Test

Viscosity

Definition

Measurement of a material's resistance to flow.

History

One of the most important physical characteristics of oils, it's accurate measurement was one of the first tests to require standardized methods. This enabled lubricant classification into viscosity grading systems such as the widely accepted SAE weights shown on motor oils. There have been numerous methods of determining oil viscosity. Early methods, such as Saybolt and Redwood, timed used the number of seconds required for a certain volume of liquid, at a set temperature to flow through an accurately measured orifice. Later, viscosities have been measured by flow rates  through various sized capillary tubes providing kinematic values reported as centistokes.