For moulding experiments I identified a number of moulding clays which I think could be used as both the material being cast and as the material to hold the impression. Commercial products included air-drying clay, polymer clay (Fimo), modroc.

I also researched homemade dough options and found a selection of ‘playdough’ type recipes and salt dough.

Microwave Salt Dough Recipe for Fun & Easy Crafts