What is cracking by thermal shock?
Thermal shock is caused by rapid temperature change; this may be from hot to cold or cold to hot. Some of the glasses are made up of both thick pieces and thin pieces of glass. For example, the jugs, which are thick at the handle and base and thin throughout the main body of the piece. When the thin pieces change temperature they expand or contract while the thicker pieces remain the same, this causes pressure at the junction, which may alleviate by cracking. Another example of thermal shock is when candles are allowed to burn too closely to the rim of the candleholders causing rapid temperature change.
