We do everything we can to prevent scratches on glass. We continue to educate ourselves on this issue but since we are typically the last company on a construction project we can't guarantee how the glass has been treated prior to our arrival. The following is a standard disclaimer on all window cleaning work we do:
Due to widespread problems with poor quality heat treated glass, Keep Up Appearances, LLC will not be held responsible for any scratches on any heat treated glass. It is accepted and understood by ALL parties that properly used razor blades and scrapers are standard tools and techniques for window cleaning and can safely remove limited amounts of debris (plaster, paint, texture, tape, stickers, etc.) from quality glass, without scratching the glass surface. Please visit http://www.scratched-glass.net for further information.
Furthermore, it is accepted, that it is impossible to guarantee that there will not be any scratches on the surface of the glass after cleaning, no matter what method is used to clean them. We take extra measures to prevent scratches, but when glass is not properly manufactured or protected, scratches will occur. These scratches are not usually discovered until after the cleaning when the light will show all the flaws in the glass at which time the scratches will stand out. Dirt and debris on the windows prior to cleaning may make prior scratches difficult to detect.