Thiourea dioxide (CH4N2O2S), also called thiox, is an organic sulfide that is a very effective reducing agent. Commercial dye houses use it to remove a missed color from textiles and start over with their new, tweaked dye formula. Craft dyers use it as the reducing agent (antioxidant) in a chemical indigo vat stock solution; 2 ounces indigo, 2 tablespoons soda lye and 2 tablespoons thiourea dioxide. Dissolved thiox is also added to the indigo vat to return it to the desired soluble leuco indigo. The Earthues thiourea dioxide is 99+ Purity Grade.