Re: B&O Freight Car Brown

Anthony Thompson <thompson@...>

Rick Aylsworth wrote:
Tiny nit, Tony and Jim. Ferrous oxide is black (Fe+2). Ferric oxide (Fe+3) is the red-brown pigment, and also rust, with Tony's caveats. Different oxidation state = different crystalline structure = different color.
True, I mistyped, reversing ferrous vs. ferric. But black ferrous oxide isn't a paint pigment. What a paint guy might call ferric oxide probably is a rather more complex material, not the chemically and structurally pure laboratory compound, nor a pure mineral.
Natural rust is a mixture of iron oxides, starting with the first film which is yellowish, followed by the familiar orange-red color (lots of ferric oxide), then darkening more and more into a really dark brown. The various iron compounds responsible for all this (relevant to freight car weathering, especially unpainted interiors of gondolas and hoppers) are complex and far beyond the scope of this list. But the color sequence is entirely relevant.

Tony Thompson Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705
(510) 540-6538; fax, (510) 540-1937; e-mail, thompson@...
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