Next to iron, brass is probably the most generally useful metal, and as the varieties of this alloy are almost infinite, the range of purposes to which it may be applied is very great. The color of the alloy inclines to red when the proportion of zinc is small, gradually changing to yellow, and ultimately white, when the proportion of zinc is very large. The ductility and malleability of the alloy increase with the quantity of copper. Ordinary brass may be hammered, rolled into sheets or drawn to wire while cold, provided it is occasionally annealed by heating it to a very low red heat. When worked hot it crumbles to pieces tinder the hammer or between the rolls. But the so-called yellow metal, or Muntz metal, an alloy of 40 parts of zinc and 60 of copper, may be wrought while red hot, rolled into sheets and forged into bolts. Brass is not so readily oxidized as copper, being harder, tougher, more easily fusible and more fluid when molten. It solidifies without becoming honey-combed, and hence is suited for making all kinds of castings; while simply by the addition of from 1 to 2 per cent, of lead, it is capable of being readily worked on the lathe, and may then be filed without, as it otherwise does, clogging the teeth of the file.
The article having been brought to proper shape by means of the lathe, file, grindstone or other means, the surface must be rendered smooth and free from lumps, utters, or scratches. If finished in the lathe, emery paper and oil may be used to smooth the surface, the final polish being imparted by rouge. In all cases where brass or other metals are polished by means of abrasive materials, great care must be taken that all cornel's are left sharp and well-defined, since nothing looks so badly as a corner which ought to be square but which is worn and rounded in the process of polishing.
In finishing brass work (and the same remark applies to the polishing of other materials) great care must be taken to avoid making any scratches which are deeper than the other marks left by the material employed. Such scratches are very difficult to remove by very fine files or by polishing powders, and therefore, whenever the work shows such scratches it is necessary to go back to the coarse file or scraper and begin anew. (See articles on Polishing Metals and Polishing Powders.)
To prevent the everyday rusting of brass goods, the trade has long resorted to means for protecting the surface from the action of the atmosphere, the first plan of which is to force a change to take place. Thus, if brass is left in damp sand, it acquires a beautiful brown color, which, when polished with a dry brush, remains permanent and requires no cleaning. It is also possible to impart a green and light coating of verdigris on the surface of the brass by means of dilute acids, allowed to dry spon taneously. The antique appearance thus given is very pleasing, and more or less permanent. But it is not always possible to wait for goods so long as such processes require, and hence more speedy methods became necessary, many of which had to be further protected by a coat of varnish. Before bronzing, however, all the requisite fitting is finished, and the brass annealed, pickled in old or dilute nitric acid, till the scales can be removed from the surface, scoured with sand and water, and dried. Bronzing is then performed according to the color desired; for although the word means a brown color, being taken from the Italian " bronzino," signifying burnt brown, yet in commercial language it includes all colors. (See article on Bronzing.)
Browns of all shades are obtained by immersion in solutions of nitrate or the perchloride of iron; the strength of the solutions determining the depth of the color. Violets are produced by dipping in a solution of chloride of antimony. Chocolate is obtained by burning on the surface of the brass moist red oxide of iron, and polishing with a very small quantity of blacklead.
Olive-green results from making the surface black by means of a solution of iron and arsenic in muriatic acid, the details of the process being as follows:
Make the articles bright, then dip in aqua fortis, which must be thoroughly rinsed off with clean water. Then make the following mixture: Hydrochloric acid, 6 lbs.; sulphate of iron, 1/2 lb.; white arsenic, 1/2 lb. Be careful to get all the ingredients pure. Let the articles lie in the mixture till black; take out and dry in hot sawdust, polish with blacklead, and lacquer with green lacquer composed of one part lac varnish, four of turmeric, and one of gamboge.
A steel-gray color is deposited on brass from a dilute boiling solution of chloride of arsenic; and a blue by careful treatment with strong hyposulphite of soda.
Black is much used for optical brass work, and is obtained by coating the brass with a solution of platinum, or with chloride of gold mixed with nitrate of tin. The Japanese bronze their brass by boiling it in a solution of sulphate of copper, alum and verdigris.
Success in the art of bronzing greatly depends on circumstances, such as the temperature of the alloy or of the solution, the proportions of the metals used in forming the alloy and the quality of the materials. The moment at which to withdraw the goods, the drying of them, and a hundred little items of care and manipulation, require attention which experience alone can impart.
To avoid giving any artificial color to brass, and yet to preserve it from becoming tarnished, it is usual to cover properly cleaned brass with a varnish called "lacquer." Tc prepare the brass for this, the goods, after being annealed, pickled, scoured and washed, as already explained, are either dipped for an instant in pure commercial nitrous acid, washed in clean water, and dried in sawdust, or immersed in a mixture of one part of nitric acid with four of water, till a white curd covers the surface, at which moment the goods are withdrawn, washed in clean water, and dried in sawdust. In the first case the brass will be bright; in the latter, a dead flat which is usually relieved by burnishing the prominent parts. Then the goods are dipped for an instant in commercial nitric acid, and well washed in water containing some argol (to preserve the color till lacquered), and dried in warm sawdust. So prepared, the goods are conveyed to the lacquer room, where they are heated on a hot plate and varnished.
The varnish used is one of spirit, consisting, in its simple form, of one ounce of shellac dissolved in one pint of alcohol. To this simple varnish are added such coloring substances as red sanders, dragon's-blood, and annatto, for imparting richness of color. To lower the tone of color, turmeric, gambogo, saffron, Cape aloes, and sandarac are used. The first group reddens, the second yellows the varnish, while a mixture of the two gives a pleasing orange. (See article on Lacquer.)