In 1133 a Cistercian abbey was established at Garendon near Loughborough. It was closed by Henry VIII in the first wave of his suppressions of religious houses in 1536. Left behind when the buildings were sold, dismantled or put to other uses, were fragments of window glass and the partly melted lead 'cames' that held the glass in place.
The plain window glass was blown to a cylinder shape and then flattened. The design was painted on using iron oxide and is known as Grisaille, common in the 12th and 13th centuries.
Coloured glass was more expensive, but from the 12th century the windows of Cistercian abbeys such as Garendon were instructed to be made from clear glass, not decorated or painted. In order to have some decoration in the windows, the glaziers created designs and intricate patterns in the lead that held the glass.