Stained glass windows at Chartres Cathedral

There is much to admire at Chartres Cathedral including its large stained glass windows with the rose imagery, famous for its cobalt blue tints. But controversy erupted in the 1970s - and it's still going really - once cleaning began. The windows, like most of the cathedral, were grimy from hundreds of years of pollution and candle smoke and there were many who found spirituality in the strange blue glow. They complained that the new brightness (which equalized the colors) also removed the mystery. After the windows it was the limestone walls of the sanctuary and the ambulatory that were cleaned up and then, most controversially of all, the repainting of the Black Madonna known as Our Lady of the Pillar so that she no longer looks Black:

Below is the North Rose Window - the rose has been a traditional symbol for the Virgin Mary, to whom Chartres Cathedral is dedicated.

In medieval times, astrology remained popular - below is part of the Zodiac window, showing Virgo, Cancer and Taurus, with Leo and Gemini partly obscured on the left.

It is worth noting that many of the great gothic cathedrals of the era had multicolored exteriors too. The front entrance in particular could be as colorful as the interior windows, as with Amiens Cathedral shown below. The west facade is even better at night - the colors were restored in the 1990's.