Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2003

Measuring Viscosity of Lacquers

Q. What are the most popular types of viscosity cups for pre and post catalyzed lacquers, conversion chart types and can you explain how to use?

A. The most popular viscosity cup for low viscosity lacquers are Zahn Cups. You must select from Zahn #1, #2, #3 or #4 depending on the viscosity of the coating. The method is very simple indeed. You simply submerge the cup in the coating. Using the handle that is attached to the cup, raise the cup up above the coating and start a stop watch. The coating will drain out from the orifice at the bottom of the cup. Stop the watch as soon as the stream of coating breaks for the first time. That is the viscosity measured in seconds. Therefore, you might quote the viscosity as, for instance, 22 seconds on a Zahn #2 cup. A thicker coating might have a viscosity of 35 seconds on a Zahn #2 cup, and an even thicker coating might require say 25 seconds on a Zahn #3 cup.

Very low viscosity liquids are measured on a Zahn #1 cup, but the higher Zahn cup numbers are for fluids of ever increasing viscosity.

Zahn cups can be purchased from www.bykgardner.com or www.gardco.com.