The simplest way to clean an oil or acrylic painting on canvas is to use a white cotton cloth soaked in a gentle soapy water; olive oil–based soaps work wonders. You’ll be surprised to see how much grime comes off. Be gentle with paintings with thick impasto, as you do not want to break hardened paint.You might want to use Q-tips and work gently into the crevasses.

If the painting still looks grimy, it’s better to see an art restorer that would use a stronger art cleaning product and may reapply pigment colors where needed. It’s surprising how a restored painting can show its true colors just by taking away the accumulation of smoke damage over the years. If your oil painting shows paint flaking off, it is better to leave the cleaning and restoration to a professional art restorer.