Stained glass, as an art and a craft, requires the artistic skill to conceive the design, and the engineering skills necessary to assemble the decorative piece, traditionally a window, so that it is capable of supporting its own weight and surviving the elements.
Although usually set into windows, the purpose of stained glass is not to allow those within a building to see out or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as illuminated wall decorations.
