Manufacturer and builder 5, 1869
A difficulty is often experienced in causing oil-colors to adhere to sheet zinc. Boettger recommends the employment of a mordant, so to speak, of the following composition: one part of chloride of copper, one of nitrate of copper, and one of sal-ammoniac are to be dissolved in sixty-four parts of water, to which solution is to be added one part of commercial hydro-chloric acid. The sheets of zinc are to be brushed over with this liquid, which gives them a deep black color; in the course of from twelve to twenty-four hours they become dry, and to their now dirty gray surface a coat of any oil-color will firmly adhere. Some sheets of zinc prepared in this way and afterwards painted have been found to entirely withstand all the atmospheric changes of winter and summer.