as is frequently the case, the 
 workmen cannot claim any payment for the labor which they 
 may already have bestowed upon it. Every man who follows 
 the occupation of a glass-cutter is capable of executing each 
 part of the process, although some will succeed better in one 
 branch than in others. In large establishments there is gene¬ 
 rally such a choice of work, that every workman has the op¬ 
 portunity of providing himself with employment in that branch 
 
238 GLASS MANUFACTURE. CHAP. XV. 
 
 which he prefers; besides this, two or more men, forming a 
 sort of partnership, will frequently undertake work in con¬ 
 junction, each of them performing that branch of the process 
 which he feels himself qualified to execute with the greatest 
 success, by which division of labor the whole work is more ex¬ 
 peditiously and probably also more satisfactorily performed. 
 
 The grinding of glass, or frosting it, in order to lessen its 
 transparency, forms a branch of the glass-cutter’s art. The 
 objects to which, in the present day, this grinding process is 
 most commonly applied, are shades for softening the light dif¬ 
 fused by table lamps. As the roughness is given to the inner 
 surface of these glasses, it is plain that they cannot be applied 
 to the cutting-wheel for the purpose. Instead of this, the 
 shades are, therefore, fixed in a lathe, and the workman, hold¬ 
 ing in his hand a piece of wood which he covers with wet 
 sand, causes this to rub with the necessary degree of force 
 against the inner surface during the rapid revolutions of the 
 glass. 
 
 The amount and description of labor bestowed upon articles 
 which pass through the glass-cutter’s hands, must necessarily 
 enhance their money value, and therefore circumscribe their 
 use. Nor is there much reason to look for the discovery of 
 any improvements in the processes whereby that labor can be 
 so abridged as that the manufacture will be brought within the 
 reach of a larger number of consumers. Under this view, any 
 method of ornamenting glass which can be offered as a toler¬ 
 able substitute for cutting it, is likely to be favorably received 
 by the public. 
 
 Such an invention has recently been made the subject of a 
 patent, under which glass vessels, having a variety of shapes, 
 are formed with ornamental figured patterns impressed upon 
 them. 
 
 The method of producing these patterns is sufficiently sim¬ 
 ple, and consists in placing a quantity of melted glass within a 
 metallic mould of the required form, in the lower division of 
 which the desired pattern is engraved; and in then bringing 
 down the upper section of the mould, and pressing the melted 
 glass between the two. The only skill required for the opera¬ 
 tion is that of apportioning rightly the quantity of melted glass 
 which is required for exactly filling the mould, so as to take a 
 faithful impression of the engraved pattern. The two parts of 
 the mould are connected together by means of a hinge, and 
 the upper portion is provided with a long handle, which acts as 
 a lever for imparting the requisite pressure. The lower sec¬ 
 tion is composed of two pieces, which being opened, the glass 
 
CHAP. XV. ETCHING ON GLASS. 239 
 
 may be removed from the mould almost at the moment of its 
 formation. 
 
 Intended as a substitute for cutting, this art must certainly 
 be considered inferior. The patterns imparted by the mould 
 are deficient in the degree of sharpness which is imparted by 
 the wheel. On the other hand, a description of ornament may 
 be thus adopted, which is otherwise unattainable; the figures 
 may be either raised or depressed, and patterns the most minute 
 and intricate may be produced. Armorial bearings, in particu¬ 
 lar, may thus be represented, in a manner far superior to any 
 engraving, not only as the glass will everywhere retain its 
 polish, but also because figures may be given in relief. Be¬ 
 tween the cost of the two processes there cannot be any com¬ 
 parison. 
 
 Many specimens are preserved in collections of ancient glass 
 which are ornamented with raised figures. These have been 
 ■ most probably produced by pressure within a mould while yet 
 softened by heat, such a practice being one of great antiquity. 
 Engraved figures were likewise executed upon hollow vessels 
 by the old Greek artists; and that celebrated engraver on 
 stones, Lawrence Natter, affirms, in his “ Treatise on the An¬ 
 tique, when compared with the Modern Method of Engraving 
 on Precious Stones,” that the same kind of instruments were 
 used for the production of these relics of antiquity, as were 
 employed for the same purpose at the time when he wrote. He 
 considers that the old artists undoubtedly used a wheel, which 
 moved in a horizontal direction above the table at which they 
 wrought; and this opinion is in agreement with a passage in 
 Pliny (Hist. Nat. lib. xxxvi. cap. 26.):—“ Aliud flatu figura- 
 tur, aliud torno teritur, aliud argenti modo Cfelatur.” On the 
 other hand, to agree with Natter would be to deprive Lehmann 
 of his reputation as an inventor, although he may still be en¬ 
 titled to the honor of having revived an art which had become 
 obsolete; and this, in the opinion of the learned antiquarian 
 Caylus, himself the re-inventor of a sister art, is the amount 
 of merit whereto Lehmann may justly lay claim. 
 
 In the middle of the sixteenth century, when glasses manu¬ 
 factured in the Venetian states enjoyed the highest reputation 
 throughout Europe, it was common to find these ornamented 
 by engravings executed with the diamond. More than an hun¬ 
 dred years had elapsed from that period, when Henry Schwan- 
 hard, a pupil of Lehmann, was incited by the accidental cir¬ 
 cumstance of the corrosion of his spectacle glass, to a method 
 of etching on glass by means of some powerful acid liquor. 
 His manner of preparing this liquor was kept secret by him; 
 and as no fluid, save fluoric acid, with which we are acquaint- 
 
GLASS MANUFACTURE. 
 
 CIIAf. XV. 
 
 240 
 
 ed, has the property of acting upon the surface of glass, while 
 the discovery of this powerful menstruum was not brought be¬ 
 fore the world prior to the publication of Scheele’s experiments 
 in 1771, it is much to be regretted that the secret of Schwan- 
 hard was suffered to go with him to the grave. 
 
 The method pursued by this artist in the application of his 
 discovery was different from that which is practised at present. 
 This is, to coat over the entire surface of the glass with var¬ 
 nish, and, through this coating, to trace out the intended fig¬ 
 ures, leaving the glass exposed to the action of the acid only 
 in those parts which are to be occupied by the figures. Schwan- 
 hard, on the contrary, first traced the figures, and, having filled 
 the outline on the glass with varnish, applied his corrosive fluid 
 to the remainder of the surface. By this means the figures 
 were left in relief, and with their original polish, the effect of 
 which was pleasing, and totally dissimilar to the appearance of 
 engravings with the diamond, which latter circumstance it 
 probably was that incited the artist to the adoption of his pecu¬ 
 liar method, since his productions would, by that means, be 
 more readily distinguished from the works of others. 
 
 The varnish employed by artists for defending, where it is 
 requisite, the surface of the glass from the corroding power of 
 the acid, is usually either a solution of isinglass in water, or 
 common turpentine varnish mixed with a small proportion of 
 white lead. 
 
