Pigment Ink
Ink in which the colourant is solid particles suspended in a carrier, sitting on the paper surface rather than dissolving into it.
In depth
Pigment particles are far more resistant to light and pollutants than dyes, giving print lifetimes measured in many decades rather than years. The trade-offs are a slightly smaller gamut on glossy media, susceptibility to bronzing and gloss differential, and a need for the print to settle before final colour is judged.
Examples in practice
A pigment print rated for 100 years of display shows no measurable fading after a decade in a lit room.