Krishna Inks Kot-Massi Series Permanent Blue Black is a special series of inks used to write documents, made by traditional Indian methods of ink making. The markings made cannot be rubbed or washed out. The old documents made by this technique have withstood decades without any fading. This is based on traditional Indian Iron gall document ink formula based on Lohabhasma, which is modified for a fountain pen. Completely non washable, Not bleachable by any acid or alkali. For important documents , this ink is highly recommended.