The term colour fastness refers to two resistance criteria of a colour of a test sample. The first criterion is the resistance of a material to change in any of its colour characteristics. The second criterion is the resistance of its colourant(s) to adjacent materials as a result of exposure of the material to any environment that might be encountered during the use of the material.

The first resistance criterion is checked by the “rubbing fastness” test. The term “rubbing fastness” is the term for the hue change of the test sample through rubbing. This test is evaluated visually with a comparative scale. Most common is the use of a “gray scale for staining”.

“Crocking” and “smudging” are both equivalent terms for the transfer of colorant(s) from the test surface to another surface or to an adjacent area by rubbing. Therefore, if the second resistance criteria is checked, you test the crock resistance (equally called smudge resistance).