Cleaning up a horribly yellow etching

This wasn't intended to be a video originally. I picked up this etching by Gertrude Ellen Hayes (1872-1956) of a cathedral scene, but it was a horrible yellow-y colour. My first thought was that the paper itself had discoloured over time (which sometimes happens and for which there would've been no fix), but it turns out that it was just residue on the glass itself. I suppose it must've been nicotine given the colour but oddly there was no cigarette smell to it. Anyway after I dabbed at one area with a wet cloth I saw that it was actually going to come off completely so I figured at that stage that I might as well record the process. All I used were kitchen towels dabbed in warm water. (It's important that they're damp rather than wet as you don't want water getting under the edges of the frame.) It's quite satisfying to remove the disgusting mess from something like this and leave it looking close to how it did a hundred years or so ago. PS if anyone knows the location shown then let me know. There's quite a few cathedrals with towers similar to this so it's hard to narrow it down.