(1) An orange tint inclining to gold is produced by first polishing the brass and then plunging it for a few seconds in a warm neutral solution of crystallized acetate of copper. Dipping into a bath of copper, the resulting tint is a greyish green; while a beautiful violet is obtained by immersing the metal for an instant in a solution of chloride of antimony and rubbing it with a stick covered with cotton. During this operation the brass should be heated to a degree just tolerable to the touch. A moire appearance, vastly superior to that usually seen, is produced by boiling the object in a solution of sulphate of copper. There are three methods of procuring a black lacquer on the surface of brass. The first, which is often employed by instrument-makers, consists in polishing the object with tripoli, and washing it with a mixture composed of 1 part nitrate of tin, 2 parts chloride of gold. Allow this wash to remain for fifteen minutes, then wipe it off with a linen cloth. An excess of acid increases the intensity of the tint. In the second method, copper turnings are dissolved in nitric acid until the latter is saturated; the objects are immersed in the solution, cleaned, and subsequently heated moderately over a charcoal fire.
This process must be repeated in order to produce a black colour, as the first trial only gives a dark green. Finally, polish with olive-oil. The third method is done with chloride of platinum. In the United States and on the Continent much pains is taken to give objects " an English look." For this purpose they are first heated to redness, and then dipped in a weak solution of sulphuric acid. Afterwards they are immersed in dilute nitric acid, thoroughly washed in water, and dried in sawdust. To effect a uniformity in the colour, they are plunged in a bath consisting of 2 parts nitric acid and 1 rain-water, where they are suffered to remain for several minutes. Should the colour not be free from spots and patches, the operations must be repeated until the desired effect is produced. (Eng. Mechan.)
(2) Copper or brass may be bronzed in various modes. The repeated applications of alternate washes of dilute acetic acid and exposure to the fumes of ammonia will give a very antique-looking green bronze; but a quick mode of producing a similar appearance is often desirable. To this end the articles may be immersed in a solution of 1 part perchloride of iron in 2 of water. The tone assumed darkens with the length of immersion. Or the articles may be boiled in a strong solution of nitrate of copper. Or lastly, they may be immersed in a solution of 2 oz. nitrate of iron and 2 oz. hyposulphite of soda in a pint of water. Washing, drying, and brushing complete the process.
(3) To prevent the every-day 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 colour, 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 spontaneously. 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 coating 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 colour desired; for although the word means a brown colour, being taken from the Italian bronzino, signifying burnt brown, yet in commercial language it includes all colours.
Browns of all shades are obtained by immersion in solutions of nitrate or perchloride of iron; the strength of the solutions determining the depth of colour. Violets are produced by dipping in a solution of chloride of antimony or of permuriate of iron. 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, polishing with a blacklead brush, and coating it, when warm, with a lacquer composed of 1 part lac-varnish, 4 of turmeric, and 1 of gamboge. A steel-grey colour is deposited on brass from a dilute boiling solution of muriate of arsenic; and a blue by careful treatment with strong hydrosulphite 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. (Eng, Mcchan.)
(4) The best means for producing a black surface on brass, pinchbeck, or silver, is said to be platinum chloride, which is allowed to liquefy by exposure to the air. It is rubbed in with the finger, or, best, with the ball of the thumb. After blacking, the object is washed and polished with oil and leather. Platinum chloride is dear, but a little of it will do a great deal of work.
(5) Ordinary gas-fittings are pickled; but if you want to get a good bronze you can use either a solution of nitrate of silver or bi-chloride of platinum. The articles will require blackleading after being bronzed, and should be warmed before being dipped into the bronzing solution.
(6) A solution of nitro-muriate of platinum will blacken brass quicker than anything else; but possibly 2 oz. corrosive sublimate dissolved in 1 qt. of vinegar will act quickly enough. This solution is brushed over the brass, allowed to remain till the latter is black; it is then wiped off, and the brass cleaned and blackleaded.
(7) A very good black varnish may be made by mixing a small quantity of pure lampblack with rather thick brass lacquer, using as little lampblack as possible. Another varnish may be made by fusing 3 lb. asphaltum, and when melted add 1/2 lb. shellac and 1 gal. oil of turpentine.
(9) Make a strong solution of nitrate of silver in one dish, and of nitrate of copper in another. Mix the two together, and plunge the brass into the mixture. Remove and heat the brass evenly until the required degree of dead blackness is obtained.
(11) Wash the brasswork with roach alum dissolved by boiling in strong lye in the proportion of 1 oz. alum to 1 pint lye, and when dry rub with fine tripoli. Either of these processes will give to brass the appearance and brilliancy of gold.