 By the aid of a very few implements, the art of etching on 
 glass may be rendered a pleasing occupation for amateurs. 
 Good crown-glass is the most proper to be chosen for this pur¬ 
 pose. Having selected a square pane of the proper size, this 
 should be first heated by immersion in a sand-bath, and then 
 rubbed over with purified bees’-wax, the temperature of the 
 glass being such as to cause the wax to melt completely and 
 uniformly over its surface. The pane, thus covered, must then 
 be set aside to cool; and it is important to observe, that every 
 part of its face must be protected by this coating of wax; 
 which, however, need not be thick, and indeed should not be 
 applied in sufficient quantity to render the glass opaque. 
 
 A paper having the design boldly drawn upon it, may then 
 be attached to the unwaxed under side of the glass; and this 
 drawing will greatly assist the artist in performing the next 
 process, that of tracing the design through the wax. The best 
 kind of tool for executing this operation is a carpenter’s brad¬ 
 awl, which, as it is flattened at the end in one direction, and 
 rounded in another, may, according to the position wherein it 
 is held, be easily made to trace lines having the requisite and 
 different degrees of fineness. The point of a penknife, or any 
 
CHxVP. XV. 
 
 ETCHING OF GLASS. 
 
 241 
 
 similar implement, may be used as a substitute for the brad-awl, 
 and with almost equal efficacy. In tracing these lines, the artist 
 must be mindful that his instrument lays bare the surface of the 
 glass throughout the whole extent of the strokes. 
 
 A shallow evaporating basin of Wedgwood ware must next 
 be employed. Its size should be such as will include within its 
 area every part of the design; and it must at the same time be 
 sufficiently small to be completely covered when the pane of 
 glass is made to rest upon its edge. Some coarsely powdered 
 fluor spar must then be placed in the basin, together with a 
 quantity of strong sulphuric acid, sufficient to form with it a 
 thin paste, when the two substances must be well mixed to¬ 
 gether by stirring them. The quantity of fluor spar must of 
 course be regulated by the size of the etching; and it may be 
 a sufficient guide on that head, to recommend that two ounces 
 of the coarse powder be used when the basin is capable of con¬ 
 taining a pint: these basins are readily procurable from any re¬ 
 spectable dealer in earthenware. 
 
 As soon as the acid and fluor spar are properly incorporated 
 together, the pane of glass should be placed upon the basin, 
 with the waxed side downwards, and a moderate degree of heat 
 must be applied to the bottom of the basin: somewhere between 
 120 and 140 degrees of Fahrenheit’s scale will be found most 
 eligible. Perhaps the best means of providing a steady heat 
 for this purpose is offered by the sand-bath, which was used for 
 heating the glass before applying the wax. On this subsequent 
 occasion, however, the temperature must never be sufficiently 
 high to melt the wax, which in that case would run over the 
 glass, and wholly destroy the effect of the etching. 
 
 Very soon after this application of heat, fumes of fluoric acid 
 will rise copiously from the basin, and attack the unprotected 
 portions of the glass. When the basin and its contents are once 
 thoroughly warmed, the heat of the sand-bath may be advan¬ 
 tageously diminished. 
 
 After the glass has been thus exposed during half an hour, 
 it may be removed from the basin; and first being rinsed in 
 water, for the purpose of diluting or washing away the fluoric 
 acid, the wax may be scraped off with a common table-knife; 
 the design will then be found perfectly etched upon the surface 
 of the glass. 
 
 A metallic basin will answer perfectly for generating the flu¬ 
 oric acid; but it will be altogether improper to use any glazed 
 vessels for the purpose, as the vitreous coating of such would be 
 entirely destroyed. 
 
 In performing this process, it is necessary to use some cau¬ 
 tion ; as fluoric acid, if brought into contact with the skin, will 
 
GLASS MANUFACTURE. 
 
 CHAP. XV. 
 
 242 
 
 quickly disorganize it, and produce wounds which may be pain¬ 
 ful and troublesome; a very little carefulness will, however, 
 suffice for preventing any accident of this nature. 
 
 When it is required thus to engrave other than plane sur¬ 
 faces, another arrangement must be provided: the glass must 
 be exposed to the fumes of fluoric acid in some deep vessel; 
 without, however, being suffered to come in contact with the 
 pasty compound whence the acid fumes arise; and the whole 
 should be covered over, to confine and retain those fumes, so 
 that they may fully act upon the glass. 
 
 Articles made of flint glass are sometimes very tastefully or¬ 
 namented, by inclosing within their substance various objects 
 formed out of bodies which, being less fusible than glass, will 
 not be altered in their form or nature by the heat contained in 
 this at the moment of their introduction. 
 
 The art was first attempted about fifty years ago, by a glass 
 manufacturer in Bohemia, who sought to incrust small figures 
 made with a grayish kind of clay. His success in this attempt 
 was but moderate; the material of which he made choice for 
 his figures, expanded and contracted very unequally with the 
 surrounding glass, and their adhesion to it was consequently 
 imperfect. 
 
 The successful accomplishment of this pleasing art has long 
 been a favorite object with the French manufacturers, who 
 have been unsparing of expense in their efforts for its perfec¬ 
 tion. For a long time, however, their success was small, and 
 the specimens produced by them were so costly, that but little 
 encouragement was offered on the part of purchasers. The 
 subject at that time principally chosen for the exercise of this 
 art, was a medallion of Napoleon, whose courtiers evinced the 
 desire of possessing his likeness in this imperishable form, as 
 being emblematic of their own unalterable attachment! Im¬ 
 provements have since been made by the French artists, which 
 have enabled them to reduce the cost of these incrustations 
 within more moderate bounds; but their manufacturers have 
 hitherto mostly restricted themselves to the ornamenting in this 
 manner of scent-bottles and trinkets. 
 
 A few years ago one of the most considerable London glass 
 manufacturers discovered the means of attaining to a higher de¬ 
 gree of success, and is now enabled thus to ornament, in a very 
 tasteful manner, various objects of considerable size; employing 
 for the purpose substances whose property it is to expand and 
 contract equally with glass upon exposure to altered tempera¬ 
 tures. This interesting art can by this means be applied to 
 represent ornaments of almost every description. The appear¬ 
 ance most usually given to them is that of silver; but as the 
 
CHAP* XVI. 
 
 243 
 
 Reaumur’s porcelain. 
 
 metallic oxides may be employed for coloring the substances 
 previous to their incrustation, every variety of hue that can be 
 used in enamel painting may also be imparted. 
 
 CHAP. XVL 
 
 ON THE DEVITRIFICATION OF GLASS. 
 
 First observed by Neumann.—Experiments of Reaumur.—Substance known 
 as Reaumur’s Porcelain.—Inappropriateness of this name.—Uses to which 
 the Substance may be applied.—Common Bottle Glass most proper for this 
 Conversion.—Method of effecting the Change.—Produced solely by Heat. 
 —Experiments of Dr. Lewis.—Revitrification.—Experiments of Sir James 
 Hall.—Proposal suggested thereby.—Observations of Guyton-Morveau.— 
 Artificial Intaglios.—Mock Onyxes.—Power of Devitrified Glass to bear 
 sudden Changes of Temperature.—Experiments with Colored Glass.— 
 Glass devitrified by burning Lava.—The Process promoted by multiply¬ 
 ing the Ingredients of Glass.—Devitrified Glass conducts Heat more per¬ 
 fectly that when vitreous.—Becomes a Conductor of Electricity.—Retains 
 this Property when revitrified. 
 
