Coloring and Polishing Brass.

Manufacturer and builder ?, 1891

In order to prevent the constant oxidizing of brass articles, agents have for a long time been experimented with to protect the surface of these articles against the influence of the atmosphere, and the following method has been proposed as the most suitable and practicable one:

If brass is left for some time in moist sand, it assumes a very handsome brown color, which, if polished with a dry brush, remains constant, and requite so cleaning or polishing. A darker or lighter green color may also be imparted if a thin layer of verdigris is created upon the surface by means of diluted acids, which aro to be left on until dry. The antique appearance imparted to the brass in this manner is very handsome, and more or less durable. But it is not always possible, for want of time, to do thin with each article, and a more rapid method for effecting the ends is therefore necessary, and the simplest way to do it is to cover the brass with a coating of varnish.

All the necessary work is to be done before the bronzing, and the brass annealed, dipped in old or dilute nitric acid until the scales cats be loosened from the surface, which is then treated with sand sand water, and dried. The next step is to produce the desired bronze. Although this word actually signifies a brown color, being derived from the Italian word bronzine, or, in English, "burned brown," it is rather loosely applied in the trades at present, and applied to all colors.

Brown of all shades is produced by immersion in a solution of nitride or chloride of iron, whereby the strengths of the bath determines the depth of the color.

Olive green, if the surface is blackened by means of a solution of iron and arsenic in muriatic acid: it is then polished with a plumbago brush, amd, when warm, coated with a lacquer composed of 1 part of varnish lacquer, 4 parts of turmeric, and 1 purt of gamboge.

A steel-gray color is precipitated upon brass by means of a weak boiling solution of arsenic chloride, and a blue by an attentive treatment with a strong sulphide of soda.

Black is much used for optical instruments, and is produced by painting with a platinum solution, or with chloride of gold mixed with nitrate of tin. The Japanese bronze their brass by boiling it in a whisker of sulphate of copper, alum and verdigris.

The success in the art of bronzing chiefly depends upon circumstances; for instance, the temperature of the alloy or solution, the proportions and qualities of the material used for alloying, the proper moment at which the article is to be withdrawn, and a hundred other minutiæ of attention and manipulation require a skill only taught by experience.

If the brass is to receive no artificial color, but simply to be protected against tarnishing and oxidizing, it is to be lacquered after having been thoroughly cleansed. In order to prepare the brass for this coating, it must be dipped after having been annealed, and, as aforesaid, rinsed maul washed, dipped either for a moment in pure commercial nitric acid and water, until covered with a white coating of the appearance of curdled milk, when the article is taken out, rinsed its clean water, and dried in sawdust.

Its the first case the brass becomes lustrous; in the latter it becomes mat, which is generally improved by smoothing and polishing the prominent places. The article is then dipped for a moment in nitric acid as found in commerce, and containing a little crude cream of tartar in order to preserve the color up to the moment of lacquering, and finally dried in warm sawdust. When prepared in such is manner, the article is taken in hand to be lacquered, for which purpose it is first to be heated upon a hot plate, to be laquered afterward. For this purpose is used is simple alcohol varnish, consisting of one ounce of shellac dissolved in one pint of alcohol. To this simple varnish are to be added the coloring substances, such as sanderswood, dragon's-blood, and annatto, which increases the luster of the color. In order to modify the shading of color, turmeric, gamboge, saffron, Cape aloes, and gum in sandarac are added. The first colors make the lacquer reddish, the second yellowish; while the two, when mixed, give a nice orange.

A good pale lacquer consists of 3 parts aloes and 1 part turmeric to 1 part of simple varnish. A gold lacquer is obtained by adding 4 parts dragon's-blood and 1 part turmeric to 1 part of simple varnish; while a red lacquer is produced from 32 parts annatto and 8 parts dragon's-blood to 1 part of the varnish.

Lacquers are subject to chemical change by heat and light, und must therefore be kept in a dark place. The vessels in which they arc stored are generally of glass or clay, and the brushes with which they are applied must be camel's hair, and have no metallie parts about them.

Ei kommentteja :