The stained glass of the cathedrals of Bourges {166} and of Chartres shows the marvellous success of these old workers in glass and their power to make enduring products. It is a mystery to see how their blues have lasted while the sun has shone through them all these years and caused no deterioration or only such as softens and adds to beauty but not really causes to fade. Blue had to be used in great profusion on the windows because the symbolism of color was well determined and blue stood for the virtue of purity and was the Blessed Virgin's color. It had to come in, therefore, on nearly all occasions. Usually by irradiation blue causes surrounding colors to lose something of their tint, and by contrast often spoils what would ordinarily be expected to prove beautiful color effects. These old workmen had found the secret of using it in such a way as not thus to spoil surrounding colors, not to permit it to be too assertive, yet we have wonderful enduring blues that have come down to us practically unchanged through all these centuries. Where the workmen of the old time set themselves producing pure color effects, their windows look like jewels and coruscate in the light of the setting sun--for their most charming effects were particularly obtained in the west windows--with a glorious beauty that has appealed to every generation since. It was not alone in the building trades, however, that these fine things were accomplished. Bookmaking reached a degree of perfection that {167} has never been excelled. Humphreys, the authority on illuminated books, declares that the manuscript volumes of the thirteenth century, illuminated as they are by the patient labor and the finely developed taste of this time, are the most beautiful ever made. We have one example of the thirteenth-century illuminated book in the Lenox Library in New York for which, I believe, the museum authorities were quite willing to pay some $18,000, and it is worth much more than that now, for it is a wondrously beautiful example of the illuminations of the time. Like the glassmakers, these bookmakers had secrets that have been lost, and that we with all our knowledge of science and of art in the modern time, or at least our fondly complacent notion of our knowledge of art and science, are unable to find the formulas for. They used blues in their illuminating work that have never faded, though blues are so prone to fade on parchment. They managed their blues in wonderful way and they still are as fresh and as undisturbing of the harmony of other colors as in the long ago. They could burnish gold and it stays as bright as when it was first applied to the leaves, even after seven centuries. We have lost the art of burnishing gold in such applied work and ours becomes dull after a time.