Navigating the details on modern black watch materials, coatings and finishes can be a confusing undertaking. Ambiguous science with misleading figures all contribute to the marketing nonsense that spews from our beloved and often hyperbolic industry. Many manufacturers will offer black variants in their collections because black is cool and has been since the 14th century! As many of you know black is my go-to and has been since 2012 (after giving up the madness that is premium denim so thick you can't bend your knees!). This was also the time Schofield was thinking about the Blacklamp (pictured), which was named for many reasons, one of which is a play on lamp black, a black pigment made by collecting the fine soot from the inside of an incandescent lamp.
Black means a surface that absorbs visible light and does not reflect it. Ultimately it will have an albedo of 0 (fully reflecting surfaces have an albedo of 1). In 2008 researchers at Rensselaer Polytechnic Institute created the blackest material ever - reflecting just 0.1% of light from carbon nanotubes stood on end. By comparison black paint reflects 5-10%. Since that time the same team have improved the coating to reflect only 0.03%. Vantablack developed by Surrey Nanosystems is at 0.045%. Both outfits argue theirs is the blackest.
As black dials go, using Vantablack is cool if you are H. Moser & Cie. Schofield spoke to Vantablack before they had made a single watch dial for anyone but I felt that as soon as you cover it with a sapphire crystal, that reflects light regardless of the coatings used, then it's all rather pointless. So for dials we have to settle for fancy paint, anodising, lacquer, enamel and plating.
Black watch cases are a recent development because there were no readily available black materials or coatings until the mid 1970s other than oxidising, anodising, powder coating or painting and most of these don’t sit comfortably beside platinum, gold or stainless steel in a chart of premium materials.
When designing watches we are limited to the materials used because of machining, safety and cost constraints. So when I say black, I also mean dark grey and sometimes with hues of brown, blue or green. I also look at all the material surface characteristics - colour, texture, slickness, temperature and sheen, finding ways to exploit these attributes favourably. These subtleties bring differentiation and make our ‘black’ watches interesting.
Let's look more closely at the materials and the language used to describe them in an attempt to make an informed decision on whether the material can work for us.
When considering a watch case, texture is generally either rough or smooth depending on the surface irregularities. We should also consider waviness and lay of the texture or whether or not the case has been engraved like the amazing Linde Werdelin Octopus Tattoo.
Slickness is synonymous with smoothness but not exclusively so. Black watches can have a rough surface finish and a DLC coating. Aluminium magnesium boride (BAM) has a record low co-efficient of friction (COF) of 0.02, DLC of 0.05 and Teflon in third place at around 0.4. These three surfaces are the only ones a gecko cannot stick to. Steel by comparison has a COF of 0.8.
Temperature is interesting because different materials feel warm or cold to touch because of varying degrees of heat conduction. Steel will take on changes in ambient temperature much more quickly than carbon fibre for example.
Sheen is the complex qualities of reflected light and colour. Tantalum for example will look black in artificial light but like blue steel in sunlight. Metal case finishes are generally limited to polished, micro-bille (bead blasted) and linished (brushed). If we were comparing to paint finishes the sheen of these would equate to gloss, matt and eggshell.
All of these factors contribute to the tactile qualities of your watch. It is after all an object you handle every day and because of this I would place as much emphasis on the visual as the tactile.
The physical properties of materials and coatings mainly only affect the longevity of the finish which would include hardness, scratch resistance and toughness.
Hardness can be measured in a few ways but we will concern ourselves mainly with Vickers (HV). This test can be done on most materials and involves impressing a pyramidal diamond (the load) into a surface and measuring the plastic deformation of the surface. To put this into perspective, stainless steel (316L) is between 150 - 500 HV. Sapphire Crystal is around 2500 HV. This is relevant because it indicates how dent resistant your watch is.
Scratch resistance is different to hardness because it involves shear and load, whereas hardness is just load. Basically scratch testing is measured by drawing a point (load) over (shearing) a surface at pressure and measuring depth and displacement of the substrate. We all know sapphire crystals to be scratch proof, right? Not quite, scratch resistant! All materials can be scratched.
Toughness is the ability of a material to absorb energy and deform not fracture, dent not break.
The ideal material for black watches would be one that is luxurious, exotic, durable and tough, has beauty and depth of blackness with a subtle hue depending on the light, and has tactility and heft that constantly pleases. A material that so utterly compelling that you just have to have it!
I think there are six practicable surfaces that have these desirable qualities - one metal, one ceramic, one composite and three coatings. They are fairly accessible with all in use across many brands. With all there is a compromise, mostly cost. The unexpected cost of repair and re-finishing of these materials could make the purchase of a black watch much more expensive in the long run.
Tantalum is a rare transition metal, bluish grey and very dense. In sunlight it is truly wonderful. Most of it comes from Australia and one of its main uses is in the electronics industry in electrolytic capacitors. It has a hardness of around 1900HV and is very scratch resistant. It is not easy to machine and the dust can combust spontaneously on exposure to air. The rarity and difficulty in machining makes this an expensive material for use in watch cases. I intend to use Tantalum one day.
