Rubbing well after this with chalk moistened with water will, in a measure, restore the luster. Another method of finishing is to apply a solution of white wax in turpentine (about 1 in 10), rubbing thoroughly with a piece of flannel or soft leather.
If the marble has been much exposed, so that its luster has been seriously impaired, it may be necessary to repolish it in a more thorough manner. This may be accomplished by rubbing it first with sand, beginning with a moderately coarse-grained article and changing this twice for finer kinds, after which tripoli or pumice is used. The final polish is given by the so-called putty powder. A plate of iron is generally used in applying the coarse sand; with the fine sand a leaden plate is used; and the pumice is employed in the form of a smooth-surfaced piece of convenient size. For the final polishing coarse linen or bagging is used, wedged tightly into an iron planing tool. During all these applications water is allowed to trickle over the face of the stone.
The putty powder referred to is binoxide of tin, obtained by treating metallic tin with nitric acid, which converts the metal into hydrated metastannic acid. This, when heated, becomes anhydrous. In this condition it is known as putty powder. In practice putty powder is mixed with alum, sulphur, and other substances, the mixture used being dependent upon the nature of the stone to be polished.
According to Warwick, colored marble should not be treated with soap and water, but only with the solution of beeswax above mentioned.
II.—Take 2 parts of sodium bicarbonate, 1 part of powdered pumice stone, and 1 part of finely pulverized chalk. Pass through a fine sieve to screen out all particles capable of scratching the marble, and add sufficient water to form a pasty mass. Rub the marble with it vigorously, and end the cleaning with soap and water.
| III.— | Ox gall | 1 part |
|---|---|---|
| Saturated solution of sodium carbonate | 4 parts | |
| Oil of turpentine | 1 part | |
| Pipe clay enough to form a paste. | ||
| IV.— | Sodium carbonate | 2 ounces |
| Chlorinated lime. | 1 ounce | |
| Water | 14 ounces | |
Mix well and apply the magma to the marble with a cloth, rubbing well in, and finally rubbing dry. It may be necessary to repeat this operation.
V.—Wash the surface with a mixture of finely powdered pumice stone and vinegar, and leave it for several hours; then brush it hard and wash it clean. When dry, rub with whiting and wash leather.
| VI.— | Soft soap. | 4 parts |
|---|---|---|
| Whiting | 4 parts | |
| Sodium bicarbonate | 1 part | |
| Copper sulphate | 2 parts |
Mix thoroughly and rub over the marble with a piece of flannel, and leave it on for 24 hours, then wash it off with clean water, and polish the marble with a piece of flannel or an old piece of felt.