Condensation-crosslinking silicones react on the crosslinker under separation of a reaction product. This is generally a short-warp alcohol which evaporates from the system during the reaction. Therefore, condensation-crosslinking silicones are not suitable for the use in closed moulds. However, they have in so far an advantage over the addition-crosslinking silicones as they are to a large extent insensitive to poisonings. The initial number of these systems is odd; the crosslinkers are marked with the letter C.