Metallurgy: Get To Know the Essential Watchmaking Metals and Alloys

In our savoir-faire series, we highlight the evolution of watchmaking metal alloys, from the conventional to the exotic, and how metallurgy has enabled wristwatches to be more advanced than ever.

Nestled in the unspoiled Jura Mountains, the Vallée de Joux is home to a constellation of villages that form the cradle of Swiss watchmaking. The discovery of local iron mines – an antecedent and naturally occurring metal vital to the fabrication of alloy steel – centuries before is one of the pivotal reasons watchmaking prospered in this picturesque region. But watchmaking is more than just stainless steel that makes up the hardened exterior of many a wristwatch.

A mechanical wristwatch is a composition of materials and crafts. Ingenuity and flair harmonise to create a coveted object that transcends time, into the realms of art, emotion and desire. At the visceral level, a mechanical wristwatch epitomises precision and refinement. Traditions, knowledge and techniques are constantly improved to beget mechanical wristwatches that boast greater precision and that are finer in execution.

As history has shown, watchmakers have risen to the challenge of keeping and ensuring watchmaking continues to thrive. In their pursuit of excellence, calibres have attained greater accuracy and svelteness, power reserves have leaped by days, and wristwatches have become more resistant than ever to the elements. Metallurgical know-how plays the role of an enabler to perfection, affording watchmakers the luxury of expanding their repertoires beyond stainless steel and experimenting with precious metals and less conventional materials.

Gold: The epitome of luxury

Thanks to opulent lustre that commands immediate reverence, gold has endeared itself to past civilisations and modern society. The enduring popularity of gold has withstood the test of time and the changing of taste. In watchmaking, it is often harnessed as a point of distinction between references of different price points. The uncanny versatility of gold allows it to be employed to various extents, such as the case, the crown, the bracelet, the indexes, the hands, the dial, the clasp, the balance wheel, the rotor and more.

Although at the lower end, gold plating, where a base metal is deposited with a thin layer of gold in a process called electroplating, is used, luxury watchmakers accept nothing less than solid gold with 18k gold as standard. It represents the ideal balance between luxury and practicality. Pure gold, or 24k, is considered relatively malleable and therefore unsuitable as the material of choice for a watch case or bracelet where durability is a concern. In some exceptional wristwatches, a gold rotor is coupled to the self-winding mechanism to raise the efficiency of the winding action. As gold is a dense metal, the higher torque it generates helps replenish the power reserve more effectively. Additionally, the greater efficiency it can achieve compared to lesser metal of the same size provides the watchmaker with extra room to manoeuvre, such as incorporating a mini rotor without compromising on winding actions. To drive further efficiency, a number of watchmakers favour 22k gold as the oscillating weight.

The difference between 18k, 22k and 24k gold lies in their purity. 24k gold denotes effectively 100% gold, while 22k and 18k are impregnated with other metals to varying degrees. This alloying process is carried out for several reasons, such as to improve durability and to acquire a unique hue. 18k gold consists of 75% gold, while 22k gold is 91.67% gold, with the remaining percentage filled in with other metals contingent on the vision of a metallurgist. The higher the purity, the warmer the colour the gold exudes.

Another characteristic of gold is its hypoallergenic nature, guaranteeing that the wearer is safe from adverse allergic reactions.

Wristwatches made of gold are typically sorted into yellow, white and rose. Displaying the most familiar golden sheen, traditional 18k yellow gold comprises 75% gold, 15% copper and 15% silver. By tweaking the formula through adding or subtracting the percentage, a different hue of gold can be achieved. For example, by substituting silver with more copper, the gold alloy will develop a pinker shade. It forms the basis for coloured gold, with rose gold typically combining gold, copper and silver, while red gold eliminates silver entirely. On the other hand, white gold typically combines silver, nickel and/or palladium to bring forth the silvery, whitish shine. In addition, rhodium plating may be enlisted to impart further scratch resistance and superior lustre to the white gold alloy.

