How does the color of rust change depending on its makeup and state, or more to the point, how would one put the rust into that state?

For example, Wikipedia shows Iron(III) Oxide as being red in the α hydrate state and yellow in the β hydrate state, while a brown pigment is shown here as being iron oxide with a +3 oxidation state (which I understand to be Iron(III) Oxide, whose color above depends on its hydration state). Finally, a black pigment can be made using Iron(II,III) Oxide.

So my question is: I have crude brown Fe2O3(aq) (which I made from simple NaCl hydrolysis of iron); If I let it dry I presume I will get brown pigment. What do I have to do to it in order to make it enter the α or β hydration states? Finally, how would one convert Iron(III) Oxide into Iron(II,III) Oxide?

I understand most of this information is explained on the wiki pages that I linked, but I'm having a hard time sorting through it and would love if someone could help me cut through it and let me know what's more or less possible in a very small home lab, as opposed to some sort of industrial process that I likely don't have access to. Thank you for your patience as I begin what I hope to be a wonderful new hobby.

α-hydrate Iron(III) Oxide β-hydrate Iron(III) Oxide Iron(III) Oxide with unknown specifics Iron(II,III) Oxide

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    $\begingroup$ Rust ( formed at ambient temperature in moist conditions) , is not Fe2 O3 or any other simple oxide. It is various hydrates and hydroxides. I have seen about a thousand XRF patterns of various rust samples done for corrosion evaluation. At ambient temperature Fe2O3 only forms under very specific conditions of fretting corrosion. It will form at modest temperature near 700F at long times . FeO ( black )will form at high temp like 1800 F. Fe3O4 forms at intermediate temperatures. We never heated rusts to try to alter them. $\endgroup$ Commented Dec 8, 2021 at 16:30
  • $\begingroup$ @blacksmith37 Okay, so I got my crude rust from electrolysis and it's rather brown. Is there anything I can try to do to refine it, i.e. remove some of those extra hydrates and hydroxides? $\endgroup$
    – JShoe
    Commented Dec 8, 2021 at 16:35
  • $\begingroup$ I never tried to modify the rusts. I expect heating will will alter it but have no experience. $\endgroup$ Commented Dec 8, 2021 at 18:51

1 Answer 1


Per a source involved in the manufacturing of pigments, to quote:

iron from the Fool’s Gold is dissolved in the sulfuric acid. If the acid is properly neutralized, it will precipitate out as a hydrated iron oxide yellow, which... can be heat-treated or “burned” to produce a red color (Figure 1).

So yes, there is, at least one path to creating a select iron pigment and thermally altering its color.


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