For frosting small brass-work, fasten a circular scratch-brush, made of very fine brass wire, on the lathe, and having previously scoured the brass with strong pearlash lye, hold the work against the revolving brush, which must be driven at a good speed.
Holtzapffel introduced the following style of ornamenting flat surfaces:-The work (after being filed, scraped, and passed over with Water-of-Ayr stone) is clouded with a piece of charcoal and water, by means of which the entire surface is covered with large curly marks, which form the ground. The curls resemble an irregular cycloid pattern, with loops of 1/4 in. to 1 in. in diameter, according to the magnitude of the work. Similar but smaller marks are then made with a piece of snake-stone, bluestone, or even a common slate pencil, filed to a blunt point. The general effect of the work much depends on the entire surface being uniformly covered; with which view the curls should be first continued round the margin; the central parts are then regularly filled in; after which the work is ready to be varnished.
Brass which is required for rolling into sheets should contain no antimony, as this metal renders the alloy very brittle, and extremely liable to crack. That which has to be turned contains invariably a small proportion of lead, usually about 2 per cent.; this addition is made when the crucible containing the fused metals is taken out of the furnace. The following is an analysis of a brass which is well adapted for this purpose:-Copper, 65.8; zinc, 31.8; lead, 2.15; tin, 0*25. The presence of tin was believed to be accidental. Brass required for engraving upon should always contain a little tin, in order to render it sufficiently firm. Brass laminates well in the rolling mill cold, as long as it is kept sufficiently soft; but as by lamination the metal hardens and becomes brittle, it is necessary to restore its tenacity by annealing in an oven or reverberatory furnace. The same process of annealing is necessary in the manufacture of brass wire, which is obtained by drawing it through holes in steel plates, polished carefully and adjusted in series, graduated in size, so as not to diminish too rapidly, and thus render it necessary to employ so much power for drawing as would cause the breaking of the wire.
Brass is not usually so prepared as to admit of its being hammered out, as is done in the manufacture of copper utensils; but a brass-foil or Dutch metal, of the colour and approaching the thinness of gold-leaf, is manufactured by beating out thin sheets of brass with hammers worked by water-power, making 300 or 400 strokes per minute.
Brass may be made either in a crucible, as in the ordinary Birmingham brass-foundries, or in a reverberatory furnace. The crucibles commonly used are circular, and made of fireclay; they are about 1 ft. deep, 8 in. diameter at the top, and 6 in. at the middle, internal measurements; they are also f in. thick at the top, and 2 in. at the bottom; they contain about 84 lb.
The copper is first placed in the crucible, and the zinc is added to it bit by bit with much caution, as soon as the former metal is in a state of incipient fusion. The ingots of copper should be heated to redness before being put into the crucible. In Birmingham, the chief seat of the brass manufacture, the furnaces employed are square, their dimensions being 10 in. in the side and 24 in. in depth. Those used in London are circular in form. The fine between the furnace and the chimney should be narrow, and should lead out from the top of the furnace; its dimensions vary with those of the chimney, and with other conditions. Coke of the very best quality is the fuel employed. When the mixture is well fused together, the cinders are removed, and it is poured, if required for casting, into sand-moulds; if, on the contrary, it is to be used for rolling, it is cooled in close iron ingot-moulds, previously heated, oiled, and dusted lightly over in the interior with powdered charcoal. A loss of zinc invariably occurs by volatilization, which is always taken into consideration when weighing out the metal.
For button brass, an alloy of 8 parts of copper and 5 of zinc is commonly used by the Birmingham makers, under the name of " platin." An alloy paler in colour, and used for the common buttons, consists of 25 of copper, 20 of zinc, 3 of lead, and 2 of tin.
For fine brass, an alloy of 2 parts of copper with 1 of zinc is the correct proportion; the metals are melted separately, poured suddenly together, and united by vigorous stirring. By raising the proportion of copper to 7 parts of copper and 3 of zinc, a bright-yellow and malleable alloy is obtained; 4 of copper and 1 of zinc yields a metal of darker colour than the last.
Brass for fine castings is an alloy of 62 parts of copper, 35 of zinc, 2 of lead, and 1 of tin; this is rather pale and brittle. An alloy used for the same purpose, and of a deep, rich colour, consists of 90 copper, 7 zinc, 2 tin, 1 lead.
For gilding, good proportions are: 64 parts copper, 32 zinc, 3 lead, 1 tin.
For malleable brass, good proportions are: 33 parts copper, 25 zinc, or, 3 copper and 2 zinc. These are malleable when hot.
For soldering, an alloy of 12 parts fine brass, 6 zinc, 1 tin, melted together, is most commonly employed.
For turning, the proportions are: 98 parts fine brass, 2 lead, both melted together; or, 65 copper, 33 zinc, 2 lead.
For wire, an alloy of 72 parts copper, 28 zinc, is commonly used; this alloy must be afterwards hardened by tempering.
John C. Bull has succeeded in producing a new copper-zinc alloy which exhibits characteristics essentially superior to ordinary brass. The advantages claimed for the new alloy, which has been named " Bull's metal" are great strength and toughness, and a capacity for being rolled, forged, and drawn. It can be made as hard as mild steel, and when melted is very liquid, producing sound castings of close fine grain. The colour can be varied from that of yellow brass to rich gun-metal; the surface takes a fine polish, and, when exposed to the air, tarnishes less than brass. These latter characteristics will meet with ready appreciation for cabinetwork, harness fitting, etc. The metal when cast in sand has a breaking strain of 21 to 22 tons per sq. in.; when rolled or forged hot into rods, the breaking strain is 43 tons per sq. in.; and when drawn into wire of 22 B.W.G., of 67 tons per sq. in.