Reusing an old canvas

There isn't a best way to re-use a canvas on which a disappointing oil sits, however reproachfully it may stare at you. A rigid board is slightly less problematic - you can remove varnish with White Spirit, sand the paint down, let it dry out entirely, hope for the best. But with a flexible canvas, the tension between coats could easily lead to cracking sooner or later; and I wouldn't offer any guarantees on painting on boards either. You can try painting on an old picture - practice pieces, or more ambitious work: but what if you produce something that's really rather good? You've got a painting then that might last, might not; you couldn't sell it, knowing it had a fundamental weakness (unless you cut your usual price and told the buyer of the possible problems). If you're going to do it, though, at least use only oil as a medium, no solvent - it has, of course, been done; and failure isn't guaranteed. But in your place I'd dispose of any painting I thought rubbish, and buy new boards. Though, I do have a few small oils painted over old work, so don't always take my own advice.

Just like to add a note of caution over sanding down oil paintings. Many artist oils contain pigments, that although quite safe in paint form, can be hazardous as dust. I'd err on the side of caution and prefer not to sand, but if your going to, make sure you have the appropriate filter mask. Something better than the simple white fibre cloth ones DIY'ers often use... Be safe !

Especially true of a painting containing lead whites, of course - of which there will be many fewer in future, at least on this side of the Atlantic. Any heavy metal could be hazardous if inhaled - lead is ahead of the pack, but you also might want to be careful with cadmiums and cobalts: any risk in these cases is slight - but it's a good point: why take any risks at all?