(1) The simplification of the iron-work. (2) The invention and use of silver stain. (3) The combination of figure work and grisaille. (4) The extraordinary development of the canopy. (5) The style of drawing the figure. (6) The use of natural plant forms in ornament. (7) The quality of the glass, and the colours used. (8) The use of painted diaper patterns on the coloured backgrounds. * * * * * [Illustration: PLATE XXIII ST. BARNABAS, FROM CLERESTORY OF NAVE OF ST. PIERRE, CHARTRES Early Fourteenth Century] [Sidenote: Tracery] [Sidenote: The iron-work.] (1) _The Simplification of the Iron-Work._--The windows of the twelfth century had been huge single lights, but the thirteenth century had seen the gradual evolution of tracery, beginning with the grouping of lancets in pairs under a rose light above. Gradually each lancet was again subdivided into a pair of lights and a rose, the spandrils were pierced, till, at the close of the century, the glazier had to design his window to fit a row of narrow lancets divided by slender mullions, which above branched into an elaborate mass of tracery containing a multitude of roses, quatrefoils, trefoils and little openings of all shapes and sizes. With this division of the window into comparatively narrow lights the need for the elaborate iron lattice of the preceding age disappeared, its work being now largely taken up by the stone-work. Instead of lights from six to nine feet wide the glazier had now to deal with lights three and a half feet wide at most, and often much narrower, and in consequence all that was necessary was a series of horizontal bars connecting the mullions, which themselves take the place of the upright bars of former days. In windows of this time, then, and later, massive rebated bars are fixed horizontally in the stone-work at intervals of between three and four feet, and these with the mullions really form the framework into the square openings of which the panels of the glazing were inserted separately. Between, and parallel with, these massive bars, three or four light "saddle-bars" are fixed on the inside of the glass, which keep the panel in its place, the glass being attached to them by means of strips of lead (called bands) soldered to the lead-work of the glazing and twisted round the bar. In order to distinguish between the massive rebated bars which hold the top and bottom of each panel and these light bars between, I shall speak of the former as "frame-bars," the latter by the name they still hold, of "saddle-bars."