Poly-Optic® 1490 Clear Casting Resin (Mercury-Free Formula) is a two-part, liquid polyurethane resin that cures (RTV) to a water-clear, Shore D80 plastic. This product has a simple 1A:1B mix ratio by volume (100A:90B by weight).
Poly-Optic® 1490 is more moisture-sensitive than other Poly-Optic products and must be pressure cast or used with vacuum casting equipment (not vacuum degassing). A high number of microscopic bubbles will form in this resin when these techniques are not used (this problem is not resolved even with the aid of vacuum degassing). Cure inhibition can occur when casting this resin in tin-cured silicone rubber molds – use a platinum-cured silicone rubber mold if working with silicones.