Stained glass is coloured glass cut into shapes and joined into panels, traditionally using grooved lead strips called cames. Rather than letting people look outside, its architectural purpose is to control incoming light and project images or patterns across a space. Because medieval churchgoers were largely unable to read, these illuminated windows served as narrative picture books.
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Medieval stained glass wasn't just decoration for cathedrals. It functioned as a visual Bible for a population that couldn't read.
Craftsmen suspended metallic salts in molten glass to turn sunlight into a narrative experience.
In the 1240s, King Louis IX commissioned Sainte-Chapelle in Paris. He replaced entire stone walls with thousands of square feet of vibrant glass.
Thin lead strips called came held the glowing panels together. Worshippers stood inside a kaleidoscope of pure color where stone seemed to vanish.
Gothic architecture used these massive windows to reach toward the divine. Centuries later, Louis Comfort Tiffany brought the medium into domestic spaces.
He developed Tiffany glass to mimic the opalescent textures of ancient Roman ruins.
Glassmakers create colour by mixing powdered metallic oxides directly into molten silica. Cobalt yields deep blues, copper oxides produce green or blue green, and gold produces wine red and violet. Because gold was costly, artisans also used copper to produce a bright vermilion red.
Glass coloured in the furnace pot is called pot metal glass. When deep colours like red turn out too dark to transmit light at standard window thickness, makers use flashed glass, fusing a thin layer of coloured glass onto a thicker, transparent base sheet.
Medieval artisans turned molten bubbles into flat window panes using two main hand-blown techniques. In the cylinder method, glassblowers blew and swung a molten gather into a long tube, cut off the ends, slit the side, and flattened it in an oven. Crown glass involved spinning a blown bubble rapidly on a pontil rod until centrifugal force flattened it into a round disc, leaving a thick bull's-eye lump in the center.
In the 1830s, commercial makers introduced rolled glass by pouring molten batches onto metal tables and flattening them with heavy cylinders. Modern stained glass artists use both hand-blown and machine-rolled sheets, assembling them into windows, sculpture, and domestic lamps like those designed by Louis Comfort Tiffany.
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Pieces of cut glass are joined using thin, flexible lead strips known as cames or calms. The assembled panel is then mounted within a rigid frame capable of withstanding wind pressure and the structural weight of the window.
Cathedral glass is a commercial trade name for machine-rolled glass produced from the mid-nineteenth century onward. It was never used in actual medieval cathedrals, which relied entirely on mouth-blown cylinder and crown glass.
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