Knockout when a fused silica ceramic is used is a straightforward process of vibrating the tree and separating the broken shell from the metal. The crystalline transformation referred to earlier in firing is used to advantage here. When other than fused silica ceramics are used the knockout process can be quite physically demanding as the ceramic retains substantial strength and resists being separated from the tree. Damage of the castings must be avoided. It must be noted that regardless of the ceramic material, the shell process shines at this point from an environmental perspective of low volume of waste material and stable chemistry.