Coloring and Decoration OF I Ceramic Ware CENT^ 'f^T' cnn^ lAL, ay we produce, after firing, a metallic coloration imitating the different tints of polished gold. To obtain prismatic colors we take ammoniuret or cyanuret of gold and of mercury, or iodide of gold or tincture of gold. These auriferous compounds are ground on a palette with tur¬ pentine so as to form a paste, which is allowed to dry in order to be broken up and reground with lavender. To one part of auriferous product we add one, two or three parts of bismuth flux and spread it with a brush on the ware that is already decorated and fired; the parts are then covered with uranium solution, with the result that we obtain tints that are more or less deep and more or less varied. All these preparations mix perfectly with one another and can overlay each other, applied with the brush to ware to be decorated they furnish, after firing, brilliant and glazed tints; their variety necessarily increases by applying these lusters on a vigorous ground. Brianchon’s productions are remark¬ able for brilliancy and fire of the colors. They are so bright that they might be taken for underglaze colors. A satisfactory theory, accounting for this process, is yet to be produced, though it may be presumed that the elements forming the rosin have reactions analogous to certain carburets of hydro¬ gen, capable of exchanging one or several molecules of hydro¬ gen foi one or several molecules of metal—iron, uranium silver—to form new compositions, abandoning the oxygen which is irreducible under the action of the fire. GOLD LUSTERS. This has all the color of gold and it acquires t'he metallic brilliancy of gold by simply rubbing it with a rag. It ap¬ pears probable that the Meissen gold, called light gold, is made in much the same way as that we are about to describe. It has in fact a similar brightness and exhibits a similar want of durability. The preparation is obtained by precipitating gold from its solution in aqua regia by means of ammonia. We know that the composition which is precipitated is a fulminant, what is known as fulminating gold. As it only possesses this prop¬ erty when it is dry, it must not be allowed to reach that state, but is taken while still wet and mixed with oil of 121 turpentine, then without adding any flux, it is spread with a brush upon the glaze of the ware, the same as is done for colors and is fired in muffle. It adheres to the ware and shows a bright metallic appearance, which is increased by gently rubbing it with a rag. Anyone can see if a piece has had gold laid on by this pro¬ cess, as it looks the same on every part of the surface, whether inside, or outside the ware. The gold exhibits the same brilliancy, the same polish and does not show in any part a trace of the burnisher. We can also cover pottery with a very thin coat of a solution of gold either in aqua regia or in alkaline sulphides, but it is more difficult, with this method, to get a coat which is quite equally polished and reflects the light from every part equally well. The German methods of preparing this gold are very little better known now than they were years ago and any one who wishes to use the best brilliant gold, still buys it from the German maker. The old Dutertre patents are the basis of the French preparations, and old as they are they may become a basis for further research, enabling a substance to be re¬ produced, which plays so large a part in the decoration of porcelain. We put into a vessel, which is gently heated: Pure gold . 32 grams Nitric acid . 128 Hydrochloric acid . 128 When the metal is dissolved we add: Metallic tin .0.12 Butter of antimony .0.12 After all is completely dissolved we dilute the solution with 500 grams of distilled water. In a second vessel we put: Sulphur . 16 grams Venice turpentine . 16 Spirits of turpentine . 80 This is heated until the contents are intimately combined, after which 50 grams of essence of lavender is added. In this way we make a true balsam of sulphurized turpentine. We now pour the solution of gold from the first vessel into the one containing the turpentine and apply heat, at the same time we beat the mixture until the gold has incorporated with the oils. The water charged with acids, separated from the gold, is then poured off, the mixture is washed with warm 122 water until the last trace of acid disappears, it is then dried and 65 grams of essence of lavender and 100 grams of common turpentine added; the whole is heated until complete mixture. The clear portion is allowed to stand for a while in a separate vessel with 5 grams of bismuth flux. It is gently heated to bring it to the right consistence. The liquor then presents itself in the form of a viscid and odorous liquid, giving greenish reflections; the gold is present in a state of solution, after the liquid has been left standing long enough for all the particles of undissolved matter to pre¬ cipitate in a crystalline form and settle to the bottom; the liquid is separated from these dregs by decantation. The Venice turpentine gives to the liquor the drying prop¬ erty which it must possess in order that the work should dry promptly. The auriferous resins decompose, at a low tem¬ perature, without melting, into a deposit of carbon charged with gold, this carbon burns off and leaves the metal in the form of a laminated pellicle of exceeding thinness. The beauty of the gilding results, among other things, from the absence of all fusion during the destruction of the auriferous matter. This is a theory I suggested a very long time ago and I have not yet seen reason to change it. The process used by Carr6 differs somewhat from the above; 10 grams weight of laminated gold is treated in a matrass with 100 grams of aqua regia, when dissolved the solution is diluted with 150 grams of plain water to which 100 grams of rectified ether is added. The liquid is well shaken to make the ether lay hold of the gold. The liquid is then poured into a glass jar and allowed to stand for a moment, the ether charged with gold will float on top, it is drawn off by means of a stop-cock in the bottom of the jar. The ether is yellow in color. In another matrass a solution of 20 grains of potassium sul¬ phide is made, this is decomposed by means of 200 grams of nitric acid. The precipitate is first washed until the water comes off quite pure, then it is dissolved in 5 grams of nut oil and 25 grams of common turpentine; in this way a sul¬ phurized balsam is formed to which 25 grams of essence of lavender is added. This solution is poured into the ether so¬ lution, shaken up for a few minutes and the whole is de¬ canted into a porcelain bowl; the solution is concentrated to a sirupy consistence and we then add: 123 Sub-nitrate of bismuth. 15 decigrams Borate of lead . 15 “ The quantity of flux varies, however, with the nature of the pottery which we want to guild. To use it, we spread the oily material in a thin coat, first thinning it with a mixture of equal parts of turpentine and essence of lavender. It will be seen that in this process, neither tin nor butter of antimony is used. It is objected to both these methods that they only give us an oily liquid, which does not retain the gold in a state of solution, or suspension, for long; after a time it crystallizes and separates. The gold which comes from Germany is better; it keeps well and gilds well. That which is on the market contains from 14 to 15 per cent of metallic gold, while that prepared by the French method does not contain more than from 9 to 10 per cent of the metal; it becomes poorer in use and finally does not give a brilliant gilding, but only a gold luster, which, at last, is no better than Burgos luster. I think that the intervention of the balsam has the effect of producing a certain kind of oil in which the essence of turpentine loses a little of its hydrogen; the new composition is apt to combine with the gold to form a complex molecule, in which the gold is dissolved in a particular condition. The Germans, perhaps, possess the secret of some other essence than lavender, which dissolves the oily composition without reacting upon the gold and without precipitating it. Whatever it may be the gold prepared by them has a notably different odor to the similar compositions prepared in France. This question merits a new examination. I believe that cer¬ tain of the natural sulphurized oils and the mercaptans among the artificial compounds, may furnish the key to a practical solution. Some attempts which I have made in this direc¬ tion make me believe in the possibility of a success. Mercaptan, as we know, is nothing else than a sulpho-hydrate of ethyl sulphide. Other analogous compounds, probably, possess similar properties. ENGLISH FORMULA FOR LIQUID GOLD. The translator of Brongniart’s works considers it of suf¬ ficient interest to insert here a formula, taken from a book of recipes published in England in 1896. It is evidently noth- 124 ing but Dutertre’s method, which was published six decades ago, but it is stated differently. “Take an evaporating dish, put into it 2 oz. of pure gold, then 10 oz. of hydrochloric acid and 8 oz. of nitric acid, place over a flame of gas until the gold is dissolved and then add to it 22 grains of pure tin; when the tin is dissolved add 42 grains of butter of antimony. Let all remain over the gas until the mixture begins to thicken. Now put into a glass and test with the hydrometer, it should give about 1,800 specific gravity. Pour into a large glass and fill up with water until the hydrometer shows 1,090; pour all the solution into a chemical pot and add to it 4 oz. balsam of sulphur, stirring well all the while and put it over the gas again, in an hour it should give, on testing, 125° Fah.; gradually increase the heat up to 185°, when it should be well stirred, then left to cool about 12 hours. Now pour into a large vessel the watery fluid and wash the dark-looking mass five or six times with hot water; save each lot of water, as it contains some portion of gold. Take away all moisture from the dark mass by roll¬ ing on a slab and warming before the fire occasionally so as to keep it soft; when quite dry take two and a quarter its weight of turpentine and add to it and put it over a small flame for about two hours, then slightly increase the heat for another hour and a half; allow it to stand for about 24 hours and then take a glazed bowl and spread over the bottom of it 4 oz. of finely powdered bismuth, pour over it, in several places, the prepared gold; now take a vessel containing water and place the other vessel containing gold in it and heat so as to cause the water to boil for three hours; allow it to remain until settled and pour off the gold from the settlings of the bismuth and try it, if not quite right continue the last process with bismuth until good. The bismuth causes the gold to adhere. To prepare the balsam of sulphur take: Oil of turpentine. 16 oz. Spirits of turpentine . %y 2 “ Flour of sulphur . 8 “ Place all in a chemical pot and heat until it boils, continue the boiling until no sulphur can be seen in it; now remove from the heat and thin it with turpentine until about the thickness of treacle, then warm it again, stirring well; allow 125 it to cool until it reaches 45° Fah., then test it with the hydro¬ meter and if specific gravity is not 995 continue the addition of turpentine and warming until correct, let it thoroughly cool, then bottle, keeping it air tight. To purify the bismuth take: Bismuth meal . 6 oz. Saltpetre.% Melt together in a biscuit cup, pour out onto a slab and take away all dirt, then grind into a fine powder. TO RECOVER THE GOLD FROM THE REMAINS OF THE FOREGO¬ ING PROCESS. “Put all the ‘watery’ solutions into a large vessel and mix with a filtered saturated solution of copperas, this will cause a precipitate of pure metallic gold to gradually subside, wash it with cold water and dry in an evaporating dish. “All rags and settlings that are thick should be burned in a crucible until a yellow mass is seen, then take this and dissolve it in two parts of hydrochloric acid and one part nitric acid, let it remain in a porcelain dish until it begins to thicken and crystals form on the sides, add little nitric acid and heat until crystals form again. Now take this and mix with cold water, add a solution of copperas to it and allow it to settle; pour off the water and with fresh water wash until quite free from acid, the gold may then be used again and, if great care is exercised, almost one-half the original quantity may be recovered. “The quantities given in the recipe should make about 13 to 15 oz. of the liquid gold. “It should be fired at rose color heat and does not require any burnishing. If desired it can be fluxed with Venice tur¬ pentine, oil of lavender, or almonds.” PLATINUM LUSTER. We take a concentrated solution of platinum and mix essence of lavender with it, or any other essential oil, without adding any flux. This solution is spread upon the glaze of the ware to which we wish to give the metallic luster of silver, or rather of platinum. The piece is thereupon fired. 126 Platinum exhibits the full brilliancy of the metal. It spreads evenly over the surface, the color of which it entirely con¬ ceals and possesses a polish as lively and as brilliant as if it had been burnished. BURGOS LUSTER. This is a pink chatoyant and, at the same time, yellowish- metallic luster, similar to that of several kinds of natural shells; it is not opaque, the glaze upon which it is placed, is distinctly seen, consequently it participates in the color of the glaze and takes very varying and remarkable tints. There are several ways of making this; sometimes we melt together sulphur, gold and potash, or we may melt the gold in an alkaline sulphide, which is already made; the whole is dis¬ solved in water and precipitated with a weak acid; the precipi¬ tate is collected and preserved as a thick syrup, in essence of lavender. When it has to be used on hard porcelain it is rubbed up with a small quantity of flux; it is spread on the surface of the glazed ware with great care, laying it on as cleanly and as thinly as possible; it is then fired in a muffle, to increase the effect we lay on a second coat. The action of the fire alone is sufficient, without any rub¬ bing afterwards, to give it its characteristic polish and bril¬ liancy, but the least moisture in the muffle, the least dust, or if laid on too thickly, will spoil it, will make it dull and dirty and take away all its merit. It is also produced with fulminating gold, but laid on ex¬ tremely thinly, for if put on thickly it will simply give the luster of gold. Burgos luster can be placed on any kind of pottery, provided it has a cover or glaze. This luster often shows circular spots, the circumference of which shine with the metallic brightness of pure gold. It is by means of a very simple expedient that we are able to pro¬ duce these. It is only necessary, while the ground is spread out and Is still in a viscid state, to distribute a few drops of essence over it; these drops spread themselves out, carrying with them the luster, which they accumulate on their circum¬ ferences. There the thickness of the luster becomes more con¬ siderable, does not give any chatoyant, but the sheen of che gold in all its brilliancy. 127 The brightness of these little discs is increased by rubbing them with a cloth. COPPER LUSTER. This luster shows the same rose colored chatoyant and metal¬ lic yellow as the preceding luster. It is perhaps, rather more purple, but its composition is altogether different. Thu common Spanish earthenware, of Manassez near Val¬ encia, offers remarkable examples of these lusters, of which the eclat and richness give way in no degree to those obtained from gold itself. The nature of these lusters was not known with any cer¬ tainty until Mr. Laurent submitted them to a number of tests and proved conclusively the absence of gold, while several of the reactions which he obtained proved the presence of cop¬ per. We continued these researches and have been so for¬ tunate as to determine, beyond a doubt, their true nature. If we boil the luster in concentrated acid, even in aqua regia, no change takes place, but it is altogether different if, instead of acids, we use caustic potash and in a state of fusion. In this case all the purple color disappears and, if the action of the alkali is not prolonged for more than a few minutes, the color is dissolved, leaving the white glaze of the earthenware upon which it is applied, unaltered. If the potash is then re¬ dissolved in water, saturated with hydrochloric acid, it pre¬ cipitates, with sulphuretted hydrogen, a black substance, which shows all the reactions of copper sulphide. It is this reaction which removed all uncertainty in regard to this. We had certainly found copper in the glaze that was removed from the body of the ware, on melting it with car¬ bonate of soda and dissolving the result of the fusion in hydro¬ chloric acid, though this copper which we found might come, wholly or in part, from the minium that is an essential part of the glaze. In what condition is the copper in the luster? how has it been brought to this condition? are the questions that are not very easy to answer. The coloring surface is so thin that it is impossible to seek for the presence of oxygen. It seems probable that it is composed of an inappreciable pellicle of silicate of protoxide of copper; the color of this composition on the one part, Its reactions in presence of acids and alkalies on the other, corroborate this opinion. 128 If this is not so then how are we to suppose that the copper is found in the metallic state when it resists the action cf strong and even boiling acids, without at least admitting that it is covered with a thin coat of glaze which protects it like a varnish? We cannot suppose that the metal can be in the state of a free oxide at the melting point of copper in the pres¬ ence of a very siliceous body. We do not possess positive data as to the manner in which this luster is made. Our own attempts to reproduce it, though very imperfect in their method and in their results, have, nevertheless, left us the conviction that we were not far from the method used at Valencia. We placed some sherds of com¬ mon earthenware in a small muffle and after they were brought to a red heat, we introduced, through a small opening made for that purpose, some coarse paper containing oxide of copper; we then immediately closed the kiln, carefully luted all the open¬ ings and left it to cool. CANTHARIDIN LUSTER. This, notwithstanding its varied and brilliant metallic color¬ ing is very little used because it is so difficult to lay on and to make a success of it. It is generally chloride of silver, partly decomposed by vapors of combustion, that takes these colors, under the in¬ fluence of the vapors. To obtain it we make a mixture of a verifiable and a plumbiferous glaze, of a little oxide of bismuth and of chloride of silver. This mixture is put onto the ware with the brush; either making a ground of it or designing ornaments. The piece is then fired in a muffle to a red heat and while it is still red it is taken out of the muffle and ex¬ posed to the smoke of some vegetable or animal combusti¬ ble, or else this smoke is introduced to the muffle. The por¬ tions covered with the luster take green, reddish, yellowish, bluish, in fact all the rainbow colors which chloride of silver and lead are capable of acquiring under the influence of the gases. We can understand what a variety of effects may be obtained by varying the color of the glaze of the pottery upon which we apply the cantharidin luster. It will be seen that the great difficulty in employing this luster results from the operation of smoking the piece while in an incandescent state and the risk we run of breaking it by 129 the too sudden change of temperature to which it has to be exposed. LITHARGE LUSTER. We are not very certain as to the way in which this singular luster is made; we have only seen it on the very coarsest pot¬ tery coming from Germany and the East. It is a yellowish luster, with a golden metallic sheen, greenish, bluish, even with something of the cantharidin luster, but with yellow pre¬ dominating. It is, probably, a glaze highly charged with oxide of lead, to which, the colors have been given by smoking. Lead often con¬ tains some silver, which it would not pay to extract and the presence of this metal may influence the results attributed to the lead, which was regarded as pure. The resemblance in color and tints of the litharge to the cantharidin luster seems to confirm this hypothesis. These lusters, like everything showy and cheap, were at one time very much the fashion and when, through the ease with which they could be produced, the market was flooded by them the demand for them ceased. They have fallen into oblivion the more readily as it was found that they did not keep their bright appearance long, but they soon became dead and the lusters easily rubbed off. PREPARATION AND APPLICATION OF THE COLORS—THEIR ME¬ CHANICAL PREPARATION—TRITURATING THE COLORS. After a color is made in the way we have indicated, there is still something more to be done to it before it can be placed in the hands of the artist, it has to be subjected to a final operation, which requires considerable care, without which the best color may be spoiled; for, as has been shown, many of the colors are composed of vitreous matters which are of the right hardness and which must be protected from the intro¬ duction of any other coloring matter, either hardening or fluxing. The trituration, which precedes the grinding, is done in a mortar of biscuit porcelain, which must be kept very clean; it is even a good plan to have several of these, as to triturate the delicate colors in different mortars. We can also use an agate mortar, which would be still better. We commence by crushing the material with our pestle, laying a cloth over the 130 mortar to catch pieces that fly out, then the fragments thus formed are crushed against the sides of the mortar. GRINDING THE COLORS. The color thus triturated is then reduced to a state of im¬ palpable powder by grinding. To grind the colors well is always important, in regard to the preservation of the color, of the desired fusibility of the color and of its greater or less tenuity. It will be of the greatest importance in that which we will call artistic paint¬ ing. The success of a work of art may depend upon the great and equal fineness of all the colors and of their purity; in con¬ sequence the most certain means of attaining these conditions should be employed, no matter what the expense. The success of a high priced work of art will repay the outlay. In common decorations of commercial porcelain, these considerations though not so important, are not to be altogether neglected, but as the time demanded by these, determines to a great ex¬ tent the price of the color, it has been sought to cheapen the processes by mechanical means; mills have therefore been con¬ structed, suitable for crushing a quantity of color at one time. These mills may be made of various substances, but however hard they may be they will wear out and the very fine particles which are detached and mix with the colors, modify their fusibility. Biscuit porcelain, hard glass and the soft glass called crystal are the materials employed; the two latter sub stances are those which approached nearest in their composi¬ tion to that of the verifiable colors and if some particles from them enter into the pulverized colors the defects which they may cause are very much less noticeable. Crystal may soften the color more than a hard glass will harden it, so that the latter, it seems to us. will be preferable as we can now make glass almost as hard as porcelain. At Sdvres they have made porcelain mills, of the shape here shown, which have, in practice, proved quite satisfactory. A. is a cylindrical vase, which receives the muller and the substances to be ground; the center of the bottom has a round or conical projection C., forming, with the bottom of the ves¬ sel, a wide furrow in which the mill or muller runs. The mill DB. is a porcelain cylinder that works in the vase and is a little higher than the sides of the vase. A. represents the bottom of the furrow, where the color is ground. The upper part of the mill is flat and has attached to it a disc of lead P. or any other metal which will increase its weight; to this disc a handle is fixed to turn the mill. M. Honore constructed a mill on the same principles, but he has preferred glass to porcelain, considering it better to soften his colors than to run the risk of hardening them. The bot¬ tom is flat and is of glass, the muller is of bottle glass and grooved like a millstone for grinding hard substances. By the use of this mill there is an economy of seven-eighths of the time over grinding with a muller and slab. To use this mill we put the color in the bottom part, wet the color with water and then start the mill. This method of grinding always possesses the advantage over the muller and slab, of working up a larger quantity of material ait once, but it does not reduce it to a sufficiently fine powder for colors in¬ tended for fine art decoration. For these colors we commence the grinding in'the mill and finish it on the slab. The slabs that are used for grinding on should be square glass plates, sufficiently thick and without any bubbles, per¬ fectly flat and having a ground surface, they must be kept very clean and a separate slab should be kept for each delicate color, if we have not enough slabs to do this then the glass must be cleaned with fine sand or feldspar, until the powder of the substance used for cleaning remains perfectly white. 