Knoop hardness test 

The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes， was developed as an alternative to the Vickers method and is used in particular for the testing of thin layers and brittle materials.

It is one of the standardised procedures (ISO 4545, ASTM E92, ASTM E384).
The Knoop method has a test load range of 1 gf to 2 kgf according to ISO and ASTM, which means that this method can be used for hardness testing in the micro and low-load ranges.
It is an optical method. This means that the size of indentation left by the indenter is measured to determine the hardness value of a test specimen.
Indenter shape and material: The indenter consists of a pyramid-shaped diamond with a rhomboid base, with a longitudinal edge angle of 172.5° and a transverse edge angle of 130°.