Ultimate Carbon Ink for Fountain Pens, Achieving the Deepest Black To meet the demand of deeper black ink, Platinum Pen has developed the ultimate carbon ink for fountain pens that achieves the deepest black yet. The ink also boasts exceptional water and light resistance, resulting in the unparalleled "Blackest Black" ink. ※When cleaning the pen nib after using Chou Kuro ink, use purified water available at pharmacies, etc. Avoid washing it with tap w ater as it reacts with minerals contained in the water and makes it diffi cult to remove the stains.