The featured image is a picture of a rose window in Soissons cathedral, ‘Cathédrale Saint-Gervais-et-Saint-Protais de Soissons‘, a Gothic cathedral in France.
I came across a blog entry on Hewn & Hammered that led me to a very interesting article by the U.S. National Park Service about historic stained glass: specifically stained glass in old homes and how to date it, photograph it, clean, preserve, and repair it. The article is titled Preservation Brief 33: Historic Stained Glass.
I had no idea that this sort of information was available from the National Park Service. The article, written in 1993 by Neal A. Vogel and Rolf Achilles, is absolutely fascinating.
I was most interested to read the details about the history of stained glass in America, which is necessary to know in order to properly date historic stained glass. I also learned intriguing facts about the composition of lead came and the reasons that it has changed several times from medieval times to modern times.
This is an excellent essay containing a great deal of technical information, yet written in a clear and engaging style. I will be adding this site to my History of Stained Glass page.
Here is a picture of Chartres Cathedral, the Cathédrale Notre-Dame de Chartres, which was under restoration at the time.