The late John C. Trautwine, who was one of our most experienced engineers, tells us that the best paints for preserving iron exposed to the weather, are prepared from the pulverized oxides of iron, such as yellow and red iron ochers, or brown hematite iron ores finely ground, and simply mixed with linseed-oil and a dryer. White lead, applied directly, requires incessant renewal; and, indeed, probably exerts a corrosive effect. It may, however, be applied over the more durable colors where appearance requires it. Red lead is said to be very durable when pure. An instance is recorded of pump-rods in a well 200 feet deep, near London, England, which having first been thus painted, were in use forty-five years, and at the expiration of that time their weight was found to be precisely the same as when new, showing that rust had not affected them. When the size of the exposed iron admits of it, Faraday suggests that its freedom from rusting may be promoted to a large extent by first heating it thoroughly, and then dipping it into or washing it with linseed-oil, which will then penetrate slightly into the iron. For tinned iron exposed to the weather on roofs, rain-pipes, etc., Spanish brown is a very durable color. The tin is frequently found perfectly bright and protected where this color has been used, after an exposure of forty or fifty years. Paint containing much white lead generally washes off in a few years by the action of rain.
Where the article is exposed to mechanical action, however, the addition of red lead generally improves the paint; and in some cases, such as carriage-irons, pure red lead is decidedly the best for a first coat. It may, when dry, be painted over and concealed by any other color. To secure the best results the red lead must be selected with great care, and mixed and applied properly. Pure red lead powder, after being slightly pressed down with the finger, shows no lead crystals. When they are visible it is merely partly converted, and not first quality. It should be ground in pure old linseed-oil, and if possible used up the same day to prevent it combining with the oil before it is applied, losing in quality. No drier is necessary, as in the course of a few days the oil forms a perfectly hard combination with the lead. American linseed-oil is as good as any imported, where the manufacturer has given it age, and not subjected it to heat, as is the custom, by steaming it in a cistern to qualify it quickly for the market. It deteriorates in quality when heated above 100 deg. Fah. This red lead paint spreads very easily over a surface, and the best of finish can be made with it, even by a novice in painting.