There is filament residue on my glass bed that is so thin that it wont come off. I have had residue buildup for over a year now and none of it has come off. This residue appears with both the PETG and the PLA filament I have. Is there anyway to remove this residue?
I would try a single edge razor blade at a low angle used as a scraper. If you can't feel the blade catching in the residue, it probably isn't an issue.
If you must get rid of it you don't have good choices of solvents. Maybe you can burn it off by placing the class in an oven through a clean cycle. With luck the hearing and cooling won't break the glass.
If you can't scrape it off with a sharp razor blade, I would just let it be.
Heat the bed to around 90 °C and then scrape everything off with a metallic scraper, like the ones used to fill gaps in walls. No need of a super sharp one, since the plastic will be very soft a that temperature.
If you have a razor blade and a proper handle to avoid cutting yourself, you won't need to heat the bed to more than 40 °C, since you dont want the plastic to be too soft.
It's probably not practical, but what would be ideal is to put the glass from the bed in an oxygen plasma asher used in the semiconductor industry. It would probably be difficult to get a used one large enough, since your bed size probably matches state of the art wafer sizes.
What would be even more practical is for someone to develop an oxygen plasma cleaning torch that wouldn't overheat the glass (https://www.semanticscholar.org/paper/FINAL-REPORT-U-.-S-.-Department-of-Energy-Plasma-of-Hicks/fc32a874806de71f1d10f2d979d3a74e2bb7c0d0?p2df). Plasma cutting torches already exist.