Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/250

242 water; 1 pound litharge in fine powder is then added, and the mixture is gently simmered until only a whitish sediment remains; 1 pound of levigated litharge is next diffused through $2 1/2$ gallons of linseed oil, and the mixture is gradually added to the lead solution previously diluted with an equal bulk of water; the whole is now stirred together for some hours with heat and is lastly left to clear itself by exposure in a warm place. The lead solution which subsides from the oil may be used again for the same purpose by dissolving in it another pound of litharge as before.

Into linseed oil, 236 gallons, pour oil of vitriol 6 or 7 pounds, and stir the two together for three hours, then add a mixture of fuller's earth 6 pounds, and hot lime 14 pounds, and again stir for three hours. Next, put the whole into a copper, with an equal quantity of water, and boil for about three hours; lastly, withdraw the fire, and, when the whole is cold, draw off the water, run the oil into any suitable vessel, and let it stand for a few weeks before using.

Pale Drying Oil. The oil should be macerated two or three days at least upon about an eighth of its weight of litharge, in a warm place, occasionally shaking the mixture, after which it should be left to settle and clear; or it may be prepared, without heat, by levigating the litharge in the oil. Acetate of lead may be substituted for litharge, being soluble with less heat, and its acid, being volatile, escapes during solution and bleaches the oil, to which coarse smalt may be added to clear it by subsidence, increase its drying and neutralize its brown dolor. This affords pale drying oil for light and bright colors.

Boiled Oil. The above mixture of oil and litharge, gently and carefully boiled in an open vessel till it thickens, becomes strong drying oil for dark colors. Boiled oil is sometimes set on fire purposely, in making printer's