Boiled oil, if of good quality, will, when applied to glass, dry in 24 hours.
Tar should always be applied hot.
Dark boiled oil may be pure, but it will not produce good work.
A little varnish added to paint, often improves both its appearance and durability.
In painting over bad stains, tar, etc., a coat of shellac varnish will usually give a good surface on which the paint will dry.
Ochre makes a good and cheap priming coat, if it is very fine.