Window damage expert examines window scratching from a metal blade (see above photo). A California glass failure analysis expert was asked to evaluate window damage at a newly constructed home. The windows at this site were scratched during cleaning with a six-inch metal blade. The blade traps abrasive dirt and drags it across the glass. Because the dirt is the same hardness as the glass, the window is scratched. The scratches are in a linear array, and their visibility is enhanced by direct sunlight. Glass expert recommends that windows be cleaned per GANA recommendations. GANA recommends that blades never be used to clean windows.