Standard Test Method for Measuring Optical Retardation in Flat Architectural Glass

SIGNIFICANCE AND USE
5.1 Stress may be applied intentionally through a heat treatment or tempering process to increase mechanical strength and improve safety characteristics of glass sheets. The process itself makes it practically impossible to achieve a homogenous residual stress profile over a full glass panel. These variations are due to variations in type of glass (clear, tinted, coated, etc.), the fabrication, sheet geometry, heating, quenching, and cooling. Even though the level of inhomogeneity may not interfere with the global mechanical property of the glass sample, it can produce optical patterns called anisotropy (often commonly referred to as leopard spots). Today to evaluate this stress homogeneity people may use the subjective, non-standardized method of viewing through a polarized filter or employing a polariscope. The present test method provides guidelines for measuring a physical parameter, the optical retardation, directly linked to the local residual stress, at many locations on each heat-treated glass sheet.  
5.2 Through this test method one can obtain in a non-destructive manner, on-line to the tempering furnace equipment, a map of the retardation value of all glasses. That information can then be used:  
5.2.1 By the tempering operator to adjust the settings of the heat treatment process to optimize/tune both the levels optical retardations and its homogeneity on heat treated glass sheets.  
5.2.2 To provide a standardized way to measure optical retardation values for each glass panel that can be archived and communicated when desired.  
5.2.3 By customers and other stakeholders to develop/write specifications for the optical retardation values (not the visibility of the pattern) that are independently verifiable.  
5.3 This test method can also be used off-line to evaluate the optical retardation level and homogeneity of any heat-treated glass, for quality assurance or other purposes.
SCOPE
1.1 This test method addresses the measurement of optical anisotropy in architectural glass.  
1.2 This test method is a test method for measuring optical retardation. It is not an architectural glazing specification.  
1.3 The optical retardation values may be used to calculate/predict the amount of visible pattern, commonly known as anisotropy or iridescence, present in heat-treated glass.  
1.4 This test method applies to monolithic heat-treated (heat-strengthened and fully tempered) clear, tinted and coated glass.  
1.5 This test method does not apply to:  
1.5.1 Glass that diffuse light (that is, patterned glass, sand blasted glass, acid etched, etc.), or  
1.5.2 Glass that is not optically transparent (that is, mirrors, enameled or fritted glass).  
1.6 The optical measurement is integrated through the glass thickness, and therefore cannot be used to assess the level of tempering. It does not give information on the surface stress or center tension.  
1.7 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

Status
Published
Publication Date
31-Dec-2020
Technical Committee
Drafting Committee
Current Stage
Ref Project

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ASTM C1901-21e2 - Standard Test Method for Measuring Optical Retardation in Flat Architectural Glass
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Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: C1901 − 21
Standard Test Method for
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Measuring Optical Retardation in Flat Architectural Glass
This standard is issued under the fixed designation C1901; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1
ε NOTE—The title of Section 9 was corrected editorially in March 2021.
1. Scope 2. Referenced Documents
1.1 This test method addresses the measurement of optical 2.1 Referencetothesedocumentsshallbethelatestrevision
anisotropy in architectural glass. unless otherwise specified by the authority applying this test
method.
1.2 This test method is a test method for measuring optical
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2.2 ASTM Standards for Glass:
retardation. It is not an architectural glazing specification.
C162Terminology of Glass and Glass Products
1.3 The optical retardation values may be used to calculate/
C1036Specification for Flat Glass
predict the amount of visible pattern, commonly known as
C1048Specification for Heat-Strengthened and Fully Tem-
anisotropy or iridescence, present in heat-treated glass.
pered Flat Glass
1.4 This test method applies to monolithic heat-treated
2.3 ASTM Standards for Optical Stress and Retardation
2
(heat-strengthened and fully tempered) clear, tinted and coated
Measurements:
glass.
C1279Test Method for Non-Destructive Photoelastic Mea-
surement of Edge and Surface Stresses in Annealed,
1.5 This test method does not apply to:
Heat-Strengthened, and Fully Tempered Flat Glass
1.5.1 Glass that diffuse light (that is, patterned glass, sand
D4093Test Method for Photoelastic Measurements of Bire-
blasted glass, acid etched, etc.), or
fringence and Residual Strains in Transparent or Translu-
1.5.2 Glass that is not optically transparent (that is, mirrors,
cent Plastic Materials
enameled or fritted glass).
1.6 The optical measurement is integrated through the glass
3. Terminology
thickness, and therefore cannot be used to assess the level of
3.1 Definitions:
tempering. It does not give information on the surface stress or
3.1.1 For definitions of terms used in this test method, refer
center tension.
to Specifications C1036, C1048, and Terminology C162,as
1.7 The values stated in SI units are to be regarded as
appropriate.
standard. The values given in parentheses after SI units are
3.2 Definitions of Terms Specific to This Standard:
provided for information only and are not considered standard.
3.2.1 analyzer, n—a polarizing element, typically rotatable
and positioned between the specimen being evaluated and the
1.8 This standard does not purport to address all of the
observer.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.2 anisotropy, n—property of being directionally depen-
priate safety, health, and environmental practices and deter-
dentwherebymeasurementstakenalongdifferentaxesproduce
mine the applicability of regulatory limitations prior to use.
differences in a material’s physical or mechanical properties
1.9 This international standard was developed in accor-
(absorbance, refractive index, conductivity, etc.).
dance with internationally recognized principles on standard-
3.2.3 Babinet-Soleil compensator, n—an optical compensa-
ization established in the Decision on Principles for the
tor that can be used to measure phase shifts locally in a
Development of International Standards, Guides and Recom-
polariscope or polarimeter using shifting quartz wedges.
mendations issued by the World Trade Organization Technical
3.2.4 birefringence, n—the optical property of a material
Barriers to Trade (TBT) Committee.
having a refractive index that depends on the polarization and
propagation direction of light.
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This test method is under the jurisdiction of ASTM Committee C14 on Glass
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and Glass Products and is the direct responsibility of Subcommittee C14.08 on Flat For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Glass. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 1, 2021. Published February 2021. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
C1901-21E02. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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C1901 − 21
3.2.5 compensation methods, n—(1) Sénarmont compensa- homogeneity people may use
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