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: $17.95Sale price: $14.36 Mexican Pottery- Terracotta 5 Pounds MexicanP-5Regular price: $17.95Sale price: $14.36 Marblex- Gray 25 Pounds Marblex25Regular price: $48.00Sale price: $38.40 Mexican Pottery- Terracotta 25 Pounds MexicanP25Regular price: $48.00Sale price: $38.40