STAINED glass is, next to illumination, the most characteristic embodiment of medieval thought and feeling. Its beauty was an expression of the spirit of the age, and perished with it: later developments and attempted revivals have but faintly echoed that beauty, and never surpassed it.
The art appeared in England for the first time in the latter part of the twelfth century, and was inspired directly from France, a country which was already in 1100 the chief seat of glass-painting. The idea of using colour in glass windows had apparently been brought to western Europe at the time of Charlemagne from Byzantium, although in the East nothing more elaborate than pieces of coloured glass set in pierced stone had been attempted. Stained glass as we know it to-day, i.e. figure-subjects or other designs in coloured glass, outlined by strips of lead, appears to have been a Western and medieval invention. We hear of it in Germany in the ninth century, and at Rheims under Bishop Adalbert in the tenth: but the earliest surviving windows are those in the clerestory of Augsburg Cathedral, containing huge, stiff figures of prophets of the early eleventh century.
The Benedictine monasteries spread a knowledge of the craft through all western Europe. At Cluny the glaziers and metal-workers had a separate building to themselves. But little remains in France before the beginning of the Gothic period, when glass-making played an important part in the schools of art connected with the French cathedrals.
The processes in use are described by Theophilus in his treatise, De diversis artibus.1 The glass is coloured when molten in the pot (hence it is sometimes called pot-metal) by the addition of copper and iron oxides and other chemicals.____________________