18-40 Grit Crushed Walnut Shells. Walnut media blasting is especially effective when you want to clean paint, grease and other dirt from the surface of a material but maintain the integrity of the substrate materials. Cleans and polishes glass, fiberglass, wood, plastic, stone and soft metals. For use with blasting or vibratory tumblers. It’s environmentally friendly and 100% silica free. ALLERGY ALERT! This media contains walnuts.