Stained Glass First Aid

Owners of older homes appreciate the beauty of stained glass. In some cases, the stained glass windows may have been the emotional “reason” that prompted you to buy your house. But as with so many other aspects of old house ownership, stained glass needs maintenance and care. Below are some suggestions on how to care for your windows — and how to recognize when to call in an expert.

A stained glass panel is constructed of 1) individually cut pieces of clear or colored glass, or bevels; 2) held together by a matrix of lead came or copper foil. Lead came dates to mediaeval times and is the traditional method of assembling leaded glass panels. Zinc came is associated with the prairie designs of Frank Lloyd Wright and his contemporaries. Copper foiling is the method introduced by Louis Comfort Tiffany, and is the preferred method for constructing intricately designed art glass panels and lampshades. An additional step in the construction of leaded glass panels is the application of cement to fill the space between the glass and the inside surface of the lead or zinc came. Cement is applied to the front and back of the panel to weatherproof and add strength to the panel. Large panels also should be braced with saddle bars or reinforcement bars.

Inspect your windows for age and buckling. To assess the condition of the lead or zinc cames, look for telltale signs of metal fatigue and corrosion. Old lead is still functional if the exposed face of the metal (the flanges) can be lifted and flattened without cracking. Lead covered in a fine white powder has oxidized and has reached the end of its useful life. Zinc covered with small white spots is worn out, too. Examine the metal for hairline cracks near the joints, particularly around the border of the panel. These indicate metal fatigue.

Large or especially elaborate glass panels are often reinforced with steel or brass bars. These saddle bars, about 1/8″ thick by ¼” wide, are attached to the cames and notched into the sash to stiffen the window and help support the panel’s weight. Some reinforcement bars are soldered to the cames, while others are fastened with twisted copper wires. If the bars have separated from the came, they should be reattached using the original method. Bars that have split the came will require releading by a professional restorer.

If the panel has developed a bulge, measure its depth. A panel that is 1″ or less out of line and does not rattle should be professionally examined, but may not need to be repaired. Panels more than 1½” out of true need to be removed from the window and professionally flattened and releaded.

Check the glass. Because of the difficulty in matching some old glass, it is preferable to repair cracked glass rather than replace it. And not every crack needs to be repaired. If the crack is small and in no danger of falling out, leave it alone. If glass is missing or badly cracked, call a professional. If repairs are minimal and the panel is large, an on-site repair may be possible.

If you have to transport the glass to a professional restorer, start by securing loose cames and glass panes with painter’s tape. (Do not use duct tape!) Remove the sash with panel still attached. For added security, lay the panel on a larger sheet of plywood and tape it down. Smaller panels can be wrapped and laid flat in a wooden box.

Clean a sound leaded or copper foiled glass panel with a soft rag and a neutral pH soap. Wring the rag out well. Avoid abrasive products which can scratch the glass or metal. Do not use spray products or those containing ammonia. The liquid can get under the foil or lead came and the ammonia can react with the lead or cement. Windows in bathroom or kitchen settings can be cleaned with a dampened #0000 steel wool pad to remove soap residue, grease, and mildew. Polish with a paste product such as Glass Wax or a stained glass polish available at any stained glass supply retailer. Use a soft rag to apply the paste, let dry, and buff. CAUTION: This process may release lead dust into the work area. Clean any surfaces surrounding the panel (sashes, sill, and floor) with soap and water to contain any lead residue. And wear a dust mask.

Protective glazing, while not necessary, can provide protection to your stained glass panel from vandalism or a wayward baseball. To maintain aesthetics, the storm window sash should be of similar material to the original sash. Depending on local building codes, the glazing can be double strength glass or Plexiglas(R). Note that plastic glazing will yellow and scratch over time. Lexan(R), which will not yellow, is nonetheless very easily scratched. Tempered double strength glass is expensive, but offers the best protection.