The key distinction is end-use and formulation: printing inks are engineered for high-speed press application—specific viscosity, tack, and drying mechanism—whereas writing inks are fluid and designed for pen or marker delivery. Documentation such as technical data sheets specifying press type, viscosity range, and pigment loading helps support the printing-ink classification at entry.

Generally yes at the SITC heading level—both fall under black printing ink—but at the HTS 10-digit level, the carrier medium and curing chemistry can affect the specific tariff line. Importers should verify the applicable HTS subheading with a licensed customs broker, as UV-curable formulations may be reviewed differently depending on their resin base.