What is the best way to clean a very old oil painting without damaging the painting itself?

Answer 1

If it is a very old painting take it to a professional, they know what to use for every kind of paint and varnish. If you use the wrong stuff you can damage it irreversibly.

Answer 2

White bread seems to work. Ball up soft, sticky, doughy white bread and gently rub it against the canvas. You'll see it blacken like a pencil eraser. Brush off the crumbs. You also might try a low-suction vacuum with a brush nozzle. This should remove pet hair and dust balls in a deeply textured painting.