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Marble and Alabaster

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40. Cleaning marble. 41. Paint for marble and alabaster.
42. Artificial painting of marble. 43. Communication of hardness to gypsum.
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40. Cleaning marble

Prepare a thick solution of gum arabic and with a brush cover them with marble, and then give the gum arabic to dry completely. When the latter dries, it is separated from the surface of the marble (dried gum arabic easily lags behind the marble), and together with the gum arabic, all extraneous substances contaminating the marble are removed, which are difficult to remove by simple washing of marble.
Another way: prepare a mixture of 1 part by weight of chalk, the same amount of finely ground pumice and 2 parts of soda. From this mixture a dough-like mass is prepared on the water, which is covered with contaminated parts of marble, then washed with water and soap. For the removal of greasy spots, the latter are covered with chalk: the chalk is poured in a powder form on the marble with a rather thick layer, after which the chalk layer is well wetted with gasoline and to cover the rapid volatilization of the latter, the chalk washed with gasoline is covered with a saucer tipped upside down. After a few hours, the chalk is removed and, if the fat stain still remains, the same operation is again repeated with fresh chalk and a new portion of gasoline. Sometimes marble is covered with rusty metal stains. To remove them proceed as follows: in ammonium sulphide, good quality clay is disengaged until a pulpy mass is obtained. Mass this is applied quite a thick layer on the stain. After 10-15 minutes, remove the mass and apply a fresh portion, which is removed after 5 minutes, after which the marble is washed with water and dried. If the stain still remains, then proceed to a secondary treatment: the stain is covered with a dough-like mass, prepared from 1 part by weight of a white bolus and 4 parts of a solution of the sodium cyanide (a poison that requires careful handling). This mass is left on the marble for 30 minutes, after which it is removed and the same operation is repeated; then marble is washed and dried. In this way, it is possible to remove even the most ancient metallic rusty spots from the marble surface.

41. Paint for marble and alabaster.

Not every paint is suitable for painting marble or alabaster. That the paint has begun and firmly adhered, it should be prepared as follows: make a solution of borax and vegetable dye, and then add to this solution a few drops of nitric acid or some nitric acid salt. For example, to paint marble in blue, prepare a borax solution with indigo and add a few drops of nitrogen-iron salt (as a liquid). For coloring in red, any red plant paint is dissolved with borax. Replacing the coloring matter with ink nuts, get a solid black paint for marble and alabaster.

42. Artificial painting of marble.

As you know, all color grades of marble are very expensive. In view of this, artificial dyeing of cheaper white marble has recently become widespread. The method of staining is as follows: unpolished marble is laid horizontally and covered with a dye solution (see below), so hot that it still foam. The coloring material then penetrates the marble deeply and holds very firmly. The dye solution is prepared in alcohol. For coloring in blue, litmus is dissolved in alcohol, and the amount of the latter is determined by the desired density of color. For yellow color, a solution of gummigut is used. And if you put the second (gummogut) on top of the first color (litmus), then you get an excellent green color.
The root solution of alan, cochineal, etc. prepared in this way. stains marble in red. Finally, a solution in alcohol of equal parts of zinc sulfate, ammonia and honey-colored copper color the marble in golden color. You can make a very effective mosaic of pieces of marble of different colors, painted in this way: the beauty and strength of color, it does not inferior to the mosaic of expensive varieties of marble, although it costs much less.

43. Communication of hardness to gypsum.

It is known that gypsum, mixed with water and then hardened, does not differ strength: it becomes extremely fragile and therefore finds relatively little use. To eliminate this defect and tell the gypsum more hardness, in America the following method is used: 6 parts of gypsum are mixed with 1 part of slaked lime and with this mixture is then manipulated as with ordinary gypsum.
Items made from such a mixture, after a good drying, are impregnated with a solution of zinc sulfate. Items made from gypsum, processed in this way, are much stronger than ordinary gypsum handicrafts.