(1) The process whereby glass becomes partly crystallized as it cools (usually too slowly) from the molten state; (2) the crystals formed by this process. Devitrification can also occur on the surface as a result of unsuccessful annealing or accidental heating to a high temperature. It is not caused by chemical reaction between glass and its environment, which is known as weathering.

A substance, usually clay with a high silica content, capable of resisting high temperatures. Furnaces and pots are made from refractory materials.

Any crystalline inclusion present in glass. Stones consist of unmelted particles of batch, fragments of refractory material from the pot, or devitrification crystals. Stones of the first two varieties are generally irregular but rounded; those of the third variety are angular and well formed.

The mixture of raw materials (often silica, soda or potash, and lime) that is melted in a pot or tank to make glass. Cullet, as well as minor ingredients such as colorants, can be added to the batch to help the melting process.

A fire-clay container in which batch is fused and kept molten. The glassworker gathers glass directly from the pot.