Stained Glass: Colored Glass, Lead Frames, and the Architecture of Light

Walk into Chartres Cathedral on a sunny morning and the walls disappear. The stone is there, but what you see is color. Red, blue, green, and gold pour through 167 windows and turn the interior into a lantern. The glass at Chartres was made between 1145 and 1235, and nobody has produced anything on that scale since. The 2,500 square meters of medieval stained glass at Chartres represent the largest surviving ensemble from the Middle Ages, and the technology that produced it is essentially the same one used today.

Stained glass is colored glass cut into shapes, painted with details, and joined together in a network of lead strips called cames to form a window. The color is in the glass itself, produced by adding metal oxides to the molten batch. The lead holds the pieces together structurally. The whole assembly sits in an iron armature mounted in the window opening. It is one of the oldest surviving art technologies still in active use, and it is one of the few art forms where the medium and the architecture are inseparable.

This entry covers how stained glass is made, where it came from, who made it, and how to read it when you stand in front of a cathedral window.

What Is Stained Glass and How Is It Made?

The term "stained glass" is misleading. The glass is not stained. It is dyed in the melt. Metallic oxides are added to the raw glass batch while it is molten, and the color penetrates the entire thickness of the sheet. Copper oxide produces ruby red. Cobalt oxide produces sapphire blue. Iron oxide produces green. Manganese produces purple. Sulfur or soot produces yellow. These five colors form the basic palette of medieval stained glass, and they are the colors you see at Chartres.

Once the colored sheets are produced, the glass painter works from a full-size drawing called a cartoon. Individual pieces are cut from the sheets using a hot iron or, in modern practice, a diamond wheel. Details that cannot be cut from glass, such as faces, drapery folds, and inscriptions, are painted onto the surface using grisaille, a dark paint made from iron or copper oxide mixed with ground glass and a liquid binder. The painted pieces are fired in a kiln at 650 to 700 degrees Celsius, fusing the paint permanently to the glass surface. A 2023 study published in npj Heritage Science analyzed 23 grisaille samples from the 13th to the 20th century across nine countries, confirming that iron oxide was the dominant coloring agent throughout most of history, while copper oxide was preferred in central and south-central Europe. The study is available at Nature.

The finished pieces are then assembled into panels using H-shaped lead cames. The lead strips hold each piece of glass in a channel, and the joints between cames are soldered with a tin-lead alloy. The completed panel, typically about one meter square, is sealed with a putty made from linseed oil and whiting to make it weatherproof. Multiple panels are mounted in an iron armature that fits into the window opening. A 2019 doctoral study from UCL analyzed the glass of York Minster's Great East Window (1405-1408) using handheld X-ray fluorescence, identifying two distinct glass groups: one consistent with production in Staffordshire and the other with the Rhenish region. The research revealed that medieval glassmakers had greater control over color generation and composition than previously recognized. Read the study at UCL Discovery.

Origins and History

Colored glass has been made since ancient Egypt and Rome, but stained glass as architectural window art emerged in the medieval period. The earliest known figural stained glass survives from the 9th century, and by the 12th century, the technique had become sophisticated enough to produce large-scale narrative windows. The breakthrough was structural. Romanesque churches had thick walls and small windows. Gothic architecture, with its pointed arches, rib vaults, and flying buttresses, allowed for much larger openings, and those openings demanded glass.

Abbot Suger of Saint-Denis, just outside Paris, is generally credited with launching the Gothic stained glass tradition. Between 1135 and 1144, he rebuilt the choir of the Abbey Church of Saint-Denis with large windows filled with colored glass. Suger believed that light was a manifestation of God, and stained glass was the medium that turned physical light into divine illumination. The windows at Saint-Denis established the model that Chartres, Notre-Dame de Paris, and every other Gothic cathedral would follow.

Chartres Cathedral holds the most complete surviving collection of medieval stained glass. The four windows in the west facade date to around 1145 and survived the fire of 1194 that destroyed the rest of the Romanesque cathedral. The bulk of the glass, over 150 windows, was installed between 1205 and 1235. The famous "Blue of Chartres," a deep cobalt blue produced with cobalt oxide, became the signature color of the cathedral and has never been exactly replicated. A 2025 study published in the journal Heritage analyzed the rose window of Sant'Ambrogio Chapel in the Basilica of San Petronio in Bologna, dated to the early 16th century, and found that the grisaille on the window had degraded severely due to low-quality mixtures and improper firing, resulting in the loss of the original drawing. Read the findings at MDPI Heritage.

The 14th century saw the introduction of silver stain, a silver oxide paint that produced yellow tones when fired. This expanded the palette significantly and allowed for more nuanced color effects on a single piece of glass. By the 16th century, the Reformation and the rise of Renaissance taste for clear glass and classical architecture led to a decline in stained glass production across northern Europe.

