. (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° 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. ]