Blued steel

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Dial segment of a Rainer Brand Panama Dualtime with blued hands

For blueing the steel parts are slowly and carefully heated ("started") to about 300°C. The metal then coats with an ultra-thin, cornflower blue shimmering layer of magnetite (Fe304).

The blueing is used in the field of watch manufacturing for the refinement (finishing) of movement parts, especially of screws and watch hands.