In kilncasting, “suckers” are unsightly depressions or wrinkles that can pop up during the cooling process. Suckers get their name because they appear to have been sucked infrom the form of the mold.
Suckers are the result of differences in temperature during the cooling process. Often, these differences in temperature are caused by differences of thickness in a piece. Thinner or narrower areas will change temperature more quickly than thicker or wider parts. These differences can cause the glass to contract, resulting in suckers.
You can prevent stuckers by keeping your glass at a uniform temperature during the cooling process. We recommend soaking/holding the glass at 1250 F during the rapid cooling stage to thoroughly unify the temperature, then cooling gradually to the anneal soak phase.
We also recommend incorporating a large reservoir into the casting, which will remain full enough to be the thickest part of the casting, and therefore the last area to cool off.
For more information on suckers and how to prevent them, see TechNote 4: Heat & Glass and TipSheet 8: Basic Lost Wax Kilncasting.