THE COLLECTED WRITINGS OF HERMANN AUGUST 8EGER Professor at the Royal Technical Institute, Berlin Chief of the Chemical-Technical Experiment Station, Royal Porcelain Factory, Berlin PREPARED From the Records of the Royal Porcelain Factory at Berlin BY DR. H. HECHT and E. CRAMER TRANSLATED BY THE MEMBERS OF THE AMERICAN CERAMIC SOCIETY EDITED BY ALBERT V. BLEININGER, B.Sc. Instructor in Ceramics, Ohio State University Published jointly by the Society and the Chemical Publishing Company VOIvTJME II EASTON, PA.: THE CHEMICAL PUBLISHING COMPANY 1902 CONTENTS B {Continued') IV. Treatises Referring to Whiteware 1.. Examination of Some Fine Whiteware Bodies - - 553 2.. Defects of Glazes and Their Causes - - - 557 3. A Discussion of Glazes with Special Reference to Whiteware Glazes Free from Dead - - - . 4.. Whiteware Glazes with Use of Barium Sulphate - 634 5. The Influence of Sulphuric Acid on Glazes and Bodies - 645 6.. Underglaze Colors and Their Preparation - - 651 7.. Grinding Mills for Glazes and Colors - - - 667 V. Treatises Referring to Porcelain 1.. On the Relation between the Composition of the Sennewitz Kaolins and their Behavior in Burning - - 669 2.. The Composition of Some Foreign Hard Porcelain Bodies - 678 3.. Some Raw Materials of the Porcelain Industry at Dimoges 695 4.. The Wegeli Porcelain Bodies - - - 700 3.. Colored Porcelains - - - - . 704 The Composition of a Bisque Body - - - 707 7. Japanese Porcelain, Its Decoration, and the Seger Porcelain. The Red and Flamed Cuprous Oxide Glazes - - 708 c Reports of Travel and Letters (Polemics) I. Letters from the Year 1872 I- The Oldenburg Clinkers - - - . 7^^ 2. The Belgian and Dower Rhine Brick Industry - - 762 3» The Staffordshire Potteries - - . 769 4m The English Brick Industry - - - . 78^ 5. Notes on the Manufacture of Bricks Pressed from Clay Dust 801 6 m The Manufacture of Black Vitrified Bricks - - 807 7m The Nassau Stoneware District - - . 809 ID Reports from Vienna Exposition, 1873 Im The English Pottery - - . . 821 2 m The Indian Clay wares - - . . 829 3m The French Clay Industry - - - . 830 IV CONTENTS PAGE. 4. Brick Machines ----- 835 5. Manufacture of Sewer Pipes - - - 843 6. The Wienerberg Brick Yards - - - - 848 7. Means of Transportation - - - - 860 8. Italian Pottery ----- 866 9. Stoves ------ 869 10. The Belgian and Dutch Clay Industries - - - 874 11. The German Clay Industry - - - 877 Notes on the Brick Industry of Northern France - - 883 III. Report from the Paris Exposition, 1878 1. Brick Products and Brick Machines - - - 890 2. Wall and Floor Tiles ----- 897 3. Fine Clay wares ----- 9°^ Examination of Two Floor Tiles - - - - 920 The Manufacture of Gas Retorts - - - 921 IV. Report from the Berlin Trades Exhibition, 1879 1. Face-Brick and Terra-Cotta - - - - 933 2. The Manufacture of Stoves - - - 935 3. Majolica ------ 940 4. Clay-Working Machinery - - - - 944 5. Porcelain and Whiteware - - - - 94^ The Clay Industry of the Island of Bornholm - - 95 ^ The Exhibition of the Union Centrale des Arts Decoratifs, in Paris, 1884 - - - - - - 959 Phenomena and Precautions To Be Observed in the Burning of Cal¬ careous Clays. Reply to an Article by Olschewsky - 971 Public Letter of Olschewsky to Dr. Seger - - - 987 Public Reply of Dr. Seger to the Letter of Olschewsky - 992 The Hainstedt Clays. A criticism Directed against the Work of Dr. Strohecker ----- 999 Reply of Dr. Strohecker ----- 1002 Some Melting-point Determinations of a Number of Professor Seger’s Cones, by Dr. C. Bischof - - - 1005 Reply by Dr. Seger ----- Reply by Dr. C. Bischof - - - - Note on the Determination of Temperature in Kilns by Means of the Pyroscope Cones, Dr. Seger - - - 1017 On the Question of Standard Cones, by Dr. Seger - 1020 Note on the Polemics Regarding the Seger Pyrometric Cones, by the German Editors 1021 CONTENTS V PAGE. Pyrometric Trials of Seger Standard Cones in Different Kiln Systems, by Dr. P. Jochum - - - 1022 Pyrometric Measurements, by Dr. Seger - - - 1024 The Coloration of Claywares by Iron at High Temperatures. Criti¬ cism of an Article b}^ Dr. Knapp - - - 1027 Coloration of Porcelain and Glass in the Glost Kiln, by Dr. Knapp 1038 Coloration of Porcelain in the Glost Burn by Dr. Seger - 1041 The Porcelain Hard Fire Red - - - - 1042 Correction to a Statement by Professor A. Schmidt - - 1044 D Uncompleted Work and Communications from the Records of the Royal Porcelain Manufactory Communications Concerning the Testing of Brick-clays by Members of the German Association of Clay ware Manufacturers 1047 Results of an Inquiry Made by the German Society of Clayware, Lime and Cement Maufacturers, into the Fuel Consumption of different Kiln-systems - - - • 1067 Mechanical Examination of a Brick Clay - - 1108 Investigations of Materials for the Brick and Pottery Industries i^. Clay from Carlsburg (Convent Loccum) - - - 1111 2. Clay from Puchau - - • ' 3. Brick Clay from Wickendorf, near Schwerin - - 1113 4. Brick Clay from Helmstedt - - ■ ^^^4 5. Clay from Fdrderstedt, near Schoenebeck - - mS 6. Clays from Hainstedt - - • ‘ 7. Clays from the Eifel - - - ‘ -1118 8. Investigation of a Tin Glaze for Stove Tiles - - 1119 9. Glaze for the Velten Clay - - - -1121 10. Examination and Preparation of a Smalt - - 1121 11. The Cause of the Destruction of the Zinc Trimmings of a Ber¬ lin Market House - - - ■ -1121 12. Faulty Burns in the Pottery Industry - - 1124 Examination of Materials of the Fire-Brick and Stoneware Industries 1. Analyses of Fire-Brick, Glass, Pot and Stoneware Clays - 1127 2. Analyses of Fire-Brick, Etc. - - - ^^30 3. Examination of the Clays from Grossalmerode - - 1131 4. Opinions on the Raw Materials Suitable for the Manufacture of Plumbago Crucibles - - - " ^^ 3 ^ VI CONTENTS PAGE. Examination of Materials for the Whiteware and Porcelain Industries 1. Analysis of the Whiteware Clays of Lothain - - 1137 2. Tests of Kaolins ----- 1135 3. Concerning the Cause of the Rolling-up of the Glaze Rayer - 1147 4. Concerning the Origin in Yellow Spots on Biscuit Ware 1148 5. The Investigation and Method of Preparation of a Black Color for Muffle-fire - - - - - 1149 Index - - - - - - 1153 r B. TREATISES WHICH RELATE TO SPECIAL BRANCHES OF THE CLAY INDUSTRY IV. ESSAYS REFERRING TO WHITEWARE Examination of Some Fine Whiteware Bodies Professor Edward Orton, Jr., Translator The bodies, whose composition is communicated in the fol¬ lowing note, have been collected on travels undertaken by the order of the Minister of Commerce. They originate from fac¬ tories whose size as well as the quality of their products causes them to occupy a high rank. The bodies designated as A and B are worked in two French establishments, and the bodies C and D come from a Belgian factory, the first being used for fine table ware, the second for more ordinary articles. Body B is of German origin. The fac¬ tories located at widely distant places, of course, work very dif¬ ferent raw materials, and have also widely different methods of preparing the body. Body A is obtained by simply washing and ^ieving the raw materials just as nature has furnished it. It consists of the washed kaolin of St. Yrieux, high in feldspathic residue, a fat and a fine sandy clay ; an addition of feldspar as such, or ground silica as quartz, flint or sand, does not take place. Body B is made up of kaolin and a plastic clay of unknown French origin which receive an addition of ground Norwegian feldspar and pure quartz sand. For the bodies C and D, English kaolin (china clay), plas¬ tic clay from Belgium, ground English cornish stone and flint 554 WHITEWARE from Dieppe are used. The difference between the bodies con¬ sists in the fact that the former is higher in kaolin and cornish stone, the second higher in plastic clay. The origin of the raw materials for body E is not known to me. The biscuit made from the bodies is in every case pure white in color, and with the exception of body A, which appears least resistant, cannot be scratched with a steel blade. Of the others body B seems to be the hardest one, possessing the clearest ring. The examination was carried out in such a way that the amounts of the separate constituents of the unburnt bodies were determined as well as the proportion of the definite mineral com¬ pounds represented by them, that is, the quartz, the feldspar and the hydrous silicate of alumina. This separation was made, ac¬ cording to the method described in detail in a previous essay, by heating with sulphuric acid which decomposes only the alumi¬ num silicate (the real plastic clay substance of the kaolin and plastic clay), while the quartz and feldspar remain unattacked. The results of the analyses are shown in the table on page 556. On comparing the column of this table which expresses the chemical composition of that part of the body decomposed by sul¬ phuric acid and representing in its main part, at least in case of the purer clays in question, hydrous silicate of aluminium which gives to the body its plastic properties we find a remarkable agreement of the figures. This result corroborates previous in¬ vestigations concerning the constitution of kaolins and plastic clays, and shows that in general we are dealing, in the plastic constituent, with a factor chemically as constant as the quartz and feldspar of the bodies. While, however, quartz and feldspar in the finely-powdered condition in which they are brought in, either intentionally or by the washed clay materials, do not show any physical divergences, this cannot be said of the hy¬ drated aluminium silicate, the real clay substance. According to previous investigations the less plastic clay substance of the kaolins shows some chemical differences from the clay substance of the plastic clays, of the lignite formation, inasmuch as in the latter the content of water is somewhat smaller and the alkali content correspondingly higher, but these differences are not so EXAMINATION OF WHITEWARE BODIES 555 great that definite conclusions can be drawn from the chemical analysis as to whether the clay substance is derived from a kao¬ lin or a plastic clay. The rational analysis gives definite start¬ ing-points in regard to the content of quartz and feldspar, and also as to the amount of clay substance, but tells nothing as to its de¬ gree of plasticity. In respect to the last point, empirical tests must always be made based on the rational analysis in order to de¬ termine the ratio between kaolin and plastic clay and to produce the desired condition of plasticity. But these empirical tests are much simplified and their success assured since it is easy to maintain the other factors^ the content of quartz and feldspar constant, by a simple calculation. Since clays contain varying amounts of these constituents by simply replacing plastic clay by kaolin and vice versa^ the other relations are changed at the same time, and the degree of this change is not known. An example might illustrate this : Supposing it is desired to produce a body of the physical constitution of the French body B from German raw materials and there are selected washed kaolin from Sennewitz as it is used in the Royal Porcelain Fac¬ tory, containing 65 per cent of clay substance and 35 per cent of quartz powder, plastic clay from Ebernhahn found to contain 86 per cent of clay substance and 14 per cent of quartz powder and ground feldspar and quartz and starting with a ratio of kaolin to plastic clay of i : 2. Thus one-third of the clay substance or 17.87 per cent is brought in by the kaolin and two-thirds or 35.74 per cent by the plastic clay. We now have the following simple calculation: 65 ; 17.87 = 100 : X = 27.49 parts of Sennewitz kaolin, 86 : 35.74 = 100 •. y — 41.56 parts of Ebernhahn clay, in addition 21.22 parts of ground quartz, 9.73 parts of feldspar, 100.00 parts of body. 27.49 pts. Sennewitz kaolin = 17.87 clay sub. -}- 9-62 quartz, 41.56 pts. Ebernhahn clay = 35.74 clay sub. -f- 5.82 quartz, 21.22 pts. ground quartz = 21.22 quartz, 9.73 pts. feldspar = 9.73 felds. 100.00 parts of body = 53.6i clay sub., 36.66 quartz 9.73 felds. This corresponds to body B. 556 WHITEWARE (■001 oi paiBinoxBO) ■piDB Duni[d -jns Xq pasoduioDaci (•jBdspxaj pnB zijbuS) •piOB oijnqdins Xq ps'sodraooap xon O >0 0 \ lo M •IBXOX 0) tv O O' O o) •■H (•ooi ox paxBinoiBO) •pioB ounqd -Xns Xq pasodniooaa [■jiBdsppjpuB ZJJBnS) •ppB Dianqdins Xq pasodniooap xom a\ o^ •I^iox M O O O (•001 ox psxBinojBO) •ppB DU nqd -jns Xq pasodiuoDDQ (U 00 O rO TO • (•XBdspXDJpUB ZXJBnS) •piDB Dianqdxns Xq pXsodraoDDp XON 00 M fO •l^iox O) O) 0^ o\ VO y • • - as VO rO O Xh VO N (•001 OX paxBxnDX'BO) •piDB DlJUlXd -Xns Xq pasodinoDDa Ov VO 0\ M rJ- (•JBdspxDX ptxB zx-iBn5) •piDB Dianqdxns Xq pDsodtnoDDp xoN •T^xox w O VO cx (•OOI ox pDXBXnDXBO) •piDB Dxanqd -xns Xq xiasodnioDDa (•aBdspxaj puB zxaBn(5) •piDB Dianqdxns Xq pDSOdnioDDp xoN o lo 00 C7v C'4 00 o to VO u O Tt 1 1 VO M O O d rn M o 0\ 'Tt* 00 fO o CM VO VO 1 1 1 1 HH 1 1 1 CM* 1 ro VO CM hH a\ Tl- . N p 03 •d .H 'o a» < ■ dark brown. Parts. Pure ferric oxide Pure chromic oxide Pure zinc oxide 76.2 [- red-brown. 