Azo pigments are colourless particles (typically earths or clays), which have been coloured using an azo compound. Azo pigments are important in a variety of paints including artist's paints. They have excellent colouring properties, again mainly in the yellow to red range, as well as lightfastness. The lightfastness depends not only on the properties of the organic azo compound, but also on the way they have been absorbed on the pigment carrier.