§ 101 Stained Glass Windows; Their Origin and History
Formerly the ancients were in the habit of filling in their windows, but only in the houses of great men, or of those at least of some importance, in such a manner as to prevent the wind or cold from entering, while not excluding the light. This plan was adopted only in their baths and sweating rooms, vapour baths and other retiring rooms, and the apertures and vacant places of these were closed with transparent stones, such as onyx marbles,264 alabasters, and other delicate marbles that are variegated or that incline towards a yellowish tint. But the moderns, who have had glass furnaces in much greater abundance, have made the windows of glass, either of bull’s-eyes265 or of panes, similar to or in imitation of those that the ancients made of stone; and they have fastened them together and bound them with strips of lead, grooved on both sides, and furnished them and secured them with irons let into the walls for this purpose, or indeed into wooden frames,266 as we shall relate. Whereas at first the windows used to be made simply of clear bull’s-eyes with white or coloured corners, afterwards the artists thought of making a mosaic of the shapes of these glasses differently coloured and joined after the manner of a picture.267 And so refined has the skill in this art become, that in our days glass windows are seen carried to the same perfection that is arrived at in fine pictures upon panel, with all their harmony of colour and finish of execution, and this we shall amply show in the Life of the Frenchman Guglielmo da Marcilla.268
In this art the Flemings and the French have succeeded better than the other nations, seeing that they, with their cunning researches into pigments and the action on them of fire, have managed to burn in the colours that are put on the glass, so that wind, air, and rain may do them no injury, whereas formerly it was customary to paint windows in colours coated with gum and other temperas that wasted away through time and were carried off by the winds, mists, and rains, till nothing was left but the mere colour of the glass. In the present age, we see this art brought to that high grade beyond which one can hardly desire further perfection of fineness and beauty and of every quality which contributes thereto. It supplies a delicate loveliness not less beneficial to health, through securing the rooms from wind and foul airs, than useful and convenient on account of the clear and unimpeded light that by its means is offered to us.
In order to produce such windows, three things are necessary, namely, luminous transparency in the glasses chosen,269 beautiful arrangement in that which is worked out with them, and clear colour without any confusion. Transparency is secured by knowing how to choose glasses that are clear in themselves, and in this respect French, Flemish, and English glasses are better than the Venetian,270 because the Flemish are very clear and the Venetian much charged with colour. In clear glasses when shaded with darker tints the light is not totally lost, they are transparent even in their shadows, but the Venetian, being obscure in their nature and darker still in their shadow, lose all transparency. Again many delight in having the glasses loaded with colours artificially laid on so that when the air and sun strike upon them, they exhibit I cannot tell how much more beauty than do the natural colours; nevertheless, it is better to have the glasses clear in their own substance, rather than obscure, so that when heavily coloured they may not be left too dim.