In-Depth The Black Watch Case (Part One)

The all-black watch case. A symbol of modernity, stealth, you know... tacticool. A counter to the centuries of luxuriously shiny precious metals. Ok, maybe I'm being a bit dramatic, but it's undeniable that through the cyclical nature of watch trends, black watch cases and the all-black aesthetic in watches have proven their staying power. 

Where did we see this start taking place in the watch space? Well, while many material innovations in watchmaking stem from more technical desires, it seems that the concept of the all-black watch came from purely an aesthetic perspective, coming in strongly during the 1970s.

Most sources seem to attribute the first black watch case to the Porsche Design Chronograph 1, from the mind of the legendary Ferdinand Porsche. However, Jeff Stein of OnTheDash seems to disagree with the crowd, as he wrote in his 2021 Hodinkee article on the Heuer Black-Coated Monaco. Before the iconic 1972 introduction of the Chronograph 1, Enicar seemed to have beaten the brand by a few years when they introduced the Enicar Sherpa OPS in the late sixties.

Fast-forward to today. We see many more manufacturing techniques and materials that allow brands to accomplish the dark watch case at many different price points and for many different reasons. Today, we're going to take a look at the three main methods that involve a coating or surface treatment of some sort to achieve a black finish. Stay tuned for Part Two, where we look at solid materials in this space.

Physical Vapor Deposition is arguably the most common method in the industry for accomplishing a black case. It's a broad term that encompasses several more specific techniques, but in this case, we'll focus on the most common version for watches—arc ion plating.

In a vacuum chamber, you put both the coating compound (often Zirconium or Titanium nitride) in its solid state as well as the the watch case. After the chamber is heated up, arcs of energy are then discharged into the coating compound. This causes the compound to vaporize in the chamber and form a plasma, positively charging the coating elements.

Then, a negative voltage is charged into the watch case. Since the coating particles flying around in the vacuum chamber are positively charged, the coating particles are attracted to the negatively charged surface of the case and settle into a thin and evenly distributed coating. Once cooled, voila! You have a black case!

In the context of watch case treatments, we must discuss durability and hardness. To frame our reference, 316L steel has a hardness of around 150HV on the Vickers scale. When looking at many PVD supplier websites, it looks like many common PVD treatments will yield 2500-2800HV. From a durability standpoint, PVD is the least durable out of the three treatments we'll examine today. In my personal experience, many of the black PVD-coated watches that I've owned have started seeing wear in less than a year. It's part of the charm, but for those who are obsessed with the condition of their watches, PVD may not be the way to go. Despite that, PVD can be very desirable because of its lower production cost. You can find PVD-coated steel watches in the entry-level range from brands like Timex and Swatch, allowing for many accessible watches to achieve a black finish.

Production methods seem to have improved in recent years to manage high-volume production, something that is sure to yield more manageable costs in addition to higher consistency and quality. "In my recent visits to manufacturers, I was excited to see that there have been new technologies implemented in order to manage the volume and consistency of output and results," says Jonathan Ferrer, Brew Watch Co.'s designer and founder. He reveals the numerous steps required to prepare parts such as watch cases before they even go into the vacuum chamber to receive a plating. "A time-consuming challenge was placing each and every component [manually] onto component trees," a wire rack designed to hold the various parts while in the vacuum chamber. Now, Jonathan says, the processes have become fully automated, improving factors such as speed and accuracy in a sterile environment.

Another process recently improved has been masking - covering up parts of a component that you wish to not get coated during the process. Instead of the painstaking manual process prior, machines now "scan watch bracelets and cases and inject a silicone solution that masks the parts before receiving plating/finishing," Ferrer says, rather than a worker individually taping over tiny sections one by one.

So, what's the difference between DLC and PVD? When looking at black-coated watches, these are usually the two finishes discussed. Often, you'll hear that DLC is "better." Technically, these aren't apples-to-apples terms. DLC is a coating material, but it can also use physical vapor deposition as its application process. It stands for "diamond-like carbon," and that means that the coating compound in question is primarily composed of carbon atoms.

If you think back to high school chemistry class, you'll remember that different crystalline structures of carbon can yield very structurally different results despite them being composed of the same carbon atoms. Graphite's crystalline structure is layered, which makes it soft. These separate sheets of carbon atoms don't have strong bonds to each other, so the individual layers can slip off - think pencil to paper. However, with diamonds, carbon atoms are very densely packed together, and each atom is connected to the others around it, resulting in extreme hardness and durability.

Think of "diamond-like carbon" as an in-between – drawing on useful properties of both structures from the perspective of a coating material. While the purest form of DLC can be purely sp³ bonded carbon atoms (the diamond kind), for a cosmetic finish for watches, you are most likely also seeing sp² bonded carbon atoms (the graphite kind) in the mix. This way, you both achieve hardness while allowing for a lower coefficient of friction. When combined, these properties translate into a harder-wearing surface.

