What was once an accepted reality in heat-treated exterior glass, optical disturbances in glass are under increasing scrutiny by developers, designers, and manufacturers. Although dimensional distortions that affect the appearance of heat-treated glass, such as bow/warp, are clearly captured, quantified, and controlled in glass manufacturing standards (e.g., ASTM C1048, EN 12150 etc.), optical distortions due to strain patterns, collectively known as “anisotropy,” are acknowledged but not formally controlled. Larger glass module sizes, now the prevailing style in facade architecture, have required more glass to be heat-treated, forcing the industry to understand and address optical distortions.
The industry is faced with many questions, such as:
- What are the physics behind optical distortions in heat-treated glazing?
- How can understanding the physics behind optical distortions in exterior glazing help influence glazing design?
- How is the glass manufacturing industry adapting to provide glass that is aesthetically acceptable?
- How can designers reasonably specify aesthetic acceptability criteria of exterior glazing if some visual distortions are qualitative?
To address the above questions, this paper provides a guide for the material design properties of heat-treated glass, including its manufacturing process, manufacturing standards, and recommended specification practices that may be used to lower the likelihood and appearance of optical distortions.
Imagine you are a building design professional. You are walking on a crowded sidewalk downtown and somehow you are early for your next project appointment. Instead of stopping off at
No, this is not a physics paper. This paper is not going to “shatter” your previous misconceptions on glass materiality and physical limitations. But to navigate the perils of funny-looking
As we mentioned at the beginning of this paper, we address optical distortions due to tempering glass. In the previous paragraph we have established why HS or FT glass is
ASTM C1048-18 Standard Specification for Heat-Strengthened and Fully Tempered Flat Glass [ASTM C1048-18] describes anisotropy as:
7.2 Strain Pattern—A strain pattern, also known as iridescence, is inherent in all heat-strengthened and
Heat-treated glass also produces changes in surface geometry, creating optical distortions. The phenomenon is most noticeable when we observe reflections (e.g., from an adjacent building) on a glass lite. Reflections
Manufacturers have adapted to client’s and consumer’s increased scrutiny to blemishes and optical distortions in glass. The expectation of greater quality of building materials is creating a demand for product
Specifying glass is as much of a science as it is an art. As a design professional, you may have various consultants suggesting to optimize your glass for structural performance
Surface geometry and anisotropy distortions are an inherent part of the heat-treated glass established in ASTM C1048. Although the industry has set limits to surface geometry distortions, it acknowledges the
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