hi
i would not suggest that. For Cosmetic Products the Amount of Heavy Metals is detected and can not exceed certain amounts for Cosmetic Grade Colour Iron oxide. I would not be Shure about that if you use Iron Oxide that is used for paint. the Risk is too high and i would say it is not alowd to be used for Cosmetic Products.
OFcours we can have a discussion about the Production line and that they are the same for Piant and for Cosmetics products but in my experience the Discussions and the problems that could generate are more expensive than just buying a cosmetic grade Pigment.