Grisaille
Grisaille is painting in shades of grey or brown on clear or pale glass. In medieval windows it was used to make large areas of decorative patterning, often with leaves and geometric designs, and clear glass of this kind let much more daylight into the church than a window filled with deep colour.
It first became popular in the thirteenth century. The Five Sisters window at York Minster, made of five tall lancets filled with grisaille, is among the best-known examples in Britain. The word is also used for a style of painting in monochrome and, in later windows, for tonal backgrounds set around coloured figures.
The tones come from vitreous paint, which is fired into the glass so that it is permanent.