In October 2005, I visited Bau 95 in Basel, Switzerland. Designed by Herzog & de Meuron this building was part of the Roche campus. The pharma company created a series of building all designed by the global most creative architects.

Glaverbel supplied the coated glass for this project.

From the curb, at a certain angle, I noticed a yellow hue in all the double-glazing. The pattern was repetitive and looked like a vertical 50 cm band. Before travelling, my friend Yves Lecoq, Glaverbel’s Quality Manager, gave me a polarized piece of plastic and I used it to observe the amplified phenomenon.

Our customer, Schollglas Technik GmbH, sent Dr. Klaus Holtmann and we agreed that it was a strong but typical case of anisotropy.  The IGU structure with three tempered lites enhances this phenomenon.  In my report, I wrote a classic explanation of the phenomenon: The toughening process produces areas of different stress in the cross-section of the glass. These areas of stress produce a birefracting effect in the glass, which is visible in polarized light.
When thermally toughened safety glass is viewed in polarized light, the areas of stress show up as coloured zones, sometimes known as "leopard spots". Polarized light occurs in normal daylight. The amount of polarized light depends on the weather and the angle of the sun. The bi-refracting effect is more noticeable at a glancing angle or through polarised spectacles.

Our coating has nothing to do with this aspect! This phenomenom caught my attention and I worked more on anisotropy later. See Cupertino.