Boiled Linseed Oil: Linseed Oil Heated with Litharge

Raw linseed oil hardens in air, but slowly. Heated with a little litharge (lead oxide) it dries much faster; that is what painters and varnish makers called boiled oil. Sheridan Muspratt (1860) gives the measure: seven or eight per cent of litharge, heated until the oil turns reddish. The lead stays in the oil: never on food surfaces. The picture: "boiled" linseed oil ground with an earth pigment into linseed oil paint.