Pam B I also made molds of
I also made molds of the shells to slump glass over. I also made molds of small shells and coated them with mica powder to fuse between two layers of glass leaving the mold in place. I have experimented with shells and the probliem is that you can never tell which shells will just turn to ash and muck up your piece. Sea glass is at a higher coe than 90 or 96 so it can not be mixed with coe compatable glass. My guess would be that the wonderful texture of the sea glass would be lost in firing anyway. You could create the look of sea glass with sandblasting or etching paste after firing though.
Experimenting creates so many failures but even though my bucket is over flowing with mistakes, it is so much fun to see what works….. trial and error is the way to learn and to create your unique teckniques..