A leaded glass window can break and may need to be repaired. This process requires patience and the proper tools. When there is broken glass in a leaded panel, window or other glass piece, you will need to use your experience of cutting glass and the following process to repair leaded glass.
Match Glass - According to Joe Ring, owner of J. Ring Glass Studio, you can shine up old glass that has become dull due to being dirty, weathered, or poorly cleaned over the years. Wash the old glass, with a clean towel, in a 7 per cent lye and 93 per cent water solution. Rinse in a 20 per cent vinegar and 80 per cent water solution, and then rinse in just water. This will make it easier to match with replacement glass.