Chartres' Perfect Blue

Chartres Cathedral (mostly rebuilt 1194-1220) preserves the finest collection of medieval stained glass — over 150 windows containing approximately 5,000 figures. The famous "Chartres blue" — a deep, luminous blue made with cobalt — has never been exactly reproduced.

Around the year 1300, glassmakers found that brushing on a silver compound and firing it stained the glass a clear yellow, from pale lemon to deep amber. It was the first color that soaked into the glass rather than sitting on top of it — and it gave us the very name "stained glass." Suddenly a single pane could carry two colors, like a yellow crown painted onto a clear face.