Before giving special recipes under the separate metals, it will be well to quote the following paragraph having a general bearing on the subject.
Metals may be coloured quickly and cheaply by forming on their surface a coating of a thin film of a sulphide. In 5 minutes brass articles may be coated with any colour, varying from gold to copper-red, carmine, and dark red, and from light aniline blue to a blue-white, like sulphide of lead, and at last a reddish white, according to the thickness of the coat, which depends on the length of time the metal remains in the solution used. The colours possess a very good lustre, and if the articles to be coloured have been previously thoroughly cleaned by means of acids and alkalies, they adhere so firmly that they may be operated upon by the polishing steel. To prepare the solution, dissolve 1/2 oz. hyposulphite of soda in 1 lb. water, and add 1/2 oz. acetate of lead dissolved in £ lb. water. When this clear solution is heated to 190° to 200° F. (88°-93° C), it decomposes slowly, and precipitates sulphide of lead in brown flakes. If metal be now present, a part of the sulphide of lead is deposited thereon, and according to the thickness of the deposited sulphide of lead the above colours are produced. To produce an even colouring, the articles must be evenly heated.
Iron treated with this solution takes a steel-blue colour; zinc, a brown colour, in the case of copper objects, the first gold colour does not appear; lead and zinc are entirely indifferent. If, instead of the acetate of lead, an equal weight of sulphuric acid is added to the hyposulphite of soda, and the process carried on as before, the brass is covered with a very beautiful red, which is followed by a green (which is not in the first scale of coleurs mentioned above), and changes finally to a splendid brown with green and red iris glitter. This last is a very durable coating, and may find special attention in the manufactures, especially as some of the others are not very permanent. Very beautiful marble designs can be produced by using a lead solution thickened with gum tragacanth on brass which has been heated to 210° F. (99° C), and is afterwards treated by the usual solution of sulphide of lead. It may be used several times.