Three oxides, many lips
Red iron oxide (haematite, CI 77491) supplies the warm rust-red; yellow iron oxide (CI 77492) shifts toward peach and coral; black iron oxide (magnetite, CI 77499) deepens and mutes. Blend ratios of these three, sometimes with a touch of white or an organic brightener, cover the realistic lip range from pale rose to deep berry-brown.
The good
Iron oxides have one of the longest safety records of any colourant, are largely inert in tissue, rarely provoke allergy, and photodegrade slowly, so healed colour stays close to intent for longer than organics.
The two quirks
Warm-then-cool fade: as the red fraction slowly clears, some iron-oxide lips drift toward a cooler mauve residual. Artists counter this by starting a step warmer than the target.
Magnetite and lasers/MRI: black iron oxide is magnetic and can react (heat, or paradoxically darken) under laser removal or, rarely, in an MRI scanner. It is a minor, manageable issue but worth disclosing.
