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Fifth Part.

SECTION EIGHTH.

ANCIENT AND MODERN PORCESSES FOR PAINTING OR

COLORING MARBLES.

ANCIENT PROCESS FOR PAINTING ON MARBLES.

186. We have already said and proved several times, that many of the new inventions are merely the reproductions of ancient methods, which have been abandoned for some unknown cause. We find a new proof of this in the Dictionnaire de l' Industrie, published in 1785, and it is somewhat remarkable that, even at that period, this invention was not given as a new one.

We make the following extract from page 408, vol. 4, of the Encyclopedie de Diderot, where the article may be found:

"In order to prepare a liquor which will penetrate into the interior of Marble in such a manner that one can paint on the surface, designs which seem to be within the material, it is necessary to proceed in the following manner:

"Take of agua fortis and agua regia, each two ounces, one ounce of salts of ammonia, two drachms of the best spirits of wine, as much gold as can be bought for a hundred pence, and two drachmas of pure silver. When you are furnished with these materials and have calcined the silver, put it in a vial, and having poured upon it the two ounces of aqua fortis, leave it to evaporate; you will thus have a water which will at first give a blue color, and finally a black. Calcine the gold in the same manner, put it in the vial, and, pouring the aqua regia upon it, leave it to evaporate. Finally pour your spirits of wine upon the salts of ammonia, leaving it also to evaporate; you will thus have a golden colored water which will furnish different colors.

"In this manner you can make many dyes of various colors, by the use of other metals. This being done, by the aid of the two others you can paint whatever you may wish upon the softest kind of white Marble, repeating the operation every day for some time by adding new liquor to the same figures; you will then find that the painting has penetrated the Marble in such a manner that, in cutting it in any manner you may please, it will always present the same figure on both sides."

MODERN PROCESSES FOR DEEPLY COLORING MARBLES.

187. We will not repeat here what we have already said several times, particularly at the head of the preceding paragraph; yet we find it curious and useful to compare the ancient methods with the modern ones, and we confine ourselves to the remark that the first have the advantage of experience. We may add that if they have been abandoned, it is because this experience has demonstrated their defects, and, consequently, that new inventions must be accepted cautiously, and with reserve.

To succeed in the coloring of Marbles, the pieces of Marbles upon which the experiments are made should be well polished, and free from any spots or veins. The harder of the Marble, the better it supports the heat necessary to the operation; on this account alabaster and the common soft white Marble are not suitable for the purpose which we propose. Heat is always necessary, to open the pores of the Marble and thus to prepare it for the reception of colors, but it never should be heated to a red heat, as the fire then alters the contexture of the Marble, burns the colors, and destroys their beauty.

Too slight a degree of heat is as bad as one too great, for in this case, though the Marble takes the color, it does not retain it well and is not penetrated deeply enough. There are some colors which it will even take when cold, but these never fix as well as when the proper degree of heat is employed.

The proper degree of heat is that which, without reddening the Marble, is intense enough to cause the liquor which is on its surface to boil. The menstruums which are used to incorporation the colors, should be varied according to the nature of the color employed; a lixivium made with the urine of the horse or dog, mixed with four parts of quick-lime and one of potash, is excellent for certain colors, the common ley of wood ashes is good for others; for some, the spirits of wine is better, some others require oily liquors, or common white wine.

The colors which succeed best with the different menstruums are the following: blue-stone dissolved in six times its quantity of spirits of wine or a urinous lixivium, and the color called litnus by the painters, dissolved in common lixivium of wood; the extract of saffron and the color made from the fruit of the buck thorn, called sap green by the painters, both succeed very well when dissolved in urine or quick-lime, and tolerably in the spirits of wine.

Vermilion, and the fine powder of cochineal, also dissolve well in the same liquids.

Dragons' blood succeeds very well in the spirits of wine, which is also used for the dye of Campeachy wood.

The root of the alkanet gives a very fine color, but the only menstruum suited to it is turpentine, as neither the spirits of wine or any lixivium has the power to dissolve it.

There is still another kind of dragons' blood, called dragon's blood in tears, which gives a beautiful color when mixed with urine alone.

188. Besides these mixtures of colors and menstruums, certain colors can be put on dry and unmixed; such as the purest dragons' blood for the red, the gamboge for the yellow, the green wax for a kind of green, the common sulphur, pitch and turpentine for a brown color.

For all these experiments, the Marble must be considerably heated, and the dry colors then rubbed upon the block.

Some of these colors, properly applied, remain immovable, some are changed and finally effaced by others; thus, the red color produced by dragon's blood or the decoction of Campeachy wood, is entirely effaced by the oil of tartar, without the polish of the Marble receiving any injury.

