The spontaneous combustion that occurs with oily rags does not happen with rags that have oil paint on them from wiping your brushes. Otherwise oil paintings would catch fire as they are also cloth with oil paint on it. To catch fire, the rags must be thoroughly soaked in just oil and you must have a large pile of them all together.

Drying oils (the vegetable oils used to make oil paint) dry by oxidation which is like very slow burning. It is not enough to feel or be dangerous unless a lot happens in the same place at the same time. So the usual cause of spontaneous combustion in oily rags is a furniture factory with a big pile of rags completely soaked in oil from rubbing oil into furniture. It is unlikely to ever happen in a home or painting studio because it requires the rags to be completely soaked in litres of oil, not just some paint on a paper towel. And there needs to be enough of them piled up to have lots of air trapped in the folds and as it gets warm it needs to hold the heat in because it is a big pile. A hot day and if the pile is in the sun can also contribute.

If you wish to be cautious you can:

  • Wash your rags if they are cloth and hang them flat to dry.

  • Use a covered metal bin, half filled with water for all your oil paint waste.

  • Some people put their rag in a ziplock bag and push all the air out before they bin it, because it needs air to burn.

  • If you get a rag soaked in oil because you are oiling out a painting or applying a layer of oil to a wooden palette then you can lay your cloth out flat so it can't trap any heat in the folds.

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