The Wolff-Wilborn Method: A Quick and Easy Way to Measure Coating Hardness

The Wolff-Wilborn method, also known as the pencil hardness test, is a simple and quick way to measure the hardness of a coating. It is performed by pushing a pencil of a known hardness across the coating at a specified angle, under a constant force, and observing the amount of graphite transferred to the coating. The higher the number of the pencil, the harder the coating is.


The Wolff-Wilborn method is widely used in various industries, including automotive, aerospace, construction, and manufacturing. It is particularly useful for on-site testing, as it requires no specialized equipment and can be performed quickly and easily. However, it is not as precise as other methods, such as the scratch test and the Rockwell test, and is generally used for a rough estimate of coating hardness.


To perform the Wolff-Wilborn method, you will need a set of pencils of known hardness, a ruler or other straight edge, and a calculator (optional). Follow these steps:

  1. Clean the surface of the coating and dry it thoroughly.
  2. Select a pencil of the appropriate hardness for the coating. For example, if you are testing a hard coating, you should use a 9H pencil. If you are testing a soft coating, you should use a 2B pencil.
  3. Hold the pencil at a 45° angle to the surface of the coating, with the point of the pencil touching the surface.
  4. Apply a constant force to the pencil and draw it across the surface of the coating in a straight line.
  5. Observe the amount of graphite transferred to the coating. The more graphite that is transferred, the softer the coating is.
  6. Compare the amount of graphite transferred to a chart or table of pencil hardness values to determine the approximate hardness of the coating.

By using the Wolff-Wilborn method, you can quickly and easily measure the hardness of a coating and determine its suitability for a particular application. However, it is important to note that the Wolff-Wilborn method is not as precise as other methods, such as the scratch test and the Rockwell test, and should only be used as a rough estimate of coating hardness. To ensure the accuracy and reliability of coating hardness measurements, it is recommended to use multiple methods and to follow established quality control standards.