BRASS, in the glass trade.—Thrice-calced brafs 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 brafs on tiles on the leet of the furnace near the oechis; let it stand to be calced 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 calced 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 calced; 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.
Brafs, by long calcination alone, and without any mixture, affords a fine blue or green colour for glass; but they have a method of calcing it also with powdered brimstone, so as to make it afford a red, a yellow, or a chaledony colour, according to the quantity and other variations in the using it. The method of making the calcination is this: Cut thin plates of brafs into small pieces with sheers, 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 brafs, 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 brafs into the arches of the glass furnaces, and leave them there till they are sufficiently calced, which the heat in that place, not being enough to melt
them, does in great perfection. The calced matter powdered, is of a dusky red, and requires no farther preparation.