With DLC, you get something that is extremely hard to scratch and can range from matte anthracite to deep gloss black, based on the proportion of the carbon mix. Looking at some supplier websites, DLC coatings can commonly range from 5000-9000HV for hardness. For reference, a diamond is rated at 10000HV on the Vickers scale.

Now, why doesn't every brand use coatings in DLC to ensure a higher level of durability?

The main reason is cost. I reached out to Giovanni Moro, one of the co-founders of Unimatic, as the Milan-based brand has incorporated DLC coatings in its design language since its very early days. Giovanni recalls that they found the black-out trend fascinating early on – he had even thought about applying a coating on his personal Omega Speedmaster. While the improved hardness that comes with DLC was desirable, he notes that costs can sometimes trend up to 350% higher when compared to a same-quality finish with standard PVD compounds. Despite this, the brand sticks with using DLC across its black-cased products.

Last but certainly not least, one other surface treatment for watch cases seen nowadays is ceramicized titanium. In theory, it combines great properties from both materials in its name — you get the high scratch resistance from ceramics while maintaining the structural integrity of titanium.

Most popular is IWC's trademarked Ceratanium, as seen on some of their models dating back to 2017, when they debuted it on the Aquatimer Perpetual Calendar. What sets this apart, however, is that ceramicized titanium is not a coating (necessarily) – nor does it refer to the base material. A bit confused? Let me explain.

DLC and PVD both involve a separate compound being ionized and then adhering to the watch case. However, in the case of a material like IWC's Ceratanium, there is no separate compound at all. Rather, you start with a fully milled, titanium watch case – IWC employs their proprietary alloy, which we'll come back to in a little bit. Once the case (and other parts like crowns, pushers, and buckles) are ready for the treatment, they enter a kiln. These parts are then fired at a high heat, and this is where the alchemy happens. IWC calls what happens next a "phase transformation [where the] surface of the metal is ceramized." This step is how these parts get a very even, matte black color. Ok, that sounds fancy. But what actually happens here?

This US patent, filed in 2002, seems to give a glance behind the curtain of it all, as it describes a process similar to the one IWC uses. In the patent, inventor Edward Rosenberg indicates that the "process for forming a metallic article having a black ornamental surface" requires an alloy that contains "between about 51 and 70 [percent] by weight of titanium, between about 3 and about 17 percent by weight of niobium, and the balance of a metal selected from the group consisting of zirconium, tantalum, molybdenum, hafnium zirconium, chromium, and mixtures thereof." I assume that a combination of these makes up the proprietary alloy that IWC currently uses, but no one can say for certain.

During the heating process, some of the metals in the alloy begin to undergo oxidation from the oxygen-rich environment of the kiln. As this happens, a ceramic crust essentially grows from the alloy, thus ceramizing the titanium. By nature of the process, this crust becomes much more resistant to separating from the unoxidized underlying titanium alloy when compared to any vapor deposition method. If we think of PVD as the red wax wrapper around a Babybel cheese, this ceramization is like a crust forming on a beautiful sourdough.

I spoke to my friend Ryan Norbauer, maker of luxury mechanical keyboards and all-around materials nerd, about Ceratanium. He mentioned that he was exploring a similar finish for his boards that utilized a process called micro-arc oxidation to form a very durable and cosmetically uniform ceramic layer on an aluminum keyboard so that the finish wouldn't wear off in the same way as PVD would have. Micro-arc oxidation, commonly used for consumer electronics, achieves a similar result to Ceratanium's process but with slightly different methods. Instead of heat treatment, this process is electrochemical and involves shooting arcs of electricity at a metal submerged in an alkali bath. With these differences in mind, Edward Rosenberg's patent is notable because it is "without requirement for use of chemicals, electrolytes, electricity, or complex heat treating apparatus." Ironically, what we consider a modern material in the watch space is supposedly made in a purposefully simpler and more primitive way.

So how hard is Ceratanium, then? IWC doesn't publicly post the hardness rating of the material, but it is safe to say it is significantly more scratch-resistant when compared to something like PVD since the outer layer that forms is literally a ceramic. Across the corners of the internet, I've seen a few people claim that their Ceratanium has scratched - though often, scratches on ceramic or ceramic layers can actually be the metal from the other object transferring onto the case, which is eventually removable. It seems the main offender has been spring bar tools, though I would be curious to see a photo of anyone who has truly scratched through the ceramic layer. I think only time will tell if this current generation of Ceratanium watches will remain as we expect them to, but for now, it seems to be more than a marketing exercise and genuinely a unique material in watchmaking with tangible benefits.

Stay tuned for Part 2.