Ring tear-off method

The ring tear-off method is a variant of the Du Noüy ring method for measuring surface tension or interfacial tension which historically precedes today's procedure. Instead of detecting the force maximum when the lamella is stretched, as is usual with modern tensiometers, the lamella is overstretched until it detaches. The value measured in this way deviates slightly from the actual value of the surface tension.

The reason for this method lay in the fact that a force maximum could not be detected using manual tensiometers which work with a torsion wire, and only the moment of detachment was available as a reference point. With modern, electronic force sensors, determining the force maximum is no longer a problem.

The ring tear-off method is still in use today as it is used in older but still valid norms (e.g. ASTM D-971).