Here's the *best* way to be sucessful with that
1) make sure your vermiculite is warm (as in, if you're torching outside, in a garage, etc--warm it up--cramming a hot bead into ice cold vermiculite = bad idea!)
2) make sure your bead is COMPLETELY re-warmed 100% through the bead when you're done making it. As in, all the way--get a good "glow" through the whole bead. Not just the outside edge, but the WHOLE thing--so it's ALL ONE TEMPERATURE!
3) Now "cool it down" while spinning till it just stops glowing (check under the table, keep spinning!). I tap mine on the metal leg of my table to hear if it will "tink" & not "smush" because I want it to be "just solid"...sometimes there's a very slight glow still in there, as long as it's solid, it's good!
4) If it's a big bead, with "appendages" it's going to be more likely to crack--sculpture is hard to batch. Round/solid/whatever shapes are better. If you can scoop a hole, it's easier--if not, just "swirl" the bead down DEEP into the vermiculite--the DEEPER the BETTER!! You want it way down in the crockpot--as deep as you can get--you want it to take a LONG time to cool--the longer the better.
5) Leave them there until "tomorrow". Seriously. When you're done torching, turn off the pot & let it cool overnight.
6) Take out the mandrels the next day, soak in water (or not, depending on which bead release you use) & grab mandrel with pliers, twist bead off & soak. Send where-ever for batch annealing.
I actually dremel mine out (or scrub 'em, depends) BEFORE I send 'em for batching. I figure if they survive the dremel before they're batched, they're pretty stable!