 It was observed very long since by Neumann, that some 
 kinds of glass, if exposed during any considerable time to a 
 high degree of heat, but below their point of fusion, are so far 
 changed in their properties and texture as to become opaque, 
 fibrous, and tough; and so hard as to give abundant sparks if 
 struck with steel, to cut any common glass readily, and to be 
 scarcely susceptible of abrasion by filing. It has also been 
 found, that in taking this form, glass so far alters its nature as 
 regards its qualities of expansion and conducting of heat, that 
 it will bear a sudden transference from freezing to boiling 
 water. 
 
 That indefatigable naturalist, M. Reaumur, made various 
 experiments and observations on this phenomenon ; and, in the 
 year 1739, communicated the result of these to the Royal Acad¬ 
 emy of Sciences in Paris. The subject becoming by this means 
 more generally known, glass, when thus converted, obtained, 
 and has since kept the name, of Reaumur's porcelain ; a desig¬ 
 nation which it owes to its appearance rather than to its real 
 properties, which do not at all entitle it to be classed with por¬ 
 celain. It is probably owing to the inappropriate name which 
 the substance thus acquired, that so little has been done to¬ 
 wards a true development of the facts and circumstances at¬ 
 tendant upon the devitrification of glass. Even the greater 
 number of such scientific men as for a time entered upon the 
 investigation, limited their labors to experiments with various 
 cementing substances, that they might arrive at the discovery 
 
244 
 
 GLASS MANUFACTURE. 
 
 CHAP. XVI. 
 
 of that one which would insure the concurrence of the greatest 
 number of good qualities that should be found in porcelain. 
 The futility of these experiments has since been made evident; 
 and it must be regretted that the same amount of research as 
 was thus unprofitably bestowed, has not been given to elucidate 
 the actual properties of devitrified glass, and to render it prac¬ 
 tically serviceable to society. 
 
 Reaumur was of opinion that its quality of resisting alterna¬ 
 tions of temperature, its toughness, as well as the power it pos¬ 
 sesses of withstanding the action of acid liquids, render this por- 
 celainous glass well qualified for the formation of chemical ves¬ 
 sels. The same opinion has been equally held and declared by 
 other philosophers who have brought their minds to the inves¬ 
 tigation of the subject; and it appears singular that their sug¬ 
 gestion should not, consequently, have been very generally re¬ 
 duced to practice. This circumstance must further excite sur¬ 
 prise, when it is considered in how many important operations 
 of the laboratory such a substitute for metallic vessels would be 
 advantageous. In operating upon any practical scale, the 
 chemist is driven, for want of such a substitute, either to the 
 employment of metals which are liable to be injuriously acted 
 upon by the matters under process, or is compelled to adopt 
 vessels of platinum, the expensiveness of which places them 
 beyond the prudent reach of most persons. In one instance, a 
 manufacturer of pharmaceutical preparations, who is exceed¬ 
 ingly particular as to the absolute purity of his productions, has 
 recently incurred the expense of constructing a pan of unalloy¬ 
 ed silver, forty inches in diameter, wherein to evaporate vege¬ 
 table extracts, many of which, in some degree or other, act 
 upon and are impregnated by copper. 
 
 Could vessels formed of this fibrous glass be adopted with 
 safety, there would be nothing in their cost, especially when of 
 moderate size, to prevent their general adoption. The only 
 circumstance hitherto assigned against this adoption is, that al¬ 
 though the inner texture of the glass is fine and white, the sur¬ 
 face is coarse and of a dirty appearance; but this must be 
 thought a very insufficient cause for foregoing such decided 
 advantages as are apparently offered through its employment. 
 
 All kinds of glass are not equally qualified to undergo this 
 conversion; with some descriptions, indeed, it will not ensue. 
 Not any vitreous compound seems altogether proper for it, with 
 the exception of common green bottle-glass, and perhaps also 
 the ordinary kinds of window glass. 
 
 The method commonly employed for effecting the change is 
 as follows :—The glass vessel is placed within a larger earthen 
 vessel, in the same manner as is pursued for baking porcelain. 
 
chap. xvi. Reaumur’s porcelain. 245 
 
 The entire space unoccupied by the glass is next filled by pour¬ 
 ing into the vessel fine white sand, or powdered gypsum, so 
 that the glass shall not be allowed at any point to come into 
 contact with the earthen case. The containing vessel is then 
 covered down, securely luted, and the whole is placed within 
 the furnace. 
 
 It was for some time generally imagined, that in this process, 
 which is very similar to that which is known to chemists under 
 the name of cementation, the glass owes the change which it 
 undergoes to some chemical action of the gypsum upon its sub- 
 stance°: but this has been proved erroneous. It is shown by Dr. 
 Lewis, in the detail of his various experiments, that not only 
 may the nature of the powder be almost infinitely varied, with¬ 
 out in the least affecting the operation, as far as regards the al¬ 
 tered texture of the glass, but that the change equally and iden¬ 
 tically goes forward in the absence of all cementing substance; 
 a fact which is conclusive upon the subject, and which proves 
 that whatever may be the particular substance employed, 
 whether sand, bone-ash, chalk, or gypsum, it acts merely by af¬ 
 fording mechanical aid, sustaining the glass in its proper form 
 during the period when it is softened by heat, and when, if de¬ 
 prive! of such support, it would be liable to irreparable injury 
 in falling together by means of its own gravity. 
 
 In the course of experiments, which are detailed by him at 
 some length* Dr. Lewis placed several pieces of common wine 
 bottles into crucibles, pouring over them the requisite quanti¬ 
 ties of white sand, and placing them in a proper furnace, where¬ 
 in they were heated during many hours. In order to ascertain 
 the progress of the change, pieces were withdrawn from time to 
 time for examination. Those pieces which were first taken out, 
 after having been during several hours in the furnace, but with¬ 
 out being heated to redness, exhibited no sort of change what¬ 
 ever. in a low red heat the change went forward very slow¬ 
 ly, but still was quite perceptible; while in a strong red heat 
 approaching to whiteness, and which only just avoided that de¬ 
 gree of intenseness which would have melted the glass, the 
 change went on rapidly, beginning at each surface, and spread¬ 
 ing towards the middle; so that, in two hours, the substance 
 had assumed throughout the appearance of porcelain. 
 
 The glass became first of a bluish color on the surface, and 
 exhibited a very sensible diminution of its transparency. After 
 this, it gradually became white and more opaque ; the texture 
 no longer continued vitreous, but became fibrous, as already de¬ 
 scribed ; and these fibres were disposed nearly parallel to each 
 
 * Commercium Philosophico-technicum, p. 150. 
 
 V 2 
 
246 
 
 GLASS MANUFACTURE. 
 
