SPECIAL HARDNESS TESTING PROCEDURES INCLUDE THE MARTENS scratch hardness determination as well as the Mohs scratch hardness. In the Martens procedure, a specimen surface under a specified test force is scratched by a diamond cone with a 90-deg apical angle. The test force F is varied until a scratch width of 10 m is microscopically measured. In this way, a particular scratch hardness value can be attributed to the specimen.