Marble, in Natural History, a genus of stones that admit of a bright and beautiful polish: they are composed of small separate concretions, moderately hard ; not emitting fire, when stricken against steel; effervescing with, and soluble in acids ; and calcining in a moderate fire.
The finest modern marbles are these of Italy, Blankenburg, France and Flanders. In some of the Western Islands of Scotland, very fine specimens of this fossil have lately been discovered. When chemically examined, marble consists of calcareous earth united with fixed air; and is, like lime-stone, or chalk, convertible into a strong quick-lime.—Black marble derives its colour from a partial admixture of iron.
Staining of Marble.—The pieces to be coloured should be of the hardest kind ; previously well polished ; and be divested of every spot or blemish. Such only are calculated for supporting the heat which is always necessary, in order to open their pores, and render them susceptible of the colours. On the other hand, too low or top high a degree of heat are equally injurious: hence a due temperature ought to be preserved; and this, without making the marble red, will cause the liquor to boil on its surface.
The principal colours used for staining marble are, red, yellow, and blue: the two first of these tints may be imparted to it, by reducing dragon's blood, or gamboge to a powder, and grinding them separately with spirit of wine in a glass mortar. But, in experiments on a small scale, a little of either of those powders should be mixed with spirit of wine in a silver spoon, and dissolved over a charcoal fire. Thus, a strong tin6ture will be extracted ; with which, by the aid of a pencil, the finest traces may be drawn on marble, while cold: on heating the latter in an oven, the marks will penetrate deeply, and remain perfectly distinct. . A fine blue colour may be communicated to marble, by a watery solution of the drug, known among dyers by the name of Canary Turn-sol, and tracing the marks designed with a pencil. These will strike deeply into the stone, and the colour may be increased, by drawing the moistened pencil repeatedly over the same lines. The staining liquor must always belaid on, cold; nor should the marble afterwards , be heated ; yet such blue is apt to spread itself irregularly, unless its outlines be circumscribed by wax, or other adhesive matter. This colour possesses the advantage of being applicable to marble that has already been stained with other drugs: it affords, besides, a very beautiful shade, and is not liable to be easily effaced.
In 1778, a patent was granted to Mr. Ricutbr, for his invention of an art or method of inlaying scagligla, or plaster in marble or metals, so as to imitiate- flowers, fruits, trees, birds, beasts, landscape.-., and every kind of ornament. This patent is now expired ; but, as, it is practicable only by statuaries and artists, the inquisitive reader will consult the 10th volume of the Repertory of Arts and Manufactures.
For the easiest method of cleanmarble, of alabaster, see p. 25 our first volume.
"Marblling, the art of painting or disposing colurs, in such a manner as to imitate marble.
Then; are several hinds of mar-hied paper, winch vary only in the forms or figures or colouring : some are dotted ; others drawn in irregular lines; but the method of tinging them, simply consists in dipping the paper in a thick solution of gum tragacanth, over which the colours are uniformly spread, after having been ground, with oxgall, and spirit of wine.
The paper must first be immersed in clear water, the sheets regularly folded over each other, and toured with a weight. It is now to be carefully laid on the co-louring solution, and pressed softly with the hand, that it may bear equally on the whole. Next, it must be suspended in order to dry; and, as soon as the moisture' is eva-popurated the paper is polished by rubbing it with a little soap, and smoothing it either with glass highly burnished, or with a polished agate.
The colours usully emloyed fo red, are, carmine lake or , vermi lion ;— for yellow, Dutch pink and yellow ochre;—for blue, Pruss.an-blue and verditer - for green, ver-digrease a mixture of Dutch-pink, and Prussian-blue, in various pro-portions ;—for orange, the orange- lake, or a composition of vermilion, or red-lead, with Dutch-pink ; and lastly, for purple, rose-pink and Prussian-blue.
These different colours are first to be finely triturated with spirit of wine, when a small proportion of gall is to be added, and the grinding of the whole repeated. The proper quantity- of gall can be easily ascertained by comparative trials ; because there must be only such a proportion of it used, wi11 suffer the spots of the various tinging matters to unite, when sprinkled on the solution of tragacanth, without intermixing, or running into each other.- The whole being thus prepared, the solution is to be poured into different vessels, according to the colours employed, which are to be sprinkled on the surface;. and the process of marbling is completed by laying the paper on the mixture, in the manner above directed.