The Calo tester is a quick, simple and inexpensive piece of equipment used to ,easure the thickness of coating film. Coating with thicknesses typically between 0.1 – 50 micrometres.

The Calo tester consists of a holder for the surface to be tested abd a steel sphere of know diameter that is rotated against the surface by a rotationg shaft connected to a motor whilst diamond paste is applied to the contact area. The sphere is rotated for short period of time but due to the abrasive nature if the diamond paste this is sufficient time to wear a crater through thin coatings.

Calculating coating thickness using the Calo tester.

An optical microscope is used to take two measurements across the crater after the Calo test and the coating thickness is calculated using a simple geometrical equation.