Well, joint compound would indeed be a quick and easy solution! Great job! Certainly a heckuva lot speedier than the paper clay method I employed. I'd like to hear how it holds up, whether it cracks or not with movement and jostling of it.
I only say that because I know wallboard joints can crack over time and those are small areas, so spread over something as broad as the cauldron I'd like to see if it can stand up to the "punishment." Regardless, terrific looking work!
You might consider using some flat black spray paint to add some "scorching" to the bottom and a little coming up the sides.
This looks really good, I too will be curious to see how well it holds up under use, abuse, storage, etc.
I need to make a mission-style bell and am thinking of using this technique. If painted with a base coat of exterior house paint, do you think the dry-wall joint compound will survive rain and other outdoor hazards?
If you let it dry thoroughly, and coat it COMPLETELY, inside and out, with the house paint, it should be fine, shy of massive flooding or something of that nature, but given where you are, I doubt you will have those kinds of issues.
You might consider using a plastic bucket, and a heat gun to stretch and distort it to the desired shape. You'll still need to add some padding to the shape. I'd use a short stub of a 2x4 or 2X6 with a large hole drilled or cut through it, screwed to the bottom of the bucket, you could add some tapering layers of MDF or plywood to the bottom of the bucket for shape too.