271. To improve Gilding.—Mix one gill of water, two ounces of purified nitre, one ounce of alum and one ounce of common salt. Lay this over gilt articles with a brush, and their color will be much improved.
272. Incombustible Varnish for Wood.—Equal parts of alum and isinglass, dissolved and mixed, applied to wood, prevents it from burning. Liquids can be boiled in a wooden vessel on a common fire, if this varnish be applied to it. The wood chars sometimes, but does not flame.
273. Cement for Iron Flues.—Common salt and sifted wood-ashes in equal parts, made into a paste with water, is a very good cement for iron flues, and may be applied when the flue is hot or cold. Iron filings and vinegar will do almost as well, or rather iron filings moistened with diluted muriatic acid. These are generally used for filling up the space between cylinders.
274. Preparation of common Cement for joining Alabaster, Marble, Porphyry, or other Stones.—Take of bees'-wax two pounds, and of rosin one pound; melt them, and add one pound and a half of the same kind of matter, (powdered,) as the body to be cemented is composed of, strewing it into the melted mixture, and stirring them well together, and afterwards kneading the mass in water, that the powder may be thoroughly incorporated with wax and rosin. The proportion of the powdered matter may be varied, where required, in order to bring the cement nearer to the color of the body on which it is employed.
This cement must be heated when applied; as must also the parts of the subject to be cemented together; and care must be taken likewise, that they be thoroughly dry.
When this composition is properly managed, it forms an extremely strong cement, which will even suspend a projecting body of considerable weight, after it is thoroughly dry and set, and is therefore of great use to all carvers in stone, or others who may have occasion to join together the parts of bodies of this nature.
Melted sulphur, applied to fragments of stones previously heated (by placing them before a fire) to at least the melting point of sulphur, and then joined with the sulphur between, makes a pretty firm and durable joining.