TO DEMAGNETISE

To demagnetise means removing the residual magnetisation acquired by a component in order to restore its magnetically neutral state. Formed from “aimant” (magnet), a word of popular origin, the verb is the everyday counterpart of the more scholarly “to demagnetise“, built on “magnetism”: both terms designate rigorously the same operation and are used interchangeably in the watchmaking workshop, although “to demagnetise” remains the most common form in trade vocabulary. Magnetisation is a frequent issue: on contact with a magnetic field — loudspeakers, bag clasps, security gates, electronic devices — the ferromagnetic parts of the Movement, in particular the Hairspring (balance spring) made of steel, can become magnetised; their coils then partially stick together, the Frequency of the oscillator increases and the watch can gain a sometimes considerable amount of time. The demagnetising device includes a solenoid powered by alternating current that generates an oscillating magnetic field; the piece is placed inside it, then slowly moved away, the decreasing amplitude of the field gradually cancelling out the magnetisation. Quick and non-destructive, this operation often precedes a running test. Modern non-magnetic hairsprings, particularly in silicon, now reduce the sensitivity of watches to this phenomenon.