66 o WHITEWARE Light reddish brown Parts. Pure ferric oxide 80.0 Pure chrome oxide 76.2 Pure alumina 51-5 Pure zinc oxide - - 243.0 Yellowish brown Parts. Pure ferric oxide 80.0 Pure chrome oxide - 76.5 Pure alumina 103.0 Pure zinc oxide - - 324.0 light reddish brown. yellowish brown. If the addition of alumina and zinc oxide is increased still more, the color is scarcely changed but the mixture is more easily attacked. Since none of the ingredients enter into fusion the oxides in these colors must likewise be ground very fine and intimately in the wet mill; The stronger they are ignited the more resistant will they become. A beautiful dark brown is also obtained from Parts. Pure manganese oxide - - 79-5 | (j^rk brown. Pure chrome oxide - - - 76-2 j A mulberry-brown, suitable, however, only for whiteware (not for porcelain), is obtained by precipitating solutions of 47.4 parts potash alum and 13.85 parts manganous sulphate (cryst.) with a solution of 30 parts of anhydrous sodium carbonate, washing the precipitate well, decanting and igniting at a medium low heat. Blue Colors The blue colors are prepared by mixing the oxide or phos¬ phate of cobalt with alumina and zinc oxide. While the pure cobalt oxide is dissolved in the glaze forming a blue transparent body, the colors become lighter but opaque as soon as the cobalt oxide is blended with alumina and zinc oxide and ignited very strongly. The mixture of the oxides must likewise be ground very fine in water. A dark, very resistant blue which is well suited for the or¬ dinary blue underglaze decoration on porcelain is obtained by mixing UNDERGLAZE COLORS AND THEIR PREPARATION 661 Cobalt phosphate Pure alumina Parts. dark blue. 103 i The cobalt phosphate is obtained by precipitation from 19.5 parts of the cobaltous chloride or from 40 parts of crystallized cobaltoiis sulphate in aqueous solution with 53.8 parts of sodium phosphate and 5.3 parts of sodium carbonate, washing and ig¬ niting at a low heat. The mixture is to be ground finely in the wet condition and to be ignited strongly; it will result in a beautifully blue-colored body. Or there are mixed Parts. Pure black cobalt oxide - - 82.8 Pure alumina - - - - 103.0 igniting the mixture. Lighter blue colors are obtained from dark blue, Pure zinc oxide Cobaltous phosphate Alumina Parts. 20.3 34.5 blue. 51.5 A very light blue is produced from Pure zinc oxide Cobaltous phosphate Pure alumina - 35-5 8.6 51-5 light blue. If it is desired to tint the blue it will be necessary to add a few more oxides. A deep blue approaching a grayish tint is obtained by mixing the oxides of cobalt and nickel. Equal parts of Black cobalt oxide and nickel oxide are mixed and the mixture ignited, tained by mixing I dark grayish blue, A dark bluish green is ob- Black cobalt oxide - Chromium oxide Alumina Parts. 165.6'^ 76.2 >■ dark bluish green. 154-53 Strong ignition here also tends to increase the beauty of the color. 662 WHITEWARE Parts. Zinc oxide - Cobaltous chromate Pure alumina Zinc oxide Cobaltous chromate Alumina lighter bluish green. light bluish green. The cobaltous chromate is prepared by precipitation from a solution of 154.8 parts of cobaltous sulphate (anhydrous) with a solution of 97.1 parts of neutral potassium chromate, thorough washing of the precipitate and weak ignition. Green Colors Chromium oxide is used as the base for the green colors. In regard to the addition of porcelain body there must be con¬ sidered that it must be as free from iron as possible, because the beauty of the color is injured by a slight content of iron. For dark green there are used Parts. Pure nickel oxide - - - i49-6 | green. Pure chromium oxide - - - 76.2 j mixed intimately and ignited strongly. For chrome green pure chromium oxide is used, obtained by weakly igniting acid potassium chromate with an equal weight of sulphur flowers followed by thoroughly washing or by igniting mercurous chromate. Lighter green colors are obtained by igniting compounds of chromium oxide with calcium carbonate and fluor spar. The receipt given in Tenax (Proessel) always gave satisfactory re¬ sults, but I modifled it by introducing the potassium chromate always in solution. For this purpose there were mixed Parts. Potassium bichromate - - 36 Calcium chloride (fused) - - 12 Finely ground quartz - - 20 Marble - - - - - 20 Fluorspar - - - - 12 Quartz, marble and fluor spar are first finely ground and then, after decanting off the water as much as possible, treated with a hot saturated solution of calcium chloride and potassium light green. (Victoria green). UNDERGI^AZE COLORS AND THEIR PREPARATION 663 bichromate, the whole being evaporated to drjmess. The dry mass is well rubbed together in a porcelain mortar and then burned at as high a heat as possible. A reducing constitution of the fire-gases gives rise to a more beautiful and brilliant color, while with a continuously oxidizing condition it approaches more the color of the darker chrome green. It also is not per¬ missible to compound the color with porcelain body because on continued oxidizing fire, it would change very easily to a dirty grayish green. A light yellowish green of another tint is obtained from Parts. Barium chromate - - - 46 . Marble.34 C light yellow Hydrous boric acid - - - 20 J g^’^en, a color which, however, is suitable only for whiteware since it is destroyed at a high temperature. It is to be ignited at about gold-melting heat. Barium chromate is produced by precipitation from 104 parts of barium chloride with 97.5 parts of neutral potassium chromate. The precipitate is to be washed and slightly ignited. Red Colors Red colors are obtained either by preparing the so-called pink, or by means of gold or finally for low temperatures by means of iron oxide preparations. A fine pink is produced by mixing the following substances : Parts. Pure ignited tin oxide Marble Quartz These are ground by themselves, then treated with a hot satu¬ rated solution of three parts of acid potassium chromate and four parts of borax, the solution being evaporated to dryness, well ground in a porcelain mortar and ignited very strongly. Then the red mass is to be ground finely and again washed. The burning must be done under oxidizing firing conditions. If the quartz is left out entirely and the proportion of tin is increased or that of the marble decreased a more reddish blue tint is produced. 664 WHITEWARE I used for this the following mixture Parts. Ignited tin oxide . - - 70 Marble - - - ■ - 23^ ground very fine as before, then treated with a hot solution of 3 parts of acid potassium chromate and 4 parts of borax evap¬ orated to dryness, well rubbed in a porcelain mortar, strongly ignited, ground very fine and washed thoroughly until all of the yellow color of the solution has disappeared. If the marble is left out entirely, tints are obtained which approach lilac, but which cannot resist a high heat, like that of the porcelain kiln even if purely oxidizing conditions prevail. However, for whiteware the following mixture is suitable : Ignited tin oxide - 5 ° 1 Potassium bichromate - - 3 r lilac. Borax - - - 20 J The two last ingredients are also, as before, used in the form of a hot saturated solution, and the mixture is burned after drying at gold-melting heat. Very beautiful purple and rose tints are obtained by intro¬ ducing gold as a coloring metallic oxide. A strong purple-red is prepared in the following manner : Of pure white kaolin, best English china clay, 90 parts are worked up in water by boiling and sieving; then 10 grams of gold are dissolved in a mixture of nitric and hydrochloric acids, the solution being freed from excess of acid as much as possible by evaporation on the water- bath. The gold solution is then mixed with the clay slip, sodium carbonate is added till the liquid is distinctly alkaline, and after an addition of about 20 grams of grape-sugar the mixture is boiled strongly for half an hour, water being added to maintain the same volume. Thus a dark purple colored mass is obtained which must be washed and then dried and ignited at a heat not exceeding silver-melting heat. It will in this way assume a somewhat lighter color. A second washing after the grinding of the color is desirable since the first washing is never as com¬ plete as is necessary. A beautiful rose color is thus obtained from 98 parts of white porcelain clay ) j-ose. 2 grams of gold j UNDERGLAZE COLORS AND THEIR PREPARATION 665 Red colors prepared from iron oxide can be used only at a lower temperature and are thus suitable only for whiteware gla- j they must never be burnt above the melting-point of silver. A good iron-red is obtained in the following manner: 27.8 parts of iron sulphate are dissolved in hot water and by addition of nitric acid, until the iron solution on further addition does not turn darker in color, but remains yellow, being changed to a ferric salt. To this is added potash alum, 189.8 parts. The two solutions are mixed and precipitated with excess of ammonia, washed thoroughly, ignited weakly and after fine grinding again washed. Finally there are mixed Parts. Of this red body (iron oxide-alumina) - - 70 Yellow whiteware glaze containing iron - - 30 which are used without further ignition. Yellow Colors Yellow colors can likewise be used only in the decoration of whiteware. They are all destroyed in the heat of the porce¬ lain kiln. An intense and brilliant yellow color is obtained from titanic acid, or better titanate of zinc. Either the raw titanic acid is ignited and then ground or it is mixed with zinc oxide by wet grinding. A suitable proportion is Parts. Raw titanic acid - - - 41.0) Zinc oxide - - - - 40.6 1 The mixture must be strongly ignited. The yellow color of the raw titanic acid, which always con¬ tains iron, seems to be due to its iron content; at least it is not possible to produce a yellow color with chemically pure mate¬ rials. This yellow color is to be used in porcelain painting only when the ware is burned at as low a temperature as possible. If the glaze, owing to overheating, is in a state of strong fusion the color disappears and a dirty gray takes its place. Another fine yellow is obtained from basic antimoniate of lead, and which may be tinted to orange by means of a larger or smaller addition of iron. 8 666 WHITEWARE A light yellow is obtained from : Parts. Lead nitrate 73-01 Oxide of antimony - 33-0 i Pure alumina 12.2 f Salt - - 100.0 J yellow. The ingredients are well rnbbed together in a mortar, then frit¬ ted at the heat of the whiteware glost kiln, and well washed. If the color is too fusible and disappears easily under the glaze it nate up to 33)^ per cent. The calcium stannate is obtained by strongly heating Parts. Pure ignited tin oxide 75 Marble - 50 ground together in the wet condition. An orange color is ob- tained by mixing Parts. Lead oxide - 50'I Oxide of antimony Ferric oxide 1 orange. Potassium nitrate - 25 J The mixture is to be rubbed together, ignited in the glaze kiln, washed thoroughly and, if necessary, like the preceding color, to be mixed with calcium stannate in order to make it more re¬ fractory. A turquoise-blue is obtained from Parts. Copper phosphate - - ^^ 9-31 Tin oxide . - - - 150.0 j The copper phosphate is obtained by precipitation from 37.4 parts of crystallized copper sulphate with a mixture of 35.8 parts of sodium phosphate and 5.3 parts of sodium carbonate, washing the precipitate thoroughly and igniting slightly. Violet-brown is produced by mixing manganous phosphate and stannic acid in the proportion: Parts. Manganous phosphate - - ^ 77-5 | ^iojet-brown. Pure ignited stannic acid - - 75 -o j Like the copper phosphate, manganous phosphate is pre- MILLS FOR GRINDING GLAZES AND COLORS 667 pared by precipitation from 41-6 parts of crystallized manganous sulphate with 35.8 parts of sodium phosphate and 5.3 parts of sodium carbonate, washing and slight ignition. Fine gray tints are obtained either by dilution of the black colors with soft burned porcelain body or better by mixing the latter with indium oxide or platinum ammonium chloride. Irid¬ ium oxide is the better material furnishing the purest gray. I use as a gray color Parts. Iridium sesquioxide - - . ^ Porcelain body - - . * 95 These are ground intimately, ignited weakly, at about the melt- ing-point of silver and again ground. Mills for Grinding Glazes and Colors Albert Bleininger, B.Sc., Translator It is often necessary in clay-working establishments that a larger number of small mills must be kept in operation in order to reduce the colors, enamels and col¬ ored glazes used, to the required fineness. 