Zirconium dioxide is the most common ceramic used in watches. There are others and ceramic technology moves fast with companies concocting their own recipes, like Hublot’s Magic Gold and Rado’s Silicon Nitride. Zirconium dioxide has a density similar to aluminium and is very scratch resistant with a hardness in excess of 2000 HV, but it has a low fracture toughness. It is this last fact that has caused some concern with consumers over the risk of the case shattering or splitting in two. It is the Achilles heel in what would be an almost perfect material. Ceramic watches are sintered, which is a way of making a solid object from powders, done by moulding and heating. IWC and Redo introduced it to us in the late 1980s. Chanel then widened its appeal in 2000 with the introduction of the J12. Schofield continues to experiment with and prototype full ceramic cases but has for some time concentrated on ceramic coatings. These are more resilient in real world tests than most coatings outlined in this article.
Carbon fibre is generally known to be associated with Formula One racing and sports equipment. It has a very high strength to weight ratio. Not until recently has it caught on for watch case production and for good reason. It just does not have the homogenous density to be machined or moulded to complex shapes with small tolerances. It also lacks toughness and has a relatively low surface hardness. Over the last 10 years more and more companies use it well by experimenting with the ingredients that make the composite. The Audemars Piguet Royal Oak Concepto Carbon, Hublot’s All Black Carbon, The Bell and Ross Carbon and the Ellicott Mach One Skymaster are watches that pioneered carbon fibre.
We like to think that Schofield has played a small part in the carbon watch world with the development of our own material for the Blacklamp. We developed Morta, a special carbon fibre that is incredibly dense making it really tough, hard and scratch resistant, negating all of the downsides associated with the material. After all we don’t need it to be light weight - think Richard Mille. Morta is a textured black-grey material reflecting light with a sparkle like waves on the sea. It is autoclaved one watch sized billet at a time which gives each piece a unique textural grain. Schofield is looking to introduce a new carbon watch, a Blacklamp Evo.
PVD (Physical Vapour Deposition) is a group of coating methods that deposit thin film coatings, usually between 5-10 microns thick. It should be said that DLC (Diamond Like Carbon) is a material that is applied with the PVD process. The watch industry however has split the two with PVD generally being regarded as the inferior coating. It is not always inferior but is often cheaper. Coating watches successfully depends on a particular ‘art’. It takes experienced technicians to combat the quirks of the equipment and variations in the environment, target, compounds, processes and cleanliness to guarantee consistent results.
PVD deposits a layer of material by condensation of vapour in a high temperature and vacuum environment. It is often applied by line of sight meaning it is sprayed on. On angular shapes sometimes the crevices won’t get coated. The other issue is that PVD when applied at high temperatures can anneal the steel target and make it softer therefore more prone to denting. What is the point of having a super hard coating if the supporting structure is soft? If this is so, then the coating is nothing more that cosmetic. The coating compounds are made up of various elements such as carbides, nitrides, borides and silicides; confusingly these coatings are most often hard ceramics. PVD has had a reputation of pealing or flaking but this is occasional and is not symptomatic to the method. Coatings applied with PVD range in hardness from 1000-4000 HV. PVD is ubiquitous in the market-place, a brand example that uses particularly good PVD with different substrate textures was/is Romain Jerome.
DLC, as the name suggests, is just that. Like PVD it can be done well or cheaply and badly. The diamond like structure of DLC can be more or less diamond like depending again on variations in the process - cleaning, compounds, catalysts, temperature, vacuum etc. Really good DLC (like we use) is not only very expensive and time consuming to apply but is harder than most other PVD coatings. With a surface hardness over 4500 HV it is extremely scratch resistant. DLC like this has very few hydrogen atoms ensuring the carbon atoms bond strongly with each other in what is known as amorphous sp3 bonded carbon, A good example of ADLC is the Cartier Santos 100 carbon.
DLC is mainly used as a tribological coating, e.g. in engine parts or cutting tools to reduce wear and friction. Even your Gillette razor blades are treated this way. When handled it imparts an unusual greasy, slippery feel. The colour of DLC coatings used for watch cases range through dark grey to jet black. The Schofield Signalman DLC and Silvertop is black with subtle brown tones when viewed in daylight. We bead blast the steel prior to coating to give a matt finish which makes the case look darker. It also work-hardens the steel improving its hardness. We have been DLC coating watches since 2010 and still do on request, though we currently favour ceramic coatings.
Titanium Nitride coatings like Aluminium Titanium Nitride (AltiN) are tribological coating used to reduce wear to machine tools. I would argue that there are better coatings for mechanical properties, but it can look good especially when Urwerk use it. A variant of PVD is that containing Titanium Carbide (TiC). Tudor uses this on the Black Bay. It is very hard and less brittle than DLC - Schofield is playing with this finish to achieve new textures on our cases.
There are other exotic materials in usage like Arcap and Alusic. Also the use of femto pulsed lasers to blacken any metal. When designing watches a decision has to be made based on a materials cost, scientific pros and cons and whether it fits with the projects aesthetic nature. As consumers we can engage further with the things we touch through knowledge and for me it’s about the integrity in design that includes the science but also art. The question I ask is how can I take this thing and make it cool.
To celebrate black watches, of which there will be more from Schofield, I have made a new sticker.
British watches made by Schofield