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.