5 i were used, in places where this ^ fine grinding was not done by ^ hand on glass plates with a glass rubber, small mills constructed after the manner of the so-called or sandstone, which, however, were difficult to clean, and for this ^ ^ reason were always used for the same color. In the following paragraphs I shall describe a mill 668 WHITKWARE which will facilitate, to a very great extent, the work of fine grinding, and which also will not make the nec¬ essary cleaning of the apparatns too bnrden- some a task. The apparatus con¬ sists of a sort of ball mill of porcelain or an equally hard artificial material as, for in¬ stance, stoneware. A cylindrical porcelain pot with a lid ground on, and made tight by means of a rubber gasket, is filled with porcelain balls about 2 to 3 cm. in diameter to approximately one-quarter of its volume. The material to be ground is added, stirred to a thin slip with water, and the pot is revolved. In this manner the material to be ground is nibbed to an extremely fine powder by the friction of the balls upon each other and upon the shell of the cylinder. The accompanying figures rep¬ resent such a grinding cylinder, the kind that is furnished for the purpose designated above by the Royal Porcelain Factory at Charlottenburg. These are made in two sizes, the smaller holding about 2 kg., and the larger about 15 kg. of the material to be ground. Such cyl¬ inders are revolved around two pivots in a cylindrical casing made of wooden laths and which, by means of cross boards, is divided into from two to eight compartments; the speed of rotation is about twenty revolutions per minute, a more rapid rotation being undesirable because the balls on the inside, owing to centrifugal force, would be forced against the shell, and would thus take part in the rotating motion. This would put a stop to the grinding action. A mill of this sort is the simplest ar¬ rangement which could be imagined. The cylinder mills sold for some time by the Meissen Foun¬ dry and Machine Works are better equipped than the one de- composition of kaolins and tpieir burning 669 scribed above. These consist of a cylindrical wooden shell di¬ vided into a number of compartments, which is turned by means of belt and pulley. The cylinder is mounted on a frame or bracket; according to the number of compartments, two to five grinding cylinders are simply placed into the shell and revolve with the latter. Another illustration shows a mill made by the works men¬ tioned above, which is larger in size consisting of a porcelain cylinder enclosed by an iron shell in which the grinding is likewise accomplished by balls of flint or porcelain. A mill of this description can grind 52 kg. For many years I have used the kind of mill first described, for the purpose of grinding underglaze colors and colored frits in the experimental laboratory of the Royal Porcelain Factory, and I consider them a complete success. The porcelain pots last very long and were used for years before they had to be re¬ placed. The cleaning of the mills is done simply by flushing the pots and also washing the balls with water; however, since some color is very apt to adhere to the pebbles it is best, on changing the color material, to run the cylinders with a charge of sand for about half an hour and then to wash them again so that no un¬ desired blending of colors can take place. V. ESSAYS REFERRING TO PORCELAIN On the Relations between the Composition of Sennewitz Kao¬ lins and Their Behavior on Burning Albert Bleininger, B.Sc., Translator In procuring raw materials for the finer products of the clay industry, be it by mining or by purchase on the market, the manufacturer always endeavors to obtain such materials which have as constant a composition as possible. He does this in or- 670 ESSAYS REFERRING TO PORCEEAIN der not to be compelled, on changing his supply of raw materials, to experiment by long and expensive trials, and to determine again a new suitable working formula from the new material. For those materials which are furnished by nature in more definite chemical combinations, like feldspar, quartz, limestone, barite, or those which are manufactured by chemical works, like the lead and boracic acid preparations, this requirement is relatively easily fulfilled. In this case it is only necessary to determine whether or not these substances contain impurities which might exert an injurious influence on the quality of the products. Con¬ ditions, however, are more complicated in the case of clay ma¬ terial which shows variations not only at different sources, but even in the various layers of the same deposit. On mining the clay material for one’s own consumption, only such portions of the deposit are used which are recognized by certain exterior peculiarities and which have been tested as to their properties. In buying raw materials it is mainly the reputation which certain sources have won which is determinant in the selection and often it is preferred to obtain materials from a long distance at considerable expense and to reject material from near-by as seemingly unsuitable. Owing to the peculiar conditions and the lack of information in regard to the relations existing be¬ tween the chemical composition of a clay and the peculiarities which it shows in manufacture this was justified to some extent; but it must be the task of science to throw light upon these re¬ lations and to remove the restrictions imposed upon the manu¬ facturer in the use of his most important material and to place before him a larger selection of available sources without in any way threatening the success of the manufacture on making a change desired for commercial reasons. The methods of examining kaolins which have been prac¬ ticed so far are not suited to furnish even an approximate esti¬ mate of their behavior in the process of manufacture and hence practical men have considered chemical analysis as being of less importance than the practical tests made with the materials. In fact, it is impossible for a practical man to form an estimate in regard to the behavior of the kaolin from the figures of the em- COMPOSITION OP KAOLINS AND THEIR BURNING 67 1 pirical chemical analysis. The latter, though showing the quan¬ titative relations of the separate elementary constituents, gives no information as to the grouping of the same into mineral com¬ pounds which show a diifering physical behavior, like the hy¬ drous plastic aluminum silicate, the real clay substance and the residue of feldspar and quartz which escaped weathering but have been ground to a fine powder. Numerical data as it is furnished by the rational analysis which shows the grouping of the elementary constituents of kao¬ lin into its closer mineralogical constituents is without doubt of greater practical importance than the empirical chemical analy¬ sis. Not all of the alumina is to be considered in connection with the plasticity of the mass and its ability of being worked, but only that part which belongs to the plastic clay substance; not all of the silica imparts to the body density and stability in the fire but only that contained in the form of quartz; not all the alkali promotes vitrification but only that part which is present in the form of feldspar in the kaolin or the finished body. The practical tests which are necessary owing to the varia¬ tions in composition shown by kaolin even in the same deposit, on changing the source of supply though they permit of an esti¬ mate as to whether the material may be used without changing markedly the properties of the body in a certain body mixture, do not tell us anything whatever in regard to the manner in which the mixture is to be changed if it is found desira¬ ble to retain a kaolin notwithstanding its different composition. The rational analysis, however, informs us in regard to this quite definitely; if it shows an increase or decrease in the quartz con¬ tent of the kaolin, the quartz addition to the mixture must also be either decreased or increased by the amount brought in by the kaolin; if the kaolin itself introduces feldspar into the body it is evident that the feldspar addition must be decreased by that much in order to maintain a constant body composition. In this way the ordinary chemical analysis may be done away with en¬ tirely for practical purposes; since not only the quartz and the feldspar, but also the clay substance possesses a nearly constant composition, as shown by numerous investigations published re- 672 ESSAYS REFERRING TO PORCELAIN ferring to the pure materials under discussion, all the data neces¬ sary for practical work may be obtained from the rational analy¬ sis by calculation and with sufficient exactness. Although for theoretical reasons the estimation of the suitability of a certain kaolin for a certain body composition is only permissible accord¬ ing to the results of the rational analysis (in the absence of coarse constituents not washed out which render the kaolin entirely unsuitable), it appeared of interest to compare in a series of experiments the theoretical conclusions with the results of a purely practical test. In this way the correctness of the theo¬ retical deductions could be confirmed and the influence deter¬ mined which is exerted by a change in composition upon prac¬ tical phenomena. The material for examination consisted of fifteen samples obtained from borings made by Mr. Hecker near Sennewitz for the purpose of opening new banks for the Royal Porcelain Fac¬ tory at Berlin and from which a selection of the china clay which was to be used during the year 1878 was made based on the chemical analyses and practical kiln tests. The rock which gave rise to the formation of the kaolin is porphyry which is ex¬ posed as solid rock near the kaolin mines. The kaolin arising from it by weathering is covered by sand and soil and, according to the character of the original rock, is very irregular in its com¬ position, being colored more or less and containing sand. The samples taken for the purpose of investigation in their ex¬ terior appearance were such that their suitability for the manu¬ facture of porcelain might at least be considered. For the investigations described later on there were availa¬ ble only the washed kaolins produced from the raw kaolins ; the sand had previously been tested at the Royal Porcelain Factory in an empirical way and had been rejected. The samples of raw material used in the investigation were treated in exactly the same way as the kaolin which is prepared by washing on a large scale. It was made up to a slip and was washed through a sieve of 900 meshes per square centimeter (this being the sieve used in the Royal Porcelain P'actory) and the fine grained portion was evaporated to dryness. COMPOSITION OF KAOLINS AND THEIR BURNING According to the communication by Dr. Sarnow, referring to the burning tests, the sand separated in this way possessed the following properties: Number of raw kaolin. Sand washed out. Character of sand after burning in the porcelain glost kiln. I 9.0 Quite white, somewhat vitrified. 2 17-5 Fused completely. 3 20.0 Forming a less glossy fusion than No. 2. 4 20.5 As No. 2. 5 23.75 Fused completely, fusion dirty gray with numer¬ ous brown spots. 6 8.75 Yellow, especially the finer particles. 7 10.0 As No. 6, but colored somewhat less. 8 13.25 Strongly vitrified, dirty color. 9 18.75 As No. 8. lO 13.0 hike the preceding, but more fusible. II 12.5 Yellowish, vitrified but slightly. 12 16.75 Quite yellow, but slightly vitrified. 13 13.75 As No. II. H 11.25 Quite white, strongly vitrified. 15 12.50 As No. 14. A behavior similar to that shown by the coarse sand washed out cannot be assumed for the fine sand remaining in the kaolin. The washed kaolins, properly prepared, after softening and kneading, were molded into tiles with approximately the same content of moisture and in the stiff condition were repressed in a nicely-worked bronze mold into sharp edged tiles, 66 mm. 33 wide and lo mm. thick, their length being deter¬ mined after drying by means of a vernier rule, reading to o.i mm. The burning of the tiles took place in the same saggar in the biscuit burn as well as at the highest heat of the porcelain glost kiln, the trials being set on edge, radially, at an equal dis¬ tance from the wall of the saggar so that a uniform temperature could be assumed; two tests of the same material were always placed diametrically opposite. The shrinkage measurements in the following table are always the average of four separate measure¬ ments of two longitudinal edges of two trial pieces. The poros¬ ity measurements were made by weighing the tests in the dry ESSAYS REFERRING TO PORCELAIN 674 condition, wiping them on the outside after boiling in water for three to four hours, cooling in the water and again weighing. The figures of the table give the quantity of water in grams ab¬ sorbed by 100 grams of burnt kaolin. In regard to the determination of the quantities of feldspar and quartz present in the washed kaolin the reader is referred to earlier communications on this subject. Washed Sennewitz Kaolin Composition. Behavior in the biscuit fire (960° C. — 1000° C.) Behavior in the glost burn. Number of test. Feldspar. N t- cd S Ot Clay substance. Ferric oxide. lyincai shrinkage. Per cent. Porosity. Color. Linear shrinkage. Porosity. Color. I 1.59 33-86 64-55 0.75 0.3 31-7 cream-white 10.2 9-0 light yellow 2 3.24 32-38 64-38 0.92 0.5 30.0 cream-white II .7 2.6 grayish white 3 2.42 31-13 65.50 0.93 0.5 30.4 cream-white 12.2 2.2 grayish white 4 5-55 29.36 65.09 0.78 0.3 31-5 cream-white 14.2 0.0 bluish white, edges somewhat translucent 5 18.20 32-25 49.55 0.95 0.2 28.1 reddish white 12.0 0.0 bluish white, porcelain like 6 1.21 33-39 65.40 0.73 0.7 31.6 cream-white 10.1 10.0 yello’ish, earthy 7 0-54 34-25 65.11 0.73 0.4 30.2 cream-whitel 8.3 12.2 light yellowish 8 5.01 36.28 58.73 1-33 0.4 28.8 cream-white 11.8 2.1 grayish white 9 ^.64 31.69 59-68 0.79 0.3 28.8 cream-white 12.9 0.0 grayish white 10 8.25 35-15 56.60 0.83 0.3 28.1 cream-white 12.0 0.0 grayish white II 0.98 33-44 65.58 0.69 I.O 34.0 cream-white 6.C 20.9 yell’wish white, earthy 12 1.30 31.61 67.05 I.II 0.8 30.4 cream-white 9-9 10.3 light yellowish 13 0.53 37-44 62.03 0.59 0.5 31.8 white 4 -: 22.C nearly white, earthy 14 2.14 36.12 61.74 ^0.63 0.4 31.4 cream-white II .3 4-1 yellowish gray 15 1.21 38.22 60.5; 0.51 0.3 29.1 cream-white II./ 3-2 yellowish gray On examining the preceding table there will be observed first a decided variation in the content of unweathered feldspar in different samples, between 0.53 and 18.2 per cent. The pres¬ ence of quite a large quantity of feldspar which is not removed from the kaolin by washing and