In our series Sticks & Stones, we take a deep dive into medium. Each installment features one of art history’s most significant materials—its history, evolution, and unusual uses. (See past installments.) This week’s medium is stained glass (explore the playlist).

Early in the 12th century, a German monk named Theophilus penned an account of stained glass technique. He detailed how to melt sand, potash, and lime in clay pots to create glass, and the different metallic oxides that could be used to add color: copper creates a vibrant green, while even a tiny amount of gold yields a rich, dark red. The processes Theophilus wrote of were not new—in fact, the tradition stretched back to ancient Egypt and Phoenicia. The people of the ancient world were prolific and skilled in glass work, and stained glass was a prized, sought-after commodity around the world, from Syria to Britain. And yet, as Theophilus wrote, many of the tried-and-true recipes for the beautiful, gem-like works were only just being rediscovered.

Europe’s Dark Ages was a time of technological and scientific regression. The sophisticated practices and teachings that had been developed during the Classical period were supposedly forgotten. This drought of knowledge and progress was especially easy to see in art and architecture (perhaps deceptively so): forms became increasingly basic, complex building techniques rapidly disappeared from use, utilitarian simplicity took precedence over beauty and elegance. In early Christian churches of the Dark Ages, where the techniques of glassmaking were lost, it was not uncommon for thinly-sliced pieces of alabaster to be set into wooden frames to create a similar—though rather less impressive—result. While the artisans of the Dark Ages may have largely forgotten how to create stained glass, the symbolic importance of light in the Judeo-Christian faith prevented the medium from slipping fully from memory. Stained glass windows are tied to the Christian faith through a long and complex history. The Biblical commandment “let there be light” is just one of many links drawn in the religious tradition between the presence of God and light. Places of worship have frequently been designed to let in beams of light (quintessentially, through stained glass). Capable of presenting religious images that seemed lit from within, while also flooding church interiors with spectacular colors, the windows served the dual purposes of lighting the space while providing a sense of awe.

The Gothic period saw the revival of complex art and architecture—and with it, the rediscovery of stained glass. Gothic architecture emphasized ornate drama. The cathedrals built over the course of the 12th century boasted towering spires, flying buttresses, and massive, decorative windows. It was at this time that many of the modern conventions of stained glass were developed. The so-called ‘Rose’ window, a large circle with kaleidoscopic, radial symmetry, was one example, as were altarpiece-like multi-window religious scenes. By the Renaissance, skilled craftsmen were able to render complicated designs of artists from sketches into full-scale works of stained glass. The artist Lorenzo Ghiberti is best known for defeating Brunelleschi in a famous design competition of 1401, which resulted in Ghiberti’s beautiful bronze doors gracing the Baptistry of St. John in Florence. At the same time that Ghiberti was butting heads with Brunelleschi, however, he was deeply involved in another massive project in Florence. Partnering with master glassmaker Niccolò di Piero Tedesco, Ghiberti undertook the daunting task of redesigning the stained glass windows of the Opera di Santa Maria del Fiore. In his memoirs, Ghiberti boasts of his two oculus windows depicting Saints Stephen and Lorenzo, and a host of smaller chapel and tribune windows throughout. His designs were soon joined by works from the generation of artists immediately following his own, such as Andrea del Castagno and Paolo Uccello.

From medieval times onward, little changed in the way stained glass was used, with minimal technical innovation. Until 1880, that is—in New York City. Today, the name ‘Tiffany’ conjures diamond rings and robin egg blue boxes, but Louis Comfort Tiffany’s driving passion was stained glass. He happened to be the first Design Director at Tiffany & Co., which was started by his father, Charles Lewis Tiffany. Both a talented craftsman and designer, Tiffany revolutionized the medium, experimenting to achieve a more varied palette of vibrant colors, as well as an entirely new kind of opalescent, shimmering glass. He is most commonly associated with the Art Nouveau and Aesthetic movements, a connection felt even in a passing glance at his work. Many of Tiffany’s works now reside in museums and renowned art collections—cementing an important link between the secular art world and a beautiful medium that had for so long existed only in religious spaces.