The 19th century revived the art. The Gothic Revival in England and France drove a renewed interest in medieval techniques. In the early 20th century, Louis Comfort Tiffany in America and Art Nouveau artists in Europe pushed stained glass in new directions, using opalescent glass and organic, flowing designs rather than the geometric lead structures of the Gothic tradition.

Key Artists and Practitioners

Abbot Suger (c. 1081-1151)

Suger was not a glassmaker but the patron who conceived the Gothic stained glass program at Saint-Denis. His writings on the theological significance of light in the church established the intellectual framework that made stained glass the defining medium of Gothic architecture. Without Suger, the great windows of Chartres, Bourges, and Notre-Dame might never have been built.

John Thornton of Coventry (active 1405-1408)

Thornton was the master glass-painter responsible for York Minster's Great East Window, the largest expanse of medieval stained glass in England. The UCL study of the window identified Thornton's personal work through chemical analysis of the glass batches, suggesting that he painted specific panels himself while his workshop handled others in a cellular production system.

Louis Comfort Tiffany (1848-1933)

Tiffany transformed stained glass from a medieval architectural medium into a modern decorative art. He developed opalescent glass, which has a milky, iridescent quality that allows for subtle color transitions within a single piece. His lamps and windows, produced from the 1880s through the 1920s, abandoned the flat, leaded structure of Gothic glass in favor of organic, flowing compositions. The Tiffany Studios produced thousands of windows and lamps, and examples are held in the Metropolitan Museum of Art and the Morse Museum in Winter Park, Florida.

Marc Chagall (1887-1985)

Chagall created stained glass windows for cathedrals and public buildings across Europe and the Middle East in the second half of his career. His windows for the Hadassah Medical Center in Jerusalem (1962) depict the twelve tribes of Israel in saturated, expressionistic color. His window for the United Nations headquarters in New York (1964) is a memorial to Dag Hammarskjold. Chagall's approach treated stained glass as a painterly medium, using the lead lines as drawing rather than structure.

Brian Clarke (b. 1953)

Clarke is a contemporary British artist who has worked extensively in stained glass. His commissions include windows for the Pfizer Research Building in Sandwich, Kent, and the Alnwick Garden in Northumberland. Clarke's work bridges the gap between architectural glass and fine art, treating stained glass as a standalone medium rather than a decorative adjunct to architecture.

How to Read a Stained Glass Window

Start by looking at the structure. A large Gothic window is divided into panels, each about one meter square, arranged in vertical columns called lancets. The panels are read from bottom to top and from left to right, like a comic strip. The lower panels typically tell stories from the Bible or the lives of saints. The upper panels show enthroned figures, prophets, apostles, and Christ in majesty.

Next, look at the color. Medieval glassmakers chose colors for symbolic as well as aesthetic reasons. Blue was associated with heaven and the Virgin Mary. Red signified martyrdom and the Holy Spirit. Green suggested renewal and hope. Gold or yellow represented divine light. At Chartres, the interplay of blue and red across the 167 windows creates a color environment that changes throughout the day as the sun moves.

Finally, look at the lead lines. In the best medieval glass, the lead is not just structural. It is part of the drawing. The cames define the boundaries between colors and contribute to the composition. In Tiffany's work, the lead lines become even more expressive, following the curves of flowers, wings, and drapery. The difference between a master glass-painter and a competent one is visible in how the lead serves the image rather than simply holding the pieces together.

Related Terms and Techniques

Stained glass overlaps with several other terms in this glossary. Grisaille refers both to monochrome painting on panel and to the dark paint applied to stained glass surfaces for details. The grisaille paint used on stained glass is a different material from panel grisaille, but the visual effect is similar: tonal modelling in shades of gray or brown. Fresco is the other great medieval architectural art form, though fresco is wall-bound and permanent while stained glass is modular and removable. Trompe l'oeil shares with stained glass the ambition to dissolve architectural boundaries, though stained glass achieves this through transmitted light rather than painted illusion.

For more context, read our blog post on Gothic art and architecture, or explore our guide to reading a painting for techniques you can apply to any visual medium.

See Stained Glass in Person

Stained glass is the one art form that absolutely requires physical presence. Photographs cannot reproduce the experience of standing in a space where the walls are made of light. The color changes with the time of day, the weather, and the season. A window that looks subdued at noon can blaze at sunset.

Start at Chartres Cathedral, 80 kilometers southwest of Paris. The 167 medieval windows are the most complete ensemble anywhere, and the cathedral is small enough that you can walk around the entire glazing program in two hours. Then go to York Minster for the Great East Window, and to Sainte-Chapelle in Paris for the most intense concentration of 13th-century glass in a single space. For modern work, visit the Morse Museum in Winter Park, Florida, for the largest collection of Tiffany glass, or the Hadassah Medical Center in Jerusalem for Chagall's twelve tribe windows. For more on the broader context of medieval art, read our entries on grisaille and fresco, or explore our post on Renaissance art and the birth of modern art.