Roller Wave Distortion in Heat-treated Glass

Annealed glass that is processed through a horizontal oscillating tempering furnace will contain surface waves creating waviness or roller wave distortion, when viewing reflected images from a distance. The industry standard for heattreated glass, ASTM C1048 Standard Specification for Heat-Treated Flat Glass-Kind HS, Kind FT Coated and Uncoated Glass, specifically addresses distortion in paragraph 7.4.1, as follows:

"Thermally tempered and heat-strengthened glass is made by heating glass in a furnace to a temperature at which the glass becomes slightly plastic. Immediately after heating, the glass surfaces are rapidly cooled by quenching with air from a series of nozzles. The original flatness of the glass is slightly modified by the heat treatment, causing reflected images to be distorted. When viewing images through the glass, the distortion, in most glazing applications, is less than that of the reflected images and is not as noticeable."

Paragraph 7.4.5 states further that regardless of the flatness achieved, the perceived reflective distortion is primarily due to the symmetry of the object being reflected. For instance, linear objects (telephone poles and building curtain walls) and moving objects (such as cars, etc.) may appear distorted, whereas irregular free-form objects (such as trees, clouds) may have little perceived distortion. Roller wave distortion is inherent in all heat-treated glass.

Currently, there is no ASTM or industry standard for maximum allowable roller wave distortion in heat-treated glass