The balance spring is arguably the single most critical component of a wristwatch. It's responsible for making sure that the oscillations of the balance are consistent, but to do so, it has to address both metallurgically and in its configuration a number of challenges. Magnetism, temperature changes, and the fact that the balance spring needs to be shaped so as to expand and contract as perfectly concentrically as possible, are all issues with which watchmakers have grappled over the centuries. Innovations such as overcoil outer terminal curves (Breguet and Phillips), and the use of materials like, in the past, glass and even bamboo, and in the modern era, silicon, are all intended in one way or another to reduce the degree to which external influences interfere with with the balance spring.*
This is an area of watchmaking in which advances in materials science have overtaken more artisanal and craft-focused activities, and hand-pinning balance springs to the collet, and hand-forming inner and outer terminal curves, have given way in the last hundred or so years to increasingly sophisticated alloys such as Nivarox, and more recently, variations on the theme of silicon. The latest innovation from TAG Heuer uses a material which has long been considered a promising candidate for use in a balance spring, but which until now no one's quite managed to tame: carbon. The material is being used by TAG Heuer for the first time, in the Carrera Calibre Heuer 02T Tourbillon Nanograph.
The only previous attempt to use carbon or carbon fiber as a basis for a balance spring that I'm aware of, was by a company founded by inventor Gideon Levingston and which he proposed in a 2004 article for the Horological Journal. His company, called Carbontime, produced a balance spring at one point for Kari Voutilainen, who in 2006 debuted a chronograph with a Carbontime continuous carbon fiber balance spring, and a transparent ceramic balance wheel. However, the company appears to never have transitioned to producing its balance springs at anything approaching an industrial scale, leaving the field open (Cartier experimented with carbon fiber balance springs at one point, while developing its ID1 and ID2 concept watches, but opted instead to use a glass-ceramic composite called Zerodur, as reported here by Ben Clymer in 2012).
TAG Heuer has gone a different route than that explored in the past. Rather than use carbon fiber, the TAG Heuer Institute in La-Chaux-de-Fonds, where the manufacturing process for the balance springs was developed, and where they're produced, has opted for pure molecular carbon graphene. The carbon atoms are arranged in a hexagonal lattice, and grown in a special reaction chamber on silicon wafers. Once the basic form of the balance spring has been established, a second step in the process introduces individual carbon atoms into the lattice at a high temperature; these atoms form an amorphous (non-crystalline) matrix within the hexagonal structure. The graphene lattice is also the inspiration for the design motifs found on the dial and winding rotor of the Carrera Calibre Heuer 02T Tourbillon Nanograph.*
This is a highly complex process, however the upside is considerable. Unlike Nivarox-type balance springs, which can show variations in their coefficient of thermal expansion from batch to batch (achieving consistency in this critical property is one of the bigger challenges of making alloy balance springs and one of the reasons that to this day, relatively few companies make balance springs in-house) these amorphous carbon composite balance springs can be made to a high degree of precision and consistency from one batch to the next. This is also one of the advantages of silicon balance springs, of course, which is why they've been so widely adopted across the industry by companies which hold the rights to use them (Patek Philippe, Ulysse Nardin, and the Swatch Group, as well as, on a relatively small scale, Rolex).*
As with silicon, amorphous carbon composite balance springs are unaffected by magnetism; they're also very light, which makes them more shock resistant (TAG Heuer's carbon balance springs easily pass the 5,000 G drop test, according to the firm) and they can be fabricated so as to ensure concentric expansion and contraction without the need for an overcoil. The springs can also be fabricated with the collet a tiny hub at the center of a traditional balance which attaches the innermost coil to the balance staff as an integrated element, which removes one possible area where inconsistencies might be introduced to the performance of the balance.
A microscope at TAG Heuer's presentation of the watch in Geneva shows the inner coils of the amorphous carbon composite balance spring under high magnification.
The amorphous carbon balance spring on the microscope stage.
The innermost coil of the balance spring transitions seamlessly into the collet.
An additional interesting feature of the Nanograph is the balance wheel it's made of aluminum. The stated reason from TAG Heuer for using aluminum, is that it offers "optimal thermal behavior." We're looking into specifics but for now, a little digging shows that single-layer graphene has a negative coefficient of thermal expansion and it may be that aluminum was chosen because its coefficient of thermal expansion tends to cancel out any changes in elasticity which temperature would induce in the balance spring. Oh, and on a completely different note, it's coated with Super-LumiNova, which is pretty nifty looking just from a design standpoint and which addresses the long-standing problem of not being able to appreciate the oscillations of your open-dial tourbillon watch in the dark.
As with many such watches, design-wise this one is intended to signal its next-gen technical sophistication as unambiguously as possible, which is merely to state the obvious it's a love-it-or-hate-it design. While I'm not entirely sure how I'd feel about looking at it every day, I also don't feel this is especially an everyday watch; it's really more a very unusual watch with a first-ever technical feature that might appeal very strongly to early adopters, as well as anyone who's a fan of this sort of design idiom, and who want something other watches designed along similar lines don't have. Purely from a technical perspective, it's potentially an extremely useful arrow in TAG Heuer's quiver, and in that of the LVMH Group as a whole, which doesn't make use of silicon components and which may benefit considerably from a high performance alternative to Nivarox-type alloys. It's a development well worth watching.
Price, $25,000, and this will be a regular production timepiece, not a limited edition. For full specs check out Stephen Pulvirent's Introducing article on the Nanograph, and for more on watchmaking at TAG Heuer, and the Nanograph, visit TAGHeuer.com.


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