Were the pattern in lines of colour upon white, the crosslines strengthening them would of course be lost in the darker tint; but, as it happens, we do not find in the earliest glazing lines of interlacing colour, though they occur by way of border lines, as at S. Serge (below), where a marginal line of yellow is enclosed between strips of white.
The interlacing character of several of the white glazing patterns illustrated betrays of course Romanesque influence; but there would not have been so many designs consisting of interlacing bands of white upon a white ground, enclosing, at intervals more or less rare, what had best be called jewels of colour, had it not been that the forms of interlacing strapwork lend themselves kindly to glazing.
Every time a strap disappears, as it were, behind another, you have just the break in its continuity which the glazier desires, and if only the interlacings are frequent enough (as on page 96) they give him all he wants.
So far the examples illustrated are, for the most part, in outline; that is to say, on a ground of white the pattern appears as a network of leads, flowing or geometric as the case may be, emphasised here and there by a touch of dark colour, focussing them as it were. Without such points of colour a design looks sometimes too much like a mere outline, meant to be filled in with colour, and, in short, unfinished; but as yet the darker and lighter tints of white are not used to emphasise the pattern, as they would have done if, for example, the interlacing straps had been glazed in a slightly purer white than the ground. On the contrary, notwithstanding the very great variety in the tints of greenish-white, which resulted from the chemically imperfect manufacture of the glass, they were employed very much at haphazard, and so far from ever defining the design, go to obviate anything harsh or mechanical there may be in it. There is else, of course, a tendency in geometric pattern to look too merely geometric. One wants always to feel it is a window that is there, and not just so many feet of diaper.
Another practical form of design is that in which it is not the network of leads, but the spaces they inclose, which constitutes the pattern; where lines are not so much thought of as masses; where the main consideration is colour, and contour is of quite secondary account. The leads fulfil still their artistic function of marking the division of the colours, as they fulfil the practical one of binding the bits of coloured glass together; the glazier still draws in lead lines; but attention is not called to them especially; indeed, with identically the same lead lines one could produce two or three quite different effects, according as one emphasised by stronger colour one series of shapes or another. In the case of a framework of strictly geometric lines, straight or curved, one gets patterns such as we see in marble inlay. The slab of marble mosaic and the stained glass border opposite are more than alike; the one is simply a carrying further of the other. The glass design might just as well have been executed in marble, or the marble design in glass. In the upper church at Assisi are some borders of geometric inlay, one of which is given on page 96, identical in character with the minute geometric inlay (which, by the way, was also in glass, though opaque), with which the Cosmati illuminated, so to speak, their marble shrines and monuments. This species of pattern work, appropriate as it is to glass mosaic, transparent as well as opaque, does not seem to have been much used in glass, even in Italy; where it does occur it is in association, as at Assisi and Orvieto, with painted work of the thirteenth or fourteenth century, though from its Byzantine character it might as well be centuries earlier. It appears that this, which was, theoretically, the simplest and most obvious form of leaded pattern work, and might, therefore, well have been the earliest, was never adopted to anything like the extent to which interlacing ornament was carried.
Mediæval glaziers did not attempt anything like foliated ornament in leaded glass, and for good reason. In such work the difficulty of doing without lines detrimental to the design is greatly increased, whereas abstract forms you can bend to your will, as you can bend your strip of lead. The more natural the forms employed the more nature has to be considered in rendering them, and nature declines to go always in the direction of simple glazing. It might seem easy enough (to those who do not know the difficulty) to glaze together bits of heart-shaped green glass for leaves, and red for petals, with a dot of yellow for the eye of the flower, and to make use of the lead not only for outlines but for the stalks of the leaves and so on, all on a paler ground; but it is not so easy as that. The designer cannot go far without wanting other connecting leads (besides those used for the stalk); and when some leads are meant very emphatically to be seen and some to be ignored, there is no knowing what the actual effect may be: the drawing lines may be quite lost in a network of connecting leads. Again, the mediæval glazier did not, so far as we have any knowledge, build up in lead glazing a boldly pronounced pattern, light on dark or dark on light. This he might easily have done. On a small scale plain glazing must perforce be modest; but, given a scale large enough, almost any design in silhouette can be expressed in plain glazing. You may want in that case plenty of purely constructional leads, not meant to be seen, or in any case meant to be ignored; but if the contrast between design and background be only strong enough (say colour on white or white on colour), they do not in the least hurt the general effect. On the contrary, they are of the utmost use to the workman who knows his materials, enabling him to get that infinite variety of colour which is the crowning charm of glass.
What the designer of leaded glass had to consider was, in the first place, the difficulty of shaping the pieces. That is now no longer very great, thanks to the diamond, which makes cutting so easy that there is even a danger lest the workman’s skill of hand may outrun his judgment, and tempt him to indulge in useless tours de force. The absurdity of taking the greatest possible pains to the least possible purpose is obvious. The more important consideration is now, therefore, the substantiality of the window once made. Think of the force of a gale of wind and its pressure upon the window: it is tremendous; and glazing does not long keep a smooth face before it. Except there is a solid iron bar to keep it in place, it soon bulges inwards, and presents a surface as undulous, on a smaller scale, as the pavement of St. Mark’s; and, as it begins to yield, snap go the awkwardly shaped pieces of glass which the glazier has been at such pains to cut. The mediæval artist, therefore, exercised no more than common sense, when he shaped the pieces of glass he employed with a view to security, avoiding sharp turns or elbows in the glass, or very long and narrow strips, or even very acutely pointed wedge-shaped pieces. No doubt the difficulty of cutting helped to keep him in the way he should go; probably, also, he was under no temptation to indulge in pieces of glass so large that, incapable of yielding, they were bound to break under pressure of the wind. That he sometimes used pieces so small as in time to get clogged with dust and dirt, was owing to the natural desire to use up the precious fragments which, under his clumsy system of cutting, must have accumulated in great quantity. Where most he showed his mastery was, in foreseeing where the strain would come, and introducing always a lead joint where the crack might occur, anticipating and warding off the danger to come. He was workman enough frankly to accept the limitations of his trade. Occasionally (as at Bonlieu) he may have shirked work; but he accommodated himself to the nature of his materials. Never pretending to do what he could not, he betrayed neither its weakness nor his own.
Mere glazing has here been discussed at a length which perhaps neither existing work of the kind nor the modern practice of the craft (more is the pity) might seem to demand. It is the most modest, the rudest even, of stained glass; but it is the beginning and the foundation of glass window making, and it affects most deeply even the fully developed art of the sixteenth