Another unique feature is that each pen allows for two different ink colors to be employed, bringing gradation and color variation when you touch the tips together. Each pen comes equipped with one black cartridge, one red cartridge, a converter, and a tip cleaner for clean and enjoyable writing. For even more variety, you can add on two packs of 12 colorful cartridges, specifically designed to offer gradation when used with the Pilot Parallel 2-Color Calligraphy Pens, or some CON-50 piston-style converters to use with bottled fountain pen ink.