Hardness is a term that expresses the degree of hardness or softness of a material, and is measured by the resistance shown by the latter when an object is pushed into another object, and is usually approximated by the following methods. (1) Indentation method: A constant sphere or cone is pressed perpendicularly into the specimen surface, and the relationship between the pressure and the depth of the indentation or the area of the indentation is used to determine the resistance of the specimen. (2) Scratching method: A diamond cone with a 90-degree apex angle is used to scratch the sample, and the relationship between the pressure and the width of the scratch mark is used to determine the hardness. Mohs’ hardness tester uses the scratch method. (Ceramic Industry Dictionary)
