Linseed oil dries too slowly for general use by the painter, hence various ways have been devised to hasten the drying process. If the foregoing theory is correct, the process which will cause the oil to dry to a good wearing body in the time desired, and leave it in the best condition to resist the action of the elements and the absorption of oxygen, is the best. I regard the lead oxides as the best dryers for this purpose—at least according to my experience. When we add an oxide to linseed oil as a dryer in the small quantity which experience has taught us is best to use, it is evident that it is not sufficient in itself to oxidize the whole of the oil to an appreciable extent. Writers differ as to the peculiar action of the oxides upon the oil, but I think it safe to say that the dryer sets up some chemical reaction which increases the affinity between the linolein and the oxygen of the atmosphere; at any rate, there is no dispute upon the point that linseed oil in drying absorbs a large per cent. of oxygen.
A knowledge of this unanimously conceded point led me to believe that a coat of pure linseed oil might make the best possible priming coat for iron work which had commenced to rust. Why? Because iron rust is an oxide of iron, having an excess of oxygen. Spread on rusty iron, it penetrates the rust, absorbs its excess of oxygen and dries with the remaining neutral oxide held fast in its body. This is my theory; whether correct or not, numerous tests have proved to me that a coat of linseed oil will stop the rusting of iron if applied under proper conditions. When rust is thick or scaling there is no safety short of taking it off. Iron rust is more or less hydrated; to free it from moisture, give it the flame of the gasoline paint burner.
WHITE ENAMEL (SELECTED).
First, the wood is primed with a composition consisting of three parts of turpentine and one part of oil, japan gold size being used as a dryer. On this drying thoroughly the work is rubbed down until perfectly smooth. Next are applied two or three coats of pure white lead mixed entirely flat; each coat is rubbed down, time being allowed for it to dry. Equal parts of lead and zinc are used for the next coat, and three-fourths zinc and one-fourth lead for the one succeeding. After this has become thoroughly hard it is rubbed down very smooth. A thin coat of color made of zinc and turpentine is now rubbed on; for the next coat the same flat color is used, with the addition of about one-half the quantity of good light coach varnish. For the last coat enough zinc is used in the varnish to make it white if the last coat of zinc is not white and solid before varnishing. If the work is to be gilded or striped the zinc must be left out of the last coat of varnish.
VARNISH TO IMITATE GROUND GLASS.
An expert has sent the following to the British Journal of Photography: To make a varnish to imitate ground glass, dissolve 90 grains sandrac and 20 grains of mastic in 2 ounces of washed methylated ether, and add, in small quantities, a sufficiency of benzine to make it dry with a suitable grain—too little making the varnish too transparent, and excess making it crapy. The quantity of benzine required depends upon its quality—from half an ounce to an ounce and a half, or even more; but the best results are got with a medium quality. It is important to use washed ether, free from spirit.
VARNISH FOR RUSTIC WORK.
One quart of boiled linseed oil and two ounces of asphaltum, to be boiled on a slow fire until the asphaltum is dissolved, being kept stirred to prevent its boiling over. This gives a fine dark color, is not sticky, and looks well for a year; or, first wash the article with soap and water, and when dry, on a sunny day do it over with common boiled linseed oil; leave that to dry a day or two, then varnish it over once or twice with hard varnish. If well done this will last for years and prevent annoyance from insects.