yellowing

I made a white test of zinc white (Beckers "A", here). In one patch I added linseed oil. It has experienced clearly visible yellowing after half a year. Another patch was mixed with Liquin (alkyd medium). It also became more yellow, but decidedly less so. The third patch consisted of zinc white...

I ham having some trouble and am hoping the art community can help. I paint mountainscapes, which by its nature uses a lot of pure white. I paint oil on canvas but I use palette knives so I need the paint to be elastic as the paint layers are thick. The trouble I am having is that after 6...