Heavy handed users will appreciate the durability of the larger nibs that provide dark, black pen strokes that last. Includes patented black Pigma ink which is waterproof, chemical resistant, fade resistant, bleed free, quick drying and pH neutral. This special formulation of pigment based ink is more complex and stable than dye based inks. Sakura's Pigma ink, invented and patented in 1982, has become the standard for what is defined as reliable, permanent, archival quality ink.