We haven’t tested this but, generally speaking, writing on leather shouldn’t be a problem if it’s light in colour. Due to the fact that leather may be subject to heavy wear or may be heavily impregnated, we are unable to provide details on the durability of the ink. For a wash-resistant finish on textiles, iron on a no-steam setting. If you want to be sure of a satisfactory result, we recommend you try it out on a test piece first.