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Crystalline materials have a definite structure, whereas amorphous ones do not, and therefore only rather general statements can be made about a material which, when hot, is ductile but when cold is brittle, and fractures if there is a sudden change of temperature.
The thermal history of glass is of particular importance, because glass that has been cooled quickly retains an imprint or ‘memory’ of its state at the moment before it was cooled.