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To make your own mold from epoxy, cover an extra ball with a thick layer of epoxy (at least an eight eighth of an inch). It's important that the mold remains rigid, or it will not remain spherical and the shape mismatch will prevent the ball from working. You can then remove the extra ball by chipping away and dissolving with acetone.
To float the ball you'll want several small holes in the base. Depending on your setup, it's probably easiest to create a chamber underneath the bowl connected to your source of air.
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