 CHAP. XVI. 
 
 other, and transverse to the thickness of the piece. The fibres 
 from both surfaces meeting in the middle, formed there a kind 
 of partition, in which cavities were occasionally perceptible. 
 By degrees this opacity and fibrous change were completed, the 
 blue color disappeared, and was succeeded by a dull white or 
 dun color. 
 
 When exposure to the same high degree of heat was con¬ 
 tinued after the production of this effect, the glass was seen to 
 undergo a still further change of texture : the fibres appeared 
 to be divided or cut into grains; beginning, as before, at the 
 outer ends, and proceeding onwards towards the middle, until 
 the entire substance assumed a granular form, similar to ordi¬ 
 nary porcelain. A still further continuance of heat caused the 
 grains, which at first were fine and glossy, to become enlarged 
 and dull, and to change from a compact to a porous, and at 
 length to a friable substance, resembling a slightly cohering 
 mass of white sand, not easily distinguishable from that wherein 
 it was embedded. 
 
 If glass, which has been withdrawn from the furnace at the 
 time it has assumed the fibrous state, be afterwards subjected to 
 a very strong heat, it will melt into a semi-transparent mass, 
 and may be drawn out in strings, which on cooling are found to 
 have lost their fibrous quality, and to have resumed their for¬ 
 mer vitreous state, being no harder than before the original 
 cementation. This fusion of porcelainous glass cannot, how¬ 
 ever, be effected, without the application of a degree of heat 
 considerably more intense than is required for melting glass in 
 its more usual form; and it is also found that the farther the 
 process of cementation has been carried, the higher must the 
 temperature be raised for its fusion; so that specimens which 
 have been rendered granular are much more refractory than 
 such as are simply fibrous. 
 
 Although, throughout the experiments of Dr. Lewis, no dif¬ 
 ference in the actual properties of Reaumur’s porcelain follow¬ 
 ed the employment of different substances for embedding the 
 glass,—its internal color, hardness, texture, and the regular 
 succession of its changes being the same in all cases;—yet con¬ 
 siderable difference was occasioned in its outward color. If 
 charcoal or soot had been used, these produced a deep black 
 color, which was not affected by long exposure to heat in an 
 open furnace. Clay or sand which was colored, communicated 
 different shades of brown ; and white earths gave either gray 
 or brown tinges. The greatest degree of whiteness followed 
 upon the use of white sand, calcined flints, or gypsum ; and the 
 highest state of glossiness or brightness was caused by the em¬ 
 ployment of pipe-clay. 
 
chap. xvi. reaumttr’s porcelain. 247 
 
 In the account published by Sir James Ilall of his highly in¬ 
 teresting course of experiments on the effects of compression 
 in modifying the action of heat upon a certain class of substan¬ 
 ces, incidental mention is made of an important circumstance 
 connected with this change in the texture of glass, and which 
 seems to point the way towards the institution of a further 
 course of useful investigations. 
 
 Having placed in the closed end of a porcelain tube a portion 
 of the substance which he was about to subject to the action of 
 heat under pressure, it became necessary to introduce likewise 
 within the tube some other substance, which could be brought 
 to such a state as would oppose an effectual barrier against the 
 communication of the principal substance with the atmosphere. 
 The use of various bodies was attempted for this purpose, and 
 each was successively rejected as inadequate. Among these, 
 Sir James determined upon trying the effect of pounded glass; 
 which, being placed within the tube, above and nearly in con¬ 
 tact with the principal substance, could be subjected to such a 
 degree of heat as would fuse the glass, while the closed end of 
 the tube might be sufficiently withdrawn from the action of the 
 furnace; and when, in the prosecution of the actual experiment, 
 this end should come to be placed in the strongest heat, that 
 portion of the tube in which the then compact body of glass was 
 contained could be equally removed from a temperature which 
 would again alter its form. 
 
 The description of glass accidentally chosen by Sir James 
 Hall for his experiment, was that which is best of all qualified 
 for conversion into Reaumur’s porcelain. Having introduced 
 the tube wherein the pounded glass was contained within a 
 muffle heated to the temperature of 20° of Wedgwood’s scale, 
 3677° Fahrenheit, he discovered, that in the space of one 
 minute it entered into a state of viscid agglutination, similar to 
 that of honey; and that when only one more minute had elaps¬ 
 ed, the entire particles were consolidated into a firm compact 
 mass of Reaumur’s porcelain: during the short period here men¬ 
 tioned, the heat of the muffle had been uniformly sustained at 
 the same degree. 
 
 If a solid cylinder of glass, having the same bulk as the pow¬ 
 der thus placed within the tube, had been exposed to the same 
 temperature, it would equally have undergone a change from 
 the vitreous to a fibrous state; but the time required would 
 have amounted to at least an hour. 
 
 The result of the discovery thus unexpectedly made by Sir 
 James Hall, renders it probable, that if common green bottle- 
 glass, previously ground to powder, were introduced within ap¬ 
 propriate moulds, and exposed to an adequate temperature, it 
 
248 GLASS MANUFACTURE. CHAP. XVI. 
 
 would speedily and satisfactorily be converted into vessels of 
 Reaumur’s porcelain; and by this means, not only would the 
 time expended be materially abridged, and fuel economized, 
 but the manufacturer would be relieved from one of the great¬ 
 est practical difficulties which has been found to attend the 
 conversion, and which arises from the tenacity wherewith the 
 sand usually employed is found to adhere to the glass. 
 
 This evil is frequently experienced to so great a. degree, that 
 the force required for their separation endangers the breaking 
 of the vessel. Moulds of every requisite form might be made 
 without difficulty, of substances sufficiently refractory to remain 
 uninfluenced by the temperature employed for the conversion, 
 and which would deliver the glass freely upon its completion. 
 
 M. Guyton-Morveau read, in 1810, before the French Na¬ 
 tional Institute, a paper containing observations with a view to 
 explain some phenomena that occur in the fabrication of glass.* 
 In the course of his remarks, this celebrated chemist drew the 
 attention of his auditors to several specimens of devitrified glass 
 collected by him, which had been rendered opaque and fibrous 
 by the long-continued action of heat in a porcelain furnace. 
 Some of these pieces were converted, without having been sur¬ 
 rounded by sand or gypsum, or any other cementing substance, 
 and yet exhibited the completest change throughout their sub¬ 
 stance. 
 
 One of his specimens, composed of bottle glass, had been ex¬ 
 posed, during three entire days, to the heat of 50 degrees of 
 Wedgwood’s pyrometer, and had acquired interiorly a rosy tint, 
 its fracture exhibiting fibrous lines, arranged in the form of 
 stars, and converging towards the centre: this glass was suffi¬ 
 ciently hard to scratch rock crystal. Another specimen of flint 
 glass, which had been exposed during the same time, in the 
 same furnace, exhibited only the commencement of crystalliza¬ 
 tion at its surface; the interior retaining, unaltered, its original 
 vitreous quality. 
 
