Volume 26, Issue 5 - September/October 2012

Glass Tech

Acceptable Perfection
Where the Science of Glass Meets the Art of Architecture
by Joe Erb

Architecture is a visual art. When done well, it inspires, creates emotion and it’s functional. When it comes to glass, higher performing technologies have enabled architects to expand their creativity with colors, coatings, shapes and creative facades that add to the visual aspect without sacrificing sustainability and energy performance. As with any work of art, however, the creator often seeks absolute perfection as their concepts become realities.

There’s much truth in this quote from artist Salvador Dali: “Have no fear of perfection—you’ll never reach it.” Perfection is an impossible pursuit in art, architecture and glass, yet glass fabricators are often tasked with attaining flawlessness in the insulating glass (IG) they produce—all while minimizing costs.

But somewhere between the science of IG and the end user expectations is what I’d like to call “acceptable perfection” or standard practices in how to view and judge the quality of IG unit edges for buildings. That’s what the Glass Association of North America (GANA) had in mind when it developed the Glass Information Bulletin (GIB), “Guidelines for the Appearance of Insulating Glass Unit Edges in Commercial Applications.”

The newly introduced bulletin (GANA ID 02-1011) addresses both vision and spandrel IG units, provides a glossary of terms for uniformity and graphically depicts the proper construction of double-glazed IG units, including the locations of the spacer, primary and secondary IG sealants and sightlines. It also addresses many common glazing techniques used today, including captured-glazed, structural glazed, point-supported and spandrel units.

Viewing Conditions
Use GANA’s guide to walk through the proper methods and criteria for judging the visual quality of IG edges in both captured and silicone structural-glazed commercial glazing systems. Now everyone along the supply chain has an industry-specific guide on how to view the units for “eye appeal,” which is found in the Viewing Conditions section. Viewing the IG unit with your nose pressed against the glass is obviously not an acceptable approach, so GANA recommends the following:
Visual inspections of IG unit edges should be made with 20/20 vision (naked eye or corrected) at a distance of three feet (one meter), or from the closest normal viewing position (sidewalk, ground floor, walkway, etc.), whichever is larger. The viewer should look at the IG unit edge at a 90-degree angle (perpendicular) to the surface using daylight (without direct sunlight) or other uniform diffused background light that simulated daylight. The same viewing conditions should apply to coated glass except the viewing distance should be 10 to 15 feet, depending on the application (see ASTM C 1376 for details).

Appearance Guidelines
The bulletin then goes on to detail appearance guidelines for various types of IG, answering common questions, such as:
• What abnormalities should I look for when judging glass edge quality?
• What’s the maximum acceptable separation between primary and secondary sealants?
• Why are there color variations in secondary sealants?
• How much of the IG spacer can be visible under normal viewing conditions?
• Are color variations acceptable in coated glass edges?
• What is the acceptable amount of sealant infringement along sightlines and corners?

By providing answers to these questions and more, GANA effectively bridges the gap between the desire for perfection and what is acceptable in reality.

While perfection might seem unattainable, high-performance technologies exist today to help glazing fabricators come closer to meeting the premium aesthetics and energy performance architects desire. The best approach for all involved is to be educated about what acceptable perfection is through industry guidelines like GANA’s GIBs and to work with IG component suppliers to find the solutions that best balance acceptable aesthetics, performance and cost. This GANA GIB can be purchased online at, along with more than 30 additional bulletins on various subjects.

Joe Erb is the commercial product specialist for Quanex Building Products. He serves on GANA’s marketing committee, insulating division education committee and as the chair of the insulating division website committee.


Architects' Guide to Glass & Metal
© 2012
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