132 The mullers used for crushing the material on the glass should be of hard glass or porcelain. They often chip at the edges, any such chips should be removed, as by mixing with the colors they alter their fusibility. While the wet color is being ground upon the glass slab it is necessary, in order to bring every portion of it under the muller, to continually gather the color to the center of the slab, for this purpose we use a palette knife, but we have to bear in mind the nature of this and be sober in its use or we shall alter the color. Steel knives seem to us preferable, if they are not used more than is necessary; they are hard and they do not give up much to the color, except traces of oxide of iron, which is but a slight inconvenience, even for light colors, such as pale yellows, which already contain a certain pro¬ portion of iron oxide in their composition. The knives of horn and ivory, generally preferred by artists, seem to us much more dangerous. They wear down quicker than steel knives and the large quantity of phosphate of lime contained in them hardens the colors and may prevent them taking a brilliant glaze. These are the means and precautions to be employed to obtain a good color ready for use for art decorating; they are not all indispensable in the decorating of ordinary or coarse pottery, nevertheless it is always a great advantage to observe them. There are plenty of other materials and other kinds of apparatus suitable for grinding all sorts of colors well and quickly, but we are only speaking here of vitrifiable colors intended for painting on fine ware and porcelain and these necessitate the precautions which there is no need to take for colors intended for use with larger objects on a manufacturing scale, such as large vases for decorative purposes, floor and wall tiles and similar ware. APPLICATION OF THE COLORS AND METALS. The color, reduced to a powder of extreme tenuity, by the mechanical means we have indicated, is ready to be applied to the ware that is to be decorated. We must mix it with something that will enable us to use it easily and that will give it a certain amount of adhesion to the piece, or we cover this piece with a viscid coating that will hold the color, whi n it is dusted over the surface. 133 MEDIUMS. The substances to which the name mediums is applied, should satisfy the following conditions, which somewhat lim¬ its our choice. Water would, probably, be of all materials that which we would prefer; at the heat at which the colors are fired it dis¬ appears without leaving a residue and if we reach this temper¬ ature carefully the water goes off entirely, without doing any damage, but when the color is dry the pigment does not con¬ tract the slightest adhesion to the piece upon which it has been applied and the tints are liable to fall together; then, too, re¬ touching, if not impossible, becomes very difficult. The first of these defects is easily remedied by adding a little gum or sugar to the water. This medium has been employed for a long while for painting on tender porcelain, the glaze of which always contains lead, but we cannot use gum for colors when the nux has much borax in it. Nevertheless It has been found that the colored fillets, either green or blue, that could only be made slowly or imperfectly with essence, could be executed much better and quicker when worked with gum water. As for the second inconvenience, that respecting the retouching, we have not been able to entirely overcome this in any way and in consequence of this, gum or sugar water is now in nearly every case, abandoned, and spirits of turpentine, mixed with a little thick turpentine, is used instead. Any kind of turpentine cannot be used. It is an indis¬ pensable condition that it should be distilled twice so as to be entirely freed from every trace of rosin. The rosin, not being volatile will form a deposit of carbon at a red heat, which may reduce some of the oxide of lead, that enters into the composition of the flux, to the metallic state. The thick turpentine which we add to the distilled essence must be properly prepared; this is done by simply exposing the distilled turpentine to the air, in shallow vessels, for several days. In this way we get a good fat turpentine, which will completely dissolve in the essence, in whatever proportions we mix them experience has proved that it will not dissolve well except in an essence that is chemically identical with the source from which it comes itself, so that the best course is to take the spirit of turpentine and transform this into fat turpentine. 134 In whatever this fat essence is prepared, we should only use just so much as is necessary; the fat essence of lavender should be entirely rejected, as it produces too much carbon, which will take away the oxygen from the lead of the flux and destroy the brightness of the color. This defect, for the pur¬ pose we are now considering, becomes a precious quality in the application of metallic lusters; the excess of carbon, either re¬ duces the metals, or it opposes their oxidation during the fusion of the flux that makes them adhere. If the fat oil of lavender is to be rejected for the application of vitrifiable colors it is not the same thing with the essential oil, which, under several circumstances, renders great service; it is less volatile than spirit of turpentine, and when mixed with it it will keep this liquid for a longer time, For extensive grounds, which occupy wide zones on large vases and which should be spread out well and evenly, we have to take care that the part done first is not dry before the end is joined up to it. The dusting bag, which is used to spread the powder color over in the most even manner, will not have any effect on the part that is dry; we prevent the too rapid drying by adding essential oil of lavender to the spirit of turpentine. Virgin olive oil has sometimes been used for painting on porcelain and it is always employed for painting on enamel. When it is fresh it has but one disadvantage, it remains liquid up to the moment of firing. Nut oils and poppy oils are good when they are fresh, they dry spontaneously in a few days, but when they are rancid they lift up and shift the colors. MORDANTS. What French artists call mordants and in English is known as tacky, is a sticky substance used in decorating for the pur¬ pose of holding the powdered color laid on by dusting. These mordants were formerly very much more difficult to compound and were very complicated; several bitumens were put in and garlic and they were boiled with litharge. They are very much simplified now, but for all that their prepara¬ tion requires great aptitude and above all a special tact, in order to attain exactly the right degree of viscosity. Linseed oil is mostly used for dusting-on grounds, but nut oil is preferable. It is heated until it becomes sticky; we always add a little litharge, when boiling it, to give it drying *35 properties. It is laid oil the piece to be decorated, with a brush, as we will describe further on. The use of garlic or onion, to give the mordants a strongei viscosity, is a very ancieni process, which, perhaps, ought not to be rejected without a trial. We therefore give the composi¬ tion of two of the most esteemed of the old mordants, the first was known at Sevres, about 1750 as Brother HippolyteT mordant for gold. It was verified by Hellot and entered by him in the register. Five pieces of garlic and as much of white onion were chopped finely and digested, boiled for eight hours and reduced to a syrupy state in about a quart of white vinegar. The second mordant, also intended for gold and above all for use on a ground of tender porcelain, has an entirely differ¬ ent composition. In equal parts of essence of turpentine and of fat oil, asphalt, of the kind called “mummy” is boiled, the quantity of asphalt is one eighth in weight of the liquid; dur¬ ing the time of boiling a piece of linen, containing twice the weight of litharge is suspended. After the boiling the mordant is complete. , y LAYING ON, EMPLOYMENT AND POSITION OF THE COLORS ON POTTERY. Vitrifiable colors and the finely divided metals with which we decorate pottery are difllcult to use. They are what is called in the workshop “short” and “hard;” we have, therefore, been compelled to seek for every means to employ them more easily and with success. The way in which we place, lay on, and use the vitrifiable colors on pottery, demands careful consideration upon a num¬ ber of important points. The colors, prepared either chemically or mechanically, as we have described in the preceding pages, must be capable of adhering to the ware, either the dead surface of the biscuit or the bright surface of the glaze, before they are finally fixed by the fire which vitrifies them. To accomplish this it is neces¬ sary that the color should be mixed with either a simply watery liquid when it has to be put on the matt suriace of the biscuit, or, if it is to be applied upon the bright, smooth surface of the glaze, the color must be mixed with a viscid material, whether this be first spread out over the glaze in order to retain the powdered color when dusted on, or mixed 136 with the color before applying with a brush. In the first case we call the viscid liquid a mordant, in the second a medium. VARIOUS METHODS OF LAYING ON COLORS. 1 o accomplish the desired end the processes used for laying on colors are very varied, according to the nature of the color and ihe position it should occupy in relation to the body of the ware or the glaze. These processes are, by hand, with the pencil, with the stippler, with a mordant; there are, too, the special means of introducing color into the paste or body of the ware; where it is applied upon the biscuit and, conse¬ quently, becomes an underglaze color; introduction of the color into the glaze itself; application upon the glaze, or china paint¬ ing propeily so-called; finally the method by reserves and mechanical printing and dusting on. We will consider these different processes in their regular order. LAYING ON AND USE WITH THE PENCIL. In the gi eater number of cases the colors and metals are applied upon ware which is already fired and glazed. It is easy to understand that the color will not readily adhere to so smooth a surface; this surface can be made somewhat adhesive by giving it a thin coat of essence, which will cause a crayon mark to adhere to it. As has been explained, the colors must be reduced to the greatest state of fineness by grinding and they must be made viscid by the addition of fat oil, which holds the vitreous and heavy colors in place. I he color thus prepared is applied with a pencil having long haiis. 1 he choice of pencils is a question for the artist; we cannot say anything very definite on this subject. We must avoid going over a color again until it has, by dry¬ ing, acquired a sufficient adhesion to the surface of the ware. STIPPLING. When, instead of ornamenting pottery with paintings, it is desiied to give a uniform color to a considerable surface of the piece, the color must be laid on as evenly as possible; this cannot be done simply by means of a pencil, every touch would show and it would be with the greatest difficulty that we could get an even ground. After mixing the color with essence and fat oil in suitable proportions—it is well to let the 137 color stand in a warm place tor a time to get still fatter, or thicker—we lay it on the ware by means of an ordinary pencil, as evenly as possible, we then take another pencil, very much larger than the first and having the hairs terminating in a plane at a right angle to the handle. This pencil is called a stippler. By dabbing over the color, laid onto the ware, with this species of brush, we get the color of an equal thickness all over and cause the streaks and spots to disappear, which result from laying on with the pencil. This operation is called stippling. Stipplers may be of various sizes; there are small, medium and large sized. The small ones are used in art decoration to equalize a rather large tint, such as a sky, or to blend one tint into another. The large sized stipplers are used for laying on grounds. in the application by this means it is necessary to have the color thicker than for painting, or laying on with the pencil. It is indispensable that the join between the commencement and the finish of a band of color shall be made easily, so as not to show a difference. In order to have a fine and even ground, we must nearly always lay it on in two coats. In addition to this the color must not contain any moisture, otherwise it will run together in tears; we should also avoid dust, as much as possible; little particles of dust draw the color to themselves, producing thicker places which make spots and which are also very liable to scale off. It is found that colors put on in this way are not quite so bright as the others. LAYING ON WITH A MORDANT. There are certain colors which, in order to produce their effect, have to be laid on rather thickly or, in consequence of their vitreous nature, they cannot be spread evenly with the stippler. These colors are laid on by means of a mordant. The color, in this case, does not need to be ground so finely as for painting with the pencil; it must, however, be perfectly dry. The portion of the ware to which the color is to be applied has a thin coat of “tacky” or mordant given to it; this, as stated before, is a fat oil rendered viscid by boiling with litharge. This oil is laid on with a pencil or a stippler and as it has a color of its own it is easy to spread it evenly. 138 After the piece, or portion ot the piece, that is to receive the color is coated with the mordant, we take the powdered and thoroughly dried color, put it in a sieve, the silk mesh being of the required fineness and sift the color over the ware. The color will only attach itself to those parts that are coated with the mordant. We then clean oft any dust from the color that may be on the other portions. This method is employed prin¬ cipally for laying on grounds for sharp-fire colors. POSITION OF THE COLORS AND SPECIAL METHODS OF APPLYING THEM. In the preceding article we described the different means of laying cn colors, without any reierence to the colors them¬ selves, or to their positions on tne body of the ware. Tnese positions have, nevertheless, a considerable influence not only upon the color, but also upon the way in which it is applied. We can introduce the color into the paste of the body rtself, or it can be put on the green ware, or upon the ware when it is partly or fully burned, 'ine color may be mrxed with the aiaze, or laid on Uie glaze, or it may be desired to have the color in certain parts only, leaving the remainder of the sur- lace without any color. The various methods employed to obtain these results, we will now proceed to examine. COLOR IN THE PASTE OR BODY OF THE WARE. All color introduced in the clay forming the body of the ware becomes more developed and more lively in proportion as we approach to vitrifaction, but the coloring oxides make the clay more fusible and this means of coloring is thereby reduced when the paste is intended to be fired at a high temperature. Therefore among all the pastes the one which admits of the least variety in coloring is hard porcelain. Its coloration, which is very fine and regular, is almost entirely confined to pale blue; this is done with cobalt, an oxide which has a high coloring property even in very small quantities and only slightly changes the composition of the paste. We have suc¬ ceeded in obtaining porcelain pastes with considerable vari¬ eties of color; these were, a fairly deep blue, green, bluish- green; black, pale yellow and several shades of pink. The coloring oxides used were, chrome, cobalt, iron and manganese, titanium, and purple of Cassius. But by these means we get near to the composition of stoneware paste, of earthenware 139 and of tender porcelain. This latter ware is the one the paste of which is capable of taking nearly all the colors and exhibit them with the more vivacity and purity in proportion as their composition is of a vitreous nature. Thus tender porcelain, which contains the elements of glass and fine English faience, that considerably resembles it in composition, are the kinds of pottery that offer the greatest variety of and the most vivid colors. Since the publication of the second edition of Brongniart’s work, containing the preceding lines, the manufacture of col¬ ored porcelain paste has made considerable progress. The general principles stated by Brongniart are an exact expression of the greater portion of the facts, but they have to be modified in part through the introduction of new coloring materials, of new oxides, or of new mineral matters. The few observations devoted to this matter, though so interesting, were certainly not enough for the consideration of all the colors that can be introduced into the clay for underglaze. Although it was recognized that to color porcelain pastes it was only necessary to modify their composition and that the lower the temperature at which the paste was burned the easier it was to color, the attempts to do this were confined to the addition of some color elements to the white paste, in order to get a particular tint. i cannot, in the space at my disposal, give a full exemplifica¬ tion of all the processes for this purpose and must confine myself, on this subject, to stating as concisely as possible the principles which serve as a basis lor the work of today. Up to the present time the irregularities that have been noted in the colored pastes have been due to the conditions of the atmos¬ phere in which they have been burned. A real progress was accomplished by the studies which resulted in the conditions being clearly defined of a reducing, an oxidizing, or a neutral fire, suitable for any particular oxide or coloring matter. This was a great service rendered to the art by the royal works at Sevres in calling the attention of manufacturers to the point. COLORING MATTERS. Blue.—Before the year 1848 no other blue pastes were known than deep blue, agate blue and a bluish gray called chalcedony blue. The first was made by means of a sharp-fire blue, the 140 others were obtained by the addition of pure oxide of cobalt to the white paste. After this I prepared, for the first time, a much brighter blue by fritting the sharp-fire blue with an equal weight of flowers of zinc for six hours, in a porcelain biscuit kiln. This blue is now known as Persian blue and has become the base of a number of other colors, the tints of which have been modified by oxide of chrome, oxide of uranium, pitch-blende and artificial and native chrome iron. The sharp- fire colors in which oxide of zinc is present, can only be burned in an oxidizing fire, otherwise we run the risk of the oxide being reduced and volatilized. In a reducing fire the color takes a violet shade. Gray.—Platinum is capable of giving a very superior gray color to pastes for burning in a sharp fire and competes in this respect with sequioxide of iridium. These colors are of great value in the sharp fire for regular and constant grounds. They will stand the hard fire of the porcelain kiln. Yellow.—Oxide of uranium in small quantities, five parts at most to 95 parts of paste; burned in a hard fire and an oxidiz¬ ing atmosphere, that is to say, with a current of air going dur¬ ing the whole time of burning, produces a fine, pale yellow, with an inclination to greenish. In a neutral atmosphere it tends to a pale gray-green. In a reducing atmosphere the body is more gray. By increasing the doses of oxide of uranium, or of pitch¬ blende when it is pure, we obtain fine reddish, chocolate, brown and black tones, if burned in an atmosphere charged with reducing gases. Browns.—Oxide of iron combined, under the influence of heat, with oxide of chrome, has been used for a long time in the preparation of pale and deep browns. I prefer to use native chrome iron, but regard must be had to the exact com¬ position of the ore, which appears to admit of considerable variation; in consequence of this some very serious variations are possible when using different samples, which are experi¬ enced, either in the colors obtained, the fusibility given to the paste, or the reactions that may occur with the gases in which they are burned. Rose.—The classical researches of Ebelmen upon the crys¬ tallization of spinel ruby and corundum are well known and it occurred to me to use the aluminates of chromium and among others the artificial ruby crystals for coloring porcelain pastes. I soon found that there was no need for the aluminate of chromium to possess the crystalline form in order to resist the solvent action of the paste with which it was incorporated. In consequence of this the preparation was very easy. It suf¬ ficed to prepare an aluminate colored rose with chrome and submit this mixture of pure anhydrous alumina and bichromate of potash to the hard fire of a porcelain kiln in a current of air. The anhydrous alumina is obtained from the calcination of crystallized sulphate of alumina. The proportions may he varied from my first attempts and may be made 5, 10 or 15 of bichromate for 100 of calcined alumina. Five per cent gives a pale pink tint, 10 per cent produces a bright pink, some¬ times greenish, 35 per cent a decided green, which changes its appearance in artificial light. The most suitable proportion for obtaining a bright pink appears to be seven and a half per cent, but the paste must always be burned in an oxidizing atmosphere, in order to avoid greenish reflections. The rose-colored oxides are transformed to mauve, lavender, violet, lilac, by adding, along with the bichromate of potash, pure oxide of cobalt. The introduction of alumina, magnesia and oxide of zinc, has enabled us to form products analogous to the aluminates, which are highly refractory and of great value for colored pastes, particularly when they are melted, or only fritted, with feldspar or pegmatite. COLORED PASTES. The composition of colored pastes should be arranged accord¬ ing to fixed principles; it is based upon the mixture with the paste of various oxides in certain proportions. These coloring matters are, in some cases, more fusible than the white paste and, in other cases, less fusible, or if of the same degree of fusibility v/hen alone, they may when added to the paste increase or diminish its fusibility. It is obvious that the degree of fusibility must correspond with the normal temper¬ ature of burning, which has been determined beforehand. Let us therefore admit the following principles: First Principle.