To set themselves apart, a handful of watch brands have pioneered proprietary gold alloys. OMEGA is perhaps the most prolific in this regard, debuting Moonshine™ Gold, Canopus™ Gold, Ceragold™ Gold and Sedna™ Gold all in a span of several years. Blancpain has also benefited from the occasional inclusion of Ceragold™ Gold and Sedna™ Gold. In 2021, Montblanc introduced Lime Gold on the limited-edition 1858 Split-Second Chronograph, which exhibits a fascinating greenish-gold colour by melding gold, silver and iron.

Platinum: The pinnacle of luxury

If gold embodies the meaning of luxury, platinum is considered luxury par excellence. The prices of platinum-encased wristwatches reflect their exclusivity and are almost always produced in highly limited numbers. Unlike gold which has been de rigueur for millenia, platinum is a more recent discovery.

Yet, it has gained much traction in haute horlogerie for its strength and resistance to corrosion. However, it also makes platinum a painstaking material to work with. 950 platinum is used extensively in platinum wristwatches. It consists of 95% platinum, with the remaining 5% typically iridium or ruthenium. Like gold, platinum is also hypoallergenic.

The ductility of platinum makes it particularly arduous to be milled into a watch case. Fabrication consumes significantly more man-hour and exerts greater wear and tear on machinery. It has been observed that a platinum watch case could take three times longer to produce than gold. Denser than even gold, it isn’t surprising to see a prodigious company of watch manufacturers such as Bulgari, Cartier, Franck Muller, H. Moser & Cie. and Parmigiani Fleurier go a step further by adapting the precious metal as a rotor in some of their wristwatches. Breguet has even conceived a platinum peripheral rotor.

Stainless steel: Ever the trusted material

There is not another material that can rival stainless steel when it comes to ubiquity in watchmaking. Compared to other materials, it is relatively inexpensive, durable and its lustre doesn’t wane over time.

Stainless steel doesn’t occur naturally. It is an alloy composed of iron with chromium, as well as other trace elements. As alluded to by its name, this rustless steel alloy is resistant to corrosion. Its cleanability is comparable to glass, making it easy to look after. Stainless steel used in watchmaking tends to be austenitic, containing a high percentage of nickel and chromium for elevated corrosion resistance, with 316L and 904L preferred by watchmakers. They vary on the amount of nickel, chromium, copper and molybdenum used. The former is considered a marine grade stainless steel, offering exceptional resistance when exposed to salt and other chlorides, while the latter provides superior resistance, takes on a higher polish while also more challenging to be milled into a watch case.

In recent development, steel has become the focal point of innovation. Lucent Steel™, is Chopard’s brainchild coalescing the advantages of steel and sustainability. The exclusive alloy is made from at least 80% of recycled steel, yet it is said to be 50% harder and radiate a signature lucent quality.

Corum introduced an homage to Damascus steel in 2019 when it launched the DLC-treated Lab 01 collection. The alloy is recognisable for its hardness and swirling pattern created by repeatedly layering, heating, compressing and forging the steel.

Titanium: A lightweight marvel

Titanium is winning over watch collectors with its excellent strength-to-weight ratio and gorgeous silvery-greyish sheen. An alternative to stainless steel, but unlike stainless steel which is notable for its heft, titanium is remarkably light. It is around 40% lighter, hence, presenting a compelling proposition to those who seek lighter wristwatches. Thermal conductivity of titanium is also lower than that of steel, resulting in less conspicuous heat transfer between the wearer and the wristwatch.

In watchmaking, titanium is grouped into Grade 2 and Grade 5. The former is wholly titanium, while the latter is an alloy, with 6% aluminium and 4% vanadium. This tiny but significant contribution imbues Grade 5 titanium with superior hardness and scratch resistance. At the same time, titanium is much harder to machine compared to steel, further contributing to manufacturing costs. But similar to steel, titanium is a durable and corrosion resistant material that can take on an array of finishes, transforming it into a capable watch case and bracelet.

