Small articles of brass or copper may be whitened by boiling them in a solution of 3/4 lb. cream of tartar, 2 quarts of water, and 1 lb. grain tin or any pure tin finely divided. The tin dissolves in the cream of tartar and is again precipitated on the brass or copper.
The first step is to thoroughly cleanse the articles, either by means of emery, or by laying them overnight in a weak bath of sulphuric acid. They are then washed off with water, a weak soda solution, and then immersed as the cathode of a bath consisting of 2 1/2 parts of sulphate of copper, 20 parts sulphate of zinc, and 46 parts cyanide of potassium, in 300 parts of water. The anode should be two plates of zinc and copper of equal size. The color of the resulting brass coating may be modified by varying the depth of immersion of one or the other of the plates. The galvanic current should be a strong one, and the liberation of hydrogen bubbles on the object to be brassed should be plentiful. It is important, however, to note that the objects should be first coppered to insure a strong attachment of the brass coating.
The following valuable process for coating brass with copper, is given by Dr. C. Puscher: Dissolve ten parts, by weight, of sulphate of copper, and five of sal-ammoniac, in one hundred and fifty parts, by weight, of water. Place the brass, well cleaned and free from fatty matter on its surface, into this mixture; leave it in it for a minute; let the excess of liquid drain off first, and heat the metal next over a charcoal fire, untd the evolution of am-moniacal vapors ceases, and the coppery film appears perfect. Wash with cold water and dry. The coating of copper adheres firmly.
Large articles of brass and copper which have become very much soiled may be cleaned by a mixture of rotten-stone powder (or any sharp polishing powder) with a strong solution of oxalic acid. After being thoroughly cleaned, the metal should be wiped off with a cloth moistened with soda or potash, and a very light coating of oil should be applied to prevent the further corroding action of the acid.
A more powerful cleaning agent, because very corrosive, is finely powdered bichromate of potash mixed with twice its bulk of strong sulphuric acid and diluted (after standing an hour or so) with an equal bulk of water. This will instantly clean the dirtiest brass, but great care must be taken in handling the liquid, as it is very corrosive.
Brass which has been lacquered should never be cleaned with polishing powders or corrosive chemicals. Wiping with a soft cloth is sufficient, and in some cases washing with weak soap and water may be admissible. Dry the articles thoroughly, taking care not to scratch them, and if, after this, they show much sign of wear or corrosion, send them to the lacquerer to be refinished.