AMAGNETISM

Amagnetism refers to the property of a Material to remain unaffected by magnetization under the effect of a magnetic field, unlike ferromagnetic Metals such as Iron or nickel. In watchmaking, this quality primarily concerns the regulating organ: a magnetized Balance, a Hairspring (balance spring) or a Pallets (lever) lose their Isochronism and cause inaccurate timekeeping. The physicist Charles-Édouard Guillaume developed Invar in 1896, then the Elinvar in 1920, two iron-nickel alloys with low sensitivity to magnetism; the Glucydur, Alloy Copper–Beryllium, and the Nivarox succeeded them in the 20th century for common balances and hairsprings. Silicon, used since the 2000s, offers genuine amagnetism, whereas these metallic alloys remain only weakly sensitive. The ISO 764 standard governs the designation “antimagnetic watch,” requiring that a field of 4,800 A/m not cause a rate deviation exceeding 30 seconds per Day; calibers certified Master Chronometer by METAS withstand up to 15,000 gauss. This intrinsic amagnetism of the Movement differs from soft iron shielding, which is ferromagnetic but has low remanence, another way of obtaining an antimagnetic watch.