—If the coloring matter is more fusible than the paste, we must make the latter less fusible, that is, we must increase the refractoriness of the paste. Second Principle.—If the coloring matter is more refractory than the paste we must compose a paste that is more fusible. 142 Third Principle.—In the exceptional case of the coloring matter and the paste being of equal fusibility we only need to mix the two elements in their regular proportions. It is well not to lose sight of the fact that every porcelain paste is necessarily formed of an infusible plastic element, the kaolin, and a fusible element the pegmatite, feldspar, or feldspathic flinty sand. These data being admitted we have only, in the first case, to increase the proportion of kaolin, in the second, we increase the feldspar, pegmatite or feldspathic sand. These general principles being agreed upon it must be con¬ sidered as of prime necessity that the composite paste shall have a uniform shrinkage, both in the biscuit and in the final burning. As instances of this I will confine myself to the two following examples: A. COMPOSITION OF PERSIAN BLUE PASTE. Parts. Material called Persian blue (composition given above.. 500 Washed kaolin (St. Yrieix clay) . 2,000 B. ROSE PINK PASTE. Materials of artificial ruby. 640 Containing: Alumina.800| j 860 Bichromate of potash. 60| White clay from Dreux . 200 Pegmatite hard porcelain glaze. 160 As for the coloring matters whose fusibility does not differ notably from that of the normal paste, it is advisable, or I would say, indispensable, to first find how much of the coloring matter can be mixed with the paste without any objectionable results, such as blisters, tears, cracks, etc. Thus the stand¬ ard paste used at Sevres cannot take more than 5 per cent of oxide of nickel, above this proportion makes the paste unfit for use, but any quantity less than 5 per cent can be mixed with the paste. I consider this point of the highest importance and we find in practice that two colored pastes, taken alone, may each possess excellent qualities and yet, when mixed together, be absolutely worthless. 143 When a paste is not sufficiently vitreous in itself the coloring matter should he put in in the shape of a frit. As the coloring of the pastes of fine faience and fine stoneware is based upon compositions which are very similar, the same formulas will serve for the two. The composition for black bodies has been given elsewhere, as well as that for fine stoneware in gray, pale blue, deep green, pale green, bluish green, pure black and brown, so that we will only give here the compositions not before mentioned, of colored bodies for hard and tender porce¬ lains: I COLORED PASTES FOR HARD PORCELAIN AND FINE STONE¬ WARE. A special paste. A, is prepared by taking— Flinty kaolin .48 Pure white plastic clay . 16 Pure quartzose sand .-. 16 Porcelain glaze . 16 Carbonate of lime . 4 This is the base for most of the colored pastes that follow. BLUE PASTE. Paste A. 89 or 70 Sharp fire blue (preparation previously given) . 10 or 20 Plastic white clay . 0 or 10 These plastic white clays remain blue under the porcelain glaze. PALE BLUE PASTE KNOWN AS AGATE. Paste A.95 Oxide of cobalt . 5 DARKER AGATE. Paste A. 90 Oxide of cobalt . 10 The oxide must be thoroughly well mixed with the paste in the usual way. When glazed the ware has the grayish-blue tint of chalcedony. H4 GREEN PASTE. Paste A. 65 or 85 Sharp-fire blue for grounds . 5 or 10 Chrome oxide . 10 or 5 These pastes are of a fine green color, which is not changed by glazing. PALE BLUISH GREEN. A fine pale bluish-green can be produced by composing a green oxide as follows; Chrome oxide . 50 Carbonate of cobalt. 25 Carbonate of zinc . 25 To make the paste we take: Paste A. 90 or 95 Green oxide. 10 or 5 These green bodies, when they are not under glaze, have a pale bluish-green tint, but they become a lively and decided green with the covering of glaze on. GREENISH-BRONZE PASTE. Paste A. 95 Calcined oxide of nickel. 5 BRONZE OR OLIVE-GREEN PASTE. Paste A. 88 Calcined oxide of nickel . 10 Oxide of cobalt . 2 We can vary the proportions of the oxides according to the tint we wish to obtain. Without a glaze this paste is a matt bronze, which can be enriched with touches of gold. When glazed it becomes a rather bright green-bronze. The glaze must not be thick. Depending upon the fire, its temperature and purity, this green-bronze tint is sometimes very fine; at other times it is dull and dirty. It is this uncertainty which has caused the use of this color for porcelain pastes to be dis¬ continued. • BROWN PASTE, Paste A. 85 or 80 Calcined oxide of iron . 15 or 20 145 The whole must he thoroughly well ground together; the paste must be washed with plenty of water and that which remains in suspension must be set on one side; re-grind that which is precipitated and rew'ash it continually until there is no more precipitate. In this way we get a paste which is extremely fine and which, according to the proportions of iron and of paste, takes upon its surface a tint which varies from reddish-brown to a brown that is almost black and which, according to the temperature and the nature of the ingredients is liable to swell and even to melt; therefore the above pro¬ portions must only be considered as indications, which may have to be modified on trial. BROWN-BLACK PASTE. A frit is made composed of: Chromate of iron . 14 Oxide of cobalt . 14 Oxide of manganese . 14 Paste A. 58 This is calcined in the hard porcelain fire and is then mixed in various proportions with paste A. BLACK PASTE. Paste A. 91.0 Calcined oxide of iron . 5.5 Calcined oxide of cobalt . 3.5 This paste, sometimes a pure black, is laid on in a not very thick coat, upon an ordinary white body and often stands well without chipping or crazing. It can be used for cameos and white has reliefs. Paste A. mixed with oxide of uranium makes a fine black paste. GRAY PASTE. Paste A . 97.5 Rutile . 2.5 This paste preserves its gray color under the glaze. PALE YELLOW PASTE. Paste A. 95 Rutile or native oxide of titanium... 10 This paste when finely ground shows a beautiful pearl gray, under the glaze. 146 FLESH TINT PASTE. Paste A. 90 Rutile. 10 This paste does not keep its color unless put under glaze; if enameled it becomes a dirty gray. PINK AND PALE PURPLE PASTE. These tints are obtained by means of the precipitate of Cas- sius; we prepare a solution of gold as has been described fur¬ ther back, mix paste A in this solution and stir it well; we then pour in, drop by drop, a solution of tin oxide which pre¬ cipitates the purple. The chalk must be left out of the paste A until after it is colored and washed, when it is added in suitable proportions. By varying the proportions of purple and of paste we can get a variety of tints which do not change under glaze. COLORED PASTES FOR ARTIFICIAL TENDER PORCELAINS. Turquoise Blue. Make a frit composed of: Peroxide of copper.5.88 Anhydrous carbonate of soda.17.65 White sand.76.47 It must be noted that if the frit is made at a very high tem¬ perature we must increase the quantity of oxide of copper, because of its great volatility. We then take: The above frit, ground.59.26 White frit for porcelain.14.81 Washed marl.11.12 Chalk.14.81 We make an intimate mixture of these materials by crushing them together. The introduction of organic matter into this paste should be avoided. The paste should not be fired at a higher temperature than an oxidizing fire. Pale Green Paste. Ordinary white paste.90 Chromate of lead. 5 White sand . 5 147 Grind this well together. The sand only serves to harden the paste, which the lead salt renders very fusible. The pro¬ portion of sand may be augmented, if necessary. There is no doubt that the chromic acid is brought to the state of a very finely divided chrome oxide. Triboullet has strong reasons for believing that it is this state of extreme subdivision which gives richness to the tint. # Blue Paste. In the composition of ordinary white frit we put one to four per cent of oxide of cobalt; this is fritted, and with this frit we mix marl and chalk in the same proportions as for the ordi¬ nary white paste. There must be a current of air in the kilns where this paste is fired. Violet Paste. Oxide, or carbonate, of magnesia (pure).5.55 Anhydrous carbonate of soda.16.65 Nitrate of potash.5.55 White sand.72.25 Frit these together. (We can also produce very fine tones by mixing a small quantity of oxide of cobalt with this.) Frit according to above formula.76.92 Chalk.11.54 Marl.11.54 The elements of this paste mix completely when they are pounded together. Lemon-Yellow Paste. Antimoniate of potash.33.34 Minium.50.00 White sand.16.66 Frit together; a high temperature is not needed, and to form the paste mix as follows: Frit, above described.7.14 White paste for tender porcelain.85.72 Biscuit for tender porcelain.7.14 Mix all thoroughly well together. 148 Nankin Yellow Paste. Antimoniate of potash.23.53 Sesqui oxide (red oxide) of iron.11.76 Minium .. 47.06 White sand.17.65 Frit this at a moderate temperature. Above frit. 7.14 White paste for tender porcelain.85.72 Biscuit of tender porcelain. 7.14 This is to be well crushed and the whole well mixed. Black Paste. This can be made with violet paste with which sulphur and peroxide of iron are mixed. A piece often appears to be formed of a colored paste which is not really colored throughout its entire thickness. The mass is a white paste and the colored paste only forms a layer, of two to three millimeters thick, on the exterior surface of the piece. It was in this way that Wedgwood made his reproduc¬ tion of the famous Portland vase, in black paste with white bas reliefs. It is in this way that, at Sevres, the white cameo figures, on a ground of blue are produced. The blue itself is applied in a thin layer upon a base of hard white porcelain. UNDERGLAZE COLORS. Slip. We referred to slips in a previous work, but as we consid¬ ered these as a means of decoration we deferred the descrip¬ tion of them to this place; we will therefore present here all that concerns this method of ornamentation. It is necessary, in order that a color that is put under a ceramic glaze should become glazed and brilliant by the fusion of the cover glaze, that the color should be spread evenly and should not bjecome detached, either during or after firing. The metallic oxides in a pure state very rarely fulfill these condi¬ tions, even when, as with porcelain, the ware is fired at a very high temperature. It is, therefore, necessary that all the colors with which we decorate a piece in placing them under the glaze, should have some connection, in their composition and nature, both with the body of the ware and with the glaze which covers the colors. The colors, too, must have sufficient H9 adhesion, both in themselves and to the body of the ware, so that they will not be diluted, weakened, or washed off by the application of the glaze. The special process which is called slipping (engobage) fairly fulfills all these requirements. It consists in covering a ceramic paste with an earthy ma¬ terial, be it white or colored, which, by its opacity, conceals and seems to change the color of the paste, to such a degree that a piece of pottery which has a body (paste) of a reddish or yellowish color can show on its interior a fine white and on its exterior an equally fine chestnut brown ground. The glaze which is placed upon these grounds gives to them the brill¬ iancy required. It is to the earthy, colored material that the name of slip (French, engobe) is given. This invention, which reached a remarkable degree of development in England, had its origin in Italy, somewhere about 1300, though some Egyptian pot¬ tery, covered with a silico-alcaline glaze, shows the application of a white slip between the yellow body and the turquoise-blue glaze. The museum of ceremics at Sevres possesses fragments of Arab pottery brought by M. Lenormant, attributed to the eleventh century, the body of which is very dark, covered with a transparent glaze, that has the appearance of being opaque, by means of a vei’y white and thin slip, applied direct upon the body and receiving the glaze. Some antique pieces of pottery, though without glaze, have been embellished with slips which have remained matt and which easily become dirty. Such are the white, yellow and violet colors of the Greek, the fine white slips of the Athenian vases and the whitish slips upon reddish-yellow bodies upon some vases of Roman manufacture. Slips are essentially composed of an earthy, clayey base, colored naturally by ochres, or artificially by various oxides. In the first we do not introduce any vitreous matter; we use them just as nature gives them to us; all that we do is to wash them and' reduce them to a fine powder. But in the slips which are colored by the introduction of various metallic ox¬ ides it has been noticed that it is necessary to add an alkali, to improve the colors and to give better adherence to the ware. The mixture of alkali, sand and oxide is first fritted together. We give here examples of the compositions of some of these slips. The slips that are entirely earthy, that is, those without a frit are: The red, produced by calcined yellow ochre. The brown, produced by earths of Sienna or Umber, which owe this color to manganese. The black, which results from a mixture of calcined and manganese, 99 parts, and white clay, 1 part. The white, which results from a mixture of white clay, or clayey kaolin, 96 parts, and tin oxide, 4 parts. As for the slips that contain frits, they are composed, in the first place, of colored vitreous frits, which, after being pulver¬ ized, are added to the white clay to form the slip. Yellow Slip. A frit is made of: Sand. 25 Carbonate of potash.50 Naples yellow.25 Of this frit one part is taken and two parts of white clay. Violet Slip. Frit: Sand.32 Carbonate of potash .66 Manganese... 2 Two parts of this frit is added to two of white clay. Blue Slip. Cobalt, azure blue.32 Minium.3 White clay.65 This is not fritted. Green Slip. Blue frit.40 Yellow frit. .40 White clay. 20 Slips are more frequently put upon green ware than upon biscuit; in the first case they may be simple earths and not contain any frit, but it seems that in the second case the color¬ ing matters should be fritted. Slips should be very finely ground, then mixed with Avater to the consistence of a soup; they easily remain in suspension in the midst of the clay which sustains them. The ware to be slipped is allowed to become sufficiently firm fo permit of its being handled, and even of being plunged into the slip without there being any risk of damage, but ordinarily we prefer to place the slip on the ware, or in it, if it is the in¬ terior that has to be covered. Sometimes the slip is spread over the ware, at others it is blown onto it, projected onto it by insufflation. By this latter process the slip is put into a vase, resembling a teapot, but with the spout straight and contracted (see figure). Then on blowing into the large open¬ ing O of this vase the slip is forced out of the spout B, the opening of which can be made smaller by means of a straw that can be adjusted, and in this way the ware is sprayed with slip. The whole or part of the piece can be covered, as desired. In order that the slip should be spread as equally as possible we usually put the piece to be slipped on the lathe and turn it while spraying. 0 We let the slip harden, which takes place immediately in consequence of the property that articles nearly dry possess of absorbing moisture; we then put the piece back upon the lathe so as to get a sharp edge to the slip, or we can cut away some of the slip, showing a band, or bands, of the color, whatever that may be, of the body. Sometimes the portions that are scraped off are covered with slip of another color and the piece is ornamented in this way by bands and fillets of different widths and colors. Or we may cut designs on the piece, either in the ordinary lathe or the guilloching (engine turning) lathe, producing incised ornamentation; then the surface is covered with a slip, which fills all the hollows, but on putting the piece again in the lathe and, with the knife or chisel, cutting away all the slip until the elevated portions of the ware are reached, the slip will only remain in the incised parts. 152 These operations finished—and it can be readiy understood that an infinite variety of designs and colors are possible—the. 4 piece is fired in a biscuit kiln as ivould be done if no slip were used. We thereupon apply the glaze that is suitable, but which must be a transparent one. The Chinese have placed extensive ornamentation in white, under the glaze of hard porcelain, which must have been put on by slipping. It is supposed that this was done with a white talc. The true slips are only applied upon faience, either fine or coarse. This is the principal method of using colors under glaze for this ware, though we may consider as in the same category, first, the blue and chrome-green ornaments that are applied direct upon the biscuit of hard porcelain and on the biscuit of tender porcelain; second, the blue grounds of these porcelains, because the cover in the first case and the crystal¬ line glaze in the second are placed over the colors. Neverthe¬ less we shall consider this placing of the colors as belonging to a process different to slipping, and we will describe this under the classification of applied colors. COLORS APPLIED UNDER GLAZE. Under glaze colors are those verifiable colors which are under the cover glaze and play the part of a slip. The slip, properly so called, is an earthy color; the under¬ glaze color is a verifiable slip. As a striking and complete example of underglaze color when it is not a slip, but an appli¬ cation of color, we cite the process of application of blue on tender porcelain biscuit beneath a crystalline (flint glass) glaze, which we have given elsewhere, but repeat here. The beauti¬ ful Sevres blue for grounds, which has had, and still possesses, a great reputation, is made as follows: We take cobalt ore, either Swedish or Saxon, which is a sulphide of cobalt, iron and arsenic; calcine it, to get rid of the sulphur and a portion of the arsenic; it is then dissolved in nitric acid, and we precipitate the arsenate of cobalt by means of carbonate of potash, taking the customary precautions, though it is not necessary to have a perfectly pure oxide, and Hellox believes that it is even advantageous for the develop¬ ment of the color that a certain quantity of arsenate should remain in the oxide of cobalt to be used. 153 This cobalt, properly dried, is combined by fusion with the following substances: Arsenate of cobalt. > Siliceous sand from Fontainbleau. 4 Carbonate of potash (pure). 110 2 This mixture is melted in a crucible. It sometimes happens that the tint of the blue ingot which is obtained is not quite satisfactory; in such case we remelt it, adding either nitre or crushed silex, according as we find it too hard or too tender. DECORATION WITH THICK SKIP OK PASTE. When the vitreous ingot, resulting from the fusion, has the desired tint we reduce it by pounding and grinding it to a powder, which must not be very fine. This is mixed with water and laid on the porcelain biscuited body with a small steel palette, and spread as evenly as possible. It is fixed to the biscuit by firing it in the kiln. The ware comes out with a rough and bubbly surface. This is rubbed smooth with a piece of stoneware. Very often a second coat of blue is put ou and again fired. This also has to be smoothed by rubbing. Upon this we place the glaze for tender porcelain, of which more than one coat is sometimes put on. It is by the preparation of the oxide, of the blue, laying it on of a suitable and equal thickness, the exact temperature which it receives, both the two coats of blue and the two coats of glaze, that we get the beauty, the brilliancy and the velvety character of this color. As it was extremely difficult and, consequently, very rare that all these conditions could be equally fulfilled, it was also rare to have a fine blue ground on tender porcelain, as it Is difficult to obtain it, exempt fiom faults, on hard porcelain. We can see from this that the tender porcelain of Sfivres. 154 the manufacture of which was discontinued in 1804, must, in order to have got its beautiful appearance, have gone through the sharp fire four or five times. This method of decoration in blue underglaze is also that employed by the Chinese, the Saxons and by a number of Ger¬ man factories, and has been imitated in some of the French factories, with slight differences of detail, according to the place and the circumstances. After making the biscuited body less absorbent, either by covering it with or soaking it in a solution of gum, an albumin¬ ous liquid such as milk, or a greasy liquid such as essence, or even by soaking it in water, we are able to apply colors and spread them over the surface, or make ornamental designs upon it. If we have simply moistened the biscuit, we let the color on its surface dry, then dip the piece in the glaze and fire in the glost oven. If it has been necessary to saturate the biscuit with a ma¬ terial which completely destroys its absorbent property, then we must destroy this material by the application of heat, so as to restore to the biscuit its property of absorbing liquid, thus permitting the glaze to spread over it and attach itself to the body. The course which is adopted depends upon the nature of the color and particularly of the designs that are to be applied upon the biscuit; thus the burning off is indispensable when printing on the biscuit, as will be seen in the description of this mechanical process. In these cases the color is under the glaze, not in it. 