 M. Guyton-Morveau likewise exhibited some artificial intag¬ 
 lios, made of bottle glass, which had been first softened and 
 moulded in a cupelling-furnace, on an impression taken with 
 rotten-stone, and subsequently devitrified in the heat of a por¬ 
 celain furnace. These specimens were sufficiently hard to 
 scratch rock-crystal; a quality which points out the fitness of 
 such productions to be used as dies for the preparation of in¬ 
 taglios and cameos, the impression which they receive and im¬ 
 part being exceedingly chaste and perfect. The same quality 
 suggests the advantage that would probably be found in the em- 
 
 * Ann. (Ip Chim. voj. lxxiii. p. 113. 
 
CHAP. XVI. REAUMUR’S PORCELAIN. 249 
 
 ployment of Reaumur’s porcelain in the composition of mock 
 onyxes; but, for this purpose, the ground and figures must be 
 formed of separate layers of different-colored glass, which must 
 be brought together by means of some fluxing material, and 
 afterwards devitrified, in order to give them the requisite opa¬ 
 city, and, in some degree, also, that hardness which is the dis¬ 
 tinguishing characteristic of gems. 
 
 One specimen, also brought forward on the same occasion by 
 M. Guyton-Morveau, was a segment of a globe, composed of 
 bottle-glass, which had been cut in the form of a watch-glass, 
 to be used as a capsule, and afterwards devitrified. This piece 
 might be suddenly heated red-hot, and immediately thrown into 
 cold water, without experiencing injury. It might also be kept 
 in heated sulphuric acid, without exhibiting the least corrosion 
 or alteration of weight; two qualities calculated to render its 
 employment eminently advantageous for the purposes of chem¬ 
 ical analysis. 
 
 The result of different experiments made to devitrify stained 
 glass taken from church windows, was likewise shown, on the 
 same occasion, by M. Guyton-Morveau. Of various pieces thus 
 treated, some were colored red by the precipitate of Cassius, 
 and others blue by oxide of cobalt. One of the red specimens 
 contained lead in its composition; this, on losing its transparent 
 quality, had become of a spongy consistency, and appeared full 
 of blebs; in the other piece, which was hard crown-glass, the 
 devitrification was seen to have pursued its usual and regular 
 course, interiorly from the two surfaces: it had acquired a pur¬ 
 ple tinge, and was so little hardened that it might be scratched 
 by rock-crystal. The piece which had been stained by oxide 
 of cobalt differed from the last in more than one particular. Its 
 hardness was so great, that scarcely could any perceptible mark 
 be made upon it by adamantine spar; its blue color, which had 
 the appearance of being somewhat weakened internally, was at 
 the same time more intense at the surface, a variance which 
 might, indeed, be more apparent than real, and which probably 
 resulted from the greater opaqueness it had acquired at that 
 part; as although the glass had lost all transparency, the devi¬ 
 trification was by no means perfect, having proceeded but a 
 short distance below the surface. 
 
 Glass has been converted into Reaumur’s porcelain during 
 volcanic eruptions, by being enveloped in burning lava. Some 
 specimens of this kind were obtained after the destruction of 
 Torre del Greco, in 1794; but it is somewhat remarkable, that 
 this devitrifying effect has been by no means uniformly exhibit¬ 
 ed under the same circumstances, since pieces of glass have 
 been found, which, although completely embedded between two 
 
250 
 
 GLASS MANUFACTURE. 
 
 CHAP. XVI. 
 
 opaque volcanic crusts, yet retain their transparency and vitre¬ 
 ous qualities. The examination of these particular specimens 
 does not appear to have been carried sufficiently far to deter¬ 
 mine the fact; but it is by no means unlikely that the varying 
 effect here noticed may have been owing to some difference in 
 their original composition. 
 
 The greater the number of suitable ingredients that are em¬ 
 ployed in the composition of glass, the more easily and promptly 
 does it become devitrified. This circumstance will sufficiently 
 account for the fact of bottle-glass being the most suitable of 
 any for conversion into Reaumur’s porcelain. Having been 
 compounded without much attention to the purity of its ingre¬ 
 dients, this substance contains a great variety of earthy salts in 
 minute quantities; while plate glass, which is a much more 
 simple body, and in the manufacture of which the purified in¬ 
 gredients are brought together in the precise proportions that 
 are required exactly to saturate each other, can be devitrified 
 only partially, and with great difficulty. 
 
 On the other hand, in the same manner as a solution com¬ 
 pounded of a great variety of saline bodies forms its crystalline 
 deposits in a confused manner, so is it also observed that the 
 fewer the number of ingredients which are contained in devit¬ 
 rified glass, the greater is the degree of regularity whereby its 
 fibrous arrangement is attended ; and for this reason plate glass, 
 where the difficulty attending its devitrification has been over¬ 
 come, furnishes, if not the most complete, yet certainly the 
 most regular and beautiful specimens of Reaumur’s porcelain. 
 
 It has been observed that glass, when devitrified, becomes a 
 much more perfect conductor of heat and electricity than it was 
 before it had changed its vitreous form. In fact, several pieces 
 of glass, when converted into Reaumur’s porcelain, could not 
 be made to exhibit any sign of electricity by friction. This 
 circumstance is rendered yet more remarkable by the fact, that 
 glass which, having been once devitrified, has been made to 
 resume its vitreous form by fusion, although it is thereby re¬ 
 invested with its original density, fracture, and other charac¬ 
 teristics, yet shows no greater disposition to become electric 
 than it exhibited during its state of devitrification. 
 
INDEX. 
 
 A. 
 
 AIKIN, Messrs., their experiments 
 on the composition of glass, 133. 
 Allint, M. his experiments on the, 
 manufacture of bottle glass, 152. 
 Alumina, 34. 
 
 Astbury discovers theElere’ method 
 of glazing porcelain, 25. 
 
 Aristotle, his problems respecting 
 glass, 106. 
 
 Attilianus, 20. 
 
 B. 
 
 Bamboo of Wedgwood, 28. 
 
 Basaltes of Wedgwood, 28. 
 
 Beads, manufacture of, 182. Imita¬ 
 tion of pearl, 184. Manner of their 
 invention and formation, ib. 
 
 Bede, the venerable, his account 
 glass in England, 112. 
 
 Blancourt, his account of the dis¬ 
 covery of casting plate-glass, 114. 
 Blowpipe, description of, 177. 
 Blunging, process of, 41. 
 
 Bricks, antiquity of the manufacture 
 of, 18. Roman manufacture of, ib. 
 Brindley, his improved flint-mill, 42. 
 Brongniart, M., his receipt for the 
 manufacture of tender porcelain, 46. 
 Buckingham, second duke of, his en¬ 
 couragement of the manufacture of 
 British glass, 115. 
 
 C. 
 
 Carlsbad, mineral springs of, 36. 
 Caylus, Count, his account of ancient 
 colored glass, 219. 
 
 Chaptal, M., his direction for making 
 glass from calcined bones, 175. His 
 process for forming white enamel,63. 
 Clay, analysis and description of, 84. 
 Wedgwood’s experiments on, ib. 
 Further analysis of, 35. Species of, 
 used in the potteries of Staffordshire, 
 37. Blue clay the best, 38. China 
 clay, ib. Dilution of, in potteries, 40. 
 Cobalt, oxide of, used as coloring 
 matter in the manufacture of por¬ 
 celain, 21. 
 
