Anisotropic Effects in Architectural Glass

New Measuring and Monitoring Approaches



Photo of Luis M. Hidalgo

Luis M. Hidalgo


Photo of Michael Elstner

Michael Elstner

Director of Technical Advisory Service & Strategic Communication




Iridescence effects, quench marks, leopard marks… The names given to optical anisotropy in toughened and heat-strengthened glass are diverse and widely used by facade contractors, architects and glass suppliers. The general term –and technically more accurate- comprising all previous definitions “anisotropy” is not fully understood from the fundamental physical and optical reasons governing it. The principles of anisotropy are presented as to provide a general overview of this phenomenon aimed to introduce later the latest technology enabling on-line monitoring through automated polariscopic techniques in tempering lines. The difficulties to objectively quantify and evaluate anisotropy in real glass units are exposed and a study about a spatial-statistical approach based in textural analysis of photoelastic images by means of Grey Level Co-occurrence Matrices is also introduced. This approach, in combination with actual first order statistic assessment using p-quantiles [1] could provide an additional tool for benchmarking and comparison purposes during production of heat treated glass.


In the last decades the architectural glazing industry has experienced an enormous technical evolution. New challenging energetic, structural and visual demands increase progressively the complexity of glazing products and the

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Principles of Anisotropic Effects in Glass

Anisotropy is the term used in physics to characterize an object or phenomenon having different properties in different directions, opposite to isotropy. In building glass, anisotropic effects appear in particular

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The number of variables influencing anisotropy visibility in heat treated glass makes tremendously impractical and inefficient any attempt to predict the potential visual appearance of glass at the intended building

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Available Measuring Approaches in Glazing Industry

Accounting for the specific data processing, optical measurement techniques and the image acquisition system used, actual approaches followed by industry and research universities differ significantly although, as remarked previously, they

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Anisotropy Quantification Procedures

As seen, different methods rely on different techniques to assess anisotropic effects. The most accurate provide precise measurements of light retardation measured all over the glass surfaces. However, the photoelastic

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Textural Analysis as an Additional Evaluation Tool

The Grey Level Co-Occurrence Matrix (GLCM)

The co-occurrence matrix is generally understood as a two-dimensional histogram of the number of times that pairs of intensity values occur in a given

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Conclusion and Future Work

The overview of anisotropic effects, their causes and impact in architectural glass have been presented together with the problematic related with the quantification and evaluation of such a complex and

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Rights and Permissions

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  • Feldmann, Markus & Kasper, Ruth & Di Biase, Pietro & Schaaf, Benjamin & Schuler, Christian & Dix, Steffen & Illguth, Marcus. (2017). Flächige und zerstörungsfreie Qualitätskontrolle mittels spannungsoptischer Methoden. pp. 276-287. 10.1002/cepa.27.
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  • Ruth Kasper, Pietro Di Biase, Markus Feldmann (2015). Quality Control of tempered glass panels with photoelasticity – Proceedings of the Institution of Civil Engineers pp. 442-449.
  • G.N. Srinivasan, Shobha G. (2008). Statistical Texture Analysis – Proceedings of World Academy of Science, Engineering and Technology Volume 36 pp. 1264-1269.
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  • Yasuschi Niitsu, Kenji Gomi, Kensuke Ichinose (1997) Development of Scanning Stress Measurement Method Using Laser Photoelasticity. JSME International Journal pp. 143-148