Smooth-Cast ONYX is a mercury-free urethane resin that cures at room temperature to a deep black, solid plastic. ONYX resins offer the convenience of a 1A:1B by volume mix ratio and have very low viscosities, so they are easy to mix and pour. ONYX resins have an ultimate Shore hardness of 80D and offer higher physical properties and higher heat resistance vs. other general purpose resins. ONYX resins are available in 2 speeds. ONYX SLOW resin has a pot life of 5 minutes and a cure time of 90 minutes.