The above mixture of oil and litharge, gently and carefully boiled in an open vessel till it thicken, becomes strong drying oil for dark colours. Boiled oil is sometimes set on fire purposely in the making of printers' varnish and printing Ink, and also for painting and the preparation of Japanners' gold size. As dark and transparent colours are in general comparatively ill driers, japanners' gold size is sometimes employed as a powerful means of drying them. This material is very variously and fancifully prepared, often with needless, if not pernicious ingredients; but may be simply, and to every useful purpose in painting, prepared as follows:- Powder finely of asphaltum, litharge or red lead, and burnt umber, or manganese, each one ounce; stir them into a pint of linseed oil, and simmer the mixture over a gentle fire, or on a sand-bath, till solution has taken place, scum ceases to rise, and the fluid thickens on cooling; carefully guarding it from taking fire. If the oil employed be at all acid or rancid, talc, powdered, or a small portion of chalk or magnesia, may be usefully added, and will assist the rising of the scum and the clearing of the oil, by its subsidence; and if it be kept at rest in a warm place, it will clear itself: or it may be strained through a cloth and diluted with turpentine for use. Gold size for gilding is commonly made of boiled oil and fine Oxford ochre.,,