Stained glass is arguably one of the most important aspects of Gothic cathedrals. As its popularity rose, mainly during the mid-twelfth-century, the increased presence of stained glass presented major changes to the way the general populace was learning about religion. The windows became illuminated visual sermons of biblical stories, which may have had an even greater impact than the spoken word of the priest. In this article, I will be primarily focusing on the stained glass windows and architectural styles employed in gothic buildings in France, each having their own unique and notable attributes pertaining to the development of stained glass windows. By looking at the architectural advancements shown in these structures built during the gothic time frame, we are able to see the impact that the widespread desire for increased height and light within these types of buildings had on the gothic cathedral.
The term “stained glass” applies to coloured glass made with metallic oxides as well as glass on which colours have been painted and then fused in a kiln. To produce a stained glass window, an artisan would first make sketches or “cartoons” of the finished window by drawing out a life-sized blueprint of the window onto a board. Following the creation of the blueprint, the glass is produced by combining sand and potash at temperatures of nearly three thousand degrees. While the glass is still in a molten state, the artisan colours it by adding small amounts of metallic oxide powders. Copper oxides were used to produce shades of green or blue-green; cobalt would create a deep blue, and gold could be used to produce a wine-red or violet coloured glass. The then-coloured molten glass would be blown and flattened into sheets. After the sheets of glass had cooled, the artisan would lay the pieces onto the cartoon and crack the glass into rough approximations of the sizes needed with a hot iron. These rough edges would then be refined by a process called grozing, in which an iron tool was used to carefully chip away the excess glass until the precise shape needed for the composition was produced.
Depending on the content of the window, the artist would sometimes be required to paint details onto the glass with a dark-coloured paint made from iron filings and ground glass suspended in a liquid binder, typically either wine or urine. This would block light and help to delineate the features of any figures in the design. At approximately the beginning of the fourteenth-century artists began using a type of paint called silver stain which was made from silver nitrate. This yielded a yellow effect that could vary in colour from pale lemon to deep orange or gold, depending on the thickness of the paint and the duration of its firing. Silver stain was often useful for turning blue glass to green in order to create an image of grass on the window. After being painted, the finished panels of glass would be fitted into H-shaped strips of lead called cames. The lines produced by the lead became an integral part of the window’s overall design and aided in keeping the colours from blending together when seen from a distance. The cames were then soldered together into a secure panel. When the panel was completed, putty would be inserted between the glass and the cames for waterproofing. Finally, multiple panels were placed into an iron frame called an armature, creating the finished window which was then ready to be placed into the wall of a cathedral. This process remained almost completely unchanged for several centuries and could take anywhere from a few weeks to many months to complete depending on the size and complexity of the window.
The two most common styles of stained glass windows made for gothic cathedrals were the tall, spear-shaped lancet windows and circular rose windows. The term rose window was coined around the seventeenth-century because of the way the windows were constructed in a circular shape with layered radiating panels giving them an appearance similar to that of an open rose. Before these windows were given this title, they were referred to as wheel windows, which were described as circular windows of panels separated by spokes of tracery radiating from a central oculus. The main difference between the two terms is that a rose window typically has a more complex design than that of a wheel window.
The use of stained glass windows gained popularity during the mid-twelfth-century. Abbot Suger of Saint-Denis has been called the “Father of stained glass” as it was he who first conceptualized the use of stained glass windows to create a “heavenly light” which was seen as the presence of God in the church. Abbot Suger of Saint-Denis oversaw the construction of the Abbey Church of Saint-Denis and, while trying to conceive a completely new church design, found inspiration in multiple texts he read by a follower of St. Paul named Dionysius (the Greek form of Denis), who considered radiant light to be a physical manifestation of God himself. Suger believed that Dionysius was, in fact, the patron saint of Saint-Denis, so he adapted the concept of divine light into his construction plans and designed the new cathedral around the use of stained glass windows. The Abbey Church of Saint-Denis became the prototype for this new type of architecture based on light, openness, and increasingly taller spaces which later developed even further into what is known as the Rayonnant style. Besides being thought of as divine light, the windows, along with gothic sculpture, have been referred to as a part of the “Poor man’s Bible” based on the fact that another purpose of the windows was to teach Biblical stories to those who were illiterate, which often compromised the vast majority of the citizenry.
A common biblical story that appeared in medieval windows was the “Tree of Jesse”, which was a sort of genealogy or family tree symbolizing the ancestry of Christ. Stained glass windows depicting the Tree of Jesse can be seen at Sainte-Chapelle, Chartres Cathedral, and Notre Dame Cathedral, among other places. In the book of Isaiah, a “shoot” coming from the stump of Jesse is described, sprouting a branch that will grow from his roots. The “root of Jesse” to which it refers is the Davidic monarchy of the eschatological age, and therefore is describing the lineage of kings beginning with Jesse who was the father of King David, proceeding through King Solomon (son of David), and eventually up to the Virgin Mary who usually is portrayed directly beneath the figure of Jesus, or depicted with him as virgin and child at the top of the tree. The oldest Jesse Tree window is at Chartres Cathedral where Jesse is depicted reclining at the bottom of the image with the trunk of a tree coming from his side and leading up to Christ who is larger than the other figures, and seated at the top with seven doves around him, which represent the seven gifts of the Holy Spirit. There are also seven prophets bearing scrolls standing along each side of the tree representing the prophets who foretold the coming of Christ (Sacred-Destinations, Chartres Jesse Window). This window also shows the use of the symbolic and holy number seven and multiples, which seems to be a commonly occurring component in the design of stained glass windows.
The idea of bringing additional light into the church also led to many other architectural advancements within the gothic cathedral. One of the most important advancements was the development and use of the flying buttress, which served as an arched exterior support that could transfer the excess weight of a building outward to where it would be supported by an attached buttress rising from the ground. This allowed an increase in window size as well as more wall space to be occupied by windows. One of the best examples of the use of the flying buttress is the Cathedral of Notre Dame de Paris (“Our Lady of Paris”), which is located on a small island on the River Seine in Paris. At least four different architects contributed to the building of Notre Dame cathedral, with construction beginning in 1163, and continuing until 1345.