Overview: Testing with Viscosity Cups

The original patent for Zahn cups was issued in 1938. These early cups, though uncalibrated and unstandardized, were worth their weight in gold in the hands of a skilled formulator. Gradual improvements in design and quality followed, but it was not until quite recently that standardization among viscosity cups became the norm.

Now, thanks to rigorous quality standards, the drain time of a liquid through a known cup can be compared from lab to lab, with a known margin of error. The EZ® and S90 "Signature" series viscosity cups are manufactured to the strictest tolerances, and, when appropriately calibrated with the standard oils, can be used with assurance for such lab-to-lab comparisons.

This method measures viscosity at only one level of shear; it cannot monitor thixotropy or other second order rheological properties, nor can its results be directly compared to readings taken in-situ from a dynamic process. Nevertheless, the viscosity cup is still – and likely will long remain – a core tool for formulators and users of inks, paints, coatings, adhesives, and many other liquids. A brief test procedure is found here.