At the risk of sounding like Monty Python's Anne Elk, I have a theory (hem, hem.) And it is this:
An enormous amount of medieval stained glass is so high up and so far from the naked eye, that it is impossible to discern the details they contain, and even windows lower down require good eyesight to see everything in them. There must have been and still are a great many people with just average or poor or failing eyesight with no access to spectacles or binoculars or telephoto lenses who have sat inside or walked around a church or cathedral, and seen only abstract patterns, blocks of colour, jumbled and kaleidoscopic views. I'm quite sure that the few people who ever saw exactly what was in a window were the makers, the glaziers, the stonemasons and architects, and it's only when glass is removed for safekeeping during wars or for conservation, that it's possible to see them close-up. Nowadays, of course, we can see much more clearly with binoculars (they are very sensible things to have with you, although I use my camera lens), but that doesn't mean that the average congregation isn't still seeing an awful lot of abstract glass.
So when, post-war, the new wave of RCA-trained stained glass artists and designers were shocking the establishment with enormous abstract windows in places like Coventry Cathedral and makers were experimenting with whole walls of dalle de verre, they were still in fact creating the same effects as the medieval makers.
My theory was borne out in the cathedral in Lyon recently. There are some wonderful late medieval windows featuring huge figures of various prophets, with larger-than-life features, lovely surrounding patterns, and interesting feet, halos and hair. But without glasses or anything to help my eyes, all I could see were blocks of brilliant colours and plays of light and dark.
Earlier this year, the cathedral installed a set of eight new windows designed by Jean-Dominique Fleury, Jean Mauret and Gilles Rousvoal and made by Ateliers Duchemin. They are close enough to the prophets for the similarities in colours, lines, and effects to be obvious even to the most myopic visitor. They are beautiful, full of richly coloured glass which has been painted, stippled, scumbled, brushed, dabbed and played with to give surface interest and to play with the light. They remind me of shade cards and jumbled up pages from a Pantone reference book.
And in the end, the effects are remarkably similar to the old glass. The windows may be abstract but they still delight and evoke a sense of wonder just as the hard-to-see, high-up medieval glass does, which is why the new glass fits into the old cathedral perfectly. The two eras, modern and medieval, are really not so far apart at all.