A light leak is evident just below the thick solder line near the top of the lamp.
Here's another view a bit closer. The split extends down one row, then moves to the right, affecting 4 of the rectangular pieces of glass.
At this point, I wedged my soldering iron into the separation and melted out the old copper foil and solder. The piece which is marked with a Sharpie pen was very loose so I removed it. This gave me better access to the split area and to the other 3 pieces of glass.
Here I'm in the process of removing more of the old solder and copper foil
I've cleaned up the old adhesive which were along the split, then I applied new copper foil to the piece I removed and to the three adjoining pieces of glass. Here I'm applying liquid flux to the foil. This is a liquid agent which allows the solder to flow smoothly on top of the foil.
In the original construction, wires were placed along the solder lines with the intention of preventing the separation. However, the zig-zag decision proved to be ineffective on the side which split. That small straight portion gave the lamp a good half inch of "play". This side held well, the other side (which I'm repairing) did not.
To reinforce that zig-zag, I soldered on a strip of the flat braided copper reinforcement wire as shown. This effectively makes the zig-zag a straight line, giving the lamp more stability with much less chance of separation.
Then I used four more lengths of flat braided copper reinforcement wire and soldered them from the pale area of the lamp to the dark area. This distributes the weight of the lamp around the dome and gives extra security that another separation cannot re-occur.
Here I'm applying black patina to the solder.
Then I clean the lamp of all flux and patina by using Kwik-Clean spray as shown. After the lamp dries, I applied stained glass finishing compound, which is a light wax. Once the wax dried and was buffed, the lamp is as good as new again.
And here's the repaired lamp, ready to go for many more years of service. Thank you so much, Elizabeth, for bringing your lamp to me. It was a pleasure to repair it!