Ink formulated specifically for inkjet printers is generally classified as printing ink under 321511 or 321519 depending on color, since inkjet printing is a recognized printing process. However, the finished cartridge assembly may be classified elsewhere based on its principal character as a complete article; consult a licensed customs broker or request a CBP binding ruling for cartridge assemblies.

Printing inks (321511 and 321519) are designed for mechanical transfer onto a substrate via a press or printer mechanism and typically have viscosity, drying, and adhesion properties suited to high-speed production. Writing inks (321590) are formulated for pen or marker application by hand. The intended application method and formulation characteristics are the primary classification criteria.