 Colbert, Monsieur, patronizes the 
 manufacture of glass in France, 113. 
 Cookworthy, his manufacture of por¬ 
 celain, 29. 
 
 Crazing, meaning of the term, 37. 
 
 D. 
 
 De Botticher, baron, discovers the 
 composition of true porcelain, 22. 
 D’Entrecolles, Francis Xavier, mis¬ 
 sionary in China, 22. 
 
 DeMontamy,M., his recipe for com¬ 
 posing a pure white color, 77. 
 
 De Montigny, M., furnace of, 57. 
 
 De Palissy, Bernard, his improve¬ 
 ments in enamelling, 64. His dis¬ 
 tresses and perseverance, 65. 
 Dial-plates of watches and clocks, 
 how formed, 185. Lettering and 
 figuring, 188. 
 
 Durcos, M., his experiments on the 
 manufacture of bottle glass, 152. 
 
 E. 
 
 Elers, the two brothers, their manu¬ 
 facture of porcelain, 25. 
 
 Enamel, coloring, antiquity ofi 69. 
 
 F. 
 
 Faraday, Mr., his experiments re¬ 
 specting the manufacture of heavy 
 glass, 134. 
 
 Felspar, Cornish, its fusibility, 39. 
 Flint, analysis of, 36. Process for 
 the preparation of* for the manufac¬ 
 ture of porcelain, 42. 
 
 Fontanieu, M., his direction for the 
 composition of artificial gems, 171. 
 His recipe for the color of the ame¬ 
 thyst, 215; of the emerald,'HO. His 
 receipt for the lustre of the semi¬ 
 transparent opal, 216. 
 
 Frauenhofer, rises from obscurity by! 
 his talents; his « icntific 
 
 ments, 201. Produces specimens of 
 perfect glass; dies at an early age, ib. 
 
 O. 
 
 Gehlen, M., his recipe for crown 
 glass, 145. 
 
 Gems, composition of, 35. 
 
 Gems, artificial; great interest for¬ 
 merly attached to the subject, 171. 
 Modes of preparation, ib. Rock 
 crystal formerly employed, 172. 
 Diamond paste, 173. Various pastes 
 for imitating different gems, 174. 
 Geobert, M., his analysis of the por¬ 
 celain earth of Baudissero, 39. 
 Gerhard, his experiments on granite, 
 38. 
 
 of Glass, nature of, 105. Its various 
 properties, ib. Its utility, 106. 
 Value of it anciently, 107. Origin 
 of the word ; Aristotle’s problems 
 respecting it, 108. A Pheniciau in¬ 
 vention, ib. Manufactories of Alex¬ 
 andria, 109. Malleable glass, ib. 
 Discussion on the malleability of, 
 110. Tax imposed on by Alexander 
 Severus; Portland vase; employed 
 in forming windows, 111. Manufac¬ 
 tured in Britain prior to the Ro¬ 
 man invasion, ib. Extract from 
 the ‘‘Northumberland Household 
 Book,” 112. Privileges granted to 
 manufacturers in France, ib. Plate 
 glass casting, 113. Establishment 
 at 8t. Gobain, 114. Flint glass, 
 manufacture of,commenced in Eng¬ 
 land, 115. Plate glass manufactured 
 in England, ib. Chinese unacquaint¬ 
 ed with glass-making, 116. Import¬ 
 ance of the manufacture in England, 
 ib. Madeasourceof revenue,117. In¬ 
 gredients employed in the manufac¬ 
 ture of, 119, Silex and alkali essen¬ 
 tial to the formation of glass; pot¬ 
 ash and pearl-ash used also, 120. 
 Barilla; kelp, ib. Borax and chalk 
 used in the manufacture of, 124. 
 Construction of a furnace for, 125. 
 Three kinds of furnaces used in the 
 manufacture of, 126. The calcar; 
 the fritting process, ib. Double fur¬ 
 nace; proportionate dimensions of 
 furnace and pots, 128. Comparative 
 consumption of fuel in wood and 
 coal furnaces; annealing oven, 129. 
 Glass pots ,■ their formation and sea¬ 
 soning, 130. Manufacture of flint 
 glass, 131. Importance of its quality 
 for optical purposes; experiments 
 for its improvement, 132. Process 
 of melting, 134. Glass gall, 135. Im¬ 
 plements used in the manufacture 
 of; rod, 186. Marvar, 137. Paraison ; 
 blowing, ib. Re-heating; elongat¬ 
 ing, 138. Pontil, ib. Procello; 
 fashioning, 139. Detaching, ib. Re¬ 
 moval to annealing oven; mould¬ 
 ing; annealing indispensable, 140. 
 Bologna phials; Rupert’s drops, ib. 
 Crown glass, description of, 143. Its 
 composition in France; in England; 
 fritting, 144. Recipes for crown 
 glass, 145. Blowing; re-heating; 
 flattening, 146. Twirling ; expand¬ 
 ing; opening, 147. Bull’s eye, ib. 
 Annealing; nice regulation of tem¬ 
 per aturein this process; qualities of 
 crown glass, 148. Broad glass ; in¬ 
 ferior to crown glass; its composi- 
 tion ; preparation, ib. Working; 
 bursting ; annealing, 149. Bottle 
 glass; manufacture of, checked by 
 an increase of duty, ib. Composi¬ 
 tion ; restrictions as to materials; 
 theiy bad tendency. 160. Superiori ty 
 of, for certain purposes, ib. Mate¬ 
 rials employed; in France; at New¬ 
 castle, 161. Fashioning; moulding. 
 Experiments of Count Chaptal, 
 Volcanu gra¬ 
 
