Mahommedan windows.
This was as far as stained glass in the East ever got. The Mahommedan conquerors seem to have taken the art as they found it, and continued it down without much change almost to modern times. Their religion debarred them from any attempt to represent living forms, so that the art as it stood sufficed for the needs of their architecture. Visitors to Leighton House may see some of these pierced and glazed lattices from Damascus, and very beautiful they are. In them the pieces are not much larger than a penny, and are set in holes cut in plaster slabs, bevelled on the inside, the glass being set at the outer edge of the hole. The glass is not really of very good quality, but treated in this way even thin poor glass looks rich and jewel-like.
Glass in the West.
What course the glazier's art first followed in the West it is impossible to say, for nothing of it remains earlier than the eleventh century, if as early. Nevertheless, in spite of repeated barbarian invasions, it seems never to have quite died out.
The Church, the refuge of the arts and civilization in the general debacle, sheltered it, and from being the luxury of the Roman millionaire it became the ornament of the house of God. From time to time we get allusions to glazed windows, but never a description that can throw much light on their construction or design. Enough is said, however, to show that coloured glass was sometimes used. For instance, we read that St. Gregory of Tours placed coloured windows in the Church of St. Martin in that city in the sixth century.
One or two facts, however, lead me to think that whereas, in the East, glass was set in stone or plaster, in the West it was usually set in metal. At Pompeii, as we have seen, panes of glass are set in a bronze lattice and fixed with nuts and screws. As colour was introduced it is probable that from the necessity, already spoken of, of keeping the pieces small, several bits would be joined together with lead to fill one opening of the rigid lattice, and so patterns could be formed. Leo of Ostia says his predecessor, the Abbot Desiderius, filled the windows of the Chapter-House at Monte Cassino in the eleventh century with coloured glass, "glazed with lead and fixed with iron"; and certain it is that the earliest existing windows consist of a large rigid lattice of massive rebated iron bars, in which leaded panels have been placed separately, and held there by light cross-bars passed through staples and keyed with wedges.
If this conjecture is correct, we may assume that the art of the glazier had for some time been perfected, and had progressed as far as was possible for it unaided, when its union, probably in the tenth century, with that of the enameller gave birth to the art of "stained-and-painted" glass—that is, stained glass as we know it.
The opaque enamel.
Without the use of enamel the glazier's craft must always have been strictly limited to patterns in glass and lead, or, as we now call it, "plain glazing." What was needed to convert it into the art as we know it was the addition of painting in the black or brown monochrome enamel described in the first chapter.
Only one who has worked in glass, and seen his work grow from a map-like combination of white and coloured glass to the finished glass painting, knows the power the enamel gives him of controlling, softening, and enriching his effects of colour. The power it gives of suggesting form is only one, and not the most important, of its functions, and it was as vital to the work of the twelfth and thirteenth as of the fifteenth century. With its introduction the glorious windows of the Middle Ages became possible.