There are three general methods to replace broken elements in a leaded glass window.
Disassembly and Replacement
Folding back the face of the lead to allow the new glass to be inserted into the opening
Epoxy Putty for Glazing
Disassembly and replacement of broken glass is the correct way to accomplish most repairs. The panel is removed from the door or window sash, laid flat, and taken apart as needed, just like a jigsaw puzzle. The channels of the metal came are cleaned out and new glass cut to fit and the panel is reassembled and waterproofed. Done properly, nobody will be able to detect a repair has ever been made.
Here is an example of a typical repair, done correctly.
Folding the face of the lead is not a common technique because it is a tedious and time-consuming process. The lead is carefully lifted away from the broken glass element and when a new piece is installed, the lead folded back into it’s original position. We only use this technique on large windows that are too difficult, too fragile, or impossible to remove from the structure. Never on an entryway door or sidelite.
Here are some photos of a completed repair using this technique. It was an antique, fragile window in a rotted sash. We replaced 20 to 30 pieces of glass, re-waterproofed the window, built a new rot-proof sash, and correctly installed reinforcing bars.
We will never use epoxy putty for glazing the replacement glass into an opening. This is visually ugly, usually fails in a short time, and absolutely guarantees a shop repair to un-do this should another repair be required on the panel. The people who use this process remove the broken glass from the panel, and cut a replacement piece that is actually too small. It is finessed into the opening, propped into place, and the edges sealed with a “bondo” putty.
Below are some photos of the outcome of this technique. You be the judge if it is what you want done in your entryway. In some of the photos the broken glass has already been removed, showing the residue of the bondo remaining in the metal. All the metal had to be replaced, as the bondo ruined the metal, increasing the price of the repair by a significant amount. We strongly recommend you avoid any repair service that uses this amateurish technique.