Medieval stained glass is the coloured and painted glass of medieval Europe from the 10th century to the 16th century. For much of this period stained glass windows were the major pictorial art form, particularly in northern France, Germany and England, where windows tended to be larger than in southern Europe (in Italy, for example, frescos were more common). In some countries, such as Sweden and England, only a small number of original stained windows has survived to this day.
Stained glass windows were used predominantly in churches, but were also found in wealthy domestic settings and public buildings such as town halls, though surviving examples of secular glass are very rare indeed. Stained glass windows were used in churches to enhance their beauty and to inform the viewer through narrative or symbolism. The subject matter was generally religious in churches, though "portraits" and heraldry were often included, and many narrative scenes give valuable insights into the medieval world.
History
Early stained glass
Window glass was in use from at least the 1st century AD and colored and painted window glass for use in religious buildings was also manufactured at an early date. The earliest extant example of ecclesiastical stained glass is possibly that from Basilica of San Vitale in Ravenna, Italy—a clear glass roundel with a depiction of Christ in Majesty, thought to be from the 6th century.
Some of the earliest known examples of colored window glass, datable to c. 800–820, were recovered in excavations at the Abbey of San Vicenzo in Volturno, Italy. Glass of the same colour ranges and similar date has also been found in England, at the monastic sites of Jarrow and Monkwearmouth, and at other sites in the north of England. These examples are not painted. However, it was not until the advent of the monumental cathedral and church building campaigns in the 11th and 12th centuries that the demand for colored glass began to increase significantly, reaching its highest level in the 14th and 15th centuries. The oldest surviving glass windows still in situ are thought to be the Prophet Windows in Augsburg Cathedral, of c. 1065.
A useful 12th-century source on medieval glass manufacture is the De diversis artibus ("On various arts") of Theophilus Presbyter, a Benedictine monk believed by some scholars to be Roger of Helmarshausen, a metal glass and pigment worker of the late 11th and early 12th centuries. It describes a number of craft processes, including glassmaking and glassworking.
In the 9th century or earlier (books 1 and 2 of a 3-vol Mss. completed by another in the 12th, Heraclius, in De coloribus et artibus Romanorum ("Of Hues and Crafts of the Romans"), gives an account of methods for producing colored glass, although he may have copied much of his text from the Natural History of Pliny the Elder of c. 77 AD. Now considered "inaccurate" date on works of Eraclius Later in the medieval period, the son of Anthony of Pisa, artist and instructor Cennino Cennini, and, in 1556, Georgius Agricola also contributed texts with aspects of glassmaking and glassworking.
Composition, manufacture and distribution
Prior to c. 1000, most coloured glass was of a soda-lime-silica composition. In Northern Europe soda glass was eventually almost totally superseded by potash-lime-silica glass (Forest glass). Forest glass continued to be used in stained glass for the duration of the medieval period until soda glass again began to be used in the 16th century.
The potash (K2O) found in Forest Glass was derived from wood ash. In De diversis artibus, Theophilus describes the use of beech wood as the preferred source of ash. Other plant matter, such as bracken, was also used. As well as containing potash, beech ash comprises an assortment of compounds including iron and manganese oxides, which are particularly important for generating colour in glass.
Medieval stained glass panels could be created either by the cylinder blown sheet or crown glass (window) method.
Forest glass was manufactured in Burgundy and Lorraine near the Rhein; in Flanders; and in Normandy, in the Seine and Loire Valleys. It was distributed throughout mainland north-west Europe and Britain in the form of ready-made sheets. The application of painted decoration to and final shaping of the sheets was carried out at glass working centres close by the final destination of the glass.