which enters the bodies pro- COMPOSITION OF KAOLINS AND THEIR BURNING 675 duced from the materials, is already shown by the behavior of the coarse sand, not washed out, indicated in the first table. The quartz content shows smaller fluctuations which are confined to the limits of 29.36 and 38.22 percent. The content of clay substance corresponds to the content of feldspar and quartz and owing to its uniform constitution, here assumed, it forms a measure of plasticity. The content of iron oxide, which is embraced by the figures for the clay substance, also fluctuates within very narrow limits from 0.51 to 1.33; this is explained by the fact that only such samples were selected which on in¬ spection appeared to be low in ferric oxide. It is not difficult to determine the relations existing between the results of the analysis and the behavior in burning from the figures deter¬ mined for the shrinkage, porosity, and degree of coloring. The shrinkage on soft burning, in which a mutual reaction of the kaolin constituents cannot be assumed, is but very small and hardly exceeds the errors of observation which were made probable in measuring. The porosity also shows but slight fluctuations, and a certain uniformity may be recognized since those trials which contain the smallest amount of clay substance show a smaller pore space and hence are denser than those high in clay substance. This is explained not only from the denser structure, brought about by the presence of the non¬ plastic constituents, feldspar and quartz, and which is carried to quite a low limit, but also by the greater loss of chemically com¬ bined water coordinate with a higher content of clay substance. The color of the soft burned kaolins, according to their content of ferric oxide and the kind of distribution, is in all cases white, tinging occasionally into yellowish and reddish. The behavior of the kaolin at the highest temperature of the porcelain glost fire is more striking than at the lower tem¬ perature. It is found here that the pieces in which the content of unweathered feldspar is very small also possess the relatively slightest degree of vitrification and retain their earthy appearance even at the highest temperatures; at the same time they show only a slight increase in density. It may be assumed that an appreciable action of the mineral constituents infusible at this ESSAYS REFERRING TO PORCELAIN 676 temperature does not take place, and that a slight content of fluxes, feldspar and iron compounds, does not suffice to begin such an action. The density increases with an increasing con¬ tent of feldspar, 2 to 5 per cent, and gives to the kaolins a white- ware-like appearance ; with a still higher content of feldspar the burnt kaolin assumes more and more the character of hard por¬ celain. The shrinkage, proceeding simultaneously with the in¬ creasing density, stands in an intimate relation to the degree of porosity in the soft burnt state ; this is demonstrated by the fact that the mixtures possessing the highest content of clay sub¬ stance, and hence the greatest initial porosity, show also the greatest fire shrinkage. This phenomenon, of course, is observed only on those trials in which shrinkage has ceased, owing to the complete closing of the pores. The color which is assumed by the trials in the highest fire appears less as an expression of the iron content (which, how¬ ever, is still within the limits permissible for white ware and porcelain) than an expression for the degree of vitrification and hence indirectly of the content of undecomposed feldspar. The color in the most porous samples is the lightest, almost white, while with increasing density it becomes yellowish and with nearly completed shrinkage is changed to yellowish gra)/ and grayish white, and finally into the bluish white of the por¬ celain. This change undoubtedly is connected with the action of the fused products upon the iron oxide. The pure iron oxide has a red or brown color and is dissolved in glasses producing a yellow color hardly perceptible with smaller quantities. Such a solution of light colored glass must take place more readily in the burning of kaolin, and the color of free oxide of iron must be the more completely destroyed the greater the quantity of the undecomposed completely fused feldspar. The condition of vitrification influences also the state of oxidation in which the iron exists after heating. In the reducing kiln condition the ferric oxide dissolved in the fusing feldspar, as well as that which has not been dissolved, is changed to ferrous oxide. In the latter state, however, a re-formation to ferric oxide may take place on cooling and this will occur in a higher degree the more porous the COMPOSITION OF KAOLINS AND THEIR BURNING 677 mass has remained, while in the perfectly dense body the action of the oxygen is at least very much lessened. This is shown quite distinctly by the determination of the ferrous iron in the two samples, Nos. 5 and 6, which, burnt in the same saggar, were exposed to the same influences. After burning in the glost-fire there was contained by No. 5 No. 6 Ferric oxide. Per cent. Ferrous oxide. Per cent. 0.00 0.98 0.42 0.34 The color which appears on burning the kaolin tiles due to the ferric and ferrous oxide can, hence, not be solely determinant for the estimation of the behavior in the body, that is, after the addition of fluxes. A much more certain indicator for the dis. coloration, to be expected from the iron content, is offered by the appearance of the sand which has been washed out and which permits us to estimate the more or less uniform distribution of the coloring iron compounds. According to the method of testing kaolins which now is generally practiced, consisting of burning them in the porcelain glost-fire and judging the appearance of the same, that kind will always appear as the best which remains most porous in burn¬ ing ; it is thus shown to be the whitest and most refractory; even a small content of residual feldspar will cause such a ma¬ terial to appear discolored by causing vitrification, unless the content of feldspar is so high that it brings about a perfect clo¬ sing of the pores and solution of the ferric oxide. According to this all kaolins which contain a small amount of feldspar are excluded from the start or must be considered of inferior quality, though this may not be true and may not be founded on the facts brought out in actual use. Still the content of feld¬ spar existing in many kaolins deserves consideration from the economic standpoint. In Germany there are used preferably the very refractory kaolins low in, or free from, feldspar; the excel¬ lence of many French kaolins, however, especially those of Limoges, may in part be traced back to their high content of 678 ESSAYS REFERRING TO PORCELAIN feldspar." If a kaolin is otherwise suitable, its content of feld¬ spar is simply corrected by a corresponding change in the body mixture which is readily carried out by an easy calculation. Thus it would be much more to the point to not subject the kaolins to a burning test, but to burn a body mixture calcu¬ lated from the results of the rational analysis in which the feld¬ spar and quartz contained in the kaolin are duly considered. The Composition of Some Foreign Hard Porcelain Bodies Albert Bleininger, B.Sc., Translator Our German porcelain works not only are using domestic raw materials, but in many cases it is believed that certain foreign raw materials are indispensable for successful manufacturing condi¬ tions. Often purely economic reasons are at the bottom of this usage and in such cases, where freight rates and cost offer induce¬ ments in the use of foreign materials, it is entirely justifiable. On the other hand, the custom is often carried on because it has been established for a long time, and because the manufacturer is afraid to replace the old raw materials with which he is thoroughly acquainted by new ones which might give rise to trouble in manufacture. It is also believed that sometimes the foreign materials possess peculiar properties which are lacking in the domestic materials. This view is especially held with reference to the French kaolins and bodies, much used in German estab¬ lishments. The manufacturer knows, in a general way only, that these bodies are easily worked and that at a relatively low Clay substance Quartz Feldspar 55.88 5-95 38.27 According to this analysis a German porcelain could be produced from this material by add¬ ing only quartz, no feldspar. COMPOSITION OK PORCELAIN BODIES 679 heat, with a very fusible glaze, they produce a fine white and translucent porcelain ; he also realizes, however, that the quality is often subject to variations. The causes of the different prop¬ erties which are in favor of the French bodies are, however, not known. For economic reasons the domestic industry must strive to use its own domestic raw materials and to be as independent as possible of the foreign sources. For this reason an explanation of the properties peculiar to the various bodies should be of great practical interest in order to show to the manufacturer a way of imparting to materials, which are not entirely satisfactory, the desired properties by suitable additions and mixtures with¬ out the use of distant and hence more expensive sources. A journey which I was enabled to undertake, thanks to pri¬ vate support and at the direction of the government, in 1878, to Belgian and French porcelain factories, gave me an opportunity to come into possession of a number of different bodies. The examination and comparison of the latter produced some very interesting conclusions, which, owing to their general interest, are published in the following paragraphs. The hard porcelain bodies examined were obtained from the following sources : 1. Tableware body from Sevres. 2. Body from J. Pouyat at Limoges (pate sup^rieure). 3. Body from J. Pouyat at Limoges (pate ordinaire). 4. Body from L. Sazerat at Limoges (pate sup 4 rieure). 5. Body from L. Sazerat at Limoges (p&te ordinaire). 6. Body from L. Sazerat at Limoges (body for heavy porcelain). 7. Body from Guerin & Co. at Limoges (pate superieure). 8. Body from Guerin & Co. at Limoges (pate ordinaire). 9. Body from Guerin & Co. at Limoges (pate de figures). 10. Body from A. Hache & Pepin Lehalleur at Vierzon (pate sup^ri- eure). 11. Body from A. Hache & Pepin Lehalleur at Vierzon (pate ordin¬ aire). 12. Body of the Soci^t^ anonyme de c^ramique at Hal, Belgium (body for heavy porcelain). 13 - I ) 14 H j from the vicinity of Carlsbad. 68o ESSAYS REFERRING TO PORCELAIN i6 17. Body of the Royal Porcelain Factory at Berlin. These bodies were examined by the method communicated by the author in previous essays; the examination was not re¬ stricted to the determination of the amounts of the elementary constituents present, but the grouping of the latter into mineral constituents was also ascertained, since these govern the behavior of the bodies on working. These constituents were the clayey bonding material (whose character was noted), the fluxes (feld¬ spar and calcium carbonate), and the main non-plastic ingredi¬ ent, the quartz. In a late work on the manufacture of porcelain and white- ware a certain contempt is expressed for this method of exami¬ nation as being entirely without value for practical purposes, and having originated merely in a scientific whim. However, this did not cause me to drop the views evolved in previous work concerning the constitution of clays and bodies. The investi¬ gations now under discussion, on the contrary, are rather adapted to confirm the correctness of the earlier results and to prove their practical value. The practical man often observes, in calculating body com¬ positions from the chemical analysis of the raw materials, that bodies from different raw materials, though possessing nearly the same total chemical composition, may show a very different behavior in regard to their working qualities in the wet condi¬ tion, their behavior in drying, and even their fusibility as well as their ability to carry a certain glaze. This is due to the fact that the chemical gross composition possesses only an indi¬ rect influence upon the properties of a body and that the latter is governed directly by those characteristic components into which the elementary constituents are grouped. These mineral components with pronounced and tolerably constant properties are the factors which express the properties of the body in the process of manufacture, not simultaneously, but gradually dur¬ ing the various stages of working. The quantity and degree of plasticity of the clayey binding material govern most decidedly COMPOSITION OF PORCELAIN BODIES 68 1 the working in the wet condition, turning and molding as well as the shrinking of the body, since the total plasticity is derived from this clay substance; on the other hand, an opposite func¬ tion is expressed by the total amount of the non-plastic material and in the first stage of working it is more or less immaterial in what proportions the separate non-plastic constituents (quartz, feldspar, calcium carbonate, grog) take part. The proportion of these constituents becomes of importance only during the burn¬ ing when their quantity and kind and the activity of the fluxes, feldspar and calcium carbonate, upon the refractory constituents of the body, clay and quartz, determine the density of the body, the resulting