RECIPE OF A WAX VARNISH FOR THE PRESERVATION OF STATUES
AND MARBLES EXPOSED TO THE ACTION OF THE AIR.
§ 174. This varnish is obtained by melting two parts of wax, in eight parts of very pure essence of turpentine.
When the statues are removed from the atelier of the sculptor, this varnish should be carefully applied, heating it and spreading it so that it may not be of sufficient thickness to destroy the harmony of the figures.
This varnish may be used upon statues which have been cleansed with water dashed with hydrochloric acid, but they must be perfectly dry when the application is made.
A similar operation upon busts, statues, vases, cups, or any other ornaments in plaster, will preserve them from injury.
§ 175. It is difficult to resolve the problem of the effect of the absorption of colors, both in respect to their lustre and durability, and also of the use which should be made of them. Many of the secrets of the ancients, when discovered, benefit us but little at the present time, since our tastes differ widely from theirs, as well as our fortunes, and the style of our houses.
Few of our buildings are rich enough to warrant the decoration of their pavements with the veritable mosaics; the painted mosaic seems hardly suitable to fill its place, yet this decoration may be employed in objects of less importance; and what we have already said in respect to the utility of paintings upon Marble, may be also applicable to the mosaics of which we are speaking, and which are, in truth, but species of painting.
The art of making mosaics in Marble by the absorption of colors, was first discovered in Italy.
This process has been experimented upon by two English chemists who have obtained the following results:
1. The solution of nitrate of silver penetrates the Marble deeply, communicating to it a deep red color.
2. The solution of nitro muriate of gold does not penetrate it as deeply, but produces a very fine violet color.
3. The solution of verdigris penetrates the Marble the twelfth of an inch, giving to the surface a fine light green color.
4. The solutions of gum dragon and of gumboge also penetrate it; the first producing a fine red, and the second a yellow color.
To cause these two substances to deeply penetrate it, the Marble should be first well polished with pumice stone, after which the substances should be dissolved in warm alcohol, and applied with a small brush.
All the dyes of wood, those of Brazil, Campeachy, etc., made with alcohol, penetrate the Marble deeply.
5. The tincture of cochineal, prepared in this manner with the addition of a little alum, gives a fine scarlet color to the Marble, penetrating it one-fifth of an inch. This Marble resembles the African closely.
6. The artificial orpiment, dissolved in ammonia and laid on the Marble with a brush, produces a yellow color in a few moments, which becomes more brilliant when exposed to the air.
7. To all the other substances employed in this use, we should add white wax mixed with coloring matters; this when placed on the marble, in a melted state, soon penetrates it.
8. If the verdigris is boiled in the wax and then laid melted upon the marble with an instrument, it will be seen on its removal when cold, that the design has penetrated the surface to the depth of from one-third to half an inch; the color is a very pure green, resembling that of the emerald.
§ 176. To facilitate this work, we shall enter into a few details respecting it. Thus, when several colors are to be successively used without blending them and destroying the clearness of the design, it is necessary to proceed in the following manner:
9. The dyes obtained by spirits of wine and the oil of turpentine should be laid on the marble when it is heated, particularly in the execution of delicate designs, but the dragons' blood and gamboge may be used on the marble when cold. For this they must be dissolved in alcohol, and the gamboge used first; the solution of this gum is quite clear, but soon becomes troubled and gives a yellow precipitate, which is used to obtain a brighter color. The lines drawn by this solution are then heated by passing a plate of iron or a chafing dish filled with lighted charcoal, over the surface of the marble, at the distance of half or two-thirds of an inch from it. It is then left to cool, after which the lines which have not been penetrated by the color are heated in the same manner. When the yellow coloring has been applied, the solution of dragons' blood, which should be concentrated as much as possible, is employed in the same manner as that of the gamboge; and while the Marble is warm, the other vegetable tints which do not require so strong a degree of heat in order to penetrate the Marble, may also be applied. The design is finally completed by the colors mixed with wax, which should be applied with the utmost care, as the slightest excess of the proper degree of heat will cause them to spread, for which reason they are less suited to delicate designs.
§ 177. If the new mosaics are not admired, the imitations can scarcely be expected to meet with more favor.
However, they are sometimes demanded of Marble workers, and, when the price of the genuine mosaics is objected to, they endeavor to make the imitations in the best possible manner; if one can give the name of mosaic to those medleys of indiscriminate colors which have been attempted in some buildings; L'Hotel des Finances, Rue de Rivoli, for instance.
The desire for the production of novelties has given rise to several processes, which are announced as inventions, but which are often only the reproduction of abortive attempts, or abandoned methods.
