Terra Sig is a surface decoration that at times can emulate the look of a leather hard piece of ceramic. It is created by adding a deflocculant like sodium silicate to a water clay slip mixture. The deflocculant assists in the separation of the clays heavier particles from the most fine. The most fine particles stay suspended in the mixture and can be siphoned off the top for terra sigillata. Colorants can be added and then the mixture is applied to dried greenware and burnished immediately. It is then fired to a lower bisque temperature, typically around 1650 deg f.