 nite, 164. Plate glass: blown plates 
 limited in size, ib. Cast plate works 
 at Ravenhead; difficulties of tha 
 process; materials, 165. Furnaces 
 and crucibles at St. Gobain, 167. 
 Method for regulating the supply of 
 fue' at St. Gobain, 158. Casting 
 tables, ib. Arrangement of the fuun- 
 dery at Ravenhead, 159. Process of 
 easting plates, ib. Squaring; grind¬ 
 ing, 161. Economical improvement; 
 smoothing ; emery powder, 162. 
 Comparative value of large and 
 small plates, 163. Polishing, 164. 
 Silvering, 165. Preparation of amal¬ 
 gam, ib. Mode of its applicat ion, 166. 
 Process of blowing, 167. Punching, 
 168. Partial cutting, ib. Transfer 
 to pontil; completion of cutting, 169. 
 Opening, ib. Sizes of plates; effects 
 of the Bun's rays on, 170. Phos¬ 
 phoric glass, pieparation of bones 
 for ; their vitrification ; process 
 known to Becher; concealed by 
 him, 175. Curious suggestion as to 
 its employment: this glass highly 
 electric when newly made, ib. Va¬ 
 rious small manufactures of glass, 
 176. Thermometer, 177. Blow-pipe, 
 ib. Method of working, 178. oeal- 
 ing tubes, ib. Bending and joining 
 tubes, 179. Forming bulbs at the 
 ends of tubes, 180. Watch glasses, 
 ib. Lunette glasses; glass beads, 162. 
 Striped tubes ; mode of forming 
 beads, 183. Mock pearl beads, 164. 
 Principal defects observable in glass, 
 192. Striae ; threads, 193. Tears, 
 ib. Knots: bubbles; whence they 
 proceed, 194. Bubbles not very det¬ 
 rimental, ib. Specific gravity of, 
 202. Augmented by lime, 204. Mix¬ 
 ed glasses, 205. Their spc< ific 
 weight, 206. Specific gravity in¬ 
 fluenced by temperature, 207. The 
 art of coloring it, and the antiquity 
 of the art ; specimens of Roman 
 mosaic, 208. Analysis of these by 
 Klaproth, 209. Metallic oxides, 2.U. 
 Gold-purple; its great coloring pow¬ 
 er, ib. Kunckel’s proficiency in the 
 art of staining glass, 2ll. Directs 
 the operationsof glass-houses at Pots¬ 
 dam, 212. Yellow color from silver; 
 from lead, ib. From tartar; from 
 beech-wood charcoal, 213. From 
 oxide of iron, green, black glass, ib. 
 Red, 214. Blue : directions found 
 in old authors, 215. Imitation of 
 the garnet; of the amethyst, ib. Of 
 the emerald, 216. Of sapphires, ib. 
 Opaque glass; black, 217. Whits 
 opaque glass, ib. Opal,218. Ancient 
 pictures formed of colored glass, ib. 
 How executed, 219. Accidental col¬ 
 oring of plate glass at St. Gobain, 
 221. The art of cutting, engraving, 
 and etching on; origin of the art of 
 cutting, 235. Implements used in 
 cutting,ib. Frosting, 238. Patterns 
 produced by moulding, ib. Engrav¬ 
 ing on glass, 239. Etching,240. In¬ 
 crustations; origin of the art, 242. 
 The devitrification of, 243. Devit- 
 rified glass; uses to which it may 
 be applied, 244. Common bottle 
 glass best suited to it; method of 
 effecting the change, ib. Experi¬ 
 ments of Dr. Lewis, 245. Revitri¬ 
 fication of, 216. Experiments of 
 Sir James Ilall, 247. Glass con¬ 
 verted into Reaumur’s porcelain, 
 by burning lava, 219. 
 
 Glazes for porcelain generally * analy¬ 
 sis of that used by the French, 64. 
 
 Green, Mr., proprietor of Stangate 
 glass-house; his specimens of good 
 heavv-glass, 196. 
 
 Guinand, M., his humble origin; 
 energy of character, 190. Ex ami nut 
 
 ib. 
 
 ai quite*' 162. Klingt-tein, 163. 
 
INDEX 
 
 252 
 
 telescopes, and constructs others; 
 unable to procure glass of good qual¬ 
 ity, 190. Is incited to examine into 
 the causes of inferiority; his extra¬ 
 ordinary perseverance amidst acci¬ 
 dents and difficulties, 197. His ulti¬ 
 mate success, 198. Accident lead¬ 
 ing to further improvement, 199. 
 Prosecutes his art in Bavaria; re¬ 
 turns home, and further pursues his 
 favorite object, 200. Dies, 201. 
 
 H. 
 
 Hall, Sir James, he experiments on 
 compression in modifying the action 
 of heat, 217. 
 
 Hanway, Jonas, his account of Chi¬ 
 nese palace at Dresden, 2*4. 
 Herculaneum, utensils of glass found 
 in the ruins of, 109. 
 
 J. 
 
 Jao teheou, precious jewels of, 97. 
 Jaquin, M., his invention of mock- 
 pearl, 184. 
 
 Jasper-ware of Wedgwood, 28. 
 
 K. 
 
 Kao-lin, analysis of, 93. 
 
 Keyaler, his description of a mode of 
 composing pictures in colored glass, 
 220 . 
 
 Kia-tsing, 99. 
 
 King-te-ching, porcelain manufacto¬ 
 ries of, 94. 
 
 Klaproth, his investigations respect¬ 
 ing the capability of dissolving silex 
 in water, 36. His analysis of the 
 specimens of Roman mosaic, 209. 
 His analysis of ancient blue glass, 
 ib. His account of ancient mosaics, 
 220 . 
 
 Ku-tong, 101. 
 
 L. 
 
 Lathe, potter’s, description of, 48. 
 Lenses, formation of; preparation of 
 the necessary tools, 189. Choice of 
 glass for, 190. Grinding and polish¬ 
 ing, ib. 
 
 Loysel, M.,his direction for the con¬ 
 struction of a fhrnace in the manu¬ 
 facture of glass, 126. Recommends 
 the use of minium in the manufac¬ 
 ture of flint glass, 132. His recipe 
 for the formation of crown glass, 
 144. His account of the composi¬ 
 tion of bottle glass in France, 151. 
 His account of the composition of 
 plate glass, at St. Gobain, 156. His 
 recipe for the composition of arti¬ 
 ficial gems, 173. His experiments 
 on the specific gravity of glass, 202. 
 Lunette-glasses, manufacture of, 182. 
 Lustre-ware, gold and silver, bO. 
 
 M. 
 
 Macquer, his remarks on Reaumur’s 
 experiments concerning porcelain, 
 23. Furnace of, 67. 
 
 Manganese, black oxide of, used for 
 clearing glass, 122. 
 
 Mansell, Sir Robert, obtains a mo¬ 
 nopoly for manufacturing glass in 
 England, 116. 
 
 Modeller,qualifications requisite for, 
 
 Morveau, Monsieur Guyton, his ex¬ 
 periments on the specific gravity of 
 melted glass, 121. His observations 
 on the devitrification of glass, 248. 
 Moulds, method of making them, 62. 
 
 N. 
 
 Neri, his recipe for imitating the 
 garnet, 216. His recipe for white 
 opaque glass, 218. 
 
 Neumann, first observes the devitri¬ 
 fication of glass, 243. 
 
 Nungarrow, factory, superiority of 
 its porcelain, 56. 
 
 P. 
 
 Pipes, tobacco, manufacture of prose¬ 
 cuted to a great extent; description 
 of material, 86. Boring, moulding, 
 polishing, baking, 87. Description 
 of the kiln of crucibles, 88. Manu¬ 
 facture of, prosecuted to a great ex¬ 
 tent in Holland. 89. Originally con¬ 
 veyed thither from England, ib. 
 
 Polo, Marco, his mention of the por¬ 
 celain manufacture of China, 96. 
 
