Petroleum Jelly is a porous surface sealer/release for use with Smooth-On^® Silicone Rubber products. Use straight or thin with mineral spirits. Petroleum Jelly is particularly useful in silicone-to-silicone applications such as making two-part molds or casting silicone into silicone. Store and use material at room temperature (73 °F/23 °C). Thinning with mineral spirits allows for a very thin layer to be applied to surfaces, helping to retain surface detail.