This is a picture of some Martius yellow that was recrystallized from acetone (this is the stuff that I rinsed off of my glassware). I hadn’t expected it to form such nice crystals. I think I will recrystallize all of it since it does.

UPDATE: This is not Martius yellow. Acetone apparently reacts with Martius yellow, as this recrystallized substance exhibits different properties. For more details, see this post.