Earth pigment
A pigment dug from the ground: clay or rock coloured by iron and other minerals.
Also: earth colours, natural earths
Earth pigments are naturally coloured clays and soft rocks. Iron oxides give them their yellows, reds and browns; manganese adds darker browns; a few special clays are green. They are dug, washed, dried and ground, and some are roasted to change the colour. Ochre, sienna and umber are the best known. They are cheap, do not fade and are found on every continent, so they are the oldest and most widespread colours in human art, from rock paintings to house walls. Synthetic iron oxides now do much the same job.