What is Distortion?
On flat, non-heat treated glass such as annealed or laminates the reflected image of an object is seen as normal with light rays reflecting at equal, but opposite angles. On heat treated glass, such as tempered units, where the glass might be curved light waves bounce off the varying angles and this causes the reflected image to be modified.
Concave surfaces cause the reflected image to appear shorter and thinner while convex surfaces cause the reflection to appear stretched. These two effects are common in heat treated glass with roll wave distortion resulting in a reflection that can stretch and compress based on the observer’s movement in relation to the glass surface.
Facts about Roller Wave Distortion
Tempered glass units are heat-treated in a horizontal oven and contain waves created when the units come in contact with the rollers during the heating process. This waviness, known in the industry as roller wave distortion, can be seen when looking at a reflected image on the glass from a distance. It does not however, noticeably affect the clarity of images when looking through the glass.
The process of heating float glass followed by rapidly cooling it, will always cause optical distortion to some degree. Heated glass will sag slightly between the carrier rollers in the furnace. After heating, the glass passes through a rapid cooling process that results in heat-strengthened or fully tempered glass. This process can result in a slight deviation from optically flat glass. Although glass thickness and size can affect the amount of distortion, the effect of distortion cannot be eliminated.
Roller wave distortion is not considered a defect in the manufacturing process of tempered or heat treated glass units.