History and technique
During the Gothic period and the Renaissance (1100s–1500s) stained glass was one of the foremost techniques of painting practiced in Europe. It may seem surprising to call stained glass a form of painting, but in fact it is. Look closely at the image here and note that the surfaces of each piece of glass are painted in a wide range of dark tones. One of the most widespread forms of painting, stained glass inspired the lives of the faithful through religious narratives in churches and cloisters, celebrated family and political ties in city halls, and even decorated the windows of private houses.
Why is it called stained glass?
The term stained glass derives from the silver stain that was often applied to the side of the window that would face the outside of the building. When the glass was fired, the silver stain turned a yellow color that could range from lemon to gold. Stained glass was usually used to make windows, so that the light would shine through the painting. It is a form of painting that began over 1,000 years ago and is still essentially made the same way today.