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Watch Report recently received the black Ion Plated Oceanus OCWM700TBA-1AV. Since I already reviewed its silver-colored titanium sibling (the Oceanus OCWM700TDA-1AV) which has identical functionality, I decided to use this opportunity to write an article on the process of turning metal watches black.
When deciding which materials to use for a watch case or bracelet, manufactures have to take several things into consideration like cost, intended use, desired color, and target weight. They also have to consider the drawbacks of various materials. For instance, titanium is strong, super light, durable, non-corrosive, non-allergenic (some people cannot wear stainless steel due to nickel allergies), and unlike stainless steel, it's unaffected by salt water. This combination makes titanium a great material for dive watches, however one drawback is that its surface hardness is relatively low which means it's easily scratched.
One method that can be used to change the surface properties of a material is called Physical Vapor Deposition, or PVD (you'll also see it labeled as Ion Plating, or IP, which is a variant on PVD). The PVD process involves placing the item to be coated in an inert (non-reactive) atmosphere, heating it up to 400° C or so (depending on the process), and basically spraying it with the molecules that you want to coat it with. That's the general process, however there are a lot of subtle variations like using charged ions for the ion plated variation. PVD has been around since 1838 and is heavily used in semiconductor manufacturing, automobiles, and many other places including, or course, watches.
PVD results in a coating up to a micron or so thick that's tightly bonded to the base material. It won't flake off, as the coating is interpenetrated with the underlying material which is what makes it different from paint, powder coats, or anodizing. If you hit it with sufficient force, however, you can go through the PVD and into the material below, and since it's still a coating, polishing to remove scratches is not recommended.
Another more advanced technique is Chemical Vapor Deposition, or CVD. The main difference between PVD and CVD is that the deposited material is produced via a chemical reaction instead of directly coating the surface. The titanium nitride hardening on the Citizen PMT56-2711 that I reviewed is the product of CVD, and holds up extremely well.
Better still is DLC, or diamond-like Carbon, where, via secret-sauce processes, the surface of a watch is coated with something very much like synthetic diamond! With an incredible surface hardness, this is very nearly impossible to scratch, and can been seen on some high-end Citizens like the Attesa, on the Casio MR-G watches, and on watches like the Rado V10K. DLC is also used in the engines of most super sport motorcycles, on implantable human heart pumps, and in other exotic tasks than can afford the artistry required to create it.
In the world of watches, PVD is most commonly used to produce a flat black "stealth" finish which is quite attractive. It wears better than the stainless or titanium underneath it, and is used on both cases and bracelets. There is a lot of variation in the technique used, so different brands and models will have different levels of durability; unfortunately, the relative quality is hard to discern when purchasing. Be aware that PVD cannot be re-applied, and even marquee brands like Panerai will only remove the coating if its damaged. Many people consider scratches in PVD finishes to be signs of real use, however. They feel that scratches give a "tool" watch some serious character, and wouldn't buff them out even if they could.
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