A procedure for determining the lightfastness of inks under the effect of natural light and is defined in DIN 16 525. A bluewool strip is tinted with up to eight different blue tones which, under the action of daylight, fade to a defined degree. The ink being tested is applied to a printing material. Half of this is covered over and the two test strips are subjected to UV light from a high-pressure xenon lamp whose spectral distribution corresponds more or less to the UV component of sunlight. The lightfastness of the ink is shown by comparing the covered up areas with the unprotected areas at specific time intervals. These comparisons can be used as a basis for specifying the lightfastness in eight time stages extending from one week to 256 weeks.
- Bluewool Scale