Deposit Of A Metal Or Of A Non-oxidizable Compound.
Black.—I.—Make a paste composed of equal parts of chloride of antimony and linseed oil. Spread on the object, previously heated, with a brush or rag; then pass over it a coating of wax and brush it. Finally varnish with gum lac.
II.—Prepare a solution of bismuth chloride, 10 parts; mercury chloride, 20 parts; cupric chloride, 10 parts; hydrochloric acid, 60 parts; alcohol, 50 parts; water, 500 parts. Add fuchsine in sufficient quantity to mask the color.
The mercury chloride is poured into the hydrochloric acid, and the bismuth chloride and cupric chloride added; then the alcohol. Employ this mixture with a brush or a rag for smearing the object. The object may also be immersed in the liquid if it is well cleaned and free from grease. It is dried and afterwards submitted to boiling water for half an hour. The operation is repeated until the wished-for tint is obtained; then the object is passed into the oil bath and taken to the fire without wiping. The object may also be placed for 10 minutes in boiling linseed oil.
Brown Tint.—A solution is made of chloride of mercury, 20 parts; cupric chloride, 10 parts; hydrochloric acid, 60 parts; alcohol, 50 parts; water, 500 parts. The object is plunged into this solution after being well cleaned. The solution may also be applied with a brush, giving two coats. It is afterwards put into hot water. The surface of the object is covered with a uniform layer of vegetable oil. It is placed in a furnace at a high temperature, but not sufficient for carbonizing the oil. The iron is covered with a thin layer of brown oxide, which adheres strongly to the metal, and which can be beautifully burnished, producing the appearance of bronze.
Brilliant Black.—The process begins by depositing on the object, perfectly clean and free from grease, a layer of metallic copper. For this purpose the following solutions are prepared: (a) Cupric sulphate, 1 part; water, 16 parts. Add ammonia until complete dissolution. (b) Chloride of tin, 1 part; water, 2 parts; and chlorhydric acid, 2 parts. The object is immersed in solution b, and afterwards in solution a. In this way there is deposited on the iron a very adherent coating of copper. The object, washed with water, is afterwards rubbed with sulphur, or immersed in a solution of ammonium sulphhydrate. A dull black coating of cupric sulphide is produced, which becomes a brilliant black by burnishing.
Blue Black.—The iron object is first heated according to the previous recipe, but the copper is converted into cupric sulphide, not by a sulphhydrate, but by a hyposulphite. It is sufficient to dip the coppered object into a solution of sodium hyposulphite, acidulated with chlorhydric acid, and raised to the temperature of 175° to 195° F.
Thus a blue-black coating is obtained, unchangeable in air and in water. After polishing, it has the color of blue steel. It adheres strongly enough to resist the action of the scratch brush.
Deposition of Molybdenum.—Iron is preserved from rust by covering it with a coating of molybdenum, as follows: Water, 1,000 parts; ammonium molybdate, 1 part; ammonium nitrate, 15 to 20 parts. Suspend the object at the negative pole of a battery. The current ought to have a strength of 2 to 5 amperes per cubic decimeter.
Deposit of Manganese Peroxide.—The {473} iron or steel is first covered with a coating of manganese peroxide by immersing as an anode in a bath containing about 0.05 per cent of chloride or sulphate of manganese and from 5 to 25 per cent of ammonium nitrate. The bath is electrolyzed cold, making use of a cathode of charcoal. Feeble currents (1 or 2 amperes) produce an adherent and unchangeable deposit.