Test methods for light fastness are mostly laboratory methods, often, and so also with us, this is done on the basis of the wool scale. In other words, the ink is exposed to a defined artificial daylight for a defined period of time and the subsequent colour change is assessed. External influences such as the weather, stress or strain on the ink application are not taken into account. A claim for years of durability of the marking would therefore be unreliable and is therefore not made by edding.