Blue is especially associated with the stained glass of Chartres Cathedral. The cathedral’s deep, luminous blue is one of the most recognizable features of its 13th-century windows.
The color appears in robes, backgrounds, borders, and architectural details throughout the collection. Its intensity helped give Chartres glass a distinctive visual identity, although the windows also contain strong reds, greens, yellows, and purples.
People often call this signature shade Chartres blue. The phrase describes the celebrated appearance of the glass rather than a single modern paint color or one uniform recipe. Medieval glassmakers created colors through mineral additives and complex furnace processes, and surviving shades can vary from panel to panel.
Chartres blue is sometimes confused with the blue of Sainte-Chapelle in Paris. Both buildings are famous for brilliant Gothic glass, but Chartres has its own particularly celebrated blue tradition.