'Ihe result, as a rule, is that it is more even, but it is often less brilliant, especially that on hard porcelain, because a feldspathic glaze is always slightly bubbly. COLORS IN THE GLAZE. In the second process, which is generally the better one not¬ withstanding the difficulties it presents, we mix the oxide, sometimes pure, sometimes with the addition of a certain pro¬ portion of feldspar, in the glaze and in such proportions as to sufficiently color it, but never in such quantity as to cause the glaze to become opaque nor too fusible. This is a condition sometimes more difficult to fulfill than might be supposed, file biscuit is dipped into this colored glaze; this appears si-m- i55 pie enough, but in order to obtain a fine and even ground there are quite a number of things to be considered and, conse¬ quently, of precautions to be taken. In the first place it is important that the biscuit should not have been very hard burned so that it should remain very absorbent. Quite fre¬ quently the exterior alone of the piece is to be colored. We must then put a clear, or uncolored glaze in the interior. If we desire to keep this off the exterior this is a condition rather difficult to fulfil, we dip the whole piece into the glaze and when it is dry we remove it from the outside by brushing. We let the piece dry completely, then dip it into the colored glaze, taking care that none of this runs inside. We either cork up the mouth of the vase where this can be done, as in pieces with narrow necks, or dip it in, mouth downwards', or else, if the mouth is uppermost, we only dip the piece in so deeply as to let the glaze come up to the edge, just to the point where the two glazes meet. This dipping demands considerable skill and here we find the second difficulty. As the glaze for the exterior is colored, but is not opaque, we have to spread it over the piece with the greatest possible exactness, otherwise the vase will be of an uneven and undecided tint and will be regarded as a defect¬ ive piece. Now we will find that on plunging the vase verti¬ cally into the colored glaze to prevent any of it running in¬ side, the foot of the vase is in the glaze twice as long as the upper part, or neck, is; we must therefore vary somewhat the times of immersion of these two portions and so arrange that the neck will remain rather longer in the glaze than the foot which is a very difficult thing to do. We know that on taking a piece out of the tub of glaze, the liquid, which does not adhere well, flows along the piece, what is called the drip, but the extra thickness of this drip, over the glaze which has been flowed evenly on the ware, forms lines, bands or veins that, being thicker, are more strongly colored. It is only by considerable skill and after observing carefully the behavior of this drip in different positions of dripping, that we can avoid these inequalities in thickness. We do not always have a choice in the matter of the positions in which we can dip a piece and when this has an opening in it that cannot be closed, where the Cblored glaze' will run in- side at the slightest false movement, it can be understood that the precautions to be taken are innumerable. This method of coloring was, formerly, sufficiently rare; as it was necessary that the color introduced in the glaze should be able to resist a temperature high enough to vitrify the glaze, this condition reduced the number of colors that could be employed, the more so in the case of a glaze that had to be subjected to a higher temperature. This is not the only cause which reduces the number of oxides that can be used; certain coloring oxides eilher increase or diminish the fusibil¬ ity of the glazes so as to interfere with the equilibrium of ex¬ pansion and contraction, or the bond, which should exist be¬ tween the glaze and the body; such are the oxides of cobalt, iron, manganese, etc.; others diminish the fusibility, rendering the glaze opaque, dull or dead; such are the oxides of tin. chromium titanium; finally the elements of the glaze itself, act more directly upon the oxides and modify them more completely, accordingly as they are in the glaze or upon its surface. Considerable difficulty has been met with in mixing with the glaze, in an intimate and permanent manner, the metallic oxides which should color it, hence the restricted use of this method of ware, in which the glaze can be durably and cheaply colored on its surface in a muffle fire; but the process with colored glazes is economical and there is yet another advan¬ tage for many kinds of ware, as porcelain for instance, by avoiding the re-firing in the sharp fire, necessary to bring up the brilliancy and gloss of the colors that are laid on the glaze we escape the expense and the numerous chances of damage to the ware attendant upon each re-firing, numerous attempts have therefore been made to overcome this difficulty in the use of colored glazes which, as for the hard porcelains, have to be fired with the paste (body) of the ware at a hign tem¬ perature. When the color is, like the glaze, spread over the whole sur¬ face of the piece, this kind of glaze is called a ground color. It is scarcely used for anything else than enameled faience (earthenware) and the hard and tender porcelains. The white enamel of white earthenware is composed, es¬ sentially, of oxi&e of tin, oxide of lead a qvrartzose sand, bay 157 salt and soda. The oxides of tin and of lead are mixed by their calcination together in a small reverberatory furnace. The combination of these two oxides gives a yellowish powder which in France,-is called calcine, in England putty powder, and which is the base of white enamel. This is made from the mixture of the metallic, siliceous and saline materials at the bottom of the furnace in a place called the basin. The compositions vary somewhat, according to locality, the material of which the paste is made and the purpose for which the ware is intended. We give here the hardest. No. 1, that is to say, that which contains the largest proportion of tin, and the softest. No. 2, which contains the most lead and is the most extensively used. No. 1. Tin and lead calcine, com¬ posed of tin oxide 23, lead oxide 77 . Minium. Sand (Nevers) . Bay salt . Soda (of Alicante) . No. 2. Composed of tin oxide 18, lead oxide 82 .‘ Sand- (Nevers) .. Bay salt . Soda (of Alicante) If we have no Nevers sand, which is rather fusible, we replace it with a pure quartzose sand and increase the pro¬ portion of flux as follows: No. 3. Calcine of tin oxide 23, lead oxide 77.45 Washed quartzose sand...45 Minium. 2 Bay salt . 5 Alicante soda. 3 No. 4. Calcine of tin oxide 18, lead oxide 82 ,..45 Washed quartzose sand... .45 Bay salt .... Alicante soda The melted mass is not always white on leaving the basin, it is sometimes even nearly black in consequence of the car¬ bonaceous matter it contains, and which could not get away from it, but when crushed and remelted on the ware it git es the desired white color. The heat required to melt this in the basin has been reckoned at from 60 to 70 degiees on Wedgwoods’ pyrometer. 158 The enamel of earthenware may be colored yellow, pure green, pistachio green, or blue by the following metallic oxides. YELLOW ENAMEL. White enamel . 91 Naples yellow (oxide of antimony) ... y BLUE ENAMEL. White enamel . y 5 Oxide of cobalt in state of azur .... 5 PURE GREEN ENAMEL. White enamel . y 5 Copper scales (protoxide) . 5 PISTACHIO GREEN ENAMEL. White enamel . y 4 Protoxide of copper .. .. 4 Naples yellow . 2 VIOLET ENAMEL. White enamel . yy Peroxide of manganese . .. 4 These colors are sometimes formed 1 by adding in the com¬ position of the enamel itself the coloring oxides, sometimes we merely add these to the crushed enamel. We must avoid putting ware that is in white enamel in the kiln alongside pieces that are colored green or blue, as these colors are capable, by their volatilization, of giving a tint to the white. Brown enamel or white, finely powdered and suspended in water in the state of a thin slip, is put on the ware by dipping, when the entire piece is of one color, and partly by dipping and partly by spraying when the piece lias to be browm, or colored, outside and white within. The piece is first dipped into the enamel for the exterior, plunging it in up to its edge; the workman holding it by the inside. Hie outside enamel is allowed to set; the piece is then taken in hand again and the white enamel for the interior is poured in, either by a ladle or cup and the glaze is distributed ®ver the whole interior surface by a suitable movement; the excess is poured back into the tub. 159 The ware, when enameled of a suitable thickness,will usually require to be retouched in places where the enamel is want¬ ing; it is necessary to remove the enamel on the foot of the piece to prevent it sticking to whatever it stands upon when being fired. This is generally done by brushing it off, an op¬ eration which produces a siliceous lead powder that is very injurious to the health of the workmen who do it. STOPPING OUT. When we have to put on a ground color, by the process of dipping, upon flat pieces, or ware with large openings, such as plates, cups or fruit stands, it is not possible to entirely prevent the color attaching itself to those portions "which are intended to remain white, we, therefore, have to make use of what is called stoppings. These consist chiefly, of a greasy material with which we coat those portions that are not to take the color. The coloring material suspended in water can¬ not attach itself to the ware except on those portions which have not received the greasy coating. Formerly oil, or some similarly greasy fluid, was used, but oils penetrate the biscuit unequally, that is, they spread and the outlines of the stopped out portion cannot be kept sharp. Melted mutton suet, which sets directly it comes into contact with the ware, is used as a stopping with perfect sharpness and success. But in order that these stopped out parts can take, in their turn, an enamel or a glaze it is necessary to de¬ stroy the stopping by the action of a heat high enough to volatilize them, after which tne ware is covered by a second dripping. This does not disturb the first coat as that becomes sufficiently set by the heat used for burning off the stopping. The work is then completed by firing in the glost kiln. It is easy to see that we can stop out the first coat if nec¬ essary, should there be any fear that it will receive too thick a glaze from the second dip; also that we can put different colors in the stoppings. The principle is to cover with the fat all those parts, in the first, second, or third dipping, that have to be stopped out; being careful, each time, to destroy the greasy material by a sufficient, but always a gentle, heat. At Nymphenburg in Bavaria, a different method was em¬ ployed. This is by covering with glaze the portions which are to remain white, the bine ground color is taken up in a MU brush alid splashed over the whole of the piece. The glaze is then removed, by scraping or brushing, from the parts which are to remain white, whereupon the whole piece is dipped in a covering glaze, which covers both the white stopped out parts and the colored ground. We have seen vases and other kinds of ware with very tine and evenly laid blue ground's, put on in this way. This stopping out, in whichever way it is done, is, neces¬ sarily, a delicate and tedious work, consequently it is expen¬ sive, this is entirely avoided by the first method, that of simple laying on of the color. Sometimes we have to paint upon a colored ground, orna¬ mentation of a different color; now, from the nature of veri¬ fiable colors it is very rare that one color can, successfully, be put upon another, for the color underneath will, frequently, act upon the one that is above it, even if the one color does not cause the other to shell off, which generally takes place wffien the underneath color is one of the kind we have clas¬ sified as lard-fire colors and the one laid over it is a tender, or light-fire muffle color (see pages 51 and 9S), the under color is seen, in consequence of the transparency of most verifiable colors and thus spoils the upper color. In most cases the only thing we can do is to remove the ground by scraping it from those places where the other color is to be laid, but this method is very tedious and re¬ quires great skill, for it is almost impossible to repair mis¬ takes. We sometimes make use of another method; this consists in painting upon the white ware, with gum water thickened with chalk, those parts that we wish to surround Avitih a col¬ ored ground. The gum and chalk are incapable of adhering to the piece after firing. The design painted on in gum is allowed to dry completely and when it is perfectly dry a ground of color mixed with an essential oil, is laid over the whole piece, without any regard to the gum and chalk de¬ sign. When the color ground is perfectly dry it is fired at a temperature sufficient to make it adhere. The ground will not fix itself upon any place where the chalk is, any of the ground color on this will not adhere to it and falls off of itself or becomes detached with the least rubbing. i6i We sometimes have recourse to another means, which is quicker and cheaper, inasmuch as no preliminary burning off is needed. We put a ground color upon the piece in the usual way and as soon as this is firm enough, but before it is quite dry, we paint upon it any required design with a thick solution of gum to which chalk is added; this is laid on with a brush. The piece is then dried in the stove and the gum contracts, carrying with it the chalk and the ground color upon which it had been laid, the ground not having yet firmly adhered to the ware. The design usually falls off itself and will always come away with the least rubbing, leaving a blank which has only to be gently dusted with a thoroughly dry dusting brush. OVER GLAZE COLORS. The fourth method of applying vitrifiable colors, that is colors upon the glaze, is the most used. It includes three kinds: Over glaze grounds for sharp fire; grounds for muffle fire, tender and hard and, finally, porcelain painting, from the simplest effects to the most precious works of art. We will consider them in this order. HARD EIRE OVER GLAZE GROUNDS. The colors called hard, or sharp, fire colors are applied upon the glaze, which is already vitrified and we have to re-fire the piece; the glaze melts again, the color becomes incorporated with it and partakes of its hardness, solidity and brilliancy, but this necessitates extra expense for firing the ware and renewed possibilities of accident and damage, nearly equal to those we meet with in the first firing. If we are working on a large piece which has taken a long time to execute, or is diffi¬ cult to produce, the possibility of loss becomes much more serious, nevertheless, in many potteries, particularly those for porcelain, this method, on account of its simplicity, is gen¬ erally preferred. There are two general methods of application—we have de¬ scribed the special methods in treating of the colors which they require—in the first and oldest, only colors that are al¬ ready vitrified are used and the ware, which is glazed and fired, is given a greasy, viscous, coat, called a mordant. That which was used at S&vres, for hard porcelain, was composed as described on pages 130 and 137. 162 We first lay it on with a brush then distribute it so evenly as possible with a stippler, so that it is exactly equal in thickness all over, then let it stand for a few hours. We then take the color, such as deep blue, agate blue, or tortoise¬ shell brown, this is vitrified and then powdered, but not too finely; some of this is put into a sieve and dusted evenly over the ware. The piece is then fired in a sharp fire. The first coat of ground is seldom equal in thickness, con¬ sequently the color is not all of equal depth. We then have to apply a second, thin, coat and again pass it through the sharp fire. Sometimes this makes it too deep and even al¬ most black. The vitrified blue not only gives off blue vapor, like all cobalt blues do in the hard fire, but also a great num¬ ber of very minute grains or dust, which will cover the white centers of plates, etc., and spoil them. We will speak of the other losses common to several colored grounds when treat¬ ing specially upon this subject. This process has, therefore, been abandoned for laying on blue grounds and has been replaced by the following: For this method it is necessary that the ware should be absolutely dry and the colors be finely and perfectly powdered. The deep blue, the pale bue, so-called agate, and the chrome green grounds are put on in the same way; the color, in the state of the prepared oxide, is ground with turpentine spirit until it begins to thicken on the slab, then we add fat oil in the,pro¬ portion of a fourth of the volume of the cobaltic oxide. The color thus prepared is laid on the piece with a brush and is spread out and equalized with a long haired stippler, taking care not to pick off any of the color by an awkward use of the stippler, which would be likely to happen if we use one with short hairs. We then dry the piece in the stove and when dry give it a second coat, this time using less fat oil in the color. This is dried and then a third coat is put on, but this time the color contains more fat oil than either the first or the second coats did. At Vienna they put on so many as five coats, but the re¬ sult is their grounds are very fine and even. For the pale or agate blue the same blue oxide is used, but it is ground up with about equal proportions of fat oil and laid on very thinly with an ordinary stippler. i63 Laying on Muffle Grounds. The grounds for tender and hard muffle colors are laid on In much the same manner as those for sharp fire, but more care, foresight and skill are necessary. The color is ground very finely and should then be reground on the slab by the workman who lays it on. It is mixed with the right quantity of essence. We have already spoken of the qualities of the essence and the effect of lavender; it is here that the employment of this particular kind, which re¬ tards the drying of the turpentine, js the most necessary. The pencils that are used for spreading the colors are those known as fish tails, because they are flat and spread out like a fish tail. Some colors are much more difficult to lay on than others, some are short, such as the blues and the grays, others lift up, such as the chrome greens, the purples, etc. The iron reds and browns are generally the easiest to use. A most important precaution to be taken is to avoid all damp: the colors must be kept perfectly dry during the whole time that they are in use. particularly if a large surface has to be covered. This can only be done by keeping the workshop, very warm, almost as hot as a stove, especially in damp weather. It has been noticed that even in the summer time, when the temperature of the shop was only the same as that of the outer air, that certain grounds could not be laid on with any success in the morning, nor on rainy days, nor when there were a large number of workpeople gathered together in one place. • , i ••• | It has also been noticed that it is often necessary to leave the prepared color, which is ready to be used, lying upon the slab for 24 hours, carefully covered to protect it from damp, before laying it on the vase The same remarks will apply to gold. PAINTING ON POTTERY IN VITRIFIABLE COLORS. Whether the decorations consist of ornamentation without merit, of flowers executed in the worst possible manner, that is to say. the decorations of the commonest articles of com¬ merce that have to be sold at the lowest price, or whether they are figure paintings or landscapes, which the art of the painter has brought to the greatest perfection, there is one general end and aim to strive for, which is that the colors shall be bright, glazed and substantial. It is more particularly of tine art painting, executed upon porcelain, that we intend to speak in this place, because the object is a. higher one and one that can only be attained by taking minute precautions, which it is not even possible to enumerate completely. The colors must be reduced to the greatest possible degree of fineness by careful grinding. This operation must be per¬ formed while protected from all dust and the powder must be thoroughly dry before the essence that is used as a medium is added to it. In order to retard still more the drying and make It easier to use the color, a little, very pure, olive oil may be added. This will not reduce the beauty of the colors, as might be supposed; indeed, we have even seen first-class artists, whq have ventured to use the oil alone as a medium, taking the risk of the least touch or rub destroying their work. The application of the color is of the greatest importance, and this is an operation which cannot be described, as it depends entirely upon the intelligence, the touch and the skill of the artist. As painters say, it must be free, light and even. The greater number of col¬ ors, prepared by chemists, which are submitted as samples, are nearly always bright and well glazed because these samples have been prepared without any regard to lines or forms to be observed, of tints to be obtained, or of retouch¬ ing. that we must be prepared for. Therefore, at Sevres, we never form our opinion as to the acceptability of these colors from the samples, but only from trials that have been made on a small scale by a painter for this purpose and with all the blendings and mixings that will, possibly, have to be employed. Colors that are laid on with the pencil are always better glazed than those that are dusted on. There is no art painting that should not receive at least two firings, and more often three, if we wish to give it the perfec¬ tion of which it is susceptible; sometimes it receives four and even five, but these are exceptions and greatly increase the risks in painting upon hard porcelain. Nevertheless, when these firings have been foreseen and the painting has been prepared as it ought, the hardest colors be- i6s ing put on for the first fire, following this by at once laying on the tints of their right intensity,without seeking to obtain them by superpositions of the same color, a process which only in¬ creases the thickness of the color without giving it much mor<4 depth or intensity: if we have been able to avoid the laying on of one color over another, which often deteriorates and some¬ times even destroys them, we may have a chance of proceed¬ ing to the fourth firing, should this be necessary, without a mishap. In any one firing we must always use colors of the same degree of fusibility and be careful, for instance, not to put in the lights with fusible colors and the shadows with hard colors. A firing that has to follow a first firing so badly ar¬ ranged as this will never set things right There are some brilliant and vigorous colors which can only be obtained by superposition. Thus we can never get a pur¬ ple. either pearly or amaranth, nor a beautiful and deep vio¬ let, with a single color. We must first use the red or brown- red iron colors, such as orange No. 55, blood red No. 58, or red¬ dish brown No. 68, and glaze them in the second fire w'ith the purple or violet colors of gold, but never with gold carmine, which will destroy them. As we have observed before, the painter is exposed to acci¬ dents or imperfections which we have designated as scaling and want of harmony or terne Scaling will never occur if he lays on his colors thinly and evenly, without trying to get too great a thickness all at once The shades of color should be prepared beforehand. Thus if it is a question of a red bowl he should commence by making the light with blood red 58 and yellow 47, the half tint, blood red 58 alone, the half tint of the shadow with 58 and reddish brown 68. and the deep shade with 75, introduced in the mix¬ ture of 58 and 68 to intensify the tint. In this way we have an object that is colored by the tint and not by the thickness of the coat of color, where we have no risk of scaling. We can, if an amaranth bowl is required, pro¬ duce this by reglazing it with purple in the second fire. Precautions in the succession of application of colors of more and more fusibility will also prevent the appearance of terne. As to this unpleasant effect, it is often the result of a bad mixture of colors, which react the one upon the other, or from the superposition of colors having tjtis defect. It is impossible to give a rule for mixing; there will be dif¬ ferences for each painting of figure, of flowers, of landscape. No prescription can regulate the matter with certainty. The painter who works for his art must not be afraid of trying all the mixtures which offer any probability of giving him the tint he seeks. He must make careful notes of these mixtures and their proportions, be quite certain of the degree of firin'g they have received and not spoil it all by overlaying colors for his second fire, which he does not know by experience or has not tested. These general rules will suffice for our object. The com¬ plete enumeration of all that we must know and do to succeed in the production of art painting on an industrial scale would require a special treatise, which would still be insufficient without study, tests and experience. There is a kind of painting in verifiable colors, which bears about the same relation to that we have just treated of as a gonache does to a water color. The colors for painting upon porcelain are transparent. Those of which we are about to speak are almost opaque. They owe their opacity to their property of mixing together with white for mixing. No. 4. also called Chinese white, which forms the base. We can. by introducing this white in the greater number of the muffle colors, give to them that remark¬ able thickness which we see in Chinese paintings and which has recently been very successfully imitated. What is more important is that we can paint on a large scale, in the manner of oil painting, upon porcelain biscuit and upon large flat plates, doing good work with even more ease than upon glazed plates. But these paintings are inferior to those done on glaze, be¬ cause they are far from possessing the fineness of the latter; they always show something of the heaviness of the gonache and of paintings upon earthenware. GILDING, PLATINIZING AND SILVERING. These metals are brought to the state of a very fine powder, as described at page 111 . and ground on the slab with flux No. 7 (p. 47) in the proportion of 1-10 to 1-13 of the metal; but -with .the. addition of a little borax for the platinum and of 1-10 for the silver. 