Pigments and Dyes

Colourants can be classified into two categories: Pigments & Dyes

Pigments

Pigments are solid, decorative materials in the form of small discrete particles that are insoluble in the medium in which they are applied to, they can be inorganic or organic and are coloured, black or white materials which are practically insoluble and are suspended within a medium. Since they are suspended in the binder the physical condition of the particles is hugely important, this is why manufactures rigidly control production conditions to ensure uniformity within each production batch as the smallest change can drastically affect the shade and strength of the pigment

The Earliest Pigments were inorganic and of natural origin: Lead White, Red Lead, Lapis Lazuli, Malachite, Cinnabar and various oxides of iron

Dyes

Dyes are a coloured substance that can be applied in a solution or dispersion to a substrate and giving it a coloured appearance, they are mainly soluble in water and in the process of dissolving lose their crystal-like structure

Whilst both pigments and dyes are very similar as far as the basic chemical composition goes, it is by physical characteristics rather than chemical composition that pigments, and dyes are different from each other

Lightfastness

Although little is known about the relation between the chemical constitution and lightfastness of pigments it is clear that it is defined by the chemistry of the molecule

Dyes are the most susceptible to the Ultraviolet Rays from the sun as they can break the bonding of a dye molecule and destroy the colour, causing the colour to appear faded

Pigments these days are mainly lightfast with the exception of a few pigments Rose Madder for example, these are usually called fugitive pigments and have mainly been replaced with a more lightfast alternative, the quinacridones for example, Pigment Violet 19 (Quinacridone Rose) has mostly replaced Pigment Natural Red 9 (Rose Madder)