 Porcelain, 17. Antiquity of, 18. 
 Made in Japan at nn early period, 
 20. Oriental porcelain common in 
 Europe in the first century, ib. An¬ 
 tiquity of the manufacture of in 
 Egypt, 21. Probable origin of the 
 word, ib. Manufactured in Saxony 
 by baron de Botticher, 22. Reau¬ 
 mur’s experiments respecting, 23. 
 Hanway’s account of that manufac¬ 
 tured at Dresden, 24. Antiquity of 
 manufacture in Staffordshire, 25. 
 Manufactured by the two brothers 
 named Elers, ib. Manufacture of, 
 important to England, 30. Manu- 
 facturedat Lambeth; Derby; Shrop¬ 
 shire; Yorkshire; at the Rocking¬ 
 ham works, 31. A tax imposed 
 upon stone battles, 33. Ingredients 
 used in the manufacture of pottery, 
 34. The quality of clay used in the 
 manufacture of, ib. Steatite or soap¬ 
 stone used in the manufacture of, 
 39. Spuma maris used in its manu¬ 
 facture, 40. Quality of water used, 
 ib. The process of blunging, 41. 
 Process for preparing the flint, 42. 
 Utility and description of Brindley’s 
 mill in the preparation of,ib. Slip; 
 slip-kiln, 43. Slip-house, 44. The 
 process of slapping in the manufac¬ 
 ture of, 45. Method of manufactur¬ 
 ing in France not kept so secret as 
 that in England, ib. Calcined bones 
 used in the manufacture of, 46. The 
 earth used in Berlin, 47. The for¬ 
 mation of utensils in the manufac¬ 
 ture of; the process of throwing, 
 48. Milled edges; the handler, 61. 
 Method of ornamenting porcelain 
 described, ib. Method of making 
 moulds, 52. Boiled plaster used in 
 making moulds, ib. Increasing skill 
 of artists, 63. Mould-maker; meth¬ 
 od of his working, 64. Method of 
 casting, ib. Beggars of imperfect 
 materials in England; Nungarrow 
 factory, 67. Furnace of MM. de 
 Montigny and Macquer, 67. The 
 biscuit-oven of Worcester: Chinese 
 method of firing, 60. Duration of 
 the baking process; oven-man ; trial 
 pieces, 61. Composition of raw 
 glazes ; bad effects of them, 62. 
 Glazes generally, 63. Inferior glazes; 
 low-priced wares, 66. Regulation of 
 temperature, ib. Qualities of good 
 porcelain; stone-ware, 67. Painted 
 ware of Worcester ; of Stafford¬ 
 shire; of Derby; of Yorkshire, 69. 
 Metallic oxides, 70. Addition of 
 fluxing bodies necessary, ib. Ve¬ 
 hicle used with the colors, 73. Pur¬ 
 ple and violet, 74. Red, 75. Yel¬ 
 low, ib. Blue, 76. Green; brown; 
 black, 77. White, 78. Compound 
 colors, 79. Giiding ; lustre-ware ; 
 preparation of colors, 80. Enamel¬ 
 ling kilns, ib. Trial pieces, 81. Gild¬ 
 ing and burnishing, ib. Analysis of 
 the fluxes and recipes for colors, 83. 
 Method of transferring copperplate 
 designs to porcelain, 84. French 
 method, 85. Manufacture of in Chi¬ 
 na, 90. Supposed superiority of old 
 China-ware, ib. Materials employ¬ 
 ed ; kao-lin; pe-tun-tse; their pre¬ 
 paration, 91. Oils or varnjphes; 
 their composition, 92. Hao-che 
 superior to kao-lin, 93. Analysis of 
 kao-lin, ib. Extent of factories at 
 King-te-ehing ; great number of 
 
 workmen, 94. Preparation of ma¬ 
 terials, ib. Method of fashioning 
 utensils ; moulds, ib. Division of 
 labor, 95. Deficiency of the Chinese 
 in the art of design, 96. Blue first 
 the only color used, 97. Chinese 
 ignorant of chemical science, 98. 
 Umiam; tsou-tchi, 99. Kia-tsing 
 method of forming it, ib. Chinese 
 furnaces, 100. Passion for old por¬ 
 celain, 101. Ku-tong, ib. Mock 
 antiques; reasons for the costliness 
 of China-ware in Europe, ib. Por¬ 
 celain tower, ib. Tse-ki; attempt 
 of the emperor to transfer the ma¬ 
 nufacture to Pekin, 102. 
 
 Pottery, antiquity of, 18. Made in 
 England before the invasion of the 
 Romans, 19. Antiquity of in China, 
 20 . 
 
 Pyrometer of Wedgwood, 35. 
 
 R. 
 
 Reaumur, experiments of, concern¬ 
 ing the manufacture of china, 23. 
 Hi9 experiments upon the devitri¬ 
 fication of glass; his porcelain,243. 
 Rockingham, -the, porcelain manu¬ 
 factory, 31. 
 
 Rose, Mr. John, his glaze for hard 
 porcelain, 63. 
 
 Rykum, boiling fountain at, 36. 
 
 8 . 
 
 Schwanhard, Henry, his method of 
 etching on glass, 240. 
 
 Seggars, proper materials for the con¬ 
 struction of them wanting in Eng¬ 
 land, 65. Use of, 66. 
 
 Severus, Alexander, his tax on glass, 
 
 111 . 
 
 Silica, 34. Analysis of, 36. 
 
 Slapping, the process of, 45. Per¬ 
 formed by steam power, 46. 
 
 Slip, the mixture used in porcelain 
 manufacture, 43. 
 
 Spuma maris, its employment in 
 porcelain works In Spain, 40. 
 
 Steat ite, or soapstone, Cornish, analy¬ 
 sis of, 39. 
 
 St. Gobaiu, glass manufactory at, 114. 
 
 Its early failure and revival, ib. 
 Stone-ware, its composition, 67. Best 
 description of it made at Lambeth, 
 ib. 
 
 T. 
 
 Table-ware of Wedgwood, 27. 
 Terra-cotta of Wedgwood, 28. 
 Thevart, his invention of plate glass, 
 113. 
 
 Thermometer tubes, 176. Mode ot 
 giving them an elliptical bore, 177. 
 Throwing, the process of, 48. 
 Tower-porcelain, at Nan-king, 101. 
 Tsou-tchi, 99. 
 
 Turning-lathe of the potter, 49. 
 
 V. 
 
 Vasa, Murrhina, formed out of a 
 transparent stone, 20. 
 
 Vase, Portland or Barberini, 53. 
 Farther account of, 111* 
 
 W. 
 
 Watch-glasses, manufacture of, 180. 
 Lunette-glasses, 182. 
 
 Webber models of Portland or Bar¬ 
 berini vase, 63. 
 
 Wedgwood, Josiah, his improvement 
 in the manufacture of porcelain, 
 26. His table-ware, 27. Queen’s- 
 ware ; terra-cotta; basaltes; white 
 porcelain biscuit; bamboo; jasper, 
 28. His porcelaiu biscuit used by 
 chemists, ib. His evidence before 
 a committee of the privy counril, 29. 
 His pvrometer, 36. His encour¬ 
 agement to artists, 53. His great 
 services in the painting of porce¬ 
 lain, 69. 
 
 White porcelain biscuit of Wedg¬ 
 wood, 26. 
 
 THE END 
 

 
 
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