Different folks have discussed the safety and danger of using razor blades in cleaning glass, and perhaps you, like many others, have found it scary to actually find out yourself. Is it a good idea to use a razor blade when cleaning glass? The answer is complicated. Many factions disagree, particularly the window cleaners and the glass manufacturers.
The correct answer is IT DEPENDS. It depends on what type of glass you’re cleaning, and who is using the razor blade. The Glass Association of North America, which represents the manufacturers, will tell you that it is never acceptable to use a razor blade on glass; it will damage it.
Window cleaners have been using razor blades for decades when cleaning glass, particularly in post-construction, when they remove paint or glue residue. Perhaps you’re at your home and you have a lot of pine trees and there’s sap on your windows. These are things where the razor blade is the tool of choice in any window cleaner’s arsenal.
Window cleaning with a razor blade is something that should only be done by a professional. It takes someone experienced to make sure that the glass is not going to be damaged. It also takes someone with experience to know the technique to be used, what angle to hold the blade at, and what type of glass he/she is cleaning.
There are several types of glass you never want to use a razor blade on: heat-tempered glass, tinted glass, and safety glass. Doing so could damage the tint on tinted glass and can drag manufacturing debris across the glass in the case of tempered glass, which would certainly cause damage and scratches to it, not necessarily caused solely by the razor blade, but by the fact that the razor blade will catch on to the glass fines and as they get pulled across the glass, scratches will be left behind.
If you’re using an experienced window cleaner, it’s okay for them to use a blade. A homeowner is never recommended to do so.