In the past century, it became practice to include hardeners in the cementing formula used to stiffen and strengthen the channels of the lead cames, and it was a practice embraced by almost all professional stained glass studios. Unfortunately, decades later, when it came time for windows to be re-leaded as is normal about every 75-100 years, restorers discovered that the inclusion of the hardening portland cement, made it virtually impossible to disassemble the window without breaking the glass. Good intentions had created an enormous dilemma, compounded by the fact that many glasses used early in the past century were no longer available. So matching and replacing broken glass becomes a nightmare for the modern artist.
Just such a situation occurred at St. Charles and here is a picture of an interior door panel that has buckled:
Sometimes the bow in the panel can be gently flattened without damaging the window, but that is not the case in this situation. More to come on how this restoration proceeds.