The structure of glass, though strong, contains a lot of empty randomly together like a pile of bricks, rather than lined up in neat columns as they would be if the bricks were made into a wall.
These cavities can be occupied by metal atoms which affect the way light is transmitted through the glass. Different metals absorb light of different frequencies, giving the glass that contains them a characteristic colour.
It was this principle that gave rise to one of the glories of the medieval cathedral, the stained-glass window.
When added to the motion glass, copper turned it ruby red, cobalt blue, iron green, antimony yellow, and manganese purple. Sheets about the size of this book were manufactured in different colours and then cut to the required shapes. They were then assembled into complete windows.
Variations in the thickness of the glass, inevitable with medieval technology, enhanced the beauty of the windows by providing a subtle variation of tone. When the techniques of glass-making improved, a lot of this subtlety was lost.
Picture Credit : Google
