Whenever I try to make a pan of gouache, it usually cracks or crumbles like the ones on top. I prefer using gouache for white and black even when doing more or less straightforward watercolors because if I'm going to that extreme I want gouachelike coverage.

My white pan is pretty good, but my black pan is a mess of chunks that you need to add water to at least ten minutes before you plan to use it. That's the other trouble I've had with gouache in pans: not all colors rehydrate the same.