What is a pencil hardness test?

Pencil hardness testing is an evaluation method used to determine the hardness of a material, usually a coating material. For the pencil hardness test, graphite pencils of different hardness are moved over the coated surface. Its hardness relative to graphite pencils depends on the softest pencil, which can leave scratches on the coated surface.

Pencil Hardness Test

The test is popular in part because it is a portable procedure. Pencils are small, and if you use a mechanical stand to carry them, they're also usually compact and easy to carry. Another reason is because it's simple. All it takes is a set of pencils and a person to drag the pencils through the coating material. These reasons make the pencil hardness test an excellent choice for testing coatings because it can be done quickly in the field.

Because of its simplicity, the pencil hardness test varies by test and Tester. It is absolutely critical that you perform the pencil hardness test the same way every time. Therefore, it is usually recommended to use some mechanical method to perform the test. A pencil holder is a mechanical device that holds a pencil at a set angle and prevents it from slipping. Pencil holders usually have wheels to allow for a smooth motion when trying to scratch the coating.

There is a range of pencils available, marked according to their graphite hardness. 6B is usually the softest pencil in a durometer pencil pack. Pencils then increase in hardness from 6B to 5B to 4B and so on until they reach a single B. Then the hardness continues to increase as the pencil goes from HB to F to H to 2H to 3H all the way to 9H. The 9H pencils are usually the hardest in the set.