Can I use a clay bowl for double boiling?!
Answers: My gut says no. I don't think it would conduct the heat well enough. The bottom would absorb the moisture from the steam but not transfer the heat. Plus your chocolate might not melt smoothly. Do you have a glass or metal mixing bowl? That's what I do. In a pinch I use my pyrex measuring cup too. Hook the handle over the side; it's not ideal but it will work.
Lead in most clay pots precludes them from being used in food prep!!!