Removing high-powered century-old-grime from windows?

Question

We recently had the windows redone in our 1920s-era condo and, in the process, had a wall opened up to reveal windows that were walled off from the inside some time in the 30s. However, the grime on the exterior of the windows will not come off (action shot below). We've tried:

• Windex
• Goo Gone acetone
• Soap and vinegar
• "Magic Eraser" sponges

Whatever substance has bonded itself to the windows, it's not just dirt. I'm guessing something like tar and soot perhaps? Regardless, I'm wondering if folks have encountered similar challenges and how they've tackled the issue.

Answer 1

A bit delayed but the answer is "it's chemical-induced hazing" and, unfortunately, using a scraper changed basically nothing. There was paint on the glass for years, as well as stripper used to remove said paint, and either or both may have been the culprit. Alas, but there will be something in front of the window so the hazing won't be visible.