until it was hot enough to scorch a feather or melt a piece of tin (good thermometers or pyrometers were not to be had then as now). Such boiled oil sold then for six cents per gallon over the price of raw linseed oil, and it would be worth at least that difference to-day for some purposes if it could be had. We know of no one that sells it, but we know of some old painters who have their own kettles and cook it. Boiled oil of this kind is rich in luster and body (a kind of varnish).

The temperature of the boiling oil and the length of time the given temperature is sustained are important factors in the quality of the product. Oil boiled at 400°-450° differs from that at 575°-600°. The one cannot be substituted indiscriminately for the other with assurance of getting the results expected.