he “thread of life” is a metaphor for human existence. The expression stems from Greek mythology, where life is imagined as a thread governed by the Three Fates, or Moirai. Clotho spins the thread at birth, Lachesis measures its length and shapes a person’s destiny, and finally Atropos cuts it at the moment of death. Together, they embody the idea that birth, fate, and death are inseparably woven into human life. The Greek idea also applies to the hairspring inside a watch. The movement’s thread of life follows a production process that involves shaping or spinning, measuring, and finally cutting. The in-house hairspring also gives a brand character. Nowadays, computer-operated machines can create a hairspring quickly and precisely. But that wasn’t always the case.

The idea of using a curved hairspring inside the regulating organ of a movement stems from British physicist Robert Hooke (1635–1703), often called ‘England’s Leonardo’ and known for his law of elasticity. Around 1657, he considered that adding a balance spring to the balance wheel would improve accuracy. He was right, but it was Dutch scientist and inventor Christiaan Huygens (1629–1695) who materialized the idea in the early 1670s. The invention not only increased accuracy but also transformed early pocket watches from expensive novelties into useful timekeepers. To put it in perspective: before the hairspring, a clock could deviate as much as perhaps several hours per day. A movement with the new, rudimentary coiled hairspring, featuring only a few curves, ensured that the balance swings back and forth at a constant frequency, bringing the deviation down to just 10 minutes per day.

The iron spiral

Huygens described his balance spring as “an iron spiral,” although it was more likely to be made from an iron-copper or a soft steel alloy. He chose the material for its malleability and elastic properties. As watchmaking advanced, watchmakers and manufacturers experimented with various steel alloys, primarily carbon steel, to improve hairspring performance. Although these alloys offered greater stability than earlier springs, they remained highly sensitive to temperature fluctuations. Watchmakers also encountered another limitation: ordinary steel springs gradually lose their elasticity due to molecular changes in the metal and the cumulative effects of material fatigue. To give you an idea, the hairspring in a modern watch will oscillate around 500 million times a year (!). It requires extraordinary resilience and endurance to cope with that.

A major evolutionary step was the introduction of Elinvar hairsprings, which were malleable, corrosion-resistant, and partially magnetic. Elinvar was invented in 1919 by Charles Édouard Guillaume, who developed a nickel-iron-chromium alloy to solve the thermal instability problems of traditional steel hairsprings. His breakthrough earned him the 1920 Nobel Prize in Physics, and it made large-scale serial production of accurate timekeepers possible, with the Hamilton Watch Company among the first major adopters introducing Elinvar hairsprings in railroad pocket watches around 1930 and in wristwatches by 1935.

In the same era, Dr. Reinhard Straumann advanced the hairspring with the development of Nivarox, a related nickel-iron alloy offering superior elasticity and durability. Nivarox, a German acronym meaning “not variable, not oxidizable,” eventually became the industry standard and is now used in millions of mechanical watches worldwide. But there are still manufacturers who decide not to use the mass-produced springs and instead produce them in-house.

Bragging rights

The manufacturers who do produce hairsprings in-house are proud of it, but also shroud the creation in mystery. In the end, “the thread of life” is not just a difficult component to produce; it’s also a strategic and brand-defining one. If you can produce a hairspring in-house, it creates independence and street credibility, giving a brand bragging rights. But crafting a hairspring typically measuring between just 0.02 mm and 0.05 mm in thickness — often thinner than a human hair — and approximately 0.15 mm in width, from raw materials, is a task of herculean proportions.

Tolerances are measured in mere fractions of a micron, with acceptable deviations as small as 0.00005 mm. Such accuracy is essential because even a slight variation of 0.001 mm in the spring’s thickness can alter its elasticity enough to cause a watch to gain or lose up to 30 minutes per day. Minerva could have chosen to develop its own hairspring by embracing modern technology, thereby creating a non-alloy silicon hairspring, as Ulysse Nardin did, for instance.

Silicon might very well be the ideal material for modern hairsprings thanks to its light weight, flexibility, corrosion resistance, and immunity to magnetism, temperature variations, and air pressure. Also, silicon hairsprings are produced directly to their final shape with micron-level precision using semiconductor fabrication techniques. It’s a consistent process that guarantees reliability and efficiency, and is cost-effective on top.

The reason for existence

Despite these perks, Minerva is among a select group of haute horlogerie manufacturers that have opted to use traditional artisanal techniques. At its historic Villeret atelier, a small group of highly specialized artisans crafts bespoke oscillators, including cylindrical and flat hairsprings. They work with a proprietary metal alloy whose composition is kept secret, which is first drawn into an ultra-thin wire, after which four strands are carefully hand-wound together to create the initial spiral. The hairspring is then individually shaped, trimmed, and fitted with the terminal curve. This is often a Phillips curve, a calculated bend at the outer end of the spring that allows it to pulse perfectly concentrically.

It is meticulously bent by hand to ensure the balance wheel and hairspring maintain the same duration for every swing, regardless of how far it travels; in watchmaking terms, this is optimal isochronism. And this is only achieved after finding the right match between different hairsprings and balance wheels, since every hand-made component differs ever so slightly; it’s the “cost” of not using uniform, industrialized hairsprings.

The painstaking process of creating a hairspring takes approximately half a day, limiting production. As a result, Minerva reserves these handcrafted components for its most prestigious movements, including the M15.08 calibre found in the recently launched Unveiled Crownless.

Minerva, like other high-end watchmakers such as A. Lange & Söhne, H. Moser & Cie., and De Bethune, chose to handcraft hairsprings to achieve total control and add value to its timepieces. In a way, these brands control their fate with an in-house-made “thread of life,” a metaphor for their existence. Who could have thought that ancient Greek mythology would apply to watchmaking?