167 The grinding of the gold is more difficult than grinding col¬ ors. for if we do not possess the right touch we pack the fine grains of gold together: these become flattened beneath thd muller. forming small scales, the use of which becomes ex¬ tremely difficult and the polishing almost impossible. If the precipitation has been properly carried out, if the gold Is very fine and the grinding, or any other circumstance, has not compacted the molecules, there will be no difficulty in us¬ ing the gold economically, and it will be easy to burnish it so as to produce a brilliant polish The gold is laid on with either a common or a sable pencil. It will be necessary to know how to use it very well to pro¬ duce. with such an instrument and with a heavy material, such fine lines and such complicated forms of pure design as our skillful gilders are able to give us. To make it flow more freely we add a little lampblack to the gold. This addition is almost indispensable when we gild upon a sharp-fire chrome green, in order to see more distinctly the lines we make Gilding is most usually done on the glaze, sometimes it is put on the colored ground. If it is a sharp-fire color the firing will not differ from that of gold laid on the white, but if it is on tender muffle colors the firing will be much more difficult, for it must be carried far enough to make the gold hold, with¬ out at the same time allowing it to sink into the color, which has been softened by the fire, and without permitting the color to boil. It is therefore a very delicate operation and too often results in a failure. But on the hard muffle colors gold is fired as easily as upon white: it holds securely and burnishes well. When the gilding of a piece is finished it is fired in a muffle. A temperature, higher by at least several degrees, is necessary for firing than is needed for the hardest among the ordinary colors. Therefore, for all good, sound work the gold should be fired before even a sketch of color is laid on. in order to be master of the work and give the colors the heat they require. This is the constant practice at Sevres. If the gold is not fired sufficiently it will not hold at all, if it is slightly underfired it may hold on being taken out of the kiln, but it will very soon wear off in use. If it is fired too much it becomes too hard and rough, it polishes with difficulty and badly. In firing the gold in the way above described we use more fuel, consequently the gilding becomes more expensive. If to the economy resulting from firing at a lower temperature we add the method of reducing the employment of gold by mixing silver with it and laying it on very thinly—this can be done easily by making it more flowing through the use of mercurial gold, or the addition of lampblack—ware is obtained which, on leaving the shop, possesses a great deal of brilliancy, but very little durability. BURNISHING THE METALS. Gold that is laid on with the pencil in the metallic state is matt after firing. If it is intended that the matt condition should be a part of the decorative effect; this is obtained by the process we have given on page 114 in order that it should be very fine; it is then burnished in parts, but if the gold is to be brilliant instead of matt it is burnished all over, rubbing strongly, but skillfully and evenly, in order to produce a sur¬ face that is equally polished everywhere and without any marks or scratches. This operation is very difficult when large sur¬ faces, called gold grounds, have to be polished. For this pur¬ pose we make use of tools that are used in a number of arts, these tools are called burnishers. We give some examples of these: 4. 5 and 6 are agate, the others, 1, 2 and B, are of a hard hematite, known by the workmen as blood stone. The first rubbing is generally done with the agate burnish¬ ers and the finishing is done with the hematite tools. Wheh these burnishers have become, as it were, dirty from use and do no£ polish well, their original smooth and polished surface is restored to them by rubbing (buffing) them with a leather and putty powder (tin oxide). When the piece is perfectly burnished it is cleaned with whiting; this must be soft and well washed, so that it con¬ tains no sand or anything that will make scratches. Some times the gold comes off when burnishing, and it is a troublesome matter to correct this fault. There is indeed noth¬ ing else to be done but remove all the gold, either by rubbing or by dissolving it off. then regild and fire it. If the piece has no painting on it this is easy and efficacious, but if it is a paint¬ ed piece at its last firing we run a risk when burning on the gold. We then have to put in more flux, often causing the col¬ ors to scale off. We therefore are careful to test the adhesion 169 of the gold by burnishing it at several different points before commencing to paint, particularly if the piece is very valu¬ able. Although the burnisher’s art does not appear to be very diffi¬ cult yet the women—for burnishing is nearly always done by women—who do this work show considerable differences in de¬ gree of ability possessed by them. There are very few who can do good work on the gilding of cups. Some of them, who are said to “burn” their gold, are much more liable to the accident of lifting, or scaling off the gold than others are. i ;o At Meissen and at Berlin an endeavor lias been made to shorten this operation, at least for the bands on plates, by put¬ ting the piece in a lathe, in such manner that the piece revolves under the burnisher, which is held by the workman. In the accompanying figure we give an idea of the arrangement. The gold, in burnishing, spreads out, and if this spreading out is not pretty nearly equal throughout, those portions which are strongly compacted will separate from those which are less so. Chuck for holding P/ate While Burnishing Printing in Colors and in Gold. This process, which consisted in transferring prints made in verifiable colors on engraved plates, was tried in England, first at Liverpool and then, about 1751, at Worcester, at the norcelain works established by Dr Wales. It was, shortlj afterwards, introduced in the Staffordshire potteries. In lTGu the process of printing upon enameled eartheware became known at Mariberg, Sweden. In 1775 Berteviu, an employe at the hotel des Invalides, communicated it to M. Parent, at that time director of the royal manufactory a Sevres. It was used in 1777 to print the outlines of antique heads, after the manner of cameos, upon the magnificent service ordered by Prince Buriatinsky for the Empress of Russia. This process remained in abeyance in France, and was ai most ignored there, until about 180 P: it was in 1808 that Potter taught the manufactory the method almost the same as it is practiced to-day, and which we will describe. The nrocess has, since then, been improved in some details. It is now carried to a high degree of excellence, and its use has been immensely extended, first in England, then in France and Germany, though less in the last country than in the other two. It can be readily understood what an immense advantage it was to be able to print with the raoidity of ordinary coppei plate printing the most complicated ornamentation, which could be as perfect as the art of the engraver was capable of making the plate, and that turned out decorations by thou sands. Nevertheless there are difficulties and obstacles present themselves that are not met with in ordinary copper plate print¬ ing, in which the damp paper has only to be applied to the surface of the plate and picks out from the lines of the en¬ graving the ink that has been deposited there, with one stroke of the press the work is done Tn printing on pottery it is necessary that the design engraved on a body that is flat and rigid should be transferred to another body that is rigid, but not flat: this necessitates two important operations instead of one. The first is the ordinary operation of copper plate printing, that is to say, transferring the design engraved upon the copper to the paper* the second is the transfer of this “proof” on the paper to the pottery, whatever its shape may be, that is to say, to an inflexible body with a hard and polished surface, possessing all sorts of sinuosities. This surface has to take away from the paper the impression it received from the copper plate, and H must take it awaj completely and promptly. We will show by what series of ingenious methods that have in practice been rendered more and more simple, we have succeeded in attaining these results. Considerable modifications had to be made in the engraver’s art and in copper plate printing from the engraving of the plate to the impression upon the ware, whether in verifiable colors—consequently in colors that are heavy and hard—or in gold; in the latter case it was necessary to have not simple lines, but fairly broad surfaces, capable of giving by tlieix aspect and burnish all the advantages that result from the brilliancy of the metal. We will see bow this is done. Engraving—The first modification in the application of en¬ graving to printing on ceramic ware commences with the en¬ graving itself. We can, if necessary, use any kind of engraved plate, but when the plates are intended especially for this purpose they should be engraved to varying depths, in order to vary, somewhat, the intensity of the colors; then the lines should be kept so far apart that there i- s no risk of their run¬ ning together during the numerous operations they have to go through. This is particularly the case when we are print¬ ing in gold. The colors used, being oxides, are hard, some of them ai’e vitreous; they wear out the plates very quickly, so that steel plates are preferable to copper ITinting Ink—The copper plate printing ink, charged with verifiable colors, instead of the usual organic or earthy colors, requires a special and very careful preparation to ensure the success of the printing upon which the quality of the ink has a great influence. The first operation is to boil the oil to bring it to the right degree of viscosity. At Sevres we use either linseed oil 0 r nut oil,, the latter Is preferred. It should be good and fresh: it at first possesses a kind of unctuousness, which it loses in the first stage of boiling, but it becomes more tenacious as the operation goes on. The quantity of oil that we wish to prepare is poured into a cast iron pot, but taking care not to put in more than two- thirds of what the pot will hold, it is then placed over a clear, but sharp fire, and the oil soon begins to boil; it becomes hotter and hotter and thickens. When we judge it to be so hot as to be on the point of catching fire, we clarify it and reduce its viscosity by throwing in some slices of ordinary bread. The bread is thrown in while the oil is still over the fire, and the slices must not be put in altogether, but one i/3 after the other. The number and size of the slices are pro portioned to the quantity of oil that is to be prepared; thus two or three slices, measuring 3 in. or 4 in. by about % lu. thick will be enough for a kilo (2.2 lbs.) of oil. The bread becomes browned and fried and the oil is cleared. We judge as to the condition of the oil, both the color and the viscosity, by taking up a spoonful from the pot at frequent intervals. The clear, yellow oil is kept on the fire until it reaches the temperature of self-ignition, and is allowed to burn for a few moments. The pot, with the oil still burning, is taken care¬ fully off the fire and set upon the hob of the furnace. The pot is then covered by putting on the lid. The knob of the pot lid is held all the while, either with pincers or a wet cloth, so as to be able to take the lid on and off, successively, four, five or six times. When the lid is taken off the oil must burst into flame again, and if it does not do this of itself it may be stirred with the iron spoon. Tf it is not hot enough to ignite spontaneously, it must be set over the fire again. This treatment is continued until the oil becomes viscous and of a chestnut color by absorption of the lampblack that Is formed in these repeated smothered ignitions. We judge whether the oil has the required properties by putting some of it on a white plate; according to its lighter or darker color we divide it into weak, medium and strong, according to the colors or metals for which we have to use it. Inking and Pulling the Plate.—To ink the plate we take one of the above mentioned qualities of oil, as much as we judge to be needed, and add to it on fhe slab the required color. The necessary bond between the color and the oil is supplied by the addition of a certain proportion of lamp¬ black; this varies according to the enlor we use: thus for blue we put, to ten parts, by volume, of the color one-tentfl of lampblack; for gold we add one-third- with black, green or red we do not put any. The mixture has the oil added, and is ground, thoroughly, on the slab with a knife or mullet. Bone black, known as ivory black, which is used for copper plate printing on paper, cannot be employed here on account of the phosphate of lime it contains. The strongest oil, which dries more slowly than the others. is used for gold. This allows us to dost all pieces together, and some time after they have been printed. The colors are, as a rule, the samp ns those used for ordin¬ ary hand-painting of the different kinds of ware, except that they have more or less flux added to them, accord.ng to whether they have to be applied to the biscuit or on the glaze and according to the nature of the glaze. The copper plates are inked, either with the finger or a cork; they are seldom large enough to require a wad The superfluous color is cleaned off the plate, either with a large and very flexible steel knife, the front of which is cut to a long bevel, with the edge perfectly straight, or else a wooden spatula, of similar form, is used. Whether it be with the spatula or the knife, the color is taken off the surface of the plate almost at one stroke, and all we have to do is to give a final cleaning with a rag or the hand. In order that the rag, which is usually of muslin, should not go into the engraved lines and take out the ink, we press hglitly. This gentle rubbing does not prevent the cloth inking off the color on the plate, but it does not allow it to pick out the color in the lines. These operations are common to ah fhe different methods of printing, but there are four kinds of printing which differ considerably from each other and reauire different treat¬ ments. These are.—Printings on paper, on gelatine, printings on the biscuit, and on the glaze. We will take first the printing upon paper; then upon the glaze; after this upon the biscuit, and. finally, that which is done by means of gelatine. PRINTING UrON PAPER AND TRANSFERRING TO TIIE GLAZE. Pulling an impression upon paper has nothing special about it, but the choice of tlm paper upon which we pull our proofs is very important. This should be of the kind known as “Joseph,” that is to say, a paper with a fine texture and abso lutely unsized. It must be properly damped. Formerly it was made to undergo various preparations, such as salting, soap¬ ing, etc., but it is now recognized that all these are useless. So soon as the design is upon the paper this is put in water, or rather it is laid upon the water. 175 We then, prepare the ware to receive the impression, by covering it with a species of mordant, which at S&vres they call “mixtion,” to which a twelfth of copal varnish is usually added; this coat is thoroughly dried in the stove. Practice has taught us that this coating is not indispensable, either upon earthenware or porcelain, but it makes the work of transferring easier. A saline mixtion can be substituted for this, as was done at SSvres by Master-Printer Tristan; this is simply a weak solution of alum, which dries very quickly without any need for stoving. We take the paper bearing the proof and drain off the excess water, laying the proof upon blotting paper or on a piece of flannel, or. better still, upon a piece of unglazed porce¬ lain biscuit; it is then.applied to the ware in such manner that the design or engraving is in the right place. The transfer of the engraving is effected by pressing upon the back of the paper with a wad of felt or with a small roller: the paper is easily pulled off. but if it should resist a little it is slightly moistened again. The engraving which it bore becomes entirely trans^ ferred to the glaze of the pottery, after this there is nothing more to do than fire the piece in a muffle. In order to fix the gold on firmly, or to glaze the lines of the print (should this be considered necessary), the firing must be rather sharp. Gold decorations are printed in the samp way, with some modifications in several of the processes We generally use the precipitated gold, which is mixed in the boiled oil that we call mordant, adding, as was said above, a third in volume of lampblack. The gold should have about one-fifteenth of flux added to it. But if we content ourselves with the small quantity of gold which enters into the compound of mordant and lamp¬ black we would have, after passing through the muffle fire, gold lines that would be extremely light and poor. We must, therefore, strengthen the gold by a method which we owe to Legros d’Anisy. We take a small auantity of the gold in powder: this must be very fine and very dry; after the gold design is transferred to the ware, while it is still in a viscous state, a fine pencil is dipped in the gold and passed over the lines of the design. The whole is then brushed off with a dusting brush to remove the excess gold and any that may 176 hang to the parts that are not to be gilt. This gold only con tains 5$ of flux, and must be ground up in nothing else but water; it covers the lines well, and even broad spaces if these are filled up with lines or dots close to eaoh other. This gilci- ing will take a burnish as even and as brilliant as that which is laid on with the pencil, and wears almost as well. This we have proved by submitting some plates on which the two methods of gilding had been applied side by side, to continuous wear for six months in ordinary domestic use. This dusting on of the gold does not increase the cost to any appreciable extent, and it is almost indispensable if we wish to produce a beautiful, solid and durable gold. The same thing is done for colored decorations, in order to give more body, both to the color and the glaze. PRINTING UPON PAPER AND TRANSFERRING TO THE BISCUIT. This method of printing, which is the principal one used in all the potteries where the ware is fired twice,—the first time for biscuiting,—requires entirely different qualities in the paper and its preparation. It must not. be sized, but instead of being soft and. in consequence, woolly and not very ten¬ acious, it should, on the contrary, be verv tenacious; it should possess a tenacity that will make it difficult to tear it. Up to the present time a good quality of this paper appears to be only made in England. The printing ink is very viscid, and it seems that there is pitch in the mordant, as In that given on page 134. The proofs should be pulled as rapidly as possible, in ordei to keep the transferrer supplied, therefore endeavors have been made to shorten the operation as much as possible. Transferring upon the biscuit of fine earthenware and of ten¬ der porcelain is much easier than upon srlazo. The matt sur¬ face of the biscuit does not always need to be prepared. The verifiable color does not have any flux mixed with it, as the glaze with which the piece is covered makes this unneces sary. The paper cannot be pulled off without tearing it and dis¬ turbing the design; the only way to remove it from the ware is to plunge it into water and allow it. tq remain for some time. The operation of printing, which is carried on upon a large scale in the manufactories of fine earthenware and ten 177 der porcelain, has been shortened by the use of a number of little dodges, which become quite important when the work is done so extensively. At Longport a plate is printed in elgln seconds. As the glaze is mixed with water it will not take upon, the lines of the engraving made with a er^asy ink. We are therefore obliged to pass the printed biscuit through a cleai fire, hot enough to burn off the greasy matter before we dip the piece in the glaze. This is an extra firing that it has to undergo, but it is not an expensive one. Tn the potteries where this kind of decoration is done on a large scale they have muffle kilns of between five and six feet high that are used only for burning off the printing ink before dipping the ware in the glaze. PRINTING ON GELATINE. This process is longer than the two preceding, but it lias two advantages over them; firstly, it gives much sharper prints; secondly, it does not wear the copper plates We prepare a clear solution of Flanders glue, or of gelatine made from clippings of glove-leather or parchment. This must be of the consistence of a thick syrup. It is poured, while warm, into earthenware plates or upon a smooth slab or any other material with a smooth surface so as to get a sheet of gelatine about an eighth of an inch thick and of the stiffness of India rubber. The copper plate is now inked—just as though we were go¬ ing to pull a proof—with a boiled, drying, nut oil, mixed with a very little essence of turpentine. This is wiped off with the hand in the way that copper plate printers do. It will be noted that nothing has been put into this oil, and consequently there is no vitreous nor vitrifiable matter in the engraved lines. The plate of gelatine above mentioned is now applied to the copper plate charged with the thick oil, or the plate may be applied by a rolling movement upon the gelatine to which a convex surface has been given by fixing it on a half cylinder of "wood covered with flannel. Or we can pull an ordinary proof upon paper and counter proof this onto the gelatine by pressing it with a roller. Whether by