A self hardening clay compound that is non toxic, durable and hard after it is dry, but not waterproof. Marblex is gray in color, and Mexican Pottery clay is terra-cotta. marblexmexican Marblex- Gray 5 Pounds Marblex5Regular price: $18.75Sale price: $15.00 Mexican Pottery- Terracotta 5 Pounds MexicanP-5Regular price: $18.75Sale price: $15.00 Marblex- Gray 25 Pounds Marblex25Regular price: $49.00Sale price: $39.20 Mexican Pottery- Terracotta 25 Pounds MexicanP25Regular price: $49.00Sale price: $39.20