To give zinc a dark or light green coating dissolve 50 parts hydro-sulphite of sodium in 500 parts of boiling water and immediately pour the solution into 25 parts of sulphuric acid. This will cause the milk and sulphur to separate and then ball together in lumps and settle. The hot liquid containing sulphurous acid and sulphate of sodium is decanted, and in it the zinc, first cleansed, is placed. It will not be long before it will acquire a brilliant light-green coating, which only needs to be washed and dried. The longer the exposure of the zinc to this hot bath, the thicker the coating and the darker and more brilliant the color. It is essential, in order to insure a fine and brilliant deposit, that the temperature should not be allowed to fall below 145 degrees Fahrenheit. Dip the articles thus treated in hydro-chloric acid; dilute 1 part of acid to 3 of water and there is a consequent evaporation of sulphureted hydrogen, and this enamel-like coating loses its lustre and becomes lighter in color. This dull surface is not affected by the aqueous solutions of aniline colors. If you desire a brownish color for your article add 15 parts of chrome alum and 15 more of the hypo-sulphite to the above solution.