Drying oil is formed of linseed oil, prepared by the means of boiling, sometimes with the addition of other substances, and sometimes without. The substances added to oil, in this preparation, are very various; there being many different recipes in the hands of different persons; some of which prescribes a less number of ingredients, and others almost every kind. These substances are, white vitriol, sugar of lead, seed lac, gum mastic, gum sandarac, gum animi, gum copal, umber, colcothar, litharge, and red lead. But the first eight of these articles being dearer; when great quantities of drying oil are prepared for common purposes, they are usually omitted; and the others, or some of them, only employed: and indeed if the linseed oil be good, and boiled for a proper time even alone, it will have nearly the same properties, as if the most efficacious of these substances be added to it. I will, however, give two of the most approved recipes for preparing drying oil, with the addition of the usual ingredients. The one for the kind supposed proper for the more nice and delicate painting: the other for common work.,