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Vermiculite is a natural mineral. It expands when exposed to heat and is used frequently in lampworking.

Many lampworkers use vermiculite if they batch anneal their beads. Used in a powdered form, it slows down the cooling of the beads and makes them cool more evenly. This reduces the internal stresses and reduces the tendency to crack.

Many people increase the time taken for a bead to cool in the vermiculite by placing it in a slow cooker on high whilst they are working and turning it off when the last bead is plunged into the substance. This can also be done on a saucepan on the hob.

Vermiculite does NOT anneal the beads, it is simply a temporary measure that stops them cracking until you can anneal them properly.

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