Zonie said:
Linseed oil oxidizes rather quickly and as it does, it creates heat.
In a wadded up rag or paper towel the heat can't escape so sometimes (not always) the oil will create what is called "spontaneous combustion" and the rags/towels will ignite.
If the rags/towels are unfolded as the oil drys the heat will escape harmlessly into the air but in a tightly wrapped rag/towel it can be dangerous.
Yeah, for years we were told to beware of "OILY RAGS".
I always thought it a bit of overreaction.
And if it is simple Motor Oil (or equiv), I still do. That stuff will burn, of course, but a source of ignition is necessary.
The entire point of Motor Oil is for it to never dry at all. And never evaporate, either.
But your Linseed Oil (and most likely Tung Oil), is supposed to oxidize and dry. And in doing so, it generates heat.
For all I know Paper Towels may, somehow, interact with Linseed Oil to produce more heat than, let's say, cotton rags.
One of these days I will reproduce my experiment again - but it may be awhile.
Ever since the day of the fire I steer far away from Linseed and Tung Oil.