The window in the photograph above was damaged during post construction
cleaning. Although glass is a hard material, dust, sand and other debris are just as hard and can damage glass. Therefore, one must be careful when cleaning glass. The damage seen in the window above is only visible in direct-oblique light; thus, it is visible at a certain time of the day in sunlight. The scratches literally “light up”. There are numerous legal disputes generated by this type of damage. The Glass Association of North America (GANA) has published a bulletin (#01-0300) that is a good reference for cleaning windows.