from The New York Times -
A Gigantic Job for Window Fixers
go to article
go to slideshow

A nice account of the daunting task of restoring stained glass windows that are exposed to the weather. The list of problems to overcome mentioned:

"The lead has deteriorated from thermal expansion, corroding in whitish, fuzzy patches that are to lead as rust is to iron. The glass is cracking as well, causing dirty-water leaks that have congealed into a hard crust through the years.

Not to mention sagging: Some windows have bowed out after years of expanding and contracting in the sun.

What is more, in 1982 a protective exterior glazing believed at the time to be useful for energy conservation was installed at St. Thomas, as in hundreds of other churches. But the glazing trapped interior condensation and heat, which accelerated the deterioration of the lead."

Yet after the restoration work is completed, the stained glass windows are: "expected to last 100 years. Then it’ll be time for the next restoration.”
.