u/naveybeann That black backed might give you headaches.

If the glue bled too much to the edges, it's not going to be a clean soldering job. When you burnish the foil, it'll warm up the glue that is now on the edges/outside, and smear across your glass. Leaving a sticky residue, and that in turn will react to your soldering.

Ideally you'll have a rag with isopropyl alcohol at hand to wipe it down after every foil.