4 value studies

These are my six four value studies. My white and black tend to get muddy. I worked outside and also from some old masters. I can see some of my errors right away now that I see the example and the painting next to each other. There are some misplaced blacks at where the forehead meets the hair line on the Michaelangelo's "Creation of the Sun and the Moon" detail. There are some missing darks behind Perugino's Jesus. and there are some missing darks between the legs of Michaelangelo's "One of the damned dragged to hell by demons." My tree by the lake with the grasses seems to be missing a central dark. My shadow pattern seems to be off in the Cherry tree in the field but I think it didn't look exactly like that when I painted because I went back to take the picture about 20 min after I painted it because I initially forgot to photograph it.