The relative amount of fading can be measured and studied by using standard test strips. In the workflow of the Blue Wool test, one reference strip set shall be stored protected from any exposure to light. Simultaneously, another equivalent test strip set is exposed under a light source defined in the standard. For example, if the lightfastness of the colourant is indicated to be 5 on the Blue Wool scale, it can be expected to fade by a similar amount as the strip number 5 in the Blue Wool test strip set. The success of the test can be confirmed by comparing the test strip set with the reference set that was stored protected from the light.