Fe2O4

from The Collaborative International Dictionary of English v.0.48
Bower-Barff process \Bow"er-Barff" proc`ess\ . (Metal.)
   A certain process for producing upon articles of iron or
   steel an adherent coating of the magnetic oxide of iron
   (which is not liable to corrosion by air, moisture, or
   ordinary acids). This is accomplished by producing, by
   oxidation at about 1600[deg] F. in a closed space, a coating
   containing more or less of the ferric oxide ({Fe2O3}) and the
   subsequent change of this in a reduced atmosphere to the
   magnetic oxide ({Fe2O4}).
   [Webster 1913 Suppl.]
    

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