All you need to
know.

Just as with the Vickers method, when using the Knoop hardness testing method, it is usually necessary to prepare the surface of the specimen to be tested, as the specimen surface quality requirements are significantly stricter than those for the Rockwell method, in which it is sufficient for the surface to be free of impurities.  The relatively small Knoop indentations can only be correctly evaluated optically on an even, smoothly polished specimen surface.

In detail, the specimen to be measured should meet the following requirements for the Knoop method  (see Vickers method):

• The specimen should be polished (micro hardness testing) or precision-ground (macro hardness testing).

• The specimen should preferably be clamped strongly, so that it cannot move during the testing process (practical tip: measure with nose cone resp. with suitable test anvil, fix embedded specimen in a specimen holder).

In addition, to avoid affecting the test result, care must be taken to ensure that the test is not disturbed by any shock or vibration (an anti-vibration table, etc., may be required).