Maintenance of the structural support system of a stained glass window is perhaps the most important aspect for the preservation of stained glass windows. The deterioration of 19th-century lead came, due to its purity and tendency to fatigue, and its replacement with lead of a stronger alloy, is the most common problem in American stained glass windows. Often there are too few saddle bars to support the window, so more should be added. Restoration of the window frames must also accompany restoration of the window. -- AATA