The hairspring, this snail-like component, has improved the lives of watchmakers since its invention in 1675. This strategic piece dictates the regularity of the oscillator, ensuring precision's delight. Its fabrication, often shrouded in secrecy, relies on a handful of suppliers, each specializing in a material (alloys first, then silicon starting in the 2000s). By venturing into carbon, TAG Heuer has taken a completely different path. The objective? To benefit from its own production and the qualities of this material: lightness—and therefore reduced sensitivity to gravity and inertia—resistance to magnetism (this "dark" force capable of stopping a watch), as well as durability against shocks, thanks to a nanotube structure. As you may have guessed, don your lab coat and nano-glasses: we are entering the high spheres of physics.
Genesis of a Daring Project
To truly understand the origins of this research on the carbon balance spring, a flashback is necessary. In the 2010s, the issue surpassed the mere technological aspect: in 2011, a lengthy saga began between COMCO and the Swatch Group, through its ETA subsidiary. The movement manufacturer was granted permission to gradually reduce its deliveries to third parties, following a predefined schedule until the end of 2020. This deadline put pressure on external brands eager to enhance their autonomy — even though Nivarox (a Swatch Group subsidiary producing, according to estimates, between 90 to 95% of balance springs in 2013) was not affected by these limitations. Furthermore, COMCO's preliminary investigation into the company, concluded in 2023, ultimately didn't result in legal proceedings.
However, the context remains a pursuit for independence. TAG Heuer presented in 2019, after three years of research, a first iteration of its carbon balance spring with the Carrera Calibre Heuer 02T Tourbillon Nanograph. But the balance spring proved to be insufficiently reliable. The project could have ended there, but it was brought back to the (lab) table in 2021. “We set milestones every three months to overcome challenges. And the project eventually made progress until we achieved the reliability of the balance spring,” explains Emmanuel Dupas, Technical Director.
The TAG Heuer LAB at Work
The TAG Heuer Institute of 2019 is now called TAG Heuer LAB. Jean Laconte, who arrived three years ago to lead it, summarizes the roadmap: "to master the product and the process, transition from fundamental research to the integration of innovations in watches, reliably, consistently, and at volume." The team consists of 13 profiles in physics and materials science within the TAG Heuer LAB, under his direction. The Technical Department, which also includes other services, accounts for around sixty employees under the responsibility of Emmanuel Dupas.
Six years later, perseverance pays off: the TH-Carbonspring balance spring is included in two models, Monaco and Carrera, certified COSC. Moreover, these watches successfully pass the tests to which all TAG Heuer watches are subjected (notably water and shock resistance) and benefit from the brand's 5-year warranty.
At the scale of nanoparticles
It all starts with a wafer. A thin layer of iron defines the shape of the spiral. This is then placed in a chemical vapor deposition (CVD) chamber where a gaseous mixture of ethylene and hydrogen provides the carbon. The nanotubes, about 10 nm, grow on the iron. The gaps are then filled with amorphous carbon, which solidifies the whole – addressing one of the instability sources of the spiral presented in 2019, which was too porous at the time.
The spiral has a rectangular section, with a thickened end to improve concentricity in operation. TAG Heuer has filed four patents related to this technology, with a fifth underway. Meanwhile, this independence in the spiral's geometry promises to pave the way for future research on different shapes of this key component.
Repeatability and Yield
The LAB has two CVD reactors. "To my knowledge, we are the only brand equipped with them, as they are usually reserved for research," notes Jean Laconte. A production cycle for spirals lasts 8 to 10 hours and produces approximately 300 to 400 spirals per wafer.
The selection remains strict. Each spiral's stiffness is measured. TAG Heuer also checks the height of the spiral, a sensitive parameter for concentricity and isochronism. The component is then paired with a balance wheel and adjusted by a watchmaker. Pieces that are outside tolerance are discarded – currently a significant source of waste. "The slightest nanometric variation affects performance," notes Jean Laconte. "We focus on reliability. If we can keep 15 adequate spirals per day, that's sufficient for us. The next step will be to work on yield and the volume of usable spirals," continues Emmanuel Dupas.
The TH-Carbonspring carbon spiral is currently suited for limited series. TAG Heuer installs it in the Monaco Flyback Chronograph TH-Carbonspring and the Carrera Chronograph Tourbillon Extreme Sport TH-Carbonspring, each limited to 50 pieces. They appropriately feature a carbon fiber case and dial – with a "snail" graphic signature reminiscent of the spiral's geometry. An aesthetic nod to the major innovation at the heart of the movement.
