In the context of quench strain anisotropy, ASTM C1048 is long out of date and unduly generous; it reads as if written by and for glass producers. It is occasionally cited to defend the outcome of poor quality control in glass processing. The current corresponding Euronorm proscribes “visual anomalies” that are tolerated by ASTM C1048.
Two unrelated phenomena, quench strain anisotropy and variations in thickness of sputter-coated low-e coatings, that would be either undetectable or unobjectionable in isolation, can become synergistic and cause conspicuous birefringence when superimposed. This has recently led to the decision to reglaze a high-rise commercial office building under construction in Melbourne, Australia. The heat strengthened glass, manufactured in China, displayed vivid iridescent blue bands and streaks in patterns that cannot be attributed to quench patterns alone. It is the combination of polarization from quench strain and from separate variations in coating thickness that caused the problem. My enquiries in Europe in 2013 and the USA in mid-2014 indicate that the potential for such super-imposition is recognized by some flat glass manufacturers but is not widely discussed. If you provide an email address, I can forward some photographs of the rejected glass in the building in Melbourne.Peter Hartog, Building Diagnostics Asia Pacific, Bangkok, October 11, 2014
Very interesting comment of Peter Harog. Can I received the pictures of the rejected building in Melbourne? I have a similar problem in Montréal, Canada.Louis Fortin, Building specialst, December 16, 2014