ASTM C1901 Test for Measuring Optical Retardation in Flat Architectural Glass

Introduction 

What is ASTM C1901?

ASTM C1901 is used to measure optical anisotropy in flat architectural glass. Optical anisotropy is calculated by measuring optical retardation. This test is used to control the quality of end-use transparent glass products. The values stated in SI units are regarded as standard. 

ASTM C1901 Scope

This Standard test practice states the procedure for measuring optical retardation in flat architectural glass. Optical retardation measurement is critical in assessing the uniformity and quality of glass. It can help determine its appearance and functionality in various building projects.

ASTM C1901 Test Procedure

The test equipment used in ASTM C1901 are as follows:

Polarizer: An instrument to polarize the light transmitted through the glass sample.

Compensator: An optical accessory used to correct for birefringence and measure retardation.

Measurement System: The system includes optical sensors and readouts devices, measuring the retardation values.

ASTM C1901 Test Method

1. Ensure the glass sample is free from dust contamination and has no surface defects.
2. The surface should be flat and uniformly processed to provide the correct measurement.
3. Place the glass sample in the test fixture or an apparatus that has been optimized for optical retardation measurement.
4. Position the glass between polarizers and compensators based on the test method.
5. Use the optical system to measure the retardation by rotating the compensator and recording the retardation values at different positions on the glass.
6. Repeat measurements several times to have the average and account for possible sample variations. Record the optical retardation values resulting from the measurement process.

Specimen Size in ASTM C1901 

For ASTM C1901, the test specimen should be a flat piece of architectural glass. The specimen size should be large enough to cover the area of interest. At least a few centimeters in all dimensions, although the actual requirement depends on both the equipment and the test standard.

Result Analysis

The result and calculation of ASTM C1901 are as follows:

Applications of ASTM C1901

ASTM C1901 shall measure the optical retardation of flat architectural glass, quantifying the birefringence caused by internal stress. This is vital where the applications demand glass to comply with specific requirements of vision and structure, as in the case of high-performance buildings. Retardation classification helps identify defects or levels of stress, which might affect transparency or colored distortion. The test made by polarized light evaluates the stress of the glass. Architectural glasses are classified in the instances of retardation values, ensuring both safety and optical clarity for application in buildings such as skyscrapers or large public facades.

Conclusion

The test offers insight into the retardation properties of glass and measures optical quality. Results can be compared against industry standards or specifications in terms of quality and suitability for use in architectural applications. Glass samples with good quality, having values of optical retardation stable or high, are encouraging and give performances consonant with aesthetic requirements. This test ensures that the architectural glass meets requirements concerning visual clarity and performance. It, therefore, becomes an intrinsic part of the control regarding quality in manufacturing glass and design architecture.

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