A finely ground, insoluble colouring material mixed into paint, ink or other media.
Pigments remain as discrete particles suspended in a binder, unlike dyes, which dissolve into the material they colour — this is the defining physical difference between the two.
'Pigment' and 'dye' are often used interchangeably in everyday speech, but they are physically different (see dye).
Ochre and ultramarine are historical pigments — see the pigments & dyes section for structured records.
Whether a colourant is a pigment or a dye affects its lightfastness, cost and historical availability.
A pigment is identified by its Colour Index generic name and constitution number, and characterised by properties that are each tested separately: tinting strength (how much it shifts a standard white), hiding power, particle size, oil absorption and lightfastness. Its colour in use is predicted from two coefficients per wavelength, one for absorption and one for scattering, which is the basis of the recipes a paint-matching machine calculates.
A paint colour is matched by eye with a different pigment combination from the original.
Two pigment mixes that agree under one light can separate under another, and they age differently. Where a repair has to stay invisible, the pigments must be the same, not just the colour.
A bright organic yellow or red is chosen for a front door or a feature wall.
These pigments absorb only part of the spectrum and scatter little, so they hide poorly and need extra coats or a tinted undercoat. The colour card does not show that.