Standard Test Method for Annealing Point and Strain Point of Glass by Beam Bending

The annealing point of a glass is defined as the temperature at which a 3-point loaded beam, nominally 3 to 4 mm in cross section on a 50 mm span, elongates under a load of between 0.2 kg and 1.0 kg at a rate determined by the span, load, and moment of inertia when it is cooled at a rate of 4°C/min. The strain point is determined by extrapolation of the annealing point data as the temperature at which the elongation rate is 0.0316 times that at the annealing temperature. Representative specimens, nominally 3 to 4 mm in cross section and 75 mm in length, are required.

$330 per glass to 1000°C
$250 per glass for beam preparation


Significance and Use

4.1 This test method offers an alternate procedure to Test Method C336 for determining the annealing and strain points of glass. It is particularly recommended for glasses not adaptable to flame working. Also fewer corrections are necessary in data reduction.


1.1 This test method covers the determination of the annealing point and the strain point of a glass by measuring the rate of midpoint viscous bending of a simply loaded glass beam.2 However, at temperatures corresponding to the annealing and strain points, the viscosity of glass is highly time-dependent. Hence, any viscosities that might be derived or inferred from measurements by this procedure cannot be assumed to represent equilibrium structural conditions.

1.2 The annealing and strain points shall be obtained following a specified procedure after direct calibration of the apparatus using beams of standard glasses having known annealing and strain points such as those supplied and certified by the National Institute of Standards and Technology.3

1.3 This test method, as an alternative to Test Method C336 is particularly well suited for glasses that for one reason or another are not adaptable for flame working. It also has the advantages that thermal expansion and effective length corrections, common to the fiber elongation method, are eliminated.

1.4 The values stated in metric units are to be regarded as the standard. The values given in parentheses are for information only.

1.5 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.


Copyright Notice

Extracted, with permission, from ASTM C598 Standard Test Method for Annealing Point and Strain Point of Glass by Beam Bending, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the standard may be purchased from ASTM International, phone 610-832-9555, e-mail:, website:


Purchase Full Standard »

View Products by Category:




Orton Welcomes New General Manager!

The Board of Trustees of the Edward Orton Jr. Ceramic Foundation announces the retirement of its General...

How Kiln Environment will affect a Pyrometric Cone

Those experienced in firing ceramics know that kiln atmosphere can have a major influence on the reaction...

TempTabs: What They Are & How They Work - Watch This Video!

TempTabs are used to measure temperature uniformity, consistency and repeatability in high temperature...