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Properties of Liquids

Working Group 3.32

Calibration glasses for high-temperature viscosity measurement

PTB offers three glasses with different viscosity-temperature (VT) behavior. The VT behavior of these glasses was determined with a special rotational viscometer set up at PTB. The traceability of this rotational viscometer to the National Standard of Viscosity was carried out with reference liquids. In addition, the viscosity measurement was monitored using a fibre-elongation apparatus, which was also designed at PTB, with a contact-free recording of the elongational speed.

Note: The working group itself does not longer perform viscosity measurements on glass melts. However, the calibration glasses can still be purchased.


The soda-lime glass G1 is certified in the temperature range from 525 °C to 1400 °C. The restriction applies, that measurements above 1200 °C are not carried out until all measurements at lower temperatures have been completed. This behavior is typical for soda-lime glasses and also valid, for example, for Standard Glass I of the Deutsche Glastechnische Gesellschaft, which can be purchased from this institution. The leadoxide glass G2 is certified in the range from 900 °C to 1400 °C and the hard glass G3 in the range from 1000 °C to 1400 °C. The fix points defined in the ISO 7884 standard (12.87) (no thermodynamic fix points) were measured - as far as they are within the certification range. For each calibration glass, the most suitable possible compensation curve was determined for the VT behavior; the calibration certificate additionally contains a VT table in 25 K steps and information on the measurement uncertainty.

Note on the measurement uncertainty: The expanded uncertainty of measurement is given in each case, which results from the standard uncertainty of measurement multiplied by the expansion factor k=2. It was determined according to the "Guide to the Expression of Uncertainty in Measurement" (ISO, 1995). As a rule, the value of the measurand lies in the assigned value interval with a probability of approximately 95 %.


The calibration glasses are delivered in pieces of about 500 g.

We will be happy to help you with your questions and provide you with a current offer.

You can find further information Initiates file downloadhere.