---
title: "ASTM C965"
url: "https://mat-cs.com/astm-c965/"
description: "This practice covers the determination of the viscosity of glass above the softening point through the use of a platinum alloy spindle immersed in a crucible of molten glass. Spindle torque, developed by differential angular velocity between crucible and spindle, is measured and used to calculate viscosity."
---

ASTM Standard

# ASTM C965

Standard Practice for Measuring Viscosity of Glass Above the Softening Point

[Back to all techniques](/analytical-techniques/)

## Significance and Use

3.1 This practice is useful in determining the viscosity-temperature relationships for glasses and corresponding useful working ranges. See Terminology C162.

## Scope

1.1 This practice covers the determination of the viscosity of glass above the softening point through the use of a platinum alloy spindle immersed in a crucible of molten glass. Spindle torque, developed by differential angular velocity between crucible and spindle, is measured and used to calculate viscosity. Generally, data are taken as a function of temperature to describe the viscosity curve for the glass, usually in the range from 1 to 106 Pa·s.

1.2 Two procedures with comparable precision and accuracy are described and differ in the manner for developing spindle torque. Procedure A employs a stationary crucible and a rotated spindle. Procedure B uses a rotating crucible in combination with a fixed spindle.