the one or the other process and by the aid of i ;8 a slight pressure, either with the roller or simply with the hand, we transfer the design engraved on the copper plate to the sheet of gelatine. It must not be forgotten that the plate was only charged with oil. e then take the sheet of gelatine that has received the impression and lay it upon the ware upon which the design is to appear, pressing it down firmly and evenly. The design in oil leaves the gelatine and fixes itself completely and very sharply upon the ware. We remove the plate of gelatine, and as the oil with which it was charged is transparent we can scarcely see the transferred design. We then take up some verifiable color on a wad of very finely carded cotton wool. The color is reduced by grinding to the state oi greatest possible tenuity, and it must be per- lectly dry. We dust the color onto the piece, where the de¬ sign is. The color only attaches itself to the oiled portions forming the design, where it is securely held. The superfluous color is easily removed with a dusting brush. The design is now shown complete, accurate and sharply defined in verifi¬ able color to which there is nothing more to do than burn it onto the ware. We can put any kind of verifiable color upon the oil design. The coloi must contain a flux if the design is executed on hard porcelain. We can also apply gold in the same way, instead of colors, with very satisfactory results. ENLARGING AND REDUCING GELATINE PRINTS. A copper plate printer named Gonord, early in the century, discovered a remarkable application of the gel¬ atine printing method by pulling proofs from the same copper plate, which were larger or smaller than the original engraving and yet were perfectly regular. He kept his process a secret for many years and no one was able to guess it. Tt was afterwards published in a record of patented inventions, but the description is so compli¬ cated that only one thing is clear, this is the property that gelatine possesses of swelling regularly in cold water and of contracting regularly in alcohol. Taking advantage of this property we have used the Gonord process at Sevres, but in a much simplier and quicker manner. A solution was made of 1 79 gelatine from parchment clippings, which is the best as it gives a clear solution. When it is of the consistence of a syrup, it is spread in thin coats upon smooth plates of copper; on cooling it becomes reduced to a sheet not thicker than a sheet of stout paper. The engraved plate is inked in the usual way with verifiable colors and a proof is pulled on unsized paper. The paper is placed, in a thoroughly wet state, upon the gelatine and. if we wish to have an impression the saxue size as the engraving, we transfer it at once by pressing it with the roller as before described and then immediately place the sheet of gelatine on the ware, upon the surface that has been coated with mixtion, and the transfer is completed in the usual way by pressing with the hand or a roller, but if we wish to have the proofs larger or smaller than the original we proceed as follows 1 For Enlarging the Proof:—The sheet of gelatine is laid upon water, with the printed side uppermost. A border forms all around which prevents the water touching the printed surface and enables the gelatine to float. It will be seen to spread out in every direction with great regularity In about an hour’s time it will have got to its full size, which will be about a third larger. It is then taken out, by slipping a sheet of trans¬ fer paper under it. taking care not to wet the printed surface; this printed surface is then placed on the ware and the im¬ pression is transferred in the usual w’ay. To remove the gela¬ tine the piece is put into hot water; the gelatine dissolves en¬ tirely and the impression remains sharp and clear on the glaze of the ware. Reducing the Print:—To do this we proceed in exactly the same manner, but lay the gelatine on a bath of alcohol instead of water; taking the same precautions to prevent the surface on which the print is from becoming wet it will be seen that the sheet will draw together with perfect regularity and in less than half an hour it will be about a quarter smaller. We must take care that no alcohol gets on the front of the gelatine for this would spoil the mixtion and prevent the transfer being properly made. The transferring is done in the usual way and the gelatine is dissolved off in hot water. The impressions are quite sharp and they can be strengthened by dusting them i8o with powdered color or with gold, as was described in another case. It Mill be seen that this process is a slow and tedious opera¬ tion and is. consequently, rather a curiosity than a commercial process and it has been but very little used. FIRING THE COLORS. The firing of verifiable colors has degrees of importance and difficulties which differ very much according to the wares upon -which they are applied. Whatever these goods are, the firing should be exactly correct in order that the colors should possess the beauty, durability and brilliancy that we have the right to expect from them, but in general there is very little latitude between the time when the firing is complete and that when it has gone too far. This small latitude makes the oper¬ ation the more delicate in proportion as the limits are more restricted, as they are where the piece to be fired is painted with greater care and a nearer approach to perfection. We have already said, in classifying the colors under three groups according to the degree of temperature at which they are fired, that one of these groups is called hard fire or sharp fire colors, because the color is applied on ware that has to be subjected to a fire intense enough to burn the ware. There remain, then, the colors that are called muffle colors; these are of two kinds, hard and tender; they are both fired in the same description of kiln. It is this muffle kiln that we will now describe. The heat that can be given in this kind of kiln extends from a dull read to the melting point of silver, or from 3° to 6° of Wedgwood’s pyrometer. MUFFLE KILNS FOR VITRIFIABLE COLORS. The kilns that are used for firing colors may be divided into two classes. In the first are those with fixed muffles, which are nearly the only ones used throughout Europe. The second class contains the kilns with traveling muffles. The use of these has been abandoned, but as it is probable that they will, some day. come into favor again, we will tell what we know about those that have existed. Fixed Muffles:—Muffles are species of rectangular boxes made of burned clay, with a round or vaulted top. In those of Sevres and of Paris, the plate at one end serves as a door 4 . 1 8 1 by which the ware is introduced. This is closed by luting it with clay. The box, or the muffle, is the laboratory. The furnace is generally below this. The door or mouth of it is in front, un¬ derneath is the grate and below this is the space for ashes. The entrance to the chimney is generally obstructed by a plate with a number of holes in it, this plate is above the muf¬ fle and a short distance from it. A tube is fixed in the top of the muffle to permit of the escape of any moisture that might be formed in the muffle. Arches over the furnace support the muffle and there is a space between the walls of the kiln and the muffle. The English muffle kilns for tender porcelain are differently arranged, A. is a sectional elevation and B. is a plan of the furnaces. These are shown at F., there are four of these on one side. The coal is thrown upon a grate. Some of the heat passes through the narrow space G. in front of the muffle, the ENGLISH MUFFLE KILN. rest of it goes under and around the muffle by the larger space C., to reunite with the flames that went up the front and escape at the vertical chimney H, These muffles are of fire 182 clay, but are closed by means of cast iron plates, which leave a space as an escape for the gas produced by the volatilization of the essences. In Germany the muffles are placed in a kiln fired at the side. They are unnecessarily complicated in construction, as is proved by the fact that we can do very good firing with the much simpler muffles used by us. Muffles are usually made of clay, that is to say of a good quality of fire clay, that is refractory enough not to melt nor to soften in a strong fire; above all it must not contain lime, pyrites nor bitumen, which might, from various causes, haver an effect upon the colors. (It is very rare that a clay which is darkened by the presence of bitumen or coal does not at the same time contain pyrites). The clay may have its plasticity reduced by the addition of sand, but only in small quantity, it is with ground calcine, well burned and made from the same clay of which the muffle is made, that the plasticity of the clay should be reduced. The calcine is ground to a suit¬ able degree of fineness, according to the size of the muffle to be made. At Sevres we use two compositions, which slightly differ ac¬ cording to the size of the muffle. The ordinary muffles are composed of— Plastic clay from Dreux. 37 The same clay, well burned and coarsely ground. .39 The same, but finely ground.24 This material shows a shrinkage of 9 per cent in the biscuil kiln. The large muffles are composed of— Plastic clay. 35 Finely ground calcine. 05 This material has a shrinkage, after drying, of 10 per cent. The muffles are made by laying the clay, very carefully with the hand, on the inside of molds of either plaster of Paris or of wood. The view hole or tube is made on the wheel and stuck on afterwards. At Sevres we have two kinds of muffles in gen¬ eral use with which we are quite satisfied; the one is used for firing pieces of moderate dimensions, the other kind is for fir¬ ing plaques or round tables in one piece, which are more than one metre in length or diameter. Pieces of this size require a muffle that is very much higher than it is wide. Our illus- 183 * tiations show a front view, a sectional elevation from the front and an elevation section seen from the side of the ordi¬ nary muffle kiln used at Sevres and Taris; m is the muffle, fthe furnace, b the fuel door, c is the air supply and ash box, c' is a removable grate for taking out the ashes, g is the iron grate, p p are grooves in the brickwork enabling the grate to be set higher or lower as desired, a a a a show the arches over the file, that support the muffle, e e is the free space between the muffle and the* kiln walls for the circulation of the flames, 1 is the escape for gas or steam from the muffle, f is the quirk or jamb into which the door or plate for closing the muffle fits and which is afterwards daubed tight, li is a perforated plate forming an arch ever the muffle. The plate which closes the front of the muffle is in three pieces, w w' w", which before being put into place and luted are held together, temporarily, by a rod t, v and v' are view holes. These very large muffles are not only very difficult to make, but they show large and irregular cracks from the first time of filing, it is, therefore, oetter to make them in several pieces, put together with a paste of fine calcine mixed with a little litharge, in this way we avoid the cracks, or if any appear they are short and do not open up much. The cracks which appear in the clay muffles, after they have been in use a certain time, have caused endeavors to be made to find some other material and muffles have been made in cast iron and strong sheet iron. The casting must be of a metal that does not give off any sulphurous, arsenical, or carbonaceous vapor. Black iron is better than white, as the latter is more brittle and more likely to be broken by a blow or by a sudden change of temperature, but these muffles are capable of weakening, of getting out of shape and even of becoming cracked. Muffles of strong sheet iron have also been made; these are covered outside with a lute of clay; they can be used for trial muffles for small pieces, but they very soon get out of shape and drop scales of iron oxide on the ware that is being fired. TUAVELING MUFFLES. I designate these muffles by this name because they are car¬ ried on iron runners or sleds and they are passed through a long furnace with lateral fires, as well as below. The middle portion of the kiln is kept constantly at the temperature nec¬ essary to melt the colors or the glaze. The chambers or por¬ tions of the kiln where the muffle enters and leaves are kept at a much lower temperature, so that the ware is heated grad¬ ually before firing and cools off slowly afterwards, thus pre¬ venting cracks from too sudden changes of temperature. A very remarkable kiln of this description was used at Sevres for a long time for firing the painting and gilding on both hard and tender porcelain, but it w r as much too complicated. It was built at Vincennes in 1751 under the direction of a man named Gerin, a very intelligent workman, who came from Chantilly and, according to Hellot, w r as the possessor of all the receipts and methods of manufacture of tender porcelain. The kiln was removed to Sevres when the manufactory was established there about 1756. The boxes or saggers of clay, 78 centimetres long by 48 wide and 40 high were filled with pieces to be fired; these were kept separate by stilts. At most, 20 plates of tender porcelain were put in a sagger or 60 of hard porcelain. When one of the boxes was filled it was first warmed in a special kiln, then it was put into one end of the firing kiln and passed successively through the four chambers, the heat increasing in each one, until it arrived at the center chamber where the principal fire was; there it was allowed to remain a sufficient time for the contents to be completely burned. The temperature was judged by the color of the fire. In order to judge correctly it MUFFLE KILNS. i»5 was necessary to have a great amount of practice, which re¬ duced the number of firemen capable of undertaking this re¬ sponsibility, to one or two persons. I had a trial piece attached to each box, which could be drawn out, by a tongs through the view hole. When the trial pieces showed that the burning was complete the box was moved on from the center of the fire through the four chambers, each one cooler than the one pre¬ ceding it. The chambers were formed by letting down parti¬ tions through slits in the roof of the kiln. A partition was lifted up to allow a box to pass from one chamber to the next, and in this way each chamber was kept at the temperature needed, the chambers gradually increasing up to the central fire and the degree of heat becoming lower towards the exit, for the purpose of annealing the goods. The principle acted upon was to keep each portion of the kiln at a certain tem¬ perature, without having to lower this for the purpose of drawing the finished ware and reheat it for the new pieces; on the contrary the same heat could be kept up nigbt and day so long as there was porcelain to be fired. After having con¬ ceived such an ingenious idea and put it into execution ut enormous cost they did not appear to know how to profit by it, for the firing was stopped every night and on Sundays. 1 kept it running without interruption, by using relays of work¬ men in eight-hour shifts and providing an assistant for the chief burner; nevertheless I found that there were serious dis¬ advantages connected with the use of this kiln, which com¬ pelled me to abandon it. In the first place, in order to get the full benefit from it, it was necessary to keep up the firing continuously for, at least, 15 days. This required either an immense output, or else the burning had to be done at such great intervals between each, in order to accumulate sufficient ware to be burned, that the general management of the works was seriously incon¬ venienced. Although I gave this method of burning a thorough test, by firing continuously for 15 days, during which time 218 boxes, containing 4,840 pieces of all kinds, principally plates, were passed through the kiln, and this in the month of -No¬ vember, consequently under the most favorable circum¬ stances, I found by a simple, but exact, calculation of all the expenses, that the cost of firing a plate with a gold band was / 186 25 centimes for hard porcelain, which is more than the cost in the ordinary muffle, while for tender porcelain, in consequence of the distance that had to be kept between the pieces, the cost was 60 centimes. Le Gros d’Anisys took up this principle of traveling muffles and built at Paris, in 1809, a kiln with four chambers in a row, this was not so heavily constructed as the one at Sevres. The heat in the two central chambers was high enough to burn the ware, the chamber at one end was hot enough to prepare the goods for the sharp fire, while that at the other end served as an annealing oven. A train of five boxes, drawn by chains and pulleys contained a large quantity of fine earthen¬ ware. The plates were put in iron cages, supported by pro¬ jections, which barely touched them. In one of these boxes a great many more pieces were fired than by the old system. These works for the decoration of fine earthenware did not run for very long and the kiln, which I saw working with per¬ fect success, was pulled down. Since that time I do not know of any further attempts being made at using a similar system. Setting in fixed muffles and, probably, also in the travel¬ ing muffles, requires to be considered from two points of view; in the first place we want to put as many pieces in the muffle as possible, having due regard to the shape of the pieces, their fineness and the quantity of color on them. Those pieces which are merely decorated with gold can be set quite closely together, but those that are charged with color must be further apart so that the essences (oils) can evaporate and also that the vapors given off by them shall not affect the colors. It is necessary to know how the heat distributes itself in the muffles in order that the setter may put his ware in the place where it will get the right heat for firing. We have to be careful when setting not to form a transverse enclosure, floor or diaphragm, which will divide the heat. The ware should be set, so far as possible, in such man¬ ner that any dust entering the muffle either before or while the colors are in a state of fusion, should not strike them. The general inclination is to set flat pieces, such as plates, saucers and dishes, horizontally, with the painted side down¬ wards, but we have been assured that in this way the colors receive the direct current of the ascending vapors, which form i»7 in the muffle and some into contact with the painted portions, alter the colors and prevent glazing, though we have not, our¬ selves, been able to establish anything on this point. We must also avoid using plates of terra cotta or even of biscuit porcelain for supports to the ware. They sometimes have an injurious effect upon the glaze of the colors by ab¬ sorbing the flux. I have seen a fragment of a new brick, that had been thoroughly put in a muffle, destroy the colors and produce very serious damage. It is for this reason that, in many cases, the interior of a muffle has a coat of red oxide of lead (minium) given to it, which prevents this absorbtion. I have seen this method suc¬ ceed with the very large muffles, but we have seldom had to use these coatings, they are sometimes made with borax. It is very rare that a new muffle will burn hard porcelain colors with purity from the first. We always have to get it into good condition by firing gold in it two or three times. Sometimes it cannot be perfectly hardened at all, we then have to have recourse to the coating of minium, as in the case of the big muffle above referred to. We can always fire colors with greater purity in an old muffle than in one that has only been used a few times, but the old muffle is invariably cracked all over, though these frac¬ tures are easily mended with clay and by tying the parts to¬ gether with iron wire, or better still with platinum wire, which does not burn out and does not expand to any appreciable ex¬ tent. The muffle should be preserved, so long as we can pre¬ vent the smoke entering it by way of the cracks. Before or during the setting, the ware should be dried and heated in a drier near the kiln and this must be brought to, and maintained at, a rather high temperature while the set¬ ting is going on. Without this precaution the damp which is given off by a cold muffle, or the fuel that is put under the muffle to fire the ware, will condense upon the pieces, if cold, and cover them with moisture, which will be very injurious in various ways. It is even necessary to bring the muffle and the ware that is set in it to a temperature above 100 degrees C.. that is to say a temperature above that of boiling water; this is a very important precaution. The dooy of the muffle must be very carefully luted at its base as well as all cracks and fissures, in order that not the least smoke or vapor may get in while firing. The upper part does not need so much care as in consequence of the draft pro¬ duced by the heat all the vapors enter at the bottom and leave at the top of the muffle. It has been noticed that colors will be all the purer for be¬ ing fired in a current of air, if this current of air is pure; that is to say they will be bi’ighter and more glazed than when fired in a perfectly enclosed space; for this reason enam¬ els are fired in an open muffle and if it were not for the well- founded fear of breakage when firing colors on porcelain, this method, which has been used sometimes for small pieces, would give very pure burns. FUEL AND THE MANAGEMENT OF THE FIRE. As we are only concerning ourselves here with firing the best sort of work we restrict the fue’o to three kinds, char¬ coal, wood and coal. charcoal.— The use of charcoal has been almost entirely abandoned, although it seems to give the colors more purity and glaze, but since it has been found that, with well con¬ structed kilns, with good draft and thoroughly dry wood, which is reduced by splitting two sticks of a few centimetres in thickness, we obtain a sharp and clear fire, by means of which the most delicate and valuable works of art can be burned as well as we can wish, we have rid ourselves of the inconveniences of charcoal. The use of charcoal has the dis¬ advantage that charging the kiln is very fatiguing to the kiln man, it produces a penetrating dust, it fires up in a way that ca'nnot be calculated and, in large muffles, the inequality of the heat is very difficult to control; finally it makes fractures more frequent and more to be feared. Nevertheless we may use this fuel for firing small pieces, which we wish to, and can without danger, subject to a sharp and quick fire. When us¬ ing this fuel the fire box or furnace must be spacious and the muffle should be surrounded on all parts by the charcoal, which must be equally light throughout. I do not think very much of this method of firing, although it was practiced at Sevres for many years and by means of it pieces were fired that were of the highest importance, both for the size and as 189 Works of art. I will content myself with quoting here the practice of firing with charcoal as employed at the imperial manufactory, of Vienna, where it is done with remarkable simplicity and despatch. The muffle, about three decimetres (12 in.) in height is extremely simple, it is placed on a sup¬ port in the furnace and completely surrounded with the quanti¬ ty of charcoal required for the burn. The charcoal (pine wood coal) is in very large pieces, it is held up by two pieces of terra cotta, forming a species of hollow walls that are removable. The door of the muffle is simply set in its place and is not luted. There is a view hole in the middle of the door, this is the only one and an opening for evaporation in the top of the muffle, but there are no other openings. The illustration shows one which I saw at Vienna and which was operated in my presence, taking only an hour and a half for the burn. M is the muffle with its door, at the upper part of this is an opening for the escape of vapors produced by the essences; V is the view hole; B B are bricks upon which the muffie stands; W W are side walls of hollow terra cotta which keep the charcoal in place around the muffle. The charcoal is lighted at top by some pieces of wood and in an hour to an hour and a half, according to the size of the ware, the paintings are fired. The burner watches the color of the heat, seen through the view hole of the muffle door and, as soon as it is concluded that this is enough, the hollow terra cotta walls are thrown down, the burning charcoal is pulled away and the muffle is allowed to cool. This rapidity in firing and in cooling off proves that the ware must possess in a very high degree the property of re¬ sisting rapid changes of temperature. Wood.