Fountain Pen Ink Cartridge - Black (6 per card) Cross Fountain Pen Cartridges are easy to use and crafted for continued performance so you never miss a note. Open up your pen, remove the expended cartridge, insert a fresh one, and close up your pen to continue writing. Cross makes the nostalgia of using a fountain pen far more enjoyable. Cross Fountain Pen Ink, in convenient fountain pen cartridges, is formulated to provide both superior writing characteristics and complete chemical compatibility with fine writing instruments.