How can you remove old linseed oil-based paint from a porous ceramic or pottery vase without damaging the vase itself?

Answer 1

To remove a linseed oil based paint from a porouse ceramic would require figuring out a way to soften the finish to make it soluble in something (like acetone). As I recall, linseed oil essentially cross-links during the curing process to create a hard, brittle, but of course, very durable finish. To get the material off of a porous ceramic material would require dissolution (rather than the typical way of softening then scraping) -- that is, the only way to remove the material from the pores is by dissolving the finish.

I would recommend one of the following: a simple paint remover, formulated for oil-based paints; gently heating the system when immersed in the paint remover using a double-boiler (of course, this would require some common sense -- an electric stove (absolutely no gas flames) and a well-ventilated area); possibly simply trying acetone (nail polish remover) and soaking the vase in the acetone and testing with a pin (or something like that) periodically to see if the finish is softening.

Some old paint books have information on linseed oil finishes that might give some insight. As you know, most of the time these finishes are on wood which can be particularly problematic for finish removal -- the wood is porous, frequently soft, and easy to damage. There are sucessful techniques for removal but I do not know details. If I get a chance, I will see if I can find some of my old paint books, but they may not be old enough. (What you are looking for would be handbooks from the 40s and 50s.

Another (less dangerous for the operator) approach may be to soak or even boil the item in water. This may cause the paint to lift away, whereas using solvents may drive stains into the porous pot.