We do not say that the process of M. Dubreuil should be classed among these, but we give it as published by the government, without guaranteeing it.-His design is, to make imitations of mosaics, by the incorporation of colors in all kinds of calcareous stones, or gypseous matter, either smooth or sculptured. He gives the following method of procedure:
Select calcareous or other stones; those which are fine grained and white, are best suited to mosaics, arrange these and smooth them as much as possible. These stones should be perfectly dry before the execution of the proposed designs.
The penetrating colors suited to dyeing, as well as inks (without gum,) are preferable; the artist should study these in order to prepare the tones best suited to this work. For this purpose, he can make trials upon pieces, to obtain the effects of the Marble which he wishes to produce, as well as the purity of the touch.
After the tracing of the design, you put in the colors which you deem suitable with a brush, leave them to dry, and then pour vitriol diluted with water, over the work.
With pumice and the same water, you then carefully smooth and unite the pieces, taking care to remove the mud which is formed.
The whole being washed and wiped by means of a soft stone and the same water, you polish and dry it a second time, and, in order to give it more vigor, you pass oil lightly over the colors with a brush, after which you again leave it to dry. You then obtain a fine polish by rubbing it with a dry linen cloth, which completes the operation.
To execute mosaic and other paintings upon gypseous stone and alabaster, after having selected the layer, coating, or block, which you deem suitable, you arrange your stone according to the demand, sculptured, or with a plane surface.
You then expose it to a heat sufficiently intense to calcine to the state of plaster, all the surfaces which you wish to paint and harden, to the depth of one-fifth or sixth of an inch; you then cool it, and pass a file or sand paper lightly over the surface, to cleanse any parts which may have been soiled by fire.
You then trace the design, and put in, with the brush, the colors which have already been described, taking care to use a sufficient quantity to enable them to penetrate deeply enough.
The small pieces, which do not crack like the larger ones in hardening, may be entirely calcined.
Your design being executed, you pour alum water over the whole work, steeping the stone in it until it rejects it.
When you judge it to be entirely hardened, you wash the piece well in order to remove the refuse of the color remaining on the surface, and finish this stone in the same manner as the preceding ones, with the sole difference of using alum, in preference to the vitriolic acids.
You can give any forms you choose to the stones, whether in plane surfaces, or in reliefs, statutes, vases, tables, chimney-pieces, and other articles.
§ 178. To obtain from gypseous materials, molded articles resembling Marble, after having first calcined the gypsum, reduce it to a very fine powder. The molding is executed in the following manner:
Take a mold of great solidity, and place the gypsum in it in thin layers, taking care to compress each layer in order to strengthen it.
The desired thickness being obtained, place several folds of linen or cloth upon it, moistened with common water, or with a solution of alum, which is preferable; and submit the mold in this state, to a strong, quick pressure, which instantly causes the moisture to penetrate to the bottom of the mold through the gypseous powder, thus giving it the proper consistency. The article is then taken from the mold and left to dry, after which it is set up and polished. If common water is used in the operation, the surface of the piece must be washed with a solution of alum when taken from the mold.
§ 179. In order to obtain the accidental shades which the different kinds of Marble naturally present, coloring matters (the mineral ones are better,) should be mixed with the gypseous powder. This mixture, thrown at hazard into the material which is to fill the mold, produces, by employing the methods before described, solid masses, imitating the natural Marbles.
To obtain mosaics, fill up the mold a little way with pulverized gypsum, either colored or white, then dexterously remove a portion of this coating, which has been sunk in such a manner as to leave the design to be produced upon the bottom of the mold, and is thus hollowed out; fill up these cavities with a colored gypseous powder, sunk in proportion, and finally fill the mold to the desired thickness with the gypseous powder, always compressing the layers, and proceeding as before described; a mass of great purity, bearing upon its surface the design in mosaic, is thus obtained.
If the pieces demand a greater thickness, fill up the mold with plaster tempered with pure water, place this upon the prepared materials when it begins to set, and place it under a strong pressure; this produces the same effect as the linen, and gives to the article the desired thickness by its inseparable adhesion to it.
When taken from the mold, the surface of the piece should be moistened with alum water. This method may always be employed when colored materials are to be worked.
The same results are also obtained in the execution of all kinds of relief, whether alto or basso, these may also serve, if necessary, by reason of their hardness, as molds for works of art.
All of these articles are polished with pumice and polishing stone.
Stuccos and other moist materials, when prepared, placed in a mold and covered over with dry, powdered plaster, and subjected to these operations, also acquire a great degree of hardness.
ANOTHER IMITATION OF MOSAIC.
§ 180. M. Simon, of Strasbourg, described a simple method of giving to stone the appearance of Marble. Upon a stone covered with thick varnish, he says, trace the design which you wish to obtain the mosaic; pour acid upon the stone after having first surrounded the sketch with a waxen border, the lines are thus acted upon, and a greater or less depth, as may be wished, obtained; then wash it well with water, and fill the hollow lines with different colored stuccos, which soon harden; after this, polish the surface, and you have the designs in mosaic.