—T o fire wih wood the wood should burn with a long and vivid flame. White wood, such as poplar, birch and deal (fir) is preferable to hard wood. It should be very dry and split into small pieces, more or less fine, according to the size of the furnace of the muffle and the season of the year. The firing of large muffles is commenced particularly when they contain voluminous and fragile pieces of ware, with the larger size pieces of wood, the fire is quickened with the fine wood and is finished with the medium sized; this course is pursued in order to be able to judge the fire and to avoid the remount or cumulative effect of the fire. When we use a fuel that produces a great quantity of heat in a short time, as charcoal does, and when we have to urge the fire in order to bring the colors to a flowing state to make them brilliant, we get a remount, as we call it, that is to say when the firing is done and we draw all the fuel from the fur¬ nace, whether incandescent wood, or charcoal, and the furnace is quite cleaned out, there is nothing at all to produce heat and yet the temperature of the muffle continues to increase and in¬ creases very perceptibly; as much as 15 degrees of the silver pyrometer in a quarter of an hour. This is what we call the remount. It is all the stronger in proportion as the fire has been urged rapidly. This phenomenon may be explained in a manner that, it appears to me, is in agreement with all the facts observed. The heat can only enter the muffle, to reach the ware con¬ tained in it, by traversing its walls. If we imagine the thick- !QI ness of these walls to be divided into two layers, it must be ad¬ mitted that the exterior layer, the one that is in immediate contact with the heat of the furnace, possesses a. considerably higher temperature than the interior layer has, and that when the pyrometer shows 260 degrees inside the muffle, if it were possible to put it on the outside it would indicate, perhaps, 290 degrees. Now at the moment when we remove the fuel, that is to say we take away all heat producing material, the outer part of the muffle possesses the elevated tempera¬ ture we have supposed. The accumulated heat distributes it¬ self by radiating in every direction to those points where the temperature is lower. Thus the 30 degrees of excess that we have supposed, will be divided between the outer space of the furnace and the interior portion of the muffle. Fifteen degrees will be lost on the outside and the other 15 degrees will be add¬ ed to the 260 degrees of the interior of the muffle, allowing the necessary time for the heat to travel. It takes about a quarter of an hour for the 15 degrees to raise the pyrometer to 275 degrees, although the fire in the furnace has been extinguished during that time. These figures are only given as examples, but they are very nearly correct. This remount varies from a number of causes, the most potent of which is the rapidity with which the last moments of firing has been done. Thus I have constantly observed that if the silver pyrometer rose by 2 degrees per minute the remount would be strong and would attain the 15 degrees be¬ fore mentioned. If towards the end of the burn the fire is allowed to slacken the remount is very much reduced or is scarcely noticed. Coal. —Attempts have been made to burn colors on hard porcelain by means of coal, but when using this fuel it is very difficult to distribute the heat equally in every part of a large muffle and above all, to prevent a little of the smoke getting into the muffle. As the smoke from coal Avill spoil nearly all the colors and as, in this case the loss is much greater than the saving from the difference in price of the two fuels, the certainty of the wood fire has been preferred to the doubtful chances of the coal. In any case it is important that the firing should be con¬ ducted with regularity, slowly at first and very rapidly to- 192 wards the end. That which is called a languishing fire may fix the colors, but it will not gloss them; they are dull, sometimes even matt. Fourmy has given a good explanation of this and has proved his explanation by the observation of some appro¬ priate facts. When a glass is kept in a state of fusion and at the same degree of temperature for a certain time, its ele¬ ments combine in a different manner, it devitrifies, it crystal¬ lizes and becomes opaque. Reaumur’s porcelain is only a glass which has been held for a long time at one temperature and has become devitrified. It is necessary, in order to bring it back to the state of a transparent glass, to subject it to a much higher temperature than that which it has experienced. This fact explains why, in consequence of a languishing fire, it is impossible to give a gloss to painting on porcelain that has come out matt or dull from the muffle, at least without firing it again and giving it a very much greater heat than at first, but when we do this we alter the colors and if the paint¬ ing is a work of art the piece becomes imperfect. Judging the Fire.— There are three means of judging the fire, that is to say of presuming to what degree of tempera¬ ture it has been carried, but none of these is absolutely reli¬ able. In the first, which is not the most uncertain, but which de¬ pends entirely upon the individual, the conclusion is drawn from the color of the fire. A skillful burner, who has a great amount of practice, will rarely make a mistake, but this power of judging is altogether a personal quality, which cannot be transferred to anyone else. The second, which is the most used, because it is available for a larger number of people who can easily acquire the habit of using it, is that of test or trial pieces. These are pieces of ware which are touched with a color that will change its tint in a definite manner according to the degree of temperature to which it is exposed. These little morsels of pottery used as trial pieces are burned in the muffle along with the painted goods. At Sevres and in the majority of the ateliers for firing paint¬ ed porcelain, the color that is used for this purpose is carmine, which is made from the purple of C'assius as described on page 38. 193 This color is painted on a small piece of porcelain and intro¬ duced in the middle of the muffle by means of an iron wire; under the influence of the different degrees of heat it takes the following tints: 1. In the fire that is known as “gold on tender ground” it becomes a reddish brown, dirty, brick-red, color with scarcely any gloss. 2. In the fire called “retouching” it is of a fine rose tint, where the color is thin and rather brick-like in the thick places. 3. In the fire called “first painting” it becomes a rose color inclined to purple. 4. In the fire called “gold on white” it is a rose, with a slight inclination to violet. 5. In the fire for “fillets of gold” or for the substantial gild¬ ing for the borders of plates, it takes a violet tint, which be¬ comes more and more pale and deteriorates in proportion to the increase of temperature to which it is exposed. 6. In the “matt gold” fire, the rose tint and even the violet tint, have almost completely disappeared. These are the principal tints, but they are linked together by a number of intermediate shades. A multitude of causes, apparently very slight, have an in¬ fluence independent of the temperature, upon the variations of tint which this delicate color is capable of taking. In the first place, the manner in which it is ground, more or less finely, in the water or oil used as a medium and the quantity, more or less, of fat oil. Then the way in which it is used. Touches of the same carmine, but laid on in different ways by different painters, although burned together and, consequently at the same temperature, will show different tints. It is affected by: The thickness of the touch; in the same touch of color the thicker part has a rather bricky tint, entirely different to the thin part. The impurity of the fire, that is to say a disengagement of vapor or of smoke produced by a smothered fire, will cause this color to pass from rose to a dirty violet, from glossy to dull, with a dull gray aureole. 194 The duration of the fire, without increase of temperature, produces notable alterations in the color. To make this method as exact and as generally useful as possible I took the following steps, which it may be worth while to describe. The first carmine, to be used for trial pieces or pyroscopes, was made by the chemist of the works in 1818. A consider¬ able quantity of it (420 grams) was made at once. After hav¬ ing tried it a sufficient number of times to be sure that it was suitable, that is to say, that it was easy to use and was ex¬ tremely sensitive to changes of temperature, it was accepted, but as this color is altered by the action of damp air, the mass was divided in a number of bottles that were hermetically' sealed. The contents of these bottles, as they were brought into use ,were again subdivided in small, well corked bot¬ tles, each of which contained only 10 grams of carmine. On¬ ly one bottle was in use at a time for making the trial pieces that were in daily use for firing the colors. The tests were, so far as possible, touched with the carmine by one man, who knew how to use the color; they were marked, first with the date of the delivery of the carmine, then with the date on which they were used and the number of the muffle. This date, the number, the description of the principal pieces contained in the muffle and the results of the firing, were en¬ tered in a record book, read in the presence of the persons responsible for the firing and signed by the superintendent. In this way, if it is desired to know in what fire a certain piece was burned, on any day during the years that have elapsed since 1818, it can be found immediately, along with the remark that was made respecting the work at the time. To carry on, through a long series of years, this method of judging the burns, when the carmine for the tests was nearly used up another quantity was prepared and used for several months along with the first lot. The new carmine was not ac¬ cepted until it was found that two touches, one of the old the other of the new carmine, laid on the same trial piece by the same artist and burned were identically similar in all the heats. The third method would be much more exact if it could be brought to perfection. This is the pyrometer. I have de- 195 scribed in another place the conditions that have to he fulfilled for measuring high temperatures, the difficulties in securing these and the attempts to overcome them. These difficulties are not so great for firing, painting or gilding. The expansion of fine silver, which does not melt at the highest temperature used for firing muffle colors, can be easily employed and gives results that are absolute and constant. It is a m,etal that can be obtained in a state of perfect purity and with always the same structure; it remains unchanged in an incandescent heat; finally, among the metals endowed with these qualities it is the most dilatable, that is it possesses the greatest ratio of expan¬ sion. No other metal could be found to reunite more complete¬ ly the necessary conditions, the sole disadvantage restricting its use is that its melting point prevents its employment for higher temperatures. It -was therefore this metal that I select¬ ed in 1805 for the construction of the pyrometer at Sevres, used for indicating the progress of the firing and the temperatures corresponding to the degrees of burning of the colors indicated by the changes of color of the gold carmine. The instrument consists of a bar of fine silver, two decimetres (8 in.) long, which is placed in the interior of the muffle among the ware to be burned, it is put in through the view hole V, shown in our illustration of the muffle kiln. The expansion of the bar should indicate the degree of heat in the muffle. In order that we can measure this expansion outside the muffle the bar of silver is fitted into a groove in a piece of unglazed hard porce¬ lain. One end of the bar butts against a stop in the groove so that the whole of the expansion shows itself at the other end, here it presses against a rod of hard porcelain biscuit, of the same kind as the piece in which the bar is fitted and by means of this rod an index is moved. The whole arrangement is con¬ trived so as to multiply by 100 the movement of expansion of the bar of silver. The free end of the index travels over an arc of a circle that is divided into 300 parts; from 27 to 30 of these degrees are equivalent to 100 degrees of the centigrade thermometer. In firing colors upon porcelain we have a latitude from 200 degrees to 280 degrees. Between about 300 degrees and 325 degrees of the pyrometer the silver melts, it is for this reason that I said that the maximum heat for firing vitrifiable colors 196 in a. muffle or reverberatory kiln was not very far removed from the melting point of silver. It will be seen that this instrument is very imperfect, be¬ cause it does not give absolute measures of temperature, but only shows the difference between the expansion of a bar of silver 20 centimetres in length and that of a bar of hard porce¬ lain biscuit of equal length. Now we do not know what the ex¬ pansion of the porcelain is, all that we know is that it is very small. We therefore have nothing but the difference between two numbers, only one of which is certain. Firing fixes the verifiable colors and, in melting them, gives them transparency and brilliancy. When they are applied upon a glaze which does not affect them no other change takes place, but this passing from the opacity of the unfired colors to the transparent, or at least, translucid, condition of the burned in colors, reduces their intensity and, sometimes, slight¬ ly changes their tint. This may destroy the harmony of a painting and diminish its vigor, w v e therefore have to strengthen the colors by applying a new coat, refire it and, sometimes, again retouch it and fire it a third time. The heat required at each firing will be less, this diminution results from this, that at each retouching we put on a thinner coat of color and that which is below facilitates the fusion of what is on top, but a frequent repetition of the same temperature may change those colors that have been subject to it. Never¬ theless we have seen several cases where valuable paintings have passed through the fire five times that were not satisfactory in the first firings, but at the fifth firing acquired all the qualities wished for. INFLUENCE OF THE MATERIAL UI>ON WHICH THE COLOR IS LAID. The nature of the surface upon which the color is applied exercises a marked influence upon the tint that the color pre¬ serves after firing. The chemical action of the glaze gives rise to some remarkable results and the relative physical properties of the material upon which the color is laid and the color it¬ self often cause defects that it is necessary for us to be in a position to explain in order to be able to remedy them. Even the paste of which the body is formed may have some influence upon the colors as we found in the case of a kaolin from Ebreuil. It was noticed that no color prepared from gold l 97 and, above all carmine, preserved its brightness and tint, when laid upon porcelain that had this kaolin for a base. CHEMICAL INFLUENCE OF THE MATERIAL. As lias already been shown when treating of the glazes, these consist of silicic acid, boracic acid, soda or potash, oxide of lead, and, sometimes, oxide of tin. Oxide of lead, which is indispensable for certain colors, is injurious to others. For instance, we may cite the colors made from gold, to which it gives a dirty appearance, making them dull and with an inclination to violet, when the flux for these colors already contains the lead needed for fusion. A similar remark applies, also, to an excess of alkali. When potash and soda are sometimes necessary for the production of fine colors they become the source of more than one defect if, dominating in the glaze of the ware, they react upon the coloring oxides, particularly if the glaze is fusible and we have to fire the color at a high temperature. Chrome oxide, from its tendency under the influence of pot¬ ash or of soda, to pass to the state of yellow chrome, offers a striking instance of the trouble that may be caused by a surface that is too alkaline when chrome greens are laid on it. On these glazes and bodies the greens made from chrom¬ ium are decomposed, they become yellow and the yellow tint even spreads beyond the place where the original green was laid on. Those enamels which owe their fusibility to boracic acid do not exhibit this defect. Finally, oxide of tin, which enters into the composition of earthenware glazes, gives to these glazes an opacity, which, if the glazes are fusible, will affect the verifiable colors and alter their properties; they will become opaque and will not mix properly in consequence of the oxide of tin which they contain. These short remarks, which it will be easy to amplify by means of those made in treating of each color by itself, will show the importance of possessing a chemical knowledge of the glazes that we intend to decorate, although, as we have seen, this becomes of less importance if the heat at which we have to fire the colors does not have to be so high as to soften the glaze. 198 PHYSICAL INFLUENCE OF THE BODY OK GROUND, DIFFERENCE IN EXPANSION—“CRAZING”—“MOLTING.” The expansion of the glaze upon which the color is applied and that of the glaze itself, are, in certain respects, intimately related. It is necessary that the two materials should expand in about the same ratio, in order that, in cooling, their con¬ traction will be alike. This is a knowledge which it is im¬ possible to acquire by reasoning out from theory, we can only get at it by trying. A difference in the expansion ratio of the ground and of the color produces defects that it is almost impossible to remedy, therefore it is most important that we should be on our guard to prevent this, the result of which will often appear at the third time of firing the color. We even have examples of paintings which have “molted” a long time after leaving the muffle. “Crazing” and “molting” are defects that are frequently in¬ dependent of the firing, when this has been brought to the proper point; these faults are more often due to a bad compo¬ sition, to bad preparation of the color. On examining a chip from a piece that has “molted” we can easily see that the piece that flew off carried with it a notable portion of the sur¬ face of the ware upon which it had been attached. The colors that are applied upon very fusible glazes, partic¬ ularly upon tender porcelain, never exhibit this defect, what- even their ratios of expansion may be. The melting of the glaze causes the flux of the color to melt, thus establishing an equilibrium between the glaze and the verifiable color, be¬ coming in this way almost identical they expand uniformly and forming, practically, but one substance, the whole con¬ tracts equally together. INFLUENCE OF SURROUNDING VAPORS DURING BURNING. The vitrifiable colors are exposed during firing to other in¬ fluences besides that of the glaze upon which they are laid. Even if they are protected from the action of smoke and ashes from the fire they will be still subject to the influence of the vapor of water, of carbonic oxide, of alkaline and plumbi- ferous vapors. It is as ivell to understand the part these ploy and the energy of their action. The muffle in which we set 199 the most delicate ware will, sometimes, be accidentally affect¬ ed by vapors whose presence leaves traces upon the ware, which are very often ineffaceable. The Vapok of Watek.