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Marble and Alabaster

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40. Marble cleaning. 41. Paint for marble and alabaster.
42. Artificial coloring of marble. 43. Post hardness gypsum.
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40. Marble cleaning

Prepare a thick solution of gum arabic and use a brush to coat the marble with it, and then allow 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 marble), and with other gum arabic also all extraneous substances that pollute the marble, which are difficult to remove by washing the marble, are removed.
Another way: prepare a mixture of 1 weight part of chalk, the same amount of finely ground pumice stone and 2 parts of soda. From this mixture, a pasty mass is prepared on water, with which the contaminated parts of marble are coated, then washed with soap and water. To remove grease stains, the latter are covered with chalk: chalk in the form of powder is poured onto the marble in a rather thick layer, after which the chalk is well wetted with gasoline and to eliminate the rapid volatilization of the latter, the chalk moistened with gasoline is covered with a tilted bottom saucer. After a few hours, the chalk is removed and, if there is still a greasy stain, the same operation is repeated again with fresh chalk and a new portion of gasoline. Sometimes marble is covered with rusty metal stains. To remove them, they do this: in ammonium sulphide, clay of good quality is melted to obtain a pasty mass. This mass impose a fairly thick layer on the spot. After 10-15 minutes, the mass is removed and a fresh portion is applied, which after 5 minutes is also removed, after which the marble is washed with water and dried. If the stain still remains, then proceed to the secondary treatment: the stain is covered with a pasty mass prepared from 1 weight part of a white bolus and 4 parts of a solution of potassium synergide (poison that requires careful handling). This mass is left on the marble for 30 minutes, after which the same operation is removed and repeated; then the marble is washed and dried. Thus it is possible to remove from the surface of the marble, even the oldest metal rust spots.

41. Paint for marble and alabaster.

Not every paint is suitable for coloring marble or alabaster. For the paint to start and hold tight, it should be prepared as follows: make a solution of borax and vegetable coloring matter, and then add a few drops of nitric acid or some nitrate salt to this solution. For example, to color the marble blue, they prepare a solution of indigo borax and add a few drops of nitrogen-iron salt (as a liquid). For coloring in red color dissolve any red vegetable paint with brown. Replacing the dye ink ink, get for marble and alabaster durable black paint.

42. Artificial coloring of marble.

As you know, all colored marble varieties are very expensive. In view of this, artificial coloring of cheaper white marble has recently become widespread. The method of coloring is as follows: unpolished marble is laid horizontally and covered with a dye solution (see below), so hot that it foams. The dye then penetrates deep into the marble and holds very firmly. Coloring solution is prepared in alcohol. For blue staining, a litmus is dissolved in alcohol, the amount of which is determined by the desired color density. For yellow color, gummigut solution is used. And if you put the second one (with a gummig) over the first color (litmus), you get a great green color.
The solution of the root thus prepared is Alans, Cochineal, etc. paints marble in red. Finally, a solution in alcohol of equal parts of zinc vitriol, sal ammoniac and verdigris paints marble in a golden color. You can make a very spectacular mosaic of pieces of marble of different colors, painted in this way: it is in no way inferior to a mosaic of expensive varieties of marble in beauty and durability, although it is much cheaper.

43. Post hardness gypsum.

It is known that gypsum mixed with water and then hardened is not very strong: it becomes extremely brittle and therefore finds relatively little use for itself. In order to eliminate this disadvantage and make the gypsum more hard, in America the following method is used: 6 parts of gypsum are mixed with 1 part of hydrated lime and this mixture is then manipulated as with ordinary gypsum.
Items made from such a mixture, after a good drying, are soaked with a solution of zinc vitriol. Objects made of gypsum, treated in this way are much stronger than ordinary plaster crafts.