Scratch hardness is a measure of a sample's resistance to fracture or permanent plastic deformation caused by friction with sharp objects.  The principle is that objects made of harder materials scratch objects made from softer materials. When testing a coating, scratch hardness refers to the force required to cut the film into the substrate. The most common test is the Morse scale, used in mineralogy. One tool for this measurement is a durometer.
Another tool used to perform these tests is a pocket hardness tester. The tool consists of a scale arm with a scale mark attached to the four-wheel carrier. A scraping tool with sharp edges is mounted to the test surface at a predetermined angle. To use it, add the weight of the known mass to the scale mark on one of the scale arms and then pull the tool across the test surface. The use of weights and marks allows the application of known pressures without the need for complex machinery.