(2) _The Mosaic Character of the Glass._--The designer depends for his effect primarily upon glass and lead, and builds up his window out of tiny pieces. He had learned the jewel-like effect this gave to his work, and seemed to grudge no labour in it. Take, for example, the Ark at Canterbury in Plate IV. Where a fifteenth century painter would have been content to make the ark of perhaps only one piece of glass, probably of white, getting his detail in enamel and silver stain only, our thirteenth century craftsman has used over fifty pieces, purple, blue, red, yellow, green and white, and that in a space less than a foot square! He was a colourist par excellence, and his waves, too, are blue, greenish-blue and green, with caps of white foam--all a mosaic of glass and lead. From this dependence for its effect on the actual material used, it follows that the work of no period is more easily damaged than this by so-called "restoration." The introduction of only half a dozen pieces of crudely coloured modern glass is often enough to upset the whole harmony of the colour and to make the window irritating instead of restful to the eye. In France, indeed, so few windows of this period have been left unrestored that the period does not always get justice done it. I doubt if many people honestly get much pleasure from the effect of the windows of the Sainte Chapelle at Paris taken as a whole; but if you notice how much of the original glass is in South Kensington Museum you will understand the reason. [Sidenote: The iron-work.] (3) _The Influence of Iron-Work._--The windows of this period consisted from the first, as we have seen, of separate leaded panels inserted into the openings of an iron lattice. This lattice was formed of iron bars of a =T= shaped section, the head of the =T= being outwards, and having staples at intervals on the inner rib, through which light iron bars were thrust and keyed with wedges, to hold the glass in its place. In the absence of any tracery to assist in the support of the glass, this iron-work in large windows was of a massive character and could not be disregarded in the design. In figure work there were two possible ways of dealing with it: one was to make the figures so large as to be independent of it; and the other was to make the figures so small that a complete figure-subject could be included in one opening of the frame work.