— Waterin the condition of vapor only, will not do any harm to vitrifiable colors, provided the tem¬ perature is suitably and regularly raised, so as to prevent con¬ densation. Experiments several times repeated, upon painted pieces that were plunged into water before firing, confirms this opinion. Humidity cannot have any other action upon a painting in the muffle, but a mechanical one; it acts by condensing on the colors and the drops of water running over the surface displace them. We have gone fully into the details of how to prevent this when setting the ware. We have said that the vapor of water alone will not have any effect upon the colors, but this is not at all the case when the vapor of water is mixed with carbonic oxide, it augments the decomposing energy of this agent, as has been proved by Malguti’s experiments. Theory only attributes to carbonic oxide a reducing action upon the lead oxide contained in the flux; Malguti’s experi¬ ments have taught us that a flux will not lose in weight if kept at a white heat for four hours in a current of dry air, nor even in a current of moist air; neither does it lose any of its weight when brought to a state of incandescence in an atmos¬ phere formed of equal parts of air, hydrogen and carbonic oxide, provided the mixture is dry; the reduction commenced so soon as the mixture became moist. Upon analysis it was found that the loss was solely in the oxide of lead contained in the flux. Is the reduction of the oxide of lead and the volatilization of the metal after it is reduced the sole cause of the dull appear¬ ance which vitrifiable colors often exhibit? Is it only the presence of moist carbonic oxide, in the smoke, that com¬ municates its destructive properties? We do not think so. SMOKY AND ACID VAPORS. No smoke will prevent the colors being bright, nor will soot itself, mixed with the flux, do this, provided it is burned off before reaching a red heat; very often we mix the blacks, 200 which do not have their full tint when laid on, a fairly strong proportion of lamp black, without preventing the vitrifiable black taking a good gloss. Carbon vapors may enter a muffle without any risk of spoiling the burn, but wood smoke has entirely different chemical characteristics, because it is strong¬ ly charged with empyreumatic oils and pyroligneous acid, which act in an entirely different manner, these are what poison the muffle and they poison, perhaps, less by means of the carbonic oxide than by the small quantity of acid princi¬ ples that they contain. This explanation appears to us to be supported by the action of sulphurous acid upon the colors in the muffle. It is gener¬ ally known that it is impossible to fire colors properly in a muffle in which copper (sulphate of iron )has been calcined and that it is of the greatest importance to thoroughly wash the reds, made from sulphate of iron, in boiling water; an imper¬ fect washing prevents them taking a gloss and the small quantity of acid that they contain will react upon the other colors. It now remains for us only to consider the influence of the plumbiferous and acid vapors. FLUXING VAPOBS. We have spoken of the volatilization of oxide of lead and pointed out the conditions, which, fortunately, are very rare, when this volatilization takes place. We should add to this that if we put a piece of ware covered with a lead glaze near a piece which is not glazed the glazed piece will lose its gloss while the biscuit will show the com¬ mencement of glazing. This fact explains the practice which manufacturers pursue, of coating the inside of the muffles with litharge, in which they burn their lead glazed ware. This should impress upon us the importance of the precau¬ tions to be taken in setting art paintings in the kiln. The lead vapors, sucked in, so to say, enter into combination with the silica contained in the substance upon which they condense and if this is colored with colors prepared from gold the gold colors will be at once changed by a flux containing too much lead, they will certainly be spoiled and become a dirty violet. Fine stoneware is covered with a thin, but sufficiently thick, t 201 glaze by simply burning it along with pieces charged with lead oxide. ACCIDENTS AND LOSSES. After having described in this work all means and processes employed for decorating ceramic ware in a substantial man¬ ner and suitable to its mineral nature, before concluding, we should examine the alterations and injurious changes that sometimes accompany these methods and the way to avoid them, or at least, to correct them. We will examine in succession the defects and losses that come from the fire, those that may be attributed to the ma¬ terials used for decorating and finally the alterations that may be produced in these materials, which may be caused by vari¬ ous agencies after they are fixed on the ware by the fire. CHANGES RESULTING FROM THE ACTION OF THE FIRE. The first is that which the colors suffer from through an excess of heat. They lose their vigor, they run together, they react the one upon the other, the most refractory colors, such as the blue, the green, the blacks, resist and become dominant; the others, such as the pinks, the grays, change color or dis¬ appear; the reds pass over to dark brown and the browns to black. When this excess of heat is extreme there is no remedy, but if complete decomposition has not taken place we may at¬ tempt to remove those colors that are too much changed, in order to replace them by new colors and then refire the piece. It is very seldom that this succeeds if the piece has been much over fired, where all the colors are more or less changed and it becomes necessary to give it a second, or -worse still, a third firing. If the painting has been under fired the colors will be matt, the gold will not hold on. It would naturally suggest itself to us that firing it again at a higher temperature would be an easy and efficacious remedy, but this is not always the case, at least for those colors that have become harder, for the increased temperature that we are compelled to give them alters the delicate colors without giving a fine gloss to the hard colors. We can only approach success by giving these that are matt through insufficient fire, a thin glaze of their own color. The best way to correct this fault depends upon the cir- 202 cumstances and must be left to the judgment of the practiced workman. It is a matter that concerns the person who pre¬ pares the colors and the one in charge of the firing and the painter or decorator cannot be blamed for a loss of this kind. ALTERATIONS RESULTING FROM TIIE COLORS OR FROM THEIR USE. We will suppose that the colors are good and have only been accepted, as is the practice at Sevres, after being careful¬ ly tested and submitted to the examination of the various classes of painters who will have to use them; after this their qualities are discussed in a reunion of the painters, in the presence of the director of the works and the chemist who prepares the colors, if then they are admitted to be capable of giving good results, when properly used, either alone or mixed in suitable proportions with the colors with which they may be associated, they are accepted. If, when they are used, they give poor results, this can only be caused by the fire, which is easily recognized, or else it is due to the ignor¬ ance of the painter, or from want of sufficient care in the use of the colors, that is to say in grinding or mixing them, the thickness with which they are laid on, the choice of the medium, etc. Thus, putting on one side the changes that may occur through bad qualities in the colors as we will suppose that only good ones are accepted, we have no other faults to fear than the following: Molting, which may be caused by too high a temperature, by laying on too great a thickness of color, or by an incorrect mixing. We have explained what was meant by the technical expression “molting” and what might be the cause in rela¬ tion to the color itself. Here we can only consider it as due to one of the two causes we have just mentioned and in such case, particularly from the second cause, when it is the fault of the painter, this only shows itself in certain directions and may be met by attending to the instructions we are about to give. But if the defect is the result of over firing, or of an improper use of the colors over the whole piece, the attempt¬ ed remedy is not only useless, but aggravates the evil, for the heat necessary to burn the new parts will change the neighboring portions and even make them molt. 203 Molting is a very serious fault and one that robs a verifiable painting of, wbat I venture to call its greatest merit, that of defying the action of time, for it matters little, in an art pro¬ duction, even of simple ornament, that only a part of it is spoiled; it must be complete and perfect or else it would have done just as well and would have been less expensive, to have made the entire picture with the permanent color which had to be used to repair the moltings. The pieces, decorated with ornament, that molt and are not intended for domestic or other rough use, may be repaired with non vitrifiable colors, rendered fairly durable and resist¬ ant to cold water by mixing with copal varnish. The piece will have its full effect and preserve it for a long while, though it will have lost its value as a perfect piece, but this method of repairing molting cannot be tolerated on ware that is to be used for table service, for after a very little use the mended portions will disappear through the effect of rubbing, washing in hot water, etc. There are two methods of making repairs which we will describe. The oldest method is the local and circumscribed removal of the part that has to be relaid. Formerly a piece of hard burned stone ware, called green stone or water stone, was used, with this the defective color was removed by grinding it off, but the operation was long and it was difficult to re¬ main within the limits of the color to be removed, besides this the rough and uneven surface produced, communicates this roughness to the color that is laid on the ground-off spot. The practice now is to use hydrofluoric acid, particularly at Sevres, where this method was employed for the first time by Willermet. We know with what care this very corrosive acid must be handled; we take a brush, dipped in the acid more or less diluted, and pass the brush over the color, this dissolves, and it is removed in much the same way that a lead pencil mark is effaced by rubbing it with a piece of caout¬ chouc. The ware must be immediately washed in a full flow of water, several times repeated, it must then be perfectly dried, for we must make quite sure that no trace of the hydro¬ fluoric acid remains, which would be capable of spoiling all the colors in the muffle. 204 The place where the glaze has been cleaned off by this sim¬ ple operation remains smooth; it hardly loses its gloss and the retouch is made and attaches itself perfectly. The dullness which some colors exhibit, side by side with good, bright, glossed colors, presents a very disagreeable want of harmony. When this is only partial it can come from no other cause than an improper mixture of a color that is too hard, with the principal color, for the purpose of modifying its tint. This defect may be corrected by refiring, first laying on a thin coat of the color containing a more fusible flux; several refirings may be necessary. If success cannot be attained this way the only other resource is to attempt to remove the dis¬ agreeable matt surface by polishing it by friction. A want of gloss that comes from a defect in the color which did not show itself when it was tested before acceptance, or which the examiner overlooked, is more likely to be found in azure blue. After glazing in the first fire it devitrifies in the second and becomes dull and even coarse grained. This is a defect which, as will be seen, does not come under any of our categories and can only be avoided by putting a glaze of the same blue, for the second fire, upon that which has al¬ ready been burned. Want of harmony results from an improper use of the colors and above all from the mixing; when one color has had a greater effect upon another than the artist anticipated, it de¬ stroys, more or less completely, the tint of the one upon which it has been placed. I can cite a striking example of this al¬ teration in a very valuable piece of ware, where a gray flux, laid on some portraits of dark complexioned men, to give a gray shade to the chins, bleached all the places where it was put on. If the piece has not been over fired and the accident happens in the first firing, retouching will correct it completely, but at a final firing it is better to leave the fault which, often, can then only be detected by a skillful and careful observer. A fault which is as serious and is somewhat analagous to molting, is that known as the creeping of a color, it appears to be similar, for muffle colors, to that which the blue shows in the sharp fire. The color gathers together in little streaks, leaving white places that look like moltings, but it can be distinctly seen that the color has drawn away and gathered together in places which have become thickened and melted in¬ to small lumps, they have not lifted oft' as in molting. This fault is due to the artist having used essence that has become too fat from the action of the air. When distilled essence is used this never happens. The defect shows itself more frequently in summer than in winter. As a rule it happens only in the first firing so that it is easily corrected. The portions of color that have crept together are removed and the surface is re¬ painted. Another defect, of which we neither know the cause nor the cure, is where a painting in the first fire becomes covered with a multitude of minute black specks, this seldom happens in the second firing, it has been attributed to a reduction of the oxide of lead of the flux. We have noticed that It is not distributed equally over the whole surface of the piece upon which the plumbiferous colors had been applied, and that sky blues and carnation grays were more subject to it than the other colors, also that the spots were often more abundant on the prominent portions of a glaze that was not evenly laid and some times these minute spots were only in those parts. This fault may also be met with on the enamel of faience. There is always the hope of causing it to disappear in the second firing, but this hope is not always realized, in which case the piece is entirely spoiled. When a piece, such as a vase or a painting, has one or two colors in it that remain dull in the midst of brilliant colors, we may diminish this disagreeable effect by giving them some¬ thing of a gloss by polishing them. The polishing material consists of pulverized glaze and the tool upon which it is spread is a piece of soft wood, the rubbing surface of which is cut and shaped to a suitable form. The very finely pow¬ dered glaze is placed on the end of the stick and the dull portion is rubbed hard until it shows a slight glaze. Various substances have been tried, such as tripoli, pumice powder, emery powder, etc.; some are too hard, others are too soft. The glaze has a medium hardness and is very suit¬ able. It acts strongly, without scratching the ware or remov¬ ing the colors, though there are some colors that are so ex- 2o6 tremely thin and tender that, when they become dull, no at¬ tempt at polishing can be made without the risk of rubbing them off. ALTERATIONS WHICH TAKE PLACE, FROM VARIOUS CAUSES, AFTER FIRING. After pottery has been decorated and the pieces have been fired successfully, they are by no means completely secure from damage. They must be capable of receiving the liquids, which they are destined to contain, without being affected by these in any way. Now, there are some of the food acids, such as vinegar, the juice of apples, or lemon juice, even when sweetened with sugar, that will affect certain of the hard porcelain colors when in contact with them for 10 or 12 hours. The colors that are the most susceptible to these changes are those that have the brightest tints, such as the turquoise blue No. 23 and the gold colors, above all the carmine, which even the vapor of water will sometimes attack. The following colors, though less susceptible are liable to be affected; they are: Reddish gray, No. 13; iridium black, No. 20; yellow ochre, No. 50 A; the late red 04 and violet red GO; the iridium black and the reds 04 and 00 will have to be in contact with the vegetable acid for about 24 hours before they are affected. The colors that are affected by the action of the vapor of water are very much more rare and among these, of the gold colors, we should only include carmine. We can test the col¬ ors for this susceptibility beforehand, by exposing them for 24 or 30 hours to the vapor of boiling Avater. Water in the liquid state, even Avlien hot, does not produce the same effect. This action of the vapor of water was very curiously illustrated in the case of a painted glass window that was made at Sevres in 1829, and placed in the sacristy of Notre-Dame-de-Lorette, at Paris. After the window had been in position in the newly built church for one or two years, the rose colored and pale purple glass, stained with purple precipitate of gold and an alkaline flux, appeared as if they were partly washed away by the moisture which condensed upon the windows. People hastened to say that the modern stained glass was not equal to the ancient, without stopping to think that the old masters, whose much harder colors sometimes change too, never used 207 rose and purple colors made from gold, which they had no knowledge of. It was so far as I knew then, the first time that these colors had been used for painted windows, though I found, afterwards, that they had been used in some of the modern windows in a chapel at the university of Oxford. Here, too, on the occasion of a visit in 1836 I saw that the colors were deteriorating. The rose and purple glass in the church window at Paris was taken out and replaced by harder, though less beautiful, col¬ ors. Before putting them in place they were submitted to the action of the vapor of boiling water, so as to be quite sure that they were proof against it. But what caused us to note the difference in the action of water and its vapor was that among the pieces of stained glass was one that did not show 7 any sign of change, although it was charged with the same color as the others. On examination it was found that this particular piece of glass had, inadvertently, been put into the frame wrong side out, that is to say that the stained side had been turned outwards and was exposed to the rain so that the water wrnshed over its surface. From this it was evident that the water which frequently flowed over it had less effect upon it than vapor in the interior of the church. There is no other remedy for this defect than to use harder colors and to burn them sharper. If it is impossible to combine the two things then w r e must sacrifice the brightness of the color to durability, particularly when it is a question of ware that is intended for domestic use; the delicate, tender and brilliant colors, which are liable to change in wear should only be applied as ornament or decoration to pieces that are not subject to the deleterious action of the substances we have mentioned. Burgos luster... 1 26 Burnishers. 161) Burnishing Metals . 168 Cantharidin luster . 128 Carmine Flux . 46 Carmines. 87 Cassius—purple of. 68 Causes of “molting”. 202 Changes resulting from the action of the tire.201 Charcoal. 188 Chatiron . 95 Chemical influence of the Material. 197 Chemical preparation of vitrifiable colors and metals.... 12 Chinese Red color. 49 Chloride of Silver. 67 Chromate of Baryta. 66 Chromate of Iron. 65 Chromate of Lead. 66 Chromate of Mercury. 16 Chromate of preparation. 15 Chrome Orange yellow. 80 Chuck for holding plate while Burnishing. 170 Coal. 191 Cobaltic Oxide . 24 Color grinding . 160 Color in the paste or body. 168 Color Printing. 170 Colored pastes . 141 Coloring Matters . 169 Colors in glaze . 154 Colors for hard porcelain. 48 Colors applied under glaze. 152 Colors difficult to lay. 166 Colors for Transfers.✓. 172 Colors liable to change after Burning. 206 Composition and preparation of vitrifiable colors. 16 Composition for Muffles. 182 Copal Varnish for repairing small defects. 206 Copper . 62 Copper Blue . 69 Copper Luster. 127 Copper Plate Printing . 171 “Crazing” .198 “Creeping” of colors .*..204 Cumulative effects of wood and charcoal fuel.100 Dark gray . 57 Dark green, hard . To Dark green, limber. 73 Decorative materical classification . 0 Deterioration of colors after burning.200 Difference in expansion . 198 Dullness of colors .204 Effect of Damp .103 Effects of Terra Cotta or Biscuit in kiln with Glaze.187 Egyptian Blue . 70 Enameled ware . 11 Enamels .158 English formula for liquid gold .123 English Muffle Kilns .181 Enlarging and Reducing Gelatine Prints.178 Excessive heat; its effects .201 Expansion and Contraction .108 Fine Earthern ware. 12 Fire tests.193 Firing Colors.180 Firing the Gold .107 Firing in old and new Muffles.187 Firing with Charcoal.180 Flesh Tints . 78 Flux for gray . 45 Flux, Rocaille. 45 Flux for carmine . 40 Flux for purple . 47 Flux for voilets . 47 Flux for green . 47 Flux for metallic substances ... 47 Fluxes . 42 Fluxing Vapors .200 Fuel and the management of the Fire .188 Gelatine transferring .178 Gelatine transfers .174 German gold .120 Gilding, platinizing and silvering .100 Glaze colors .154 Glazed pottery .Ill Glazing interior of muffle .187 Gold decorations for printing. 175 Gold—German . 120 Gold light .‘. 120 Gold liquid . 120 Gold luster . 120 Gold Meissen . 120 Gold, preparation of . 113 Gold printing .170 Gorge white . 55 Grass green . 72 Gray flux for . 45 Grays . 50 Green flux . 47 Greens . 70 Grinding colors .130 Hard fire colors. 48 Hard fire or underglaze colors . 48 Hard fire over glaze colors. 101 Hard muffle colors . 05 Hard porcelain . 12 Hard porcelain, colors for. 48 Horn and ivory knives .132 Humidity in muffle . 100 Hydrofluoric acid for repairing.203 Imitations of pearl.<118 Indigo blue . 05 Influence of surrounding vapors during winter.198 Influence of the material upon which the color is laid . .. .100 Ingravings for transfers .173 Inking and pulling the plate.173 Insufflation of slip.151 Iridium black . 03 Iron chromate. 35 Iron muffles .183 Iron, oxide preparation . 17 Jonquil yellow. 77 Judging the fire .103 Knives .133 Laying colors .103 Laying on colors.135 Laying on muffle grounds.109 Lead chromate . 30 Lead vapors .108 Light gold .120 Liquid gold, English formula.123 Lusliers.117 Litharge luster.120 Luster Canthauden .128 Luster copper .127 Luster platinum.125 Luster pottery. 11 Manganese oxide. 20 Material of the body; its influence on colors.107 Mechanical preparation of colors.120 Mediums.135 Meissen Gold .120 Mercury chromate. 10 Mercury nitrate . 20 Metallic lusters .117 Metallic substances, flux for. 47 Metals.Ill Methods of Repairing.203 Molting.108 Mordant .134 Muffle Kilns .184 Muffle kilns for Verifiable colors.180 Muffles . 182 Number four white. 56 Nut black . 90 Ochre colors . 41 Ochres . 93 Ochre yellows . 82 Opaque colors .166 Order of laying on shades.165 Over glaze colors.161 Oxide antimony . 31 Oxide chronium . 15 Oxide cobaltic. 24 Oxide copper. 32 Oxide-tin.33 Oxide indinum . 34 Oxide manganese . 26 Oxide of iron. 17 Oxides. 14 Oxide uranium . 20 Oxide zinc . 22 Painting on pottery in verifiable colors.163 Paper for transfers.174 Pastes, bodies or ceramic articles capable of being deco¬ rated . 11 Pearl lusters .118 Pearls, imitation of.118 Pencils for spreading colors.163 Permanent white . 54 Physical influence of the body or ground.198 Pink color . 94 Platinum.116 Platinum gray . 59 Platinum luster . 125 Position of the colors.138 Precautions when laying colors.163 Preparation and application of colors.129 Preparation of gold.113 Preparation of platinum. 116 Preparation of transfer paper.174 Preparation of verifiable colors. 15 Printing in colors and in gold.170 Printing ink for transfers.172 Printing on gelatine.177 Printing on pottery.171 Printing upon paper and transferring to glaze.174 Printing upon paper and transferring to the biscuit.176 Purple flux . 47 Purple of cassins. 38 Purples . 87 Pyrometers. 194 Reds.83 Red brown. 91 Red colors, Chinese. 49 Reddish gray . 57 Reducing the print.179 Repairs .203 Rocaille flux . 45 Rose Isabel . 107 Royal deep blue. 69 Sairg de Boceuf. 49 Scaling of colors.165 Seires reds . 85 Sepia brown .- .... 92 Setting in fixed muffles.130 Sharp fire colors.193 Silver chloride .. 37 Sky blue. 03 Slip.. Smokey and acid vapors.199 Smokey gray .100 Soft gray. 53 Soft porcelain . 12 Specks in first fire. 205 Stained glass window at Paris. 207 Steel knives .. Stippling .. Stoneware . 12 Stopping out.. Straw color .107 Strengthening gold prints. .175 Tender sky blue. 03 Tender or light muffle colors. 15 Terra cotta . n Tin . 33 Transfer “mixtion” . 175 Transferring to biscuit.170 Transfers .. Traveling muffles .. Tridium oxide . 34 Tritrurating the colors.129 Turquoise blue . 00 Turquoise shell .. Vapor of water.. Vapors and gases.. Ultramarine blue . 07 Under glaze colors. 43 Uranium orange yellow. 30 Uranium oxide . 20 Violet flux .f. Violets . 31 Water vapors .. Wood fuel .. Whites. 54 Yellow. 10 Yellow ochre . 30 Yellowish green . 75 J. Marsching & Co. Sole Selling Agents in the United States and Canada for the following WORLD-RENOWNED COLOR MAKERS: JOSEPH P. EMERY, ROBERT EMERY, WM. BOARDMAN, CHAS. COLCLOUGH, C. J. BAINES & CO., Also for BRITTAINS, LIM., HANLEY, STAFFS. Manufacturers of Pottery Printing Paper, Duplex Lithographic Transfer Paper, etc. A. LACROIX (powder colors), In France In England GEITNER & CO., I . „ MULLER & HENNIG, f Germa, 'y OXIDES AND CHEMICALS For Staining Glass, for producing Glazes and Majolica effects on Pottery, and for making and coloring Enameled Bricks. HEADQUARTERS FOR ALL CHINA AND CLASS DECORATORS’ SUPPLIES, also for BRONZE POWDERS, DUTCH METAL LEAF, Etc. 27 PARK PLACE, - NEW YORK. F. W. SILKMAN Importer and Jobber in MINERALS CLAYS CHEMICALS AND COLORS 231 Pearl Street New York City Gabriel & Schall, P. O. Box 2654, 205 Pearl Street, New York, Sole Importers in the United States of the PRECIPITATED Carbonate of Barytes The only preventative for scum and discoloration, neutralizing the Sulphate of Lime in the Clay and Water. CIRCULARS AND PARTICULARS ON APPLICATION X, COLORS OVERGLAZE & UNDERGLAZE and all material used in the Pottery, Glass, Enameled Ware, Terra Cotta, Brick, etc. Industries. 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