In the thirteenth century the practice of the earlier glaziers stiffened into something like a tradition, and design took almost inevitably the form of (1) the Medallion window, (2) the Single Figure window, (3) Ornamental Grisaille.
The full-blown thirteenth century Medallion window differed from what had gone before in that it was more orthodox. The designer begins as before by marking off a broad border to his glass, defined on the inner side by an iron bar, and proceeds to fill the space within the border with medallion shapes. But he now adapts the medallions more regularly to the spaces between the bars. At most two alternating shapes occur throughout the length of the light, without break or interruption, such as occurs in earlier work, and as a rule they keep strictly within the lines of the border. In all the nine examples here given, taken at random from Chartres, Bourges, Canterbury, and elsewhere, only in one case does a medallion cut boldly across the border in the head of the light. The slight overlapping of the quatrefoils in one case is not really an overlapping of the border but only of the marginal lines to it, not shown in the diagram [above], but clearly enough explained on [page 132], which shows the completion of a corner of the window, less its side border. In the window with large circular medallions divided into four, there is no upright bar to define the border, faintly indicated by a dotted line.
69. Bars in Early Medallion Windows.
It will be seen from these diagrams, which illustrate at once the main divisions of the glass and the position of the ironwork, what a change came over the construction of windows in the thirteenth century. The window is no longer ruled off by upright and horizontal bars into panels into which the design is fitted; it is the bars which are made to follow the main lines of the design, and to emphasise the forms of the medallions. The rare exceptions to this rule (as at Bourges, [overleaf]) may generally be taken to betray either the beginning or the end of the period; but at Poitiers they seem to have passed through the early period without ever arriving at shaped bars. The early glazier, it was said, first blocked out his design according to his leading; here he begins with the bars. The iron framework forms, itself, in many of these windows, a quite satisfactory pattern, and one which proudly asserts itself in the finished window. The designs of the period are not of course all equally ingenious. Sometimes, in order to strengthen a circle or quatrefoil of great size, the glazier, instead of breaking up the shape ornamentally as was the rule, merely supports it by cross bars; not only that, but he accepts the awkward shapes given by them as separate picture spaces. Of this comes one of two evils: either he frames his little pictures with sufficient border lines to keep them distinct, and so draws attention to the shapes, an attention they do not deserve; or he has to accept the bars, with perhaps a fillet of colour, as sufficient frame, which they are not, and his pictures run together, to the bewilderment of whoever would decipher them.
70. Spandrils of Medallion Window, Bourges.