ELINVAR

Elinvar is an Alloy of Steel (iron, nickel, chromium) patented by the Swiss physicist Charles-Édouard Guillaume. Its name sums up its key property: a modulus of Elasticity that is practically “invariable”, meaning almost insensitive to variations in Temperature, combined with a very low coefficient of Expansion. These qualities made it a Material of choice for Balance hairsprings: a Hairspring (balance spring) made of Elinvar retains its Stiffness (spring rate) — thus the Frequency of the oscillator — despite temperature variations, largely eliminating the thermal error that affected Hairsprings (balance springs) made of ordinary steel and required the use of compensating bimetallic Balances. A complement to Invar, an Alloy with near-zero Expansion due to the same scientist, Elinvar earned Guillaume, a native of Fleurier, the Nobel Prize in Physics in 1920. These discoveries marked a decisive advance in chronometry, paving the way for modern self-compensating Hairsprings (balance springs) that today equip almost all mechanical watches.