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Look at the SDS (Safety Data Sheet) on your all natural cutting board oil. Most likely it's 95% mineral oil and 5% vitamin E (a food grade antioxidant). While mineral oil is from petroleum, it is a liquid paraffin (think candle wax but liquid). It is completely unsaturated (no double bonds between carbon atoms) so it does not oxidize or turn rancid. And it is listed by the FDA as an "intestinal lubricant", and is safe to ingest. If you really want natural, then I suggest getting beeswax, melting it, and rubbing it in while liquid. Once it hardens, you can toss the cutting board in the oven on the lowest setting. Once warm, the excess beeswax can be quickly wiped away. Buff the board while warm with a clean cloth. Viola!