Polyunsaturated oils combine spontaneously with the oxygen to deteriorate into a hard film. Vegetable oil bottles tend to get sticky on the outside. Used veget

Polyunsaturated oils combine spontaneously with the oxygen to deteriorate into a hard film. Vegetable oil bottles tend to get sticky on the outside. Used vegetable oil is great for wood preservation. Many stains have heavy metals in them. https://en.wikipedia.org/wiki/Drying_oil https://en.wikipedia.org/wiki/Drying_oil https://en.wikipedia.org/wiki/Lipid_peroxidation https://en.wikipedia.org/wiki/Lipid_peroxidation https://en.wikipedia.org/wiki/Lipid_peroxidation#Hazards https://en.wikipedia.org/wiki/Lipid_peroxidation#Hazards