TO DEMAGNETISE

To demagnetise means removing the magnetic character of a magnetised component in order to restore it to a neutral state. Built on ‘magnetism’, a learned term of Greek origin, the verb is the exact equivalent of the older ‘To demagnetise’, formed from ‘magnet’: both words cover the same physical operation, with To demagnetise belonging more to the technical and scientific register — it is used just as much for a watch as, historically, for the hull of a ship exposed to magnetic mines. In watchmaking, a Movement magnetised does not work properly: when the Hairspring (balance spring) becomes magnetised, its coils tend to stick together, the Frequency of the oscillator increases and the watch runs fast, sometimes by several minutes per Day. Demagnetisation is carried out using a demagnetiser, a solenoid carrying an alternating current that creates an oscillating magnetic field; the piece is placed at the centre of the coil, then gradually moved away, the gradual decrease in the field cancelling out the residual magnetisation. Simple and harmless to the Movement, this operation is often the first diagnostic step when a watch is running abnormally fast. The development of non-magnetic alloys and Hairsprings (balance springs), particularly in Silicon, now tends to limit the need for this operation.