The popular idea of an early window is that of a picture, or series of pictures, very imperfectly rendered. It may much more justly be likened to a magnified plaque of Byzantine enamel with the light shining through it. The Byzantine craftsman, or his descendants, at all events, did produce, in addition to the ordinary opaque enamel, a translucent kind, in imitation presumably of precious stones; and it might very well be that it was from thence the glazier first derived the idea of coloured windows. Quite certainly that was nearer to his thoughts than any form of painting, as we understand painting nowadays; and, what is more, had he aimed deliberately at the effect of enamel (as practised in his day), he could not have got much nearer to it. His proceeding was almost identical with that of the enamel worker. In place of vitreous pastes he used glass itself; in place of brass, lead; and, for supplementary detail, in place of engraved lines, lines traced in paint. Side by side with the early European window glazing, and most likely before it, there was practised in the East a form of stained glass window building of which no mention has yet been made. In the East, also, windows were from an early date built up of little pieces of coloured glass; but the Mohammedan law forbidding all attempt at pictorial representation of animate things, there was no temptation to employ painting; the glazier could do all he wanted without it. His plan was to pierce small openings in large slabs of stone, and in the piercings to set numerous little jewels of coloured glass. The Romans, by the way, appear also to have sometimes filled window spaces with slabs of marble framing discs of coloured glass, but these were comparatively wide apart, more like separate window-lets, each glazed with its small sheet of coloured glass. The Oriental windows, on the contrary, were most elaborately designed, the piercings taking the form of intricate patterns, geometric or floral. Sometimes the design would include an inscription ingeniously turned to ornamental use after the manner of the Moorish decorators of the Alhambra (page 15). A further development of the Oriental idea was to imbed the glass in plaster, a process easy enough before the plaster had set hard. This kind of thing is common enough in Cairo to this day, and specimens of it are to be found at the South Kensington Museum.
M. Vogué illustrates in his book, La Syrie Centrale, an important series of windows in the Mosque of Omar (Temple of Jerusalem), erected in 1528, by Sultan Soliman. The plaster, says M. Vogué, was strengthened by ribs of iron and rods of cane imbedded in the stouter divisions of the framework, a precaution not necessary in the smaller Cairene lattices (measuring as a rule about four superficial feet), in which the pattern is simply scooped out of the half-dry plaster.
The piercings in these Oriental windows and window lattices are not made at right angles to the slab of stone or plaster, but are cut through at an angle, varying according to the position and height of the window, with a view to as little interference as possible with the coloured light. The glass, however, being fixed nearest the outside of the window, there is always both shadow and reflection from the deep sides of the openings, much to the enhancement of the mellowness and mystery of colour. In the Temple windows referred to, still further subtlety of effect is arrived at by an outer screen or lattice of faïence. Thus subdued and tempered, even crude glass may be turned to beautiful account.
Whence the mediæval Arabs got their glass, and the quality of the material, are matters of conjecture. If we may judge by the not very ancient specimens which reach us in this country, the glass used in Cairene lattices is generally thin and raw; but set, as above described, in jewels as it were, isolated each in its separate shadow cell, the poorest material looks rich. The lattices here illustrated are none of them of very early period; but, where the character of design is so traditional and changes so slowly, the actual date of the work, always difficult to determine, matters little.
It is more than probable, it is almost certain, that the Venetian glass-workers, who in the tenth century brought their art to France, were familiar with the coloured lattices of the Levant; for, as we know, in the middle-ages Venice was the great trading port of Italy, in constant communication with the East. If that was so, the Italians, always prone to imitate, would be sure to found their practice, as they did in other crafts, more or less upon Persian and Arabian models. At all events, there is every reason to suppose that at first they, practically speaking, only did in lead what the Eastern artificer did in stone or plaster, and that the windows which, according to various trustworthy but vague accounts, adorned the early Christian basilicas as early as the sixth century, bore strong likeness to Mohammedan glass—Christianised, so to speak. This is not to unsay what was before said about the affinity of early glass to enamel. A river has not of necessity one only and unmistakable source; and though we may not be able to trace back through the distant years the very fountain of this craft, we may quite certainly affirm that its current was swollen by more than one side-stream, and that its course was shaped by all manner of obstinate circumstances and conditions of the time, before it went to join the broad and brimming stream of early mediæval art.
One more source, at least, there was at which the early glazier drew inspiration—namely, the art of jewel setting. Coloured glass, as was said a while ago, was itself probably first made only in imitation of precious stones, and, being made in small pieces, it had to be set somewhat in the manner of jewellery. In all probability the enameller himself wrought at first only in imitation of jewellery, and afterwards in emulation with it.
Just as white glass was called crystal, and no doubt passed for it, so coloured glass actually went by the name of ruby, sapphire, emerald, and so on. It is recorded even (falsely, of course) how sapphires were ground to powder and mixed with glass to give it its deep blue colour; indeed, this wilful confusion of terms goes far to explain the mystery of the monster jewels of which we read in history or the fable which not so very long ago passed for it. Stories of diamond thrones and emerald tables seem to lead straight into fairyland; but the glass-worker explains such fancies, and brings us back again to reality.
Bearing in mind, then, the preciousness of glass, and the well-kept secrecy with regard to its composition, it is not beyond the bounds of supposition that the glazier of the dark ages not only intended deliberately to imitate jewellery, but meant that his glass should pass with the ignorant (we forget how very ignorant the masses were) for veritably precious stones.
Even though we exempt glaziers from all charge of trickery, it was inevitable that they should attempt to rival the work of the jeweller, and to do in large what he had done only in small. That certainly they did, and with such success that, even when it comes to glass of the twelfth, and, indeed, of the thirteenth century, when already pictorial considerations begin to enter the mind of the artist, the resemblance is unmistakable.
Try to describe the effect of an early mosaic window, and you are compelled to liken it to jewellery. Jewelled is the only term which expresses it. And the earlier it is the more jewel-like it is in effect.
So long as the workman looked upon his