What is the oldest surviving stained glass window?
Medieval stained glass
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Prior to c. 1000, most coloured glass was of a soda-lime-silica composition. In Northern Europe soda glass was eventually almost totally superseded by potash-lime-silica glass (Forest glass). Forest glass continued to be used in stained glass for the duration of the medieval period[11] until soda glass again began to be used in the 16th century.