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SPEC SHEET
Although ASTM C1651, “Standard Test Method
for Measurement of Roll Wave Optical
Distortion in Heat-Treated Flat Glass,” provides
a method for measurement of roller wave
distortion, there is no recognized industry
standard, including ASTM C1048, which
species allowable limits for peak-to-valley
measurements of roller wave distortion.
Further complicating quality control, the test
method of measuring roll wave distortion in
ASTM C1651 has largely been replaced by
measuring actual optical distortion rather than
physical techniques previously used. Typically,
specications are still referencing peak-to-valley
measurements to establish project-specic
criteria of roller wave distortion rather than the
newer optical test methods for evaluating
optical distortion (Figure 1). Even with the
newer test method, ASTM C1048 states that
“Consultation with suppliers and the viewing of
full-size mock-ups, under typical job conditions
and surroundings, is highly recommended for
THE FACTORS INVOLVED IN
CHOOSING GLASS ARE AN
INTEGRAL PART OF THE OVERALL
BUILDING PERFORMANCE.
HOWEVER, WITH ALL OF THE
AVAILABLE OPTIONS COMES
POTENTIAL PROBLEMS AND
PITFALLS FOR THE ARCHITECT.
evaluation of reective distortion” (Paragraph
7.3.6). In addition, to minimize the effect of
roller wave distortion, the lites should be set
with the roller waves horizontal to the sill of the
window. This way, anyone passing alongside the
building will not sense the repeating pattern of
the image distortion.
Prior to shipping the glass for the Farnsworth,
optical scans were provided to the project team
for review. After the measurements of the optical
distortion were accepted, the glass was shipped
and installed. The project was considered a full
scale mock-up to establish the acceptance criteria
for future glass replacement. Subsequently, the
peak-to-valley measurements of roller wave
distortion were measured in the replacement
glass as well as previously installed tempered
glass units.
After a review of optical measurements, physical
measurements and a full-scale trial, the
appropriate glass criteria can be selected for a
project. The issue of visual distortion is only one
factor in the selection of glass which
demonstrates the complexity of glass design. CA
Anthony Cinnamon and Joshua Freedland are
associate principals at Wiss, Janney, Elstner
Associates, Inc.
Visit focalpointlights.com for more information.
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