English stained glass 1325–1520
In the late medieval period, both religious and domestic settings often displayed panels or roundels of coloured glass against a background of plain glass quarries. These quarries were small panes of glass, usually lozenge-shaped and sometimes decorated with motifs painted in yellow (silver stain) or in brown.
This panel is composed of clear diamond-shaped quarries. They are painted in black/brown pigment with an interconnecting pattern of stylised oak leaves on long stems. This type of simple decoration is known as 'grisaille'. Each quarry has a thin border painted with a silver compound that, once fired in the kiln, produces a yellow/orange colour that sinks into the clear glass. This technique is known as 'silver stain' and is where the term 'stained glass' comes from.
The borders are composed of 'flashed' red glass with insertions of clear glass painted with black/brown pigment and yellow stain. Medieval glass that is coloured all the way through when it is in a liquid state is known as 'pot-metal'. However, red pot-metal glass is very dense, and not much light can pass through it. A technique known as 'flashing' developed at an early date in the glass industry. It involved coating clear glass with thin layers of coloured glass. This was very popular for producing a translucent red.
A great deal more light can pass through a window containing grisaille and flashed glass, which means that dark interiors can be illuminated much more efficiently.