structure, durability, color, translucency and the ability to carry a glaze. The practical man, as a rule, will not be able to estimate the effect produced by an increase or decrease of the separate ele¬ mentary constituents upon the properties of a porcelain body ; the success of an alteration may be directly contrary to the de¬ sired effect, according to the means which have been employed to bring about the change. To illustrate, the content of silica in a body may be raised by an increase in the quartz content as well as by adding more feldspar, or the alkalies may be low¬ ered by increasing the quartz or the clay component of the body. It will at once be evident to the practical man that the results of these changes differ widely. Although the manufacturer pos¬ sesses only an indefinite and contradictory knowledge in regard to the influence of the elementary constituents, he will find no difficulty in estimating the effects of the various mineral compo¬ nents ; he is well acquainted with the effects produced on the body by an increase in kaolin, feldspar, quartz, marble, etc. By thus grouping the elementary constituents the chemist approaches the point of view of the practical man much closer, for this conception is not derived from a purely theoretical spec¬ ulation, but it is an eminently practical requirement and, so far, it is the only reliable method of translating the language of purely scientific research into that of practice, though it cannot be denied that the method is still open to a great deal of im¬ provement. The practical man has a clear conception of the 9 682 ESSAYS REFERRING TO PORCELAIN terms clay substance, feldspar, quartz, calcium carbonate. In using the term clay substance he may think of finely washed Zettlitz kaolin of which the commercial grades contain 95 to 99 per cent of clay substance beside i to 5 per cent of finest quartz which cannot be separated mechanically, but only chemically; in speaking of feldspar he can conceive of pure crystallized feld¬ spar without any sign of weathering or foreign admixture; quartz he may consider as being the pure mineral; calcium car¬ bonate, as being marble, calc-spar, etc. These are concep¬ tions with which every practical man is familiar and which mean more to him than silica, alumina, potash, etc., terms which he can apply only rarely, and then only in a very narrow sense. Perhaps this may be the place to indicate the defects which still cling to the method of examination proposed as well as the inaccuracies connected with it in order to make proper allow¬ ance for them. The separation of the porcelain bodies into the components clay substance, feldspar, quartz, calcium carbonate depends on the comparatively ready decomposition and solution of the hy¬ drous aluminum silicate, which alone possesses plasticity, and which we call simply clay substance, but which must not be confused with the term clay, and of the calcium carbonate by hot, concentrated sulphuric acid. For a scientifically accurate separation it would be necessary to require that neither quartz nor feldspar are attacked in the least by the reagent. This is undoubtedly true of the quartz, but cannot be said with accuracy of the feldspar. A pure, unweathered Norwegian feldspar, as it is used by the Royal Porcelain Factory at Berlin on treatment with hot concentrated sulphuric acid for about fifteen hours,' this being the treatment to which bodies and clays are subjected, showed a content of soluble constituents of 3.59 per cent and a content of undecomposed feldspar of 96.41 per cent. The soluble part contained: Per cent. Potash - - - - 0.55 Alumina - - - - 0.62 Silica - . - - 2.40 1 It has been found later that the digestion with hot concentrated sulphuric acid for fifteen hours is not necessary, and that a treatment continued for one to two hours will suffice. In this manner the errors due to this method of analysis are almost entirely eliminated. COMPOSITION OF PORCELAIN BODIES 683 A previous analysis of a feldspar from another source showed a content of soluble constituents of 2.24 per cent, and of unde¬ composed feldspar of 97.76 per cent. Although the ordinary feldspar, the orthoclase, is thus proved to be attacked somewhat, yet the loss is not large enough to affect the analytical determination greatly. In using the nu¬ merical values obtained, it will be well to remember that owing to the slight solution of the feldspar the results are always some¬ what too low; with a high feldspar content of the bodies the feldspar content may be too low by i to 1.5 per cent, and that of the clay substance correspondingly high. This correction should be made in calculating the body mixtures from the analyses. This error is still more increased in practical work if the feldspar used shows indications of weathering, and also if it is intergrown with quartz, which is often the case; in a body mix¬ ture calculated according to the analysis the quantity of feldspar introduced must be increased in proportion as it contains clay and quartz. It is quite possible also that porcelain bodies in place of the orthoclase used in Germany almost exclusively, or together with it, may contain feldspathic minerals which are not so resistant to sulphuric acid, as is the case with the labradorite. In this case, of course, the determination loses much of its accuracy and it must be the task of scientific research to find suitable methods of separation applying to such cases, which, however, do not ex¬ ist at present. At any rate chemical analysis even here gives valuable data which are useful in practical work, inasmuch as it determines the content of quartz and orthoclase feldspar with sufficient exactness leaving undetermined only how much of the part decomposed by sulphuric acid consists of hydrous alumi¬ num silicate, or of a feldspathic mineral, easily decomposed, re¬ placing orthoclase as a flux. This case is very likely met in the Japanese bodies examined, though it appears that, owing to the low content of soda and lime, the orthoclase is not replaced by labradorite. After this discussion, necessary for the proper understand- 684 ESSAYS REFERRING TO PORCELAIN ing of the following analyses, the numerical results of the inves¬ tigation are collected in the accompanying tables. The conclusions drawn from these analyses are interesting scientifically as well as practically: they confirm the assumption made in previous work that in the finer ceramic materials, the kaolin and the white-burning plastic clays, we deal in the plas¬ tic component, the clay substance, with a chemically well-de¬ fined body. The hydrous aluminum silicate, the clay substance accepted by Forchhammer, having the coiuposition Al^O^.aSiO^ + 2H^O, requires a composition of: Per cent. Silica - - - - 46.33 Alumina - - - - 39-77 Water . . - . 13.90 The composition of the part soluble in sulphuric acid, obtained from the analysis by calculation, with the exception of that of the two Japanese bodies, agrees sufficiently with the above fig¬ ures to justify the acceptance of the formula given above. The relatively slight deviations are explained on the one hand, as has been shown, by the fact that a slight part of the feldspar is dissolved by the sulphuric acid and is thus considered as clay substance, and on the other hand, the raw kaolin contains small quantities of decomposition products not belonging to the feld¬ spar proper which, however, are also taken in solution by sul¬ phuric acid. To these belongs especially the ferric hydrate, which is noticed in every raw kaolin, forming yellowish streaks and bands and which is not removed by washing or grinding, but is thus distributed uniformly throughout the entire body. The portion soluble in sulphuric acid which always con¬ tains all of the clayey binding material, showed an essentially different composition only in the case of the two Japanese bodies; the clay substance in these materials possesses a composition ranging between that of the clay substance proper and that of the feldspar, inasmuch as a larger part of the water is still re¬ placed by alkali, it corresponds to a composition similar to that observed in some plastic clays,^ and also in brick clays, in which the clayey constituent not only is the carrier of plasticity, but also furnishes the fluxes on burning. 1 See “ The Constitution of Plastic Clays," page 69. COMPOSITION OF PORCELAIN BODIES 6 I,. Sazerat, I,imoges (body for heavy por¬ celain). •aouB^sqns JO noijisodraoD o^ 10 10 c^ 10 10 CO 10 Ch M 0 <0 Ov 00 00 up M d M M 8 8 M •ppB Dunxidtns m diqnxosui rj- lO 1 VO 00 'J- CO ub 4 d CO 0 Ov w M H N to •IBjox fOtN.ioaNa; lOT^•a^ lOrOt^vO U C>'^tO d vd d d 2 cs M vd VO ^ ON M 0 1 M Tf CS to ^ to d vd ON W CS U^ 5 I,. Sazerat, lyimoges (pate ordinaire). ■aDHBjsqns iCBp JO uoTjisodinoD sSBjaaoasx v£> 10 CO VO q cr\ cq cJ ON 0 M cO N uo vO vO M M d to 0 0 8 ►H ■piOB Dunqdjns UT 3 ;qnxosui 0 Ov 1 ID w 0 CO ri id d CO VO 00 CJ M M T|- vq UO •l^px ^ 10 ro d vd d ^ VO cs uo Q ov VO W M M 0 Tt- VO , CO ' 4 - M CO d vd dv 4 0 M w 10 1 M S • 2 ^ a ^ n 2 3 N (U 4 '^ aDHBjsqns ABp JO uoijisodinoo a^Bjuaojad; to 0 ov up 00 q ^ M M Tt to Q to to VO VO M ^ h? 8 8 •pxDB Dunqdtns *ui aiqnxosui VO UO 1 VO M u:) CO 3 1 d to to Ov up M »H to 10 uo •IBJOX N -^covO (UVO 0 U S ^ .2 ^ cs w Cl- oj a pH >o M o 4 vo ^^d M 2 cdidd VO Tj- 0 10 11 00 10 0 VO d vd dv d hI 0 CO M I Sevres, tableware. • aouBjsqns Abp JO noijisoduioo S^BJU 3 DJ 3 X C'- CJv 4-> .4-1 -«-> O C! » ^ 00 CO CS cfs CS + + ■e ctf p cr + 1 ) aj c 3 O4 Oh .13 -H ^ tn 42 cS TS E '3 P P Pk Ph tn tn .Q ,0 P P ' w 0 -O *> 0 H C/J Cd cd . 'y (U 4 -> Cd 001 001 u (D a. ;h 1 ^ tC rP H ■Pt P § Oh K*^ rt T) no Sh CT' <+H 0 CO 0 1 0 COMPOSITION OF PORCELAIN BODIES 693 contained in the purer, less plastic kaolins, represented in its purest form by English china clay and the Zettlitz kaolin when moistened, appears “ short ” and dries to a loose, porous, readily dusting mass, while the other, appearing in the most plastic kinds of fire-clay, is extremely sticky in the softened condition and dries to a hard, dense and bone-like mass. In the first modi¬ fication the main part of the shrinkage takes place during the burning, in the second during drying. Between these two ex¬ tremes, the short, but slightly plastic kaolin clay substance and that of the extremely plastic, soapy clays, there are a series of intermediate stages which represent the bonding material of the plastic kaolins and more or less that of the fat, plastic clays, neg¬ lecting entirely the fluctuations in plasticity brought about by admixtures with non-plastic constituents. The intermediate stages of the clay substance, in regard to its degree of plasticity, are due to a mixture of these two modifications which, though chemically the same, differ in molecular character. The larger the content of non-plastic constituents which have been introduced into the body, the more plastic must be the clay substance of the clay used in order to maintain the working quality absolutely necessary. For bodies high in clay substance, the manufacturer will hence use a less plastic kaolin, and for such low in clay substance, one whose clay substance is as plastic as possible. Although according to the present views regarding the composition of porcelain bodies the lack of plasticity due to the low plasticity of the kaolin clay substance cannot be corrected by the use of the real plastic clays, or at least seems a venture¬ some attempt, yet it might perhaps be considered whether the introduction of plastic clays would not be possible so as to de¬ crease the difficulties of working, at least as far as bodies high in quartz and feldspar and low in clay substance are concerned. An addition of plastic clay to bodies with a low quartz and feld¬ spar content is not necessary, and no essential benefits could be derived from its use. Of all the bodies examined, it is surprising to note that the highest degree of plasticity is possessed by the Japanese body I, ESSAYS REFERRING TO PORCELAIN 694 which apparently equals the plasticity of many whiteware bodies, or even surpasses them in this respect. At the same time this body possesses by far the lowest content of clayey binding ma¬ terial, that is, the highest content of non-plastic matter. It is hardly probable that in their composition a true kaolin has been used; very likely a really plastic clay has been employed for a body mixture whose content of clay substance corresponds only to 33 per cent of Zettlitz kaolin could hardly be considered work¬ able while in reality the plasticity is higher than in any of the other bodies. Synthetical experiments in which the content of clay substance, as shown by analysis, is brought in by the plas¬ tic Ebernhahn clay, without the use of any kaolin, proved that such a body produced a porcelain which softened very strongly in the coolest portions of the glost kiln at the Royal Porcelain Factory and showed the greenish translucency peculiar to Japa¬ nese porcelain. On taking half of the clay substance from Ebern¬ hahn clay and the other half from Halle kaolin, a body was ob¬ tained which was easily worked, and produced a very white and transparent, although somewhat brittle, porcelain. In commu¬ nicating these results of experiments conducted on a small scale in connection with the analyses given, I do not intend to recom¬ mend the addition of plastic clay to the body unconditionally, but this is intended to serve as an explanation why the Japanese and