Because I have found that not all oil paints are mixed the same, lets set aside the fact that student colors, artist colors are not the same it's the fact that when the paint makers make it they change up the formulation and the quality suffers, i know all about that, because of where i work, and where i work has nothing to do with painting, it has all to do with color cosmetics, plus i am looking into it if it's worth my wild to do so or just buy the premixed pigment and mix the oil into it.Welcome Mike. I'm curious as to why you want to mix your own paints.