The latest novelties to adopt titanium include Bell & Ross’ BR-X5 Black Titanium, Blancpain’s iconic Fifty Fathoms in 42mm, Breitling‘s Aerospace B70 Orbiter, Chopard’s Alpine Eagle 41 XP Tech Titanium and Zenith’s Chronomaster Sport Titanium.

Unexpected materials: Aluminium, tantalum and silver

An alloy known for its light-weightedness, corrosion resistance, high strength-to-weight ratio and formability, aluminium consists of copper, magnesium, manganese, silicon and/or zinc. It exudes an attractive silvery shine and is commonly associated with the aerospace industry.

Admirers of Bulgari might recall that long before the introduction of the Aluminium series, the Maison once purveyed the Diagono Magnesium, tapping into the durable and extremely light metal. While today Bulgari has established an enviable reputation as a serial watchmaking record breaker, it has continued to champion the holistic use of unconventional materials in its wristwatches.

Tantalum is beloved for its blue-greyish sheen. Named after the Greek mythological figure, Tantalus, tantalum is unapologetically hard, ductile, lustrous and corrosion resistant. While watchmakers and metallurgists are fascinated with it, they find tantalum a demanding material to work with. The challenge lies in its physical properties, but when the going gets tough, the tough gets going. The pricey metal is heavy and dense, regularly breaking and wearing down tools used for machining it into a watch case. Polishing is another challenge with watchmakers likening the process to lapidary, rather than buffing of precious metals.

H. Moser & Cie. is among a select group of watch manufacturers to have used tantalum in production. CEO Edouard Meylan has spoken about his experience, in awe and wonder of the metal. In a published interview, he revealed when he first pitched the idea to his team in 2017, they were quoted the substantial cost of tantalum: 17 times the cost of working with steel. Examples of tantalum-clad wristwatches include the H. Moser & Cie. Endeavor Perpetual Calendar unveiled in 2023 and the OMEGA Seamaster Diver 300M in a combination of titanium, tantalum and Sedna™ Gold launched in 2019.

Though silver has never been a common watchmaking material, it is more readily found in vintage wristwatches. Today, it is seldom used. Silver is typically separated into fine silver, which is 99.9% silver, while sterling silver is 92.5% silver. The remaining percentage is made up of other metals, usually copper. A vagary of sterling silver is that it can oxidise over time, developing a darker patina that cements the bond between the timepiece and the wearer. A paragon of silver wristwatches is Zenith’s Pilot Type 20 Chronograph Silver.

Bronze: To patinate or not to patinate

A copper-based alloy whose ancient discovery, following the smelting of copper and alloying it with tin and other trace elements, as well as its extensive use in the arts and trade, gave rise to the historical Bronze Age. In early diving equipment, bronze was the preferred material, owing to its saltwater resistance, where it merely oxidises at the surface while protecting the integrity of the layer underneath.

A hallmark of bronze is the turquoise colour it develops after a period of time. The degree of patination is a variable, subject to all kinds of external factors such as precipitation, perspiration, the sea and more. It renders the eventual patina a sort of personal achievement, which further amplifies the appeal of bronze. The composition of bronze is overwhelmingly copper, typically around 90% if not more. Nevertheless, the current crop of watch manufacturers have reassessed the process, sprinkling it with elements such as zinc, iron, phosphorus, lead and aluminium in order to produce a distinctive hue, as well as to control the extent of patination and to improve scratch resistance.

Examples of wristwatches attired in bronze include Bell & Ross’ BR-03-92 Diver Black & Green Bronze, Blancpain’s Fifty Fathoms 70th Anniversary Act 3 and Montblanc’s Iced Sea Automatic Date Bronze.

Discover more brands with Cortina Watch online, visit us at our boutiques, or contact a sales representative today to learn more.