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 oecchis; 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 nine, and recalcine it four or five days more; it will not then stick together, but remain a loose powder, of a ruffet 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.