home.bawue.de/.../ essling/english/glas02.html
http://www.mnsu.edu/emuseum/prehistory/ancienttech/glassmaking.html
http://home.bawue.de/~wmwerner/essling/english/glas01.html
http://www.bbc.co.uk/history/lj/churchlj/stained_technique.shtml
www.stainedglass.org/main_pages/association_pages/historySG.html
http://www.hermitagemuseum.org/html_En/03/hm3_3_2_1.html
www.bbc.co.uk/history/timelines/wales/middle_ages.shtml