Page:Landscape Painting by Birge Harrison.djvu/161

PIGMENTS others of which I do not know. To ensure entire safety and durability, nothing but pure linseed oil should be mixed with the colors; all cracking, gumming, etc., being due to inequalities in the drying period of the different mediums used on our canvas. If anything at all is mixed with the oil, the safest and best thing in the world is certainly pure Venice turpentine. If kerosene is used, it should be carefully washed to eliminate all of the acid which is used in refining the crude oil. Otherwise this free acid will attack the lead and discolor it.

In regard to varnishing, the important thing is to allow the picture to dry thoroughly before the varnish is applied. Six months is none too much for this, and a year is far better. A picture varnished before the oil is hard-dry is certain to crack sooner or later, as the [121]