Chinese porcelains, though so high in silica, as shown by these and older analyses, are worked without offering more diffi¬ culties in working than the German porcelains with a far higher content of clay. In connection with this work it might interest many porce¬ lain manufacturers to know that pegmatite from Limoges is used as glaze on all of the twelve French and Belgian porcelain bodies, it being the rock to which the kaolin deposits of St. Yrieux owe their origin. The pegmatite from St Yrieux is a feldspathic rock intergrown with quartz without the presence of any other mineral constituents. The dense, but slightly decom¬ posed parts of the rock are ground as such to a glaze; the weathered and soft portions of the mineral obtained by surface digging as far as they are pure white in color are ground in RAW MATERIALS OF THE LIMOGES INDUSTRY 695 mills to a porcelain body without any addition, except in a few places of a little marble. As far as the rock is penetrated by ferruginous veins it is selected by hand-picking; the kaolin washed out by very primitive appliances is made up into a body together with the finely ground harder rock. A sample of the rather hard pegmatite from the mills of Mr. L. Sazerat at Limoges on analysis was found to have the following composition: Total. Insoluble in Soluble in sulphuric acid. sulphuric acid. Per cent. Per cent. Per cent. Silica 76.11 65.21 10.90 Alumina 14.61 11.60 3.60 Ferric oxide 0.66 — 0.66 Calcium oxide 1.44 0.85 0.59 Magnesium oxide 0.42 0.42 Potash 2.99 2,11 0.88 Soda 3-03 2.81 0.22 Water 1.23 1.23 Cobalt oxide trace — 100.59 82.58 18.50 The 11.60 per cent of alumina of the second column correspond to a content of 58.20 per cent of unweathered feldspar. The composition is thus : Per cent. Unweathered feldspar - - 58.20 Quartz - - - - 24.39 Clayey decomposition products of feldspar 18.50 Some Raw Materials of the Limoges Porcelain Industry Albbrt Bleininger, B.Sc., Translator The French porcelain industry is centralized near the rich deposits of raw material of Limoges which form the foundation of this industry, just as has been done in Thuringia and in the Carlsbad district. This crowding together of many similar establishments has given the place a peculiar character. 696 ESSAYS referring TO PORCEEAIN The Limoges porcelain is considered the best, not only in France, but it is also esteemed highly in Germany, and by many Ger¬ man manufacturers it is set up as the technical ideal which they strive to attain; it is claimed that the French porcelain can not be equaled, since in Germany such excellent raw materials as the kaolin from St. Yrieux and the pegmatite are lacking. The porcelains of Limoges excel not only in lightness and ele¬ gant shape and in the tasteful decorative treatment peculiar to the French, but the body differs from most of the German prod¬ ucts also in a purer, more agreeable color, its thinness and greater translucency. The superiority of the Limoges porcelains, as far as body and glaze are concerned, is undoubtedly first of all founded on the character of the raw materials available. For this reason it was desired to obtain possession of a few of the raw materials used at Limoges in order to examine them from the point of view developed in some earlier work and we com¬ municate the results of this investigation, which brings out some interesting facts, in the hope that it may indicate to the German porcelain manufacturers how to strive toward the production of similar ware with German raw materials. We have shown in earlier investigations that of the raw ma¬ terials which usually serve for the production of hard porcelain, kaolin, feldspar and quartz, the latter two are already present in the kaolin in varying amounts according to the different depos¬ its of kaolin and the degree of its washing. It has also been shown that the variation in the chemical composition of the kaolin is due to the varying amounts of these components, while the main constituent, the clay substance (hydrous aluminum silicate), produced by the decomposition of feldspar, is nearly alike in composition in different kaolins, and we presume that very likely it possesses nearly always the same properties. The art of compounding porcelain bodies comprises the ad¬ dition of certain amounts of feldspar and quartz necessary 'for certain purposes to kaolin, as far as they are not present in the latter naturally. This artificial incorporation is accomplished either by including in the body mixture, quartz or feldspar, or both, or adding to kaolins very low in quartz and feldspar, china RAW MATERIALS OF THE LIMOGES INDUSTRY 697 clays more or less high in quartz and feldspar. Owing to the wide fluctuations shown by china clays in regard to the quartz and feldspar content in every deposit, or rather in every ship¬ ment, a different proportion of the artificial component is neces¬ sary. The ordinary chemical analysis, which considers only the percentages of the elementary constituents, does not show how much of the silica belongs to the clay substance, how much to the feldspar, and how much to the quartz, although in each of these forms the silica possesses widely differing properties; likewise it gives no definite data as to the amount of alumina belonging to the hydrous silicate and that going with the feld¬ spar, etc. The rational analysis, on the other hand, determines with an accuracy which suffices completely for all technical pur¬ poses the mutual relations between the alumina, the feldspar and the quartz in the china clay or body. With the help of the or¬ dinary means of chemical analysis, fluctuations in the composi¬ tion of these constituents may be determined. It permits us to trace, in the clays as well as the bodies, the properties whieh are connected with the fluctuating content of the mineralogically and physically different components. The Limoges materials were considered from this stand¬ point. Silica Alumina Ferric oxide Lime - Magnesia Potash Soda Loss on ignition I. Kaolin from Limoges Gross analysis. Decomposed by sulphuric acid. Not decom¬ posed by sul¬ phuric acid. Per cent. Per cent. Per cent. 58.39 32.22 26.17 - 27.52 7.49 20.03 0.36 0.36 - 1.52 0.41 - 1.71 [ 4.40 1.82 2.58 - 7.19 7.19 99.19 Composition of the clay substance de¬ composed by sulphuric acid. Per cent. 47.09 36.04 0.64 3.27 11.94 10 698 ESSAYS REFERRING TO PORCEEAIN The composition of the kaolin, assuming that the feldspar contained by it corresponds to the acidity of orthoclase, is calcu¬ lated to be Per cent. Clay substance - - - 55-88 Quartz .... 5.95 Feldspar - - - - 38-17 On comparing these figures with those obtained from a num¬ ber of German and Austrian kaolins examined, a great difference will be observed. While in the latter the non-plastic materials often amount only to a small part of the body as in the Zettlitz kaolin and the Pilsen china clays, and again frequently consist of finest quartz dust which cannot be washed out as in the clays from Sennewitz, Kaschkau and Tettin, in the case under dis¬ cussion the non-plastic matter is composed largely of fragments of undecomposed feldspar. It is obvious that thus the kaolin assumes a widely different character, and this explains why Brogniart, in giving the composition of the Sdvres body, men¬ tions that no feldspar is added but only sand; since the kaolin is naturally high in feldspar, an artificial addition of the latter is, of course, not necessary. The kaolin which is worked at Sevres is also obtained from the Timoges district and very likely has the same composition as that examined. The composition of the real clay substance corresponds nearly to that which is represented by a number of German china clays, and owing to its higher content of alkali and lower per¬ centage of water it perhaps approaches that of the so-called plas¬ tic clays examined by us. II. Porcelain Body from Limoges This on analysis was found to have the following composition : Gross analysis. Per cent. Not decom¬ posed by sulphuric acid. Per cent. Decomposed sulphuric acid. Per cent. Composition of clay substance. Per cent. Silica 66.71 47-27 19.44 45-35 Alumina 21.58 5-93 15-65 36.50 Ferric oxide 0.47 0.47 1.09 Lime - - - 0.61 Magnesia - 0-37 Potash 2.93 3-76 1.77 4-13 Soda 1.62 Loss on ignition 5-54 5-54 12.92 99-83 RAW MATERIALS OF THE LIMOGES INDUSTRY 699 The composition of the porcelain body is hence Per cent. Clay substance - - - 43.04 Quartz - - - - 26.46 Feldspar - - - . 30.50 The composition of the clay substance unlocked by sulphuric acid thus checks fairly accurately with the figures calculated from the kaolin analysis. It appears that the body is higher in quartz and feldspar than for instance the Berlin porcelain body, and this explains its greater translucency as well as the greater fusibility. The latter is also essentially influenced by the nature of the fluxes which in the German porcelains consist principally of the rela¬ tively least fusible potash, while the Limoges body shows a very high content of soda, lime and magnesia. III. Glaze from Limoges This glaze shows the following composition : Gross analysis. Per cent. Not decomposed by sulphuric acid. Per cent. Decomposed by sulphuric acid. Per cent. Silica 74-99 70.92 4.07 Alumina 14.80 12.38 2.42 Ferric oxide 0.37 — 0.37 Lime - - - - 1.09 0.20 0.89 Magnesia 0.36 0.36 — Potash 4.31 1 0.68 Soda - . . 3-49 7.17 Loss on ignition 0.65 J 0.69 100.06 These figures coincide with the data given by Salvetat in regard to the composition of pegmatite, which as in Limoges is also used at Sevres. The pegmatite is a variety of granite in which the mica has almost completely disappeared and only the quartz and feldspar are left behind. On account of the mark¬ ings on the fracture which resemble Hebrew writing caused by the intergrowing of the feldspar and quartz crystals it is also called scripture-granite. The analysis shows that the pegmatite 700 ESSAYS referring TO PORCELAIN used as glaze is undergoing weathering and contains about 9 per cent of clay. On calculating the content of feldspar, in the un¬ weathered portion, from the amount of alumina, according to the principles stated earlier, the glaze is found to have the follow¬ ing composition: Per cent. Clay substance - - - 8.93 Quartz - - - - 26.49 Feldspar - - - - 64.58 According to the amount of alkalies found in the glaze the feld¬ spar is to be considered as being composed of equal parts of pot¬ ash and soda feldspar. The Wegeli Porcelain Bodies Albert Bleininger, B.Sc., Translator As has been reported at an earlier date, some quantities of porcelain body have been found in the work of excavating for the cyclorama at Berlin on the premises of 26 Neue Friedrich Strasse, which, according to all indications, originated from the Wegeli porcelain manufactory which was closed in 1757. The bodies are partly shaped into balls of about twenty pounds weight, and were found buried between mats and boards about 2 meters beneath sand and debris; partly they were found in irregular piles, separated from the layer of sand only by blankets. Since it is probable that the Wegeli factory, the predecessor of the Royal Porcelain Factory, occupied the premises 26 Neue Friedrich strasse, there can be no doubt that we have to deal here with some old Wegeli body which perhaps has been buried on the closing of the factory in order to secure the arcanum, or to keep it for use in case of resuming the manufacture. It seemed of interest to subject these bodies to an examina¬ tion : On the one hand to determine, whether and in how far the bodies used in the first porcelain factories differ from the THE WEGEEI BODIES 701 ones used to-day; on the other hand, whether it would not be advisable to return to the original body composition. The total quantity of the body collected amounted to about 60,000 pounds. This was hauled away by the Royal Porcelain Factory, and will, after preceding washing (it being rendered impure by rotten wood, remnants of blankets and sand), be preserved for special purposes. The main quantity of the body found (body No. i) is formed into balls, as they are still at the present time furnished to the turners. It is very white and but little plastic. Its rational analysis gives the following results : Per cent. Clay substance - - - 81.55 Quartz and feldspar - - - 18.45 The sandy residue (quartz and feldspar) gave: Per cent. Silica - - - . 12.59 Alumina . . . . 2.91 Lime - - - - 0.56 Potash - - . . 0.52 Soda - - - - 0.87 18.45 On calculating the feldspar content from the content of alkali, lime, potash, and soda, the following result is obtained ; Per cent. Feldspar - - . . . 17.28 Quartz ------ 1.17 Body No. 2 was found in irregular heaps, was likewise very white, but little plastic. It consisted of : Per cent. Clay substance - . . . 84.96 Quartz and feldspar - - - - 15.04 The sandy residue consisted of: Per cent. Silica - - - . . 