The strength and performance of heat-strengthened and fully tempered glass is greatly affected by the surface and edge stress induced during the heat-treating process.

The edge and surface stress levels are specified in Specification C 1048, in the Engineering Standards Manual of GANA , and in foreign specifications.

Surface stresses can be measured nondestructively using methods, such as Test Method C 1279. The calibration of surface measuring devices used in those procedures and periodic verification of calibration are needed. This test method offers a convenient way to accomplish this task.

1.1 This test method covers calibration or verification of calibration, or both, of surface-stress measuring devices used to measure stress in annealed and heat-strengthened or tempered glass using polariscopic or refractometry based principles.

1.2 This test method is nondestructive.

1.3 This test method uses transmitted light, and therefore, is applicable to light-transmitting glasses.

1.4 This test method is not applicable to chemically tempered glass.

1.5 Using the procedure described, surface stresses can be measured only on the “tin” side of float glass.

1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.