If a hot glass object is cooled "too quickly," it may be strained at room temperature, and therefore may break easily. For small, or thin-walled shapes (particularly those made of glasses having low expansions) the effect may not be serious. For more massive pieces, the strain can be very serious. The amount of strain (observed in a polariscope) depends upon how quickly the object passes through a critical temperature range. The range depends on the composition of the glass but is usually about 450°C.

Certain types of colorless, transparent glasses, when exposed to sunlight for extended periods of time, develop a pink or pale purplish color. Bottles, insulators, and other objects having their color changed in this way are often called "desert glass," but the scientist prefers