A self hardening clay compound that is non toxic, durable and hard after it is dry, but not waterproof. Marblex is gray in color. marblexmexican Marblex- Gray 5 Pounds Marblex5Regular price: $23.00Sale price: $18.40 Marblex- Gray 25 Pounds Marblex25Regular price: $57.00Sale price: $45.60