A beautiful golden color is produced in the following manner: Take equal quantities of the crude salts of ammonia, of vitriol, and of verdigris, the white vitriol is the best for this purpose; grind these together, and reduce them all to a very fine powder.

All the shades of red and yellow may be given to the Marble with the solutions of dragons' blood and gamboge, by reducing these gums to powder and grinding them with spirits of wine in a glass mortar.

But, when little is required, the best method is to mix one of these powders with spirits of wine in a silver spoon, and hold it over a heated braisier; thus extracts a fine color, and, by dipping a small brush in it, the finest veins may be made upon the cold Marble.

When this is afterwards heated over sand from the fire, or in a baker's oven, the coloring will be absorbed and will remain perfectly distinct upon the stone.

It is very easy, by the same means, to give a ground of a yellow color to Marble, leaving white veins upon it.

This is done by covering the parts designed to retain their whiteness with white paint, or even with two or three folds of paper; either of these will prevent the penetration of the color in this part.

All the shades of red may be given to Marble simply with the aid of this gum. A weak coloring, applied without the assistance of heat, will produce a pale flesh color, but the stronger the coloring is made the deeper will the color be; to this the action of heat contributes much. By adding a little pitch to the coloring, a black shade, or all the varieties of dark red, can be given.

The archil of the Canary Islands, a species of moss, simply diluted in water and applied when cold to the Marble, communicates to it a beautiful blue color, which is more precious, as this color is rarely found in Marbles; by putting on the coloring in proportion as it dries, it becomes very fine in less than twenty-four hours, and penetrates deeply.

If the paste of archil is used, which is a preparation of the plant with lime and fermented urine, the color obtained will be more of a violet than blue; to obtain a perfect blue it must be distilled in lemon juice; this acid will not injure the Marble, as it has been weakened by its action upon the archil.

Large blue veins may thus be formed upon the cold, white Marble, which produces a beautiful effect, but as this color is apt to spread, it will not be pure or exact unless the colored parts are instantly touched with dragons' blood or gamboge, which checks it.

It may also be checked with wax, either colored, if colored veins are required, or white, if they are to remain white.

This blue color, which penetrates the Marble more than an inch, also renders it softer; this, however, is but a slight objection, as it is absorbed in but few places, and also possesses sufficient solidity to last many years without suffering any material change.

FIGURES IN RELIEF UPON MARBLE.

189. A method has also been discovered for tracing figures in relief upon Marble with great facility. For this purpose, the desired figures are first traced upon the Marble with chalk, they are then colored with a coat of varnish, made of common Spanish sealing-wax, dissolved in spirits of wine; after which a mixture of equal parts of acid of salts and distilled vinegar is poured upon the Marble, which corrodes the ground while the figures remain in relief, as if engraved on the cost of much time and expense.

PICTURES IN STUCCO.

190. We have already described the composition and working of stucco at the present day, but we find some things are more perfect in the ancient methods than in the modern.

The following extract was written in 1781.

"There is still another method of working in stucco which is superior to this, as by its pieces are so beautifully executed as to resemble the finest paintings. Landscapes are made of this stucco, and we have seen at one of the exhibitions of the Gallery, a flower picture of the greatest beauty, in which all the colors were shaded as if they had been laid on with a brush. Indeed the manner in which these pieces are executed may be regarded as a species of painting in stucco, as may be seen from the process.

"The stucco, or artificial Marble, of which these beautiful works are made, is a composition of which plaster forms the entire base; the hardness that may be given it, the different colors with which it may be mixed, and the polish of which it is susceptible, renders it suitable to imitate, with almost perfect exactness, the most costly Marbles.

COLORING OF ARTIFICIAL MARBLES.

191. This coloring, which is now given us as a novelty, was clearly described in some very ancient works, which were copied by the authors of the Encyclopedia, published in 1780, in the following words:

"When any Marble is to be imitated, soak the colors which are found in this Marble in warm glue water, in different small pots; temper a little plaster with each of these colors, then make a cake of each color, a little larger than the hand, place all these cakes alternately upon each other, placing those of the prevailing color in the greatest number, or thicker.

"Then turn these cakes, thus flatly arranged, upon the side; cut them and place them quickly upon the core of the work, afterwards flattening them down.

"By this means, the fantastical design of the different colors of the Marble can be perfectly represented.

"If the Marbles termed Breccias are to be imitated, mix in the composition of these cakes, when spread upon the core, different sized pieces of the plaster tempered with the color of the Breccia; these pieces, when flattened down, form very good imitations of Breccias.

"It should be observed that in all these operations, the glue water should be warm, without which the plaster will set too quickly, without giving time to work it."



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