The Delft Clay is a highly-refined casting sand. This process was invented by Hans Karreman, a Dutch goldsmith. It is finer than casting sand, and provides sharp, high-detailed castings in gold, silver, pewter, copper-based alloys, and more. Castings require minimal finishing work. Once you have cast your piece, the Delft Clay can be re-used. This is a cold-molding method, and molds can be made from patterns composed of wood, wax, epoxy, plastics, and metal. Not recommended for designs with undercuts. This kit includes 4.4 lbs of Delft Clay Sand, two aluminum 60 mm ring mold frames, DVD, and helpful instructions.