Broken in half.
It's a clean break (in the best possible spot), and I actually discovered that it was already broken here. There was a thin layer of clear adhesive, which I then removed. I will be able to re-repair the lamp, but it's a bit sucky. The lamp will actually be a good candidate for some Hxtal. Hxtal is a very expensive specialty glass adhesive (used by museums on irreplaceable items like the Portland Vase) that I've been meaning to buy for a few clock related restorations. I have one beautiful original glass tablet from the 1840s with a vertical crack that I wanted to repair with this glue. It takes over a week to set, it goes on very thin and liquidy and dries crystal clear. It's supposed to dry strong enough that if there's any excess, it must be ground-off.
Side notes: the original pewter burner and collar were horribly butchered, and unrepairable, so those also need to be remade/replaced. This is a rather beautiful lamp from around 1830-40.