The invention provides a method to reduce evolution of hydrogen gas especially during pouring gypsum models from addition cured silicones. In this respect the invention relates to an addition curable silicone composition, comprising an addition-curable siloxane compound, a siloxane crosslinker, a catalyst and an unsaturated silane compound with at least one methylene group directly attached to the unsaturation in an amount effective to reduce the amount of hydrogen gas evolved in the reaction of said composition.