SJX Watches
Insight: Hairspring Materials and Evolution Part I
The invention of the hairspring was among the greatest breakthroughs in horology, since its inception suddenly made mechanical timepieces portable, transforming clocks into watches. This not only marked the start of precision timekeeping, but also set mankind upon the long road to perfecting the accuracy of mechanical watches, arguably the most sophisticated pieces of kit on Earth at the time, when such precision was paramount for fields as varied as navigation, warfare, and astronomy. The hairspring turned 350 years old in 2025 and we’re marking the occasion with a series of stories on the topic, including the story of the spiral hairspring and also the importance and evolution of the overcoil. Now we turn to temperature compensation and metallurgy in a two-part story covering the evolution of the hairspring materials up until metal alloys. More exotic materials and inventions will follow in Part II. Elasticity and thermal expandability One of the fundamental factors in hairspring function is ambient temperature, simply because metal alloys expand or contract uni-directionally with a change in temperature. As a result, watchmakers used calorimetry, the science of temperature effects, and material science, specifically metal alloys, to their gain in advancing hairspring technology. The equation below shows the relation between the initial length of a metal strip L0, measured at a given temperature and the final length LT after a certain change in temperature. The equ...