The Bronze Age: the rising popularity of bronze in watch making

The clash of swords ringing out on a far flung battlefield, the dull golden glint of tarnished metal from a statue in an Iranian temple, molten liquid hand poured into moulds for ceremonial jewellery; bronze has seen it all and endured. Bronze is one of the most ancient alloys still in use today. It emerged from as early as 4000 BC and rapidly became a staple material for just about everything from weapons and armour to home wares and jewellery.

An Iranian statue of a horse. Hey horse, statue?

Initially combined with arsenic, bronze was most commonly made from the combination of two base elements - Copper and tin (10-13%) - and could be readily moulded, shaped, sharpened and remoulded into just about everything a bronze age citizen could desire. Additional elements such as aluminium or zinc were often added to achieve desirable properties such as hardness, ease of shaping or to provide colouration and corrosion resistance. Bronze rapidly became widespread across The Middle East, Europe and Asia, riding off the back of growing trade routes that could transport its constituent elements to an ever larger community. Eventually giving way to iron, due in large part to trade route disruption, bronze nonetheless remained in production, with continuous innovation leading to inclusion of a growing number of elements and uses.

Bronze has a Vickers hardness rating (resistance to penetration) in the range of approximately 70 - 250 (dependent on the included elements). Putting this in perspective, 316L stainless steel has a Vickers hardness of 155, tungsten a hardness of 3430–4600, and diamond 10,000. Bronze readily lends itself as a base material for timepiece case construction. It can be cast into almost any shape and, depending on the composition, resists scratching, corrosion and pitting.

The earliest example of bronze watches appears to be from Gérald Genta, way back in 1988 with the launch of the Gefica Kilimanjaro. The Gefica Kilimanjaro was a stunning watch, so modern in styling as to appear out of time, and should have launched the alloy into more broader circulation. However, more widespread use of bronze in watch making did not begin for about another fifteen years. More recently, watch manufacturers are increasingly turning to bronze for its unique look and tendency to patina over time due to exposure to air and water borne elements.

Gefica Kilimanjaro. Just wow

The natural colour of fresh bronze (copper / tin) is gold, but it’s a colour that doesn’t last long due to the interaction of the alloy with the environment, specifically, but not exclusively, the element of oxygen. Bronze patina veers across the spectrum from blue to green, brown and black. The colour of the patina can be forced or accelerated with the use of various chemicals applied to the metal’s surface. The colouration of bronze and its patina provides a distinct and novel counterpoint to dial, hand and strap colours, opening up a range of new aesthetic possibilities.

Eterna Contiki Bronze: Gold and green on bronze. Image copyright https://www.watches-news.com/eterna/kontiki-bronze/

Aluminium bronze is widely used for case making, containing between 6 and 10 percent aluminium, with higher content alloys making for a more metallic grey finish. An increasingly popular choice for manufacturers of late is CuSn8. With composition and construction standards defined by the ISO (International Organisation for Standardisation), CuSn8 is a solid solution strengthened copper (Cu) dominant bronze alloy with around 8% tin (Sn) and the addition of around 0.04% phosphorous (P).

Phoibos with their Bronze Eagle Ray

The tin content in CuSn8 increases the strength over straight copper, it is wear-resistant, has very good corrosion resistance and can be easily soldered. in addition, CuSn8 has good sliding properties, which in the case of wristwatches makes it an excellent choice for rotating components such as bezels and crowns. While the composition of the CuSn8 alloy is copper and tin, the specific formulation will vary according to the desired use of the alloy.

With the increase in production, the price of bronze alloys for watchmaking has reduced, making it accessible to an array of microbrands like Spinnaker with their Tesei, the Phoibos bronze Eagle Ray, Ergon’s Maelstrom and fan favourites from Zelos: the Swordfish and Mako.

The Spinnaker Tesei, a bold statement

Luxury brands are also pushing forward with bronze models, including taking existing models and casting the cases in bronze. The ironically name Tudor Heritage Black Bay Bronze (bronze is not a heritage watchmaking material) is a beautiful example of colour juxtaposition, with the bezel insert and dial colours playing beautifully off the satin gold sheen of the bronze case. It’s a real looker.

Tudor Black Bay: it’s all about the heritage…of bronze

Pushing bronze to its limits, the Hublot Classic Fusion Fuente offers a decorative moulded bronze case that looks like a piece of art with its recurring emblem of tobacco leaves and the Fuente family symbol letter of X. Finally, Bell & Ross’ Green Bronze Diver (BR 03-92) is a prime example of the expression of bronze’s natural colour and ability to create unique colour matching opportunities. Green and gold rarely looked so good.

Bell and Ross. Bronze and green are a match made in horological heaven

The recent meteoric rise of bronze in watch case making is a reflection of its great popularity, its natural beauty and flexibility as a material. From its base colours to its patinas and innate affinity for blues and greens. There’s no reason to believe this is just a fad. What we’re seeing here is a new and significant offshoot in horology and the beginning of endless new possibilities.

Thanks

Peter Sargison