ASTM C1901: Flat Glass Optical Retardation Testing Services
ASTM C1901 is used to measure optical anisotropy in flat architectural glass. Optical anisotropy is measured by measuring optical retardation. This test is used for quality control of the end use transparent glass products. The values stated in SI units are regarded as standard.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
What Is ASTM C1901 Flat Glass Optical Retardation?
ASTM C1901 is a standard test method for measuring optical retardation in flat architectural glass using polariscope-based instrumentation. Optical retardation quantifies the degree of residual stress present in glass, arising from thermal tempering, heat strengthening, or improper annealing during manufacture.
This method is essential for verifying that architectural glass meets required stress levels for safety, structural performance, and optical clarity. It is applicable to tempered, heat-strengthened, and annealed flat glass used in facades, curtain walls, glazing systems, and structural applications, ensuring compliance with quality and safety standards before installation.
Applications and Benefits of ASTM C1901 Flat Glass Optical Retardation Testing
Scope
ASTM C1901 covers the measurement of optical retardation in flat glass specimens using transmitted polarized light. The method quantifies birefringence caused by internal stress distribution across the glass thickness and surface.
The scope includes:
- Measurement of optical retardation in nm or nm/cm units
- Applicable to tempered, heat-strengthened, and annealed flat glass
- Testing of glass used in architectural glazing, facades, and curtain walls
- Evaluation of edge and surface stress distribution
- Applicable to glass thicknesses typically ranging from 3 mm to 19 mm
- Compatible with both laboratory specimens and production-line quality control
Applications
- Quality verification of tempered and heat-strengthened architectural glass
- Facade and curtain wall glazing stress evaluation
- Detection of inadequate tempering or annealing defects
- Structural glazing and overhead glazing safety assessment
- Laminated glass interlayer stress compatibility evaluation
- Glass processor quality control during production
- Failure investigation of prematurely fractured glass panels
- Research on residual stress distribution in specialty glass products
- Compliance testing for building code and glazing standard requirements
- Evaluation of glass after thermal or mechanical processing modifications
Benefits
- Non-destructive measurement with no specimen damage
- Directly quantifies residual stress through optical retardation values
- Applicable across a wide range of glass thicknesses and types
- Supports compliance with ASTM C1048 and related glazing standards
- Identifies under-tempered or non-uniform stress distributions early
- Suitable for both laboratory and in-line production quality control
- Rapid measurement with minimal specimen preparation
- Provides spatial stress mapping across the glass surface
- Reduces risk of in-service spontaneous breakage due to undetected stress anomalies
Our ASTM C1901 Testing Procedure
Specimen Preparation
Glass specimen is cleaned and positioned flat for unobstructed polarized light transmission through its thickness.
1Polariscope Setup
Instrument is calibrated with reference retardation standards before measurement begins.
2Retardation Measurement
Optical retardation is measured at defined points using transmitted polarized light.
3Reporting
Values are measured in nm, converted if required, and compared with acceptance criteria.
4ASTM C1901 Test Parameters and Requirements
| Parameter | Details |
|---|---|
| Measurement Parameter | Optical retardation (birefringence) |
| Reporting Units | nm or nm/cm |
| Glass Types Covered | Tempered, heat-strengthened, annealed flat glass |
| Applicable Thickness Range | Typically 3 mm to 19 mm |
| Measurement Method | Transmitted polarized light (polariscope) |
| Stress Type Measured | Residual internal stress from thermal processing |
| Measurement Locations | Edge zone, surface area, and mid-panel points |
- Transmission polariscope (automated or manual)
- Compensator or wave plate for retardation quantification
- Calibrated retardation reference standards
- Light source with polarized filter assembly
- Digital imaging system for stress mapping (automated systems)
- Optical bench or flat support table for specimen positioning
Equipment and Instrumentation Used for ASTM C1901 Testing
What You Receive: Test Report, Data, and Certification
- Optical retardation values in nm or nm/cm at measured locations
- Stress distribution map across the glass surface where applicable
- Pass/fail determination against specified retardation thresholds
- Edge and surface retardation comparison data
- Identification of non-uniform or deficient tempering zones
- Full test report with specimen dimensions, glass type, and test conditions
- Calibration records and instrument verification data
- Photographic or digital retardation map for automated systems
ASTM C1901 Flat Glass Optical Retardation FAQs
ASTM C1901 is a standard test method for measuring optical retardation in flat architectural glass.
Optical retardation affects how light passes through glass, impacting visual quality and aesthetic properties in architectural applications.
ASTM C1901 measures optical retardation. The test may not be capable of detecting many forms of optical defects. Other tests and inspections must be conducted to determine other defects, among which are not only excluded but also bubbles, inclusions, surface imperfections, etc.
The standard applies specifically to flat architectural glass, including tempered, laminated, and insulated glass units.
ASTM C1279 uses a similar polariscope approach but focuses on detecting stress and strain in flat glass for edge and surface evaluation. ASTM C1901 specifically addresses quantitative optical retardation measurement in architectural applications.
Why Choose Infinita Lab for Flat Glass Optical Retardation Testing
At the core of this breadth is our network of 2,000+ accredited laboratories across the USA, offering access to over 10,000 testing methods and analytical services. From advanced materials characterization (SEM, TEM, RBS, XPS) to mechanical, chemical, environmental, biological, and standardized ASTM/ISO-compliant testing, we deliver unmatched flexibility, specialization, and scale. You are never limited by geography, facility, or methodology — Infinita Lab connects you to the right expertise and testing solution, every time.
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