Knoop Testing Method
The Knoop resulting indentation is not symmetrical as Vickers indentions and will be subject to more variations of the resulting hardness values when testing to Knoop scales, especially below 200gf.
Knoop hardness is not typically being used to define bulk hardness, although at 500 gf standards like ASTM provide conversions of Knoop results to other hardness test scales. Knoop tests are not typically performed at test forces above 1000 gf although particular circumstances and or materials may need higher forces like 2 and 5 kgf. Expect larger variations in results at these loads.
The Knoop diamond indenter is designed with a significant difference between the long and short Knoop diagonals, which is often better suited for determining variations of hardness over very small distances compared to the Vickers indenter.
The success of the specimen preparation procedure in removing preparation-induced damage can, and will, influence test results; this problem becomes more critical as the test force decreases.