Anisotropy and Haze Measurement with Online Scanners

Balance Between Architect´s Expectations and Glass Supplier´s Delivery Quality





Architects and facade planners require that anisotropies or haze, optical phenomena disturbing the clear appearance of a glass, have to be avoided completely. Both phenomena are related to the production process and depending on the furnace technology and so cannot always be avoided completely. Anisotropies result from different tensions inside the glass. They mainly are found in tempered glass. Most of the producers see anisotropies as process inherent and as up to now, there were no online measurement systems available. Without an online system the glass processors cannot control or react to these issues in time, and offline systems are too slow to provide feedback fast enough to allow changes for the heating or quenching section of the furnace to avoid anisotropies or haze.

In summer 2017 a pilot project for the development of a scanner to detect and measure anisotropies and haze has been completed. Positioned directly at the outlet of the furnace, the Viprotron Anisotropy Scanner controls the exiting glasses and provides online images of the anisotropies of each glass of the furnace load. Simultaneously the localization and measurement of the intensity of the anisotropies takes place. This helps to optimize the furnace parameters to improve the delivery quality of the final product. Planners, architects, facade constructors, etc. can be informed about the abilities of the tempering equipment with samples. Accepted levels of anisotropies and White Haze can be defined. In production, this level is checked continuously and can be secured and documented in an optimal way with the help of an Anisotropy Scanner. This is why some of the leading European glass processors already use this device in their tempering facilities and the Glass Magazine has awarded this scanner as the “Most innovative Equipment or Machinery 2017.”


The case is always the same: The glass supplier describes his products as superior or the best in the market and raises the expectations of the buyer, in this case

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Anisotropies can be explained as iridescence in the glass body, which cannot be reworked in the finished product. In the past the glass processing industry just declared that anisotropies are

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Anisotropy Measurement and Visualization

Seeing the need to have the online measurement, the question about the appropriate measurement method had to be answered. Anisotropies are visible under polarized light in direct

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Data and Documentation


The data coming from the Anisotropy Scanner can be archived for each individual pane. The scanner takes the images of a complete furnace batch online and then separates and allocates

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Conclusion and Future Work

While many of the optical imperfections on or in glasses were already under online control, Anisotropies and White Haze now become manageable as well. Using the Anisotropy Scanner the production

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The author wishes to acknowledge the following person for providing information used in this paper:
Kai Vogel, Viprotron GmbH, Pfungstadt, Germany.

Rights and Permissions

Dehner, Hermann and Schweitzer, Albert. Thermisch vorgespannte Gläser für den Architekturbereich ohne optisch
wahrnehmbare Anisotropien
, Glasbau 2017, Ernst & Sohn: 397-405
Smith College. “Lecture Notes – Optics 4: Retardation, Interference Colors” (accessed September 30, 2017)