Some sources of Iron for making pigments: iron minerals, rusted waste metal, waste mine water, polluted rivers and groundwater
The various oxidation states of iron can create colours from yellow through to orange, red, brown, green, blue, brown-violet and black (and all shades in between). The principal colouring material of pigments derived from the inorganic content of the earth is iron, in conjunction with other metals and minerals. There is archaeological evidence to suggest that calcined, or burnt yellow ochre was a technology developed in the palaeolithic era where naturally occurring ochre deposits were heated below 600 celsius to produce a dramatic colour change. Calcining waste stream iron compounds will also create a wide palette of pigments. Iron-rich earth pigments are the original metal pigments and the most direct and elemental form of creating colour from metal, incontrast to using already processed metal.
London clay sample with iron staining. Hampstead Heath, 2020