It is impossible to predict the lifespan of the lead matrix due to the many variables and challenges it will face. Stained glass windows 800 years old can still be found with their original lead matrix intact. This material is usually the first to go under the knife and completely overhauled during a so called “restoration.” Although there are many cases where the lead channel may not have contained the correct composition of antimony and impurity to last hundreds of years, more often lead failure is localized rather than widespread across the entire window. This localized failure can be a result of several factors including cement loss, weak design concept, inadequate support systems, poor ventilation between storm systems and excessive movement.
When localized lead failure is observed, it is beyond time for action. At this stage an experienced craftsman should be able to visually determine the cause of failure and provide a solution. The complete re-leading of historic stained glass windows should be an absolute last resort, not common practice. This localized failure can be repaired without compromising the rest of the matrix. The methods of assembly and care to detail observed in the lead work should be considered just as priceless as the glass it surrounds. Repairs of this type of failure can be as simple as soldering broken joints, straightening a window that has bulges and deflections or in advanced situations partial lead replacement. Any and all of these repairs should be conducted by highly skilled craftsmen and performed in a manner that will preserve as much original fabric as possible and allow such work to be reversed should the need arise.
Though uncommon, there are many windows fabricated in our country surrounding the world wars that display widespread lead failure. In our experience, windows most commonly suffering from this failure were simple in their design and likely selected from catalogues and mass produced. Although there is no scientific evidence as to why the lead prematurely fails, we believe it is possibly due to the quality of lead used when glazing the panels. During the war effort, for example, the composition of lead used in stained glass may have been compromised due to the production needs for ammunition and various other products. The levels of antimony in the lead may have been drastically increased which would render the lead came stiffer and more brittle. If this was the case, the rigid matrix would not rebound from movement as easily resulting in fractures and crystallization broadcast over the entire panels. This scenario is one of the rare instances we see fit to re-lead an entire window. Imported, often heavily painted, windows from Europe of the same period do not seem to display comparable failure.
Most leaded glass windows will require additional support to provide lateral strength. These materials also require maintenance and protection from rust accomplished through galvanization, paint or powder coating. This support is most commonly achieved one of two ways. The traditional method employs round steel bars secured to the surrounding framework or sash. Copper wire soldered to the panels will be twisted around the rods. This method offers excellent serviceability should the panel require maintenance and repair. The modern alternative, which should only not be used in mason frames, consists of flat steel bars perpendicularly soldered directly to the panel. This method can be hidden into the design of the window easier than the previous. The flat bars are not easily removable if necessary to conduct future repair. Very high temperature soldering irons are necessary to facilitate their removal and extreme patience should be exercised not to damage the lead and glass directly below. We practice both methods depending on the situation; however favor the rods due to their reversibility and character.
Large suites of windows made up of several panels require support systems as well. When installed into timber frames, panels are typically separated by steel “T” bars. These bars act as mullions permanently secured to the wood frame. The steel offers greater strength and less obstruction into the overall design compared to a wood mullion. Panels installed in mason frames are often stacked upon each other and fitted with saddle bars at these junctions.