For coating with zinc large pieces that cannot conveniently be put in a bath: Mix powdered zinc with linseed oil and a dryer so as to make a kind of paint that can be applied with a brush. One coating will prevent oxidation, but two are advisable.
To coat cast-bronze goods use a lacquer consisting of shellac dissolved in alcohol with a little camphor added. Another good lacquer consists of 1 part shallac dissolved in 8 or 10 of alcohol, to which the addition is made of 1 to 4 parts of camphor, and rubbed up with a few drops of lavender.
To coat cast-iron a glossy black color that will stand washing and heat, take oil of turpentine and add to it strong sulpuric acid, drop by drop, while stirring, until a syrupy precipitate is formed and no more of it is produced on further addition of a drop of acid. The liquid is now repeatedly washed away with water, every time renewed after a good stirring, until the water does not exhibit any more acid reaction with blue litmus paper. The precipitate is next brought upon a cloth filter, and after all the water has run off the syrup is fit for use. This thickish deposit is painted over the iron with a brush; if it happens to be too stiff, it is previously diluted with some oil of turpentine. Immediately after the iron has been painted, the paint is burnt in by a gentle heat, and, after cooling, the black surface is rubbed over with a piece of linen stuff dipped and moistened with linseed oil.
One process of coating iron with copper consists of clipping the articles into a melted mixture of one pint of chloride or fluroide of copper and five or six parts of cryolite, and a little chloride of barium. If the article when immersed is connected with the negative pole of a battery it hastens the process.
Cobaltous chloride is obtained in blue crystalline scales by heating the metal in chloric acid.
Colcothar, otherwise known as sesqui oxide iron, is a by-product in the manufacture of sulphuric acid from the solution of ferrous sulphate.
To give copper a blue-black color dip it in a hot solution of 11 1/4 drachms of liver of sulphur in 1 quart of water, stirring same constantly but gently. If a blue-gray shade is desired the solution must be diluted more.
The method of coloring copper brown is as follows: As a corrosive, a liquid is used which is produced as follows: Ten portions by weight of spirits of ammonia mixed with an equal amount of vinegar, so that a piece of blue litmus paper dipped into it will be colored red, and to this mixture, which is acetate of ammonia, are to be added 5 parts of verdigris and 3 parts of ammonia. By means of this mixture large objects that you wish to color should, after being carefully cleaned of grease and rust, be painted with a soft brush and then left to dry in a warm room. By repeating this application with the brush, you can get the brown in any shade you like. Small objects should be boiled in the liquid, and during the boiling should be stirred with a tin or copper spoon. After securing the desired color they are to be washed in hot water and subsequently dried in sawdust.