Hardness Test of Coatings: How to Perform It

The hardness test is used to measure the resistance of a coating to indentation or scratching. It is an important quality control standard test that can help determine the suitability of a coating for a particular application. There are various methods for performing the hardness test, including the pencil test, the scratch test, and the Rockwell test. Here is an overview of how to perform the hardness test of coatings:

Pencil Test

The pencil test is a simple and quick method for measuring the hardness of a coating. It is performed by drawing a pencil over the coating and observing the amount of graphite transferred to the coating. The higher the number of the pencil, the harder the coating is. For example, a coating that can withstand a 9H pencil is harder than a coating that can withstand a 2B pencil.

Scratch Test

The scratch test is a more precise method for measuring the hardness of a coating. It is performed by using a stylus or other pointed instrument to scratch the coating at a specific force and observing the depth of the scratch. The harder the coating, the shallower the scratch will be. The scratch test can be performed using various instruments, such as the Mitchell instrument, the Taber instrument, and the Erichsen instrument.


Rockwell Test

The Rockwell test is a standardized method for measuring the hardness of a coating. It is performed using a Rockwell hardness tester, which consists of a indenter and a load. The indenter is pressed into the coating at a specific force, and the depth of the indentation is measured. The hardness of the coating is then calculated based on the depth of the indentation and the applied force. The Rockwell test can be performed using various scales, such as the HRB scale (for softer materials) and the HRC scale (for harder materials).


By performing the hardness test of coatings, manufacturers and users can determine the suitability of the coating for a particular application and ensure that it meets the required standards.