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Crochet: How to Crochet spiral coaster / potholder with spiral surface stitching, beginners pattern

This tutorial just uses stones and felt.

I've also seen a suggestion that one could stiffen up the trivet by sandwiching a CD in between the two pieces of felt. Though that would make something closer to the size of a coaster than a trivet.

One could also use those flat glass pebbles instead of stones.