The Wolff/Wilborn pencil test uses constant pressure and variable hardness of the graphite lead as its fundamental principle. Pencils of varying hardness, starting with the hardest lead, are moved over the surface under a fixed pressure of 7.5 Newtons (765g±2%) and at a fixed angle of 45 degrees to the surface.

The degree of hardness of the pencil which damages the surface is taken as a measurement for scratch hardness. Under ASTM, fourteen pencil leads in the range from 6B to 6H are used. (7H, 8H, and 9H are sold separately.) The pencil leads can be exchanged quickly and easily. The instrument comes complete with mechanical pencil, 14-piece lead set, abrasive paper and carrying case. The test method is fully described in ASTM D 3363-92a and ECCA T4 (1984).

The test surface needs to be correctly prepared in accordance with the specification being used. In all cases, it must be flat and smooth. The test should be performed at 73°F ±4°F (23°C ±2°C) with a relative humidity of 50 ±5% (ECCA;T4) or 73.5°F ±3.5°F (23°C ±2°C) and 50 ±5% relative humidity (ASTM D 3363). A 6 x 1” abrasion strip of 400 grit sandpaper is provided for fine dressing in compliance with ASTM D 3363.

1. Select a mid range lead or wooden pencil.
   
2. Place lead in holder. In the case of wood pencils, remove approximately 3/16 to 1/4" (5 to 6mm) of wood from the pencil using the pencil sharpener. Load the pencil in the upright alignment tool. Using the pencil alignment tool 90° to the abrasive paper, rotate until a flat, smooth and circular cross section is obtained, free of chips or nicks on the edge of the cross section.
   
3. Stand the HA-3401 onto its front end and insert the pencil until its point touches the flat surface. Tighten the
   pencil clamping knob.
   
4. Place the HA-3401 on the test surface and push it forward approximately 1/4 - 1/2" (6 - 12mm). Be sure to hold the gauge by the wheel hubs.
   
5. Rotate the pencil 90° and move the gauge 1/2" (12mm) to one side of the first test. Repeat Step 4.
   
6. Examine the coating for indentation or scratching. If there is none, repeat the test using a harder pencil. If the surface is scratched or indented repeat with a softer pencil.
   
7. Repeat step until a pair of pencils is found, one of which scratches/indents the coating, the other does not.