PAINTING GALVANIZED IRON No more puzzling problem is set before the painter than that of painting galvanized iron work so that it will stay painted. Unless a pre paratory treatment is given, almost any ordi nary paint will sooner or later peel off. The cause of this is not exactly known; but the diffi culty is so generally recognized that in many cases galvanized iron is left unpainted until the action of the weather has caused it to rust, when the paint will cling to the surface. Unfortu nately, however, this is merely substituting one evil for another, because, when once rust sets in, it will go under the paint and will eventually destroy the iron.
Different methods of preparation have been recommended for galvanized iron, the object of all being to coat the surface with a thin film of gray oxide of zinc, to which the paint will firmly cling. Washing with a strong solution of com mon soda or with dilute muriatic acid has been suggested; but the best wash to use is prepared by dissolving two ounees of chloride of copper, two ounces of nitrate of copper, and two ounces of sal ammoniac in one gallon of water, and afterward adding two fluid ounces of crude hydrochloric acid. This solution must be made in a glass or earthenware vessel to prevent precipitation of the copper salts. After the galvanized iron has been coated with this solution, it will assume a black color, but, on drying over night, will turn a light gray.
Upon this surface a priming composed either of pure red lead or of mineral brown, thinned with equal parts of raw linseed oil and turpentine, or a priming composed of half mineral brown and half red lead, ground together dry and mixed by hand with equal parts of raw linseed oil and turpentine, will form a basis upon which any oil paint may be successfully applied.
Venetian red has also been recommended as a priming coat for galvanized iron, after the pre liminary wash has been applied; but no matter whether this or the less expensive mineral brown is used, care should be taken in the selection of any oxide of iron paint for coating ironwork of any kind, to see that it is free from sulphur. Mineral brown is made from a native iron ore which is roasted and changed into peroxide of iron. It was formerly put on the market under the name of metallic paint, but this name has also been given to many inferior paints made from the refuse left after the manufacture of sulphuric acid from iron pyrites. Such paints contain a considerable percentage of sulphur and are positively injurious to iron or tin, since the action of the rain or moisture will convert the sulphur into sulphuric acid, which is a powerful corrosive agent.