BLO?
Today, "boiled linseed oil" refers to a combination of raw linseed oil, stand oil (see above), and metallic dryers (catalysts to accelerate drying).[19] In Medieval times, linseed oil was boiled with lead oxide[20] (litharge) to give a product called boiled linseed oil. The lead oxide forms lead "soaps" (lead oxide is alkaline) which promotes hardening (polymerisation) of linseed oil by reaction with atmospheric oxygen. Heating shortens its drying time