They tended to use a lot of things like lead. While I could probably duplicate their methods, it would (like it did to them) poison me. However duplicating the paint won't make me an artist. Practice painting would make me an artist and buying paint would allow more time to practice. Practice would also let me learn how modern safe paints work and so I could make something that looks like what they could do with modern paints, or I could create something they could not for lack of ability to get that color/shine/whatever (I'm not a painter and don't know the terms they would use).