Stained-glass windows, by their nature, are fairly delicate. Without careful handling, they can be damaged. The ability to repair a broken stained-glass window requires patience, dexterity and the right tools. A good eye for color and texture is also useful when looking for glass to replace the broken piece if you do not have a spare piece of the original glass.
The technique used for the repair will vary somewhat depending on what method was used to build the window. The two methods possible are copper foil and lead came. Copper foil means each piece was wrapped with copper foil, then soldered with a continuous solder line along all the seams on both sides to hold the pieces together. Lead came uses H-shaped lead that the glass fits between, tucked into the channels, and the joints are soldered to connect everything.
Removing broken glass from a copper foil stained-glass window requires a soldering iron, needle-nose pliers, a glass cutter and safety glasses. If the broken glass is already in pieces, use the pliers to gently pull out any that can be removed. If needed, score the broken piece with the glass cutter to break it further, which makes it easier to remove the shards. Use the soldering iron to melt the solder around the edge of the broken piece, pulling free the copper foil that was wrapped around the broken glass. Use care not to pull off the copper foil wrapped around the surrounding pieces, because it is very difficult to get a new piece of copper foil to adhere to the glass again, even after cleaning.
The glass is held into the lead came with putty, which may need to be carefully loosened with a sharp blade so that it releases the broken pieces. If needed, use the glass cutter to score and further break the glass so that it can be removed more easily. Use the needle-nose pliers to remove all pieces of glass from the broken section, and clean the putty out of the lead came if possible. If not, the lead came may need to be replaced as well.
Trace a pattern of the area where the broken piece was removed and use that to cut a new piece of glass. Grind it to size as needed with a glass grinder, then wrap the piece with copper foil, smooth the foil around all edges with a fid (a pointed tool) or the side of a pencil and set it in place. A nickel or quarter can be used to hold the replacement at the same level as the rest of the window. Apply either paste or liquid flux with a brush and solder the piece in place on both sides. Clean and polish the window as needed.
Trace a pattern for the replacement glass by drawing the opening where the broken piece was removed, and add about 1/8 inch around each side, depending on the depth to the middle of the lead came. To replace a piece of glass in a lead came window, remove a section of the window to provide access to the piece that needs new glass. Determine the best area to remove by assessing the number of joints that will need to be melted and replaced. If lead came is melted during this process, you will need to replace pieces of lead came as well as glass. Cut the glass to your pattern and grind it to fit. Set all sections back into place, and solder all joints that were separated. Replace the putty around the new glass, and clean and polish the window as needed.
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