BRASS, in the glass trade.—Thrice calcined brass is a preparation which serves the glassmen to give many very beautiful colours to their metal. The manner of preparing it is this: Place thin plates of brass on tiles on the leet of the furnace near the oechis; let it stand to be calcined there for four days, and it will become a black powder sticking together in lumps. Powder this, sift it fine, and recalcine it four or five days more; it will not then stick together, but remain a loose powder, of a russet colour. This is to be calcined a third time in the same manner; but great care must be taken in the third calcination, that it be not overdone nor underdone; the way to be certain when it is right is, to try it several times in glass while melting. If it makes it, when well purified, to swell, boil, and rise, it is properly calcined; if not, it requires longer time. This makes, according to the different proportions in which it is used, a sea-green, an emerald-green, or a turquoise colour.
Brass, by long calcination alone, and without any mixture, affords a fine blue or green colour for glass; but they have a method of calcining it also with powdered brimstone, so as to make it afford a red, a yellow, or a chalcedony colour, according to the quantity and other variations in the using it. The method of making the calcination is this: Cut thin plates of brass into small pieces with shears, and lay them stratum super stratum, with alternate beds of powdered sulphur, in a crucible; calcine this for 24 hours in a strong fire; then powder and sift the whole; and finally expose this powder upon tiles for 12 days to a reverberating furnace; at the end of this time powder it fine, and keep it for use. The glass-makers have also a method of procuring a red powder from brass, by a more simple calcination, which serves them for many colours. The method of preparing it is this: They put small and thin plates of brass into the arches of the glass furnaces, and leave them there till they are sufficiently calcined, which the heat in that place, not being enough to melt them, does in great perfection. The calcined matter, powdered, is of a dusky red, and requires no farther preparation.
Brass-Colour, one prepared by the braziers and colour-men to imitate brass. There are two sorts of it; the red brass or bronze, and the yellow or gilt brass; the latter is made only of copper-filings, the smallest and brightest that can be found; with the former they mix some red ochre, finely pulverized; they are both used with varnish.—In order to make a fine brass that will not take any rust or verdigris, it must be dried with a chafing dish of coals as soon as it is applied.—The finest brass-colour is made with powder-brass imported from Germany, diluted into a varnish, made and used after the following manner: The varnish is composed of one pound four ounces of spirit of wine, two ounces of gum-lac, and two ounces of sandarac; these two last drugs are pulverized separately, and afterwards put to dissolve in spirit of wine, taking care to fill the bottle but half full. The varnish being made, you mix such quantity as you please of it with the pulverized brass, and apply it with a small brush to what you would brass over. But you must not mix too much at once, because the varnish being very apt to dry, you
would not have time to employ it all soon enough; it is therefore better to make the mixture at several times. After this manner they brass over figures of plaster, which look as well as if they were of cast brass.
Brass Leaf is made of copper, beaten out into very thin plates, and afterwards rendered yellow. The German artists, particularly those of Nuremberg and Augsburg, are said to possess the best method of giving to these thin plates of copper a fine yellow colour like gold, by simply exposing them to the fumes of zinc, without any real mixture of it with the metal. These plates are cut into little pieces, and then beaten out fine like leaves of gold; after which they are put into books of coarse paper, and sold at a low price for the vulgar kinds of gilding. The parings or shreds of these very thin yellow leaves being well ground on a marble plate, are reduced to a powder similar to gold; which serves to cover, by means of gum-water, or some other glutinous fluid, the surface of various mouldings or pieces of curious workmanship, giving them the appearance of real bronze, and even of fine gold, at a very trifling expence, because the gold colour of this metallic powder may be easily raised and improved by stirring it on a wide earthen bason over a slow fire.
Brass-Lumps, a common name given by miners to the globular pyrites. See PYRITES, MINERALOGY Index.