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There is a persistent myth that glass is a supercooled liquid even at room temperature, and that medieval stained glass shows a slow liquid flow toward the bottom. Both statements are wrong.
Glassy substances are solids, but not crystalline as are most metals. Their internal atomic structure shows short-range order, but long-range disorder.
Glass flows slightly under stress, but so do metals. In metals the phenomenon is called 'creep' and is considered negligible unless the metal's actual temperature is greater than half of the metal's melting temperature (both in °K=°C+273), so lead creeps at room temperature but steel doesn't.
Consider: the lead in stained glass windows flows more than the glass! Is the lead liquid?