From the fact that the glass between the line work was left nearly clear, the work of this period is more affected by irradiation than any other, and the artist had to make his line work very black and thick in order to tell at all, especially in work far from the eye. For instance, if he wished to distinguish the fingers of a hand he separated them with solid black spaces as thick as the fingers themselves. [Sidenote: The line work.] The glass between the line work is left nearly clear, but not quite; for if quite clear the intensity of the light would have bitten into the edge of the black line and made it appear what engravers call a "rotten" line, or even be invisible altogether at a little distance. Therefore the painter softened the edges of his line work by one of two methods. The first, described by Theophilus, though I cannot say for certain that it has been used in any glass I have examined, was to slightly smear the painting when wet with a soft brush. The other, which seems to have been more used, was to edge the dark line work, so to speak, with fainter strokes in semi-transparent half-tone. In work that was meant to be placed near the eye the line work is extraordinarily fine and delicate, while in work that has to be seen from a distance, such as the clerestory windows of a cathedral, we find the whole scale of the execution increased. Lines are there used from half an inch to an inch thick, but in every case the work is equally admirable for its precision and vigour. [Sidenote: The "Matt."] In the later periods the half-tone shading became developed into the "matt" or thin coat of enamel laid evenly all over the surface of the glass, from which, when dry, the lights were brushed out and the line work became more and more delicate. Still, as long as technique remained sound, the strength of shading was really obtained by line work, the matt or half-tone serving its true use in softening the light and making the line work visible. Renaissance glass painters, in their efforts to produce the effects of oil painting in glass, tried to get rid of the effect of irradiation altogether by dulling the whole surface of the glass, with fatal results to the beauty of the material. To sum up, although the work of this period may suffer in popular esteem from the drawing being conceived in an archaic convention,--a convention different to our own,--and from having suffered from restoration, the fact remains that at no time did the artist understand better the possibilities and limitations of his art and adopt a sounder technique in regard to them. FOOTNOTE: [5] It seems to have been the practice of glass-workers in the Middle Ages to describe the different colours in glass by the jewel they most nearly resembled. A survival of this at the present day is their universal habit of calling red glass "ruby." [Illustration: PLATE VI SCROLL-WORK, FROM THE EAST WINDOW, CANTERBURY Twelfth or early Thirteenth Century] IV