Determine the relative hardness of resins, film, lacquer, and paint by testing their resistance to scratches by graphite pencils. The pencils are calibrated to specific lead grades for hardness. The lowest hardness value of the pencil that mars the material is the material’s relative hardness. Flatten the tip of the pencil lead with the included 400 grit sandpaper, then insert the pencil into the tester. As you push the tester over your material, the pencil is dragged across the surface at a constant pressure. These testers are often used in the development of synthetic resins. They meet ASTM D3363 for testing the hardness of coatings.