Let me preface this by saying that I'm not very knowledgeable about ceramics. My understanding of ceramics stops at about the point where I recognize that clay is different from potting soil. My sister, however, is a ceramics major and is extremely passionate about it. One of the methods she uses for making spheres is to cover the outside of a round object with the clay. Currently, she does this with styrofoam balls, but this is a laborious task that involves cutting the balls down to the right size and shape and can be dangerous if the ball comes off incorrectly and winds up warping the structure. She mentioned that using a balloon for this would be ideal as they're cheap and you can just pop them and pull the latex out when you're done, but balloons tend to roll around so you either have to tape them down, which is difficult and fails half the time, or keep them in a bowl, which puts too much strain on the balloon and causes it to burst. With Christmas coming up, I want to get something that would simplify some of the difficulties she's been having with hand building round shapes, but I had a few questions: 1. I did a little research and found that some people fill balloons with sand or cat litter to give them more rigidity, then drain the particles out to pull the balloon out. Is there any way to inflate the balloon with sand or other cheap particulate matter, or do you have to find a slack mold that's already the size you want to use (some mentioned using tube socks, for example)? 2. It's possible that a higher grade of balloon could hold up under the weight of the clay better. Has anyone tried doing this? Did it work? 3. Does anyone have any other suggestions for an easy and cheap spherical mold?