10.37 Alumina ------ 2.63 Lime - - - - - - 0.77 Potash ------ 0.46 Soda ------ 0.81 Total • - - - - - 15.04 On calculating the feldspar from the alkali content, this 702 ESSAYS REFERRING TO PORCELAIN gives 17.48 per cent, thus more than the quantity found by direct determination. Body No. 3 was likewise found in irregular heaps and only in slight quantity. It was of a reddish color, but little plastic. It consisted of: Per cent. Clay substance - - - - 81.37 Quartz and feldspar - - - - 18.63 The sandy residue consisted of: Per cent. Silica ... - - i 3 ' 5 o Alumina ------ 3.56 Lime ------ 0.52 Potash ------ 0.40 Soda ------ 0.65 Total ----- 18.63 From the alkali content there was found by calculation: Per cent. Feldspar - - - - - 13.10 Quartz ------ 5.53 Besides these bodies there was found a washed clay (No. 4) very likely the Auer clay used then in the Meissen factory (in the beginning used exclusively by all the porcelain factories) whose deposits are now exhausted. This contained: Per cent. Clay base ----- 96.19 Quartz and feldspar - - - - 3.81 The sandy residue consisted of : Per cent. Silica ------ 3.04 Alumina - - - - - - 0-55 Lime ------ 0.07 Potash ------ 0.08 Soda ------ 0.07 Total ------ 3.81 From this is obtained: Per cent. Feldspar - - - - - 1.72 Quartz ------ 2.08 No. 5. Raw clay.—This was very white and contained many THE WEGEEI BODIES 703 fragments of quartz. After washing out 50 per cent there re¬ mained in the part washed off: Per cent. Feldspar - - - - - 88.72 Quartz and feldspar - - - - 11.28 The sandy residue consisted of ; Per cent. Silica ------ 6.75 Alumina ------ 2.70 Lime ------ 0.85 Potash - - - - - - 0.27 Soda ------ 0.71 Total - - - - - - 11.28 From the amount of alkali a feldspar content of 16.29 cent was calculated, which is likewise more than has been found by direct determination. What makes the composition of the bodies such a peculiar one is the low potash and the high soda and lime content in the feldspar, which is present in’ the bodies. This indicates that not an orthoclase feldspar which is now being generally used in the manufacture of porcelain, but probably an oligoclase feldspar with lower silicic acid content, was employed. This would explain the fact that in the bodies Nos. 2 and 5, a higher feldspar content was calculated from the content of alkali than was actually found. Although the question as to the feldspar used is as yet an open one, we can still draw with cer¬ tainty, from the analysis, the fact that no quartz intentionally entered the body composition, for the slight quantities of 1.15 up to 5.53 per cent of quartz are derived without doubt from the china clay used, in which 2.08 per cent were found, and that the body was thus simply composed of from 15 to 18 per cent of feldspar, and 82 to 85 per cent of China clay. To this corresponds also the behavior of the bodies in burn¬ ing. They shrink more than the Berlin body, show great ten¬ dency to warp, and to bring out the molding seams prominently, burn to a cream color, and are less transparent, but considerably whiter, than the products of the following manufacturing period under Gotzkowsky and at first under the government, before the Halle clay now used, was discovered. These properties are shown 704 ESSAYS REFERRING TO PORCEEAIN also by many Meissen products of that time. Our present bodies have all a higher or a lower quartz content which fluctuates be¬ tween 20 and 45 per cent, and where the quartz is not already contained in the kaolin as in the Sennewitz clay, which con¬ tains about 35 per cent of it, an addition of quartz is always given to the body. This had apparently not yet been done in the oldest process of manufacture, and to this are due the defects of the Wegeli porcelain examined. How it was possible for Wegeli to obtain the Auer clay we are not enabled to state. It is very unlikely that it was brought to Berlin before the Sile¬ sian wars, of which the second was being fought, as is known, between 1744-45, since Wegeli commenced with the fitting up of his factory only in 1750; at any rate the fear of not being able to replenish his stock of porcelain clay, might have been the reason for the second closing down of the factory, which at the time seemed incomprehensible to the contemporaries. It is known that Gotzkowsky had worked with Passau clay. Colored Porcelains Albert Bleininger, B.Sc., Translator If we ask why colored porcelain glazes, that is, colored coat¬ ings melted on in the glost-burn are applied only by so few fac¬ tories, this question can be answered in three respects. In the production of pottery, figures and bric-a-brac, it is endeavored to retain the white color of the porcelain, thus ex¬ cluding every coloring metallic oxide from the glaze or the body—on the one hand, because we are accustomed to retain the whiteness of the porcelain as much as possible, and on the other hand, in consideration of the subsequent decoration with muffle colors. Again, considerable technical difficulties are offered in the production of such colored coatings, which without doubt are greater than those found in the production of similar glazes on whiteware and faience. These difficulties are to be found in the COLORED PORCELAINS 705 management of the burning, which, owing to the high tempera¬ ture of the porcelain kilns, and to the alternately oxidizing and reducing constitution of the gases, is not easily controlled. For this reason it is difficult to produce certain colors and be sure of results. Besides, the number of coloring metallic oxides which could be practically used at the high temperature of the glost-burn in question is only small, the color scale is limited and the products show a certain monotone. The glazes commonly used on porcelain, in whatever pro¬ portion they may be compounded from kaolin, quartz, feldspar, porcelain body, etc., have in general the formula RO, + (1-1.25) AIP3 + (10-12) SiO^, that is, with reference to the fluxes, usually potash and lime, as unity, they are ten- to twelvefold acid silicates. The lower values correspond to about the soft French porcelain, the higher to our German hard porcelain. There are only two ways of producing colored glazes from the colorless ones, either by adding simply coloring metallic ox¬ ides to the glaze, or substituting for the colorless fluxes, potash and lime, coloring metallic oxides in equivalent proportions. The flrst method is applicable only when the metallic ox¬ ides added possess a strong coloring power, so that they need be added only in small quantities because they are fluxes and would change the normal formula given above considerably. The con¬ sequence of the addition of coloring metallic oxides is crazing of the glaze, which is more pronounced on porcelain, since it is generally accompanied by a shelling off of the glaze from the body. The second method is the more proper one, inasmuch as by it the normal formula is not changed, and hence crazing cannot appear. But as the quantity of replaceable colorless fluxes is only slight, amounting according to whether the flux is lime or pot¬ ash, only from about 8 to 11 per cent, a narrow limit is set, especially since only a part of the colorless fluxes can be replaced by coloring ones. Again, the fact operates against the use of colored glazes for hard porcelain, that the latter is burned in the reducing fire and that it is almost impossible to finish burning it without the ESSAYS REFERRING TO PORCELAIN 706 application of a reducing flame. Thus a number of metallic oxides which are easily reduced are excluded from this use, and those which remain, cobalt oxide, chromium oxide, iron oxide, manganese oxide, as well as the noble metals, gold, platinum and iridium, represent but a narrow scale of colors. The conditions, however, are different and a good deal more favorable on leaving the difficultly fusing glazes of the hard por¬ celain and going over to the more fusible ones of the Seger por¬ celain. The normal formula for the glaze of the Seger porce¬ lain, which consists of the same materials as the glaze of the hard porcelain, is as follows: RO + 0.5 A 1 P3 + (4-6) SiO, The glaze is thus only a four- to sixfold silicate, referred to the colorless fluxes. Thus for the substitution of the latter by coloring metallic oxides a much wider limit is left; that is, a larger amount of coloring oxide can be introduced into the glaze with injury, without producing a dimming of the glazes owing to the segre¬ gation of metallic oxide, which appears so easily in hard por¬ celain glazes. The main advantage of these glazes consists in the fact that they can be burned in the oxidizing fire; owing to this advantage the copper oxide, nickel oxide, and uranium ox¬ ide, can be added to the above list of metallic oxides, so that the color scale is enriched by green, brown and yellow colors. Other neutral colors may also be applied, which proceed from the mixture of white glaze with pinks of different composition, which furnish a series of red and pink shades. If in producing these colored glazes there are introduced into the glaze in place of lime, equivalent quantities of monoxides, cuprous oxide, nickel oxide, cupric oxide, and for alumina, the coloring sesquioxides, chromium oxide, ferric oxide, manganese oxide and uranium oxide, there is obtained a color-scale whose members not only possess the same chemical character, but also possess nearly the same melting-point, thus permitting of burning in one Are. The colored glazes can also be blended at pleasure and so give rise to a very extensive scale of colors. The Composition of a Biscuit Body Albert Bleininger, B.Sc., Translator We know that porcelain bodies which are used for the production of unglazed biscuit figures, frequently show a certain fatty gloss on the surface, especially when receiving a very hard firing, and hence are less agreeable in appearance. This gloss appears on the busts and small figures made from it, especially prominent on those places which project from the main portions, that is, principally on the finger points, the nose and the hair parts. In a fine biscuit body such glossy places should not ex¬ ist. A select beautiful biscuit body not showing this fault, very likely a Copenhagen product, was made the object of an exami¬ nation by me. The body had the exterior appearance of frit porcelain; it was extraordinarily transparent so that the light entered it to a certain depth, showed an entirely matt surface with a conchoidal and very glossy fracture, and in no place the objectionable fatty gloss ; its coloration was of a slightly yellowish cast of an agree¬ able shade. The chemical analysis of the body was found to be as fol¬ lows : Per cent. Silica ------ 63.00 Alumina - - - - - - 24.74 Ferric oxide ----- trace lyime ------ 0.77 Magnesia - - - - - 0.64 Alkalies, especially potash - - - 10.86 Total ----- 100.01 The extraordinary high content of potash, as a rule not rising to such a height in porcelain bodies, and the low content of silica gave rise to the supposition that the porcelain body used for it is composed of a mixture of kaolin, free from quartz, and feldspar. In fact, by calculation from the theoretical com¬ position of the feldspar and pure kaolin, a composition of 68 per cent of feldspar and 32 parts of kaolin is obtained, leaving noth¬ ing for the quartz content of the body. Whether the slight con- 7o8 essays referring to porceeain tent of lime originally belonged to the feldspar used or was added intentionally (as about i per cent of marble or calc spar) could not be determined, and would also not be of great importance, owing to the small amount of lime. Such a body, from 68 parts of Swedish feldspar and 32 parts of Zettlitz kaolin, proved to be much too high in flux for the heat usually applied in the porce¬ lain industry. At the temperature of cone 6 it already had as¬ sumed the character, shown by the sample piece; at cone 8 it went completely into fusion, but retained its dull surface. A body of the composition of 65.5 feldspar, 1.5 marble, and 32 Zettlitz kao¬ lin showed the same properties. It was now tried to produce the same body, but with a lower feldspar content, in order to render it more difficultly fusi¬ ble and to compound it with different clays, and it was observed that a body of equal beauty can be produced only with kaolins free from quartz. When kaolins containing quartz were used, for instance Loethain clay with 20 per cent of quartz, or Halle kaolin with 35 per cent quartz content, there were always pro¬ duced bodies which showed more or less the disagreeable fatty gloss on the surface. For the temperature of the Seger porce¬ lain kiln (cone 8 to 10) at my disposal, the following mixture was found best suited for the production of similar biscuit ware : 45 parts of Swedish feldspar, 54 parts of Zettlitz kaolin and i part of marble. In order to diminish the tendency of the body to show raised seams, a part of the body was burned in the glost burn, ground, and then again compounded with the above body in the proportion of 30 to 70 parts. The biscuit figures thus compounded showed extraordinary beauty, similar to fine-grained marble, and this suggestion referring to bodies free from quartz should prove of interest to many interested parties. Japanese Porcelain, Its Decoration, and the Seger Porcelain Albert Bleininger, B.Sc., Translator The technique of the decoration of the Chinese and Japa¬ nese porcelains differs materially from the methods of decoration DECORATION OF JAPANESE AND SEGER PORCELAIN 709 applied in Europe, especially in one respect. In the first, be¬ side usually dull colors, fixed by means of a flux, transparent, more or less relief-like, colored glasses, and often enamels made opaque by tin oxide or alumina are preferably applied, while we use enamel colors exclusively. These enamel colors are formed by metallic oxides or metallic salts, not readily attacked by glasses, which according to the nature of the colors are com¬ pounded with colorless glasses, consisting of alkalies, lead ox¬ ide, bismuth oxide, silicic acid and boracic acid in different pro¬ portions, in such a manner that the glasses fix the mineral pig¬ ments on the body at a moderate heat and give to the color a certain gloss, without, however, dissolving the coloring bodies themselves. But the painting thus effected, for which, owing to the low burning temperature, a very rich scale of colors was created, does not prove very durable; many of the glasses used for the fixing of the colors are not only very soft, but also are attacked by acid fluids. In place of these enamel colors there often appear on Chinese and Japanese porcelains, real translucent colored glasses, in which the coloring metallic oxides are not suspended in the fluxion, but are dissolved in it. The use of such transparent glasses as a means of decoration, which are not applied like the enamel colors in extremely thin layers, but in relief-like coat¬ ings, has to contend with insurmountable difficulties in the man¬ ufacture of European porcelain, at least in the hard feldspar porcelain, while its application on soft porcelain, ivory porce¬ lain, English bone china, French frit porcelain and similar prod¬ ucts, which are provided with lead glazes, similar to whiteware glazes, seems more warranted. The use of transparent colors give to the Asiatic porcelains a peculiar charm and is one of their characteristics. The enamel colors used by us often crack when applied in thick layers, especially when exposed to a high long-continued or repeated muffle heat; they then shell off from the body. This is true of all colored transparent enamels, applied in thick layers in a still higher degree. On European porcelain they usually not only shell off completely, but also crack off the glaze and 710 ESSAYS REFERRING TO PORCELAIN burst deep holes into the body, while on the Chinese and Japa¬ nese porcelains there sometimes appear fine crazes in the glaze, but never a shelling-off of the coating. For this difference in the behavior of the Asiatic and Kuro- pean porcelain, in regard to the easily fusible glazes, an explana¬ tion must be found in the composition of the bodies and glazes, for it seems incredible to suppose that in one continent the same product, composed of materials from the most various sources, should have materially different properties in another re¬ gion of the world, while both the Asiatic and European bodies and glazes show in general a similar behavior among them¬ selves. From earlier investigations communicated in the technical literature, two things may be deduced in reference to the bodies used in the porcelain industry. The bodies of Chinese and Jap¬ anese porcelains show, on the whole, a greater content of silica, and the glazes a greater content of lime, than the European. In how far the first condition can influence the fusibility as well as the other properties of the body, cannot be determined from the earlier examinations, as from them the grouping of the elements into mineral compounds, which in different combinations have different chemical and physical properties, cannot be deduced. But the glazes are, as was to be expected from the analysis, and also has been proved by Salvetat, much more fusible than those used in Europe for hard porcelain. The examination of a number of kaolins, white burning clays, green porcelain and whiteware bodies, which I have car¬ ried out and published in the last years, has now determined that the portion which is decomposed by sulphuric acid and which at the same time gives to the body its plastic property, always has nearly the same composition. This could be proved for a great number of clays without exception. The composi¬ tion corresponds in all of them to the formula established by Forchhammer for the decomposition product of feldspar, AlO 2SiO T 2HP, and so completely that the plastic portion must be acknowledged to possess this composition. Between the plastic part of the DECORATION OF JAPANESE AND SEGER PORCEEAIN 711 kaolins and that of the real plastic, soapy clays, there is a differ¬ ence only in so far as the constantly present content of alkalies is somewhat greater in the plastic clay substance (2 to 5 per cent) and somewhat smaller in the kaolins (i to 2 per cent) and that, in consequence, the content of water in the first is some¬ what lower (8 to ii per cent) and somewhat higher in the lat¬ ter (12 to 14 per cent). In the calculation of the analysis of bodies, this fact is of ex¬ traordinary importance, because thus the possibility is given of determining the more immediate constituents of the porcelain bodies, which decide their properties, clayey bonding material, feldspar, quartz, or calcium carbonate, if not with scientific ex¬ actness, yet with an accuracy sufficient for practice. As in the determination of the clayey bonding material by dissolving in hot concentrated sulphuric acid many varieties of feldspar are likewise attacked somewhat and their ingredients calculated in with the clay base; the figures for feldspar calcu¬ lated from the analysis are sometimes found to be somewhat smaller and those for the clay base somewhat larger than the true values, but the figures for the quartz and lime content are not influenced by it. From this it follows that in calculating a body composition from the analysis the feldspar content can be taken somewhat higher and the clay substance content some¬ what lower. The fact that I came into possession of three samples of green porcelain body, a few biscuit bodies of egg-shell porcelain and two glazes of Japanese origin, through the kindness of Mr. March, caused me to study the differences existing between the composition of the Japanese and European bodies and glazes. The possibility thus arose of producing porcelain with properties similar to that manufactured in Japan from native raw materials. The porcelain raw materials mentioned originate from a factory in Arita, in the province of Hizen, Japan, and have been col¬ lected by Dr. Wagner, in Tokio. In a letter to Mr. March, he gave very interesting details about the process of manufacture, which I quote. According to these the china clay is obtained on the slopes of a round valley in irregular pits as they may be 712 ESSAYS REFERRING TO PORCELAIN reached most conveniently. It consists of portions of a gray¬ ish white porcelain stone rendered soft by weathering. The sorting of the raw china clay, which has the appearance of an impure clay rather than of a raw kaolin formed by the weather¬ ing of porphyry or granite, is done according to the color, con¬ sistency and fineness of the different qualities. The purest, whitest and most plastic is worked into thin-walled porcelain (egg-shell porcelain); for ordinary porcelain the clay is mixed with an inferior quality. A further addition of other mate¬ rials, for instance, feldspar and sand, as it is done in Euro¬ pean porcelain factories, does not take place; the partially weath¬ ered stone contains all the ingredients for the production of porcelain. The clay thus won is broken up, finely ground in very primitive stamp mills with addition of water and washed. After the stiffening of the slip it is immediately worked on a wheel. Most of the pottery is turned free-hand on ingeniously constructed wheels. In the turning down, solely a piece of band iron with sharpened edge is used. For a glaze which, as in Europe, is applied after biscuit-burning the pottery, a soft clay is used, to which is added as a flux the lixiviated and washed ash of Ficus Pyrifera, in the proportion of lOO parts of clay to 40, 60, and 80 parts of ash. According to the different degrees of heat in the different parts of the kiln, the pottery receives a more or less fusible glaze. For a greenish glaze a clay is used colored to an ochre yellow by iron, which is likewise mixed with wood ash. For the production of craquele, the green pot¬ tery receives a coating of a calcareous mineral, over which the ordinary glaze is applied. The thicker this engobe, the closer will be the mesh of the crazing. The burning is accomplished in kilns having the shape of bake ovens, built by tamping fire-clay over a wooden form with¬ out the use of brick. The kilns are built in a row of twenty up a hill slope. The fire enters from one kiln into the other, so that the entire row is burnt in succession. The lower kilns are very small, only about two meters in diameter; going up they be¬ come larger up to eight meters. Only the most valuable ware DECORATION OF JAPANESE AND SEGER PORCELAIN 713 is burnt in saggars of porcelain body, which must always be destroyed; the ordinary products are burnt in the open fire, sup¬ ported by benches of fire-clay which are built in the kiln on clay pillars up to a man’s height. Every piece in the kiln rests on a porcelain tile. In burning, care is taken that in the beginning white heat, when the porcelain commences to vitrify, the kiln is filled with flame. I. Body and Glaze In the following section, I shall give the composition of the Japanese bodies as shown by analysis, as well as the composition of several European bodies which will serve for comparison with the Japanese. From the table two conclusions can be deduced. 1. That in the European bodies the content of silica in the average is lower, but the alumina content higher than in the Japanese porcelain bodies. The European porcelain bodies have: Maximum, Minimum. Silica ... 66,78 52.94 Alumina - - - 28.91 22.70 Japanese porcelain bodies have : Maximum. Miuimum. Silica - - - 74.53 71,31 Alumina - - - 19.94 16.09 Here the Japanese body IV has not been taken into considera¬ tion, since it was brought for examination only in the biscuit state. It is probable that it is identical with body I. 2. That the clayey bonding material has a different compo¬ sition from that which we know to be present in the European porcelains. The composition of the clay substance of the Euro¬ pean porcelains corresponds, as I have stated before, to the for¬ mula Al^O^.aSiO^ + 2H^0 which requires Per cent. Silica - - - - - 46.33 Alumina ------ 39-77 Water . . . . . 13.90 The clay substance of the Japanese porcelains shows a ma¬ terial deviation from this, which becomes evident at once through 714 ESSAYS REFERRING TO PORCELAIN the high content of alkalies and the low content of water. The alkali content in the clay substance of the European porce¬ lain amounts on the average to 1.75 per cent, but in the Japa¬ nese from 5.76 to 7.12 per cent. This difference might indicate that the Japanese porcelain bodies contain as a flux, a variety of feldspar or another mineral containing potash, which, like the clay substance, is dissolved by sulphuric acid, or that the com¬ position of the clay substance approaches that modification which forms the bonding material in strongly plastic clays. Perhaps, both causes enter into the explanation of the different composi¬ tions. Now assuming, in order to be able to compare the bodies with each other, that in the Japanese as in the European there actually belongonly 1.75 per cent of alkali to the clay substance, and calculating the excess of alkali into the feldspar, the follow¬ ing composition is deduced for the Japanese bodies: I. 2. 3. Clay substance - - 24.56 30.90 34-79 Feldspar - - - 34-53 19-66 23.69 Quartz . - - 40.91 45-36 4^-52 According to these figures the feldspar content in both the European and Japanese bodies fluctuates quite widely. A striking difference is shown in reference to the proportion between clay substance and quartz. In the European bodies the clay sub¬ stance predominates always, and in the Japanese the quartz. The following tabulation shows this distinctly: European bodies. Maximum. Minimum. Clay substance - 66.37 42.05 Feldspar - 36-84 17.05 Quartz 29.62 12.05 Japanese bodies Maximum. Minimum. Clay substance - 34-70 24.56 Feldspar - 34-52 19.66 Quartz - 45-35 40.91 From the relatively small quantity of plastic bonding sub¬ stance found in the Japanese porcelains, the conclusion might be drawn that they are less plastic, and hence more difficult to work than the European bodies. However, on kneading, the body is remarkably plastic and dries to a hard, firm mass, while DECORATION OF JAPANESE AND SEGER PORCELAIN 71 Carlsbad body of pottery at Dallwitz. •ODnBjsqns iCBjD JO uoijTsodmoD ajSBjuaoaoj OVOVPN .MVOVO • 10 M q q • > 8 8 M I,imoges tableware body of J. Pouyat. ■ODiiBjsqns Xbp JO uoijisodraoo 3 ^BJU 3 DJ 13 X 0 CO • • CO Ov 0 * •cr M q • • uo 00 • uooon I IddeJ 1 ■q* CO M 8 8 *ppB Dunqdins *ni ^xqnxosui 0 00 . 10 . 00 CO . .00 . 00 . 3 G ; 0’ ; d cJ • • CO vd uo "IBIOX 00 ovt'-t'.o I-I t>.00 Ov q'q-oqt^OM O'q-vo J? 0 ” 2 CO id d VO M VO 8 Berlin tableware body 1877. •sonBjsqns XBp JO noijisodraoo a^BjaaDjo,! Ov 00 • CO 00 10 • rf- CO 0 • t>. 10 t>. • id G >-i‘ ; d pi pI I ■q- CO M 8 8 M •ppB Dunqdxns ui ^iqniosni lO . . , Tj- , . 0 I-H . . . 00 . . CO ^ • M* • • fO • . . • • 00 q IBlox !>• Ov • 0 VO O' q vq 10 • rr pi 0 • to •q- d I o' Tj- I 00 OV cfv OV S6veres tableware body 1878. ••aonBjsqns Xbjd JO noijisodraoD a^BjuaDiaj t>-CTvP< 'lOP^iOiO' M vq . p< M CC VO • id 00 d i o' M o' to ; q- to M 8 8 M •ppB Dunqdins ’ UI aiqniosui VO 10 • • • 10 M , - 0 . . . CO 10 • • w fo • • •do* • M • • VO M cs •IBJOx q-c-ieo ovt^ooo pioo OvOVTa-ovM p>.vO M Tj- pi 00' d to o' M o' cfv pi 10 PI 8 M j i Silica - - . Alumina . _ . Ferric oxide - Lime - - . . Magnesia - . . Potash - - - - Soda - - . Water and organic matter - Carbonic acid Totals ... M 10 to M o VO 10 cJ VO rt a o ,Q b TO to ^ ,