4.1 This test method is well suited for measuring the viscosity of glasses in ranges higher than those covered by parallel plate (see Test Method C1351M) and rotational viscometry (see Practice C965) methods. This test method is useful for providing information related to the behavior of glass after it has been formed into an object of commerce and in research and development.

1.1 This test method covers the determination of glass viscosity from approximately 10⁸ Pa·s to approximately 10¹³ Pa·s by measuring the rate of viscous bending of a simply loaded glass beam.2 Due to the thermal history of the glass, the viscosity may not represent conditions of thermal equilibrium at the high end of the measured viscosity range. Measurements carried out over extended periods of time at any temperature or thermal preconditioning will minimize these effects by allowing the glass to approach equilibrium structural conditions. Conversely, the method also may be used in experimental programs that focus on nonequilibrium conditions.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 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.

1.4 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.