Physical Vapor Deposition is a baffling technical term. More commonly, we get the abbreviation PVD, especially when talking about watches. But what is this miraculous process that changes the color of almost every component of watches at a whim? Let’s have a look.
These days watches and watch components come in all sorts of colors. There have been trends for black watches, and there is always a demand for gold watches. But what you may not know is that the watch case is still made from stainless steel. So how are these colors achieved on stainless steel? Why does it not chip off like regular paint? How can it achieve such a polished finish?
Physical Vapor Deposition – The Details
You do not need to be a watch enthusiast for long before you come across the three letters “PVD.” As we note above, these are the initials of physical vapor deposition. Literally, this is what happens. The material that is to be added to the surface