Thank you! Yes, mineral oil is possible. There are actually a lot of oils that can be used as sealant. Linseed oil would be the best, maybe walnut oil. Any oil will work, but we also consider polyurethane as a cheap and durableoption. In one way, you can say that oil is more natural thus more sustainable. But a cost comparison makes polyurethane a more sustainable option, with less resources required to produce it.