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Windowmaking How were stained glass windows made?

The earliest examples of windows with figurative scenes are known from St.Remi in Reims from around the year 1000.
Glass is a mixture of silicic acid and metal oxides, which solidifies after melting. It consists of up to 70% silicic acid, with up to 20% alkali's for durability and soda for fluidity.

The only colours available in the Middle Ages were saffron-yellow, purplish-red, green, blue and copper-red. Miniatures often provided the models for the stained glass windows. One cut the small coloured glass panes to size and then painted them with black solder/flux? (Schwarzlot), a mixture of iron and copper powder. After 1300 silver solder/flux? (Silberlot) was also available, which allowed for a new range of colours, for example light yellow and reddish-yellow. The colours were melted onto the glass.
The panes could be leaded as soon as they had cooled. The pliable lead strips could be easily bent to shape. The lead grid had to be carefully applied, as it provided the frame for the pictoral design. Any cracks were then filled with clay. Generally the complete window would then be inserted into the masonry window frame and fixed with mortar.

Colleagues from the Landesdenkmalamt (LDA) Baden-Württemberg and the stone-mason's workshop of Cologne Cathedral have produced a comprehensive report on the restoration and care of the medieval stained glass windows from the church St.Dionys in Esslingen. The results of their work can be read in the LDA's quarterly News Journal, "Denkmalpflege in Baden-Württemberg" ( 1/1997), or can be accessed on the server "Denkmalpflege in Baden-Württemberg": P. Berkenkopf u. O. Wölbert, Dokumentation und Restaurierung der mittelalterlichen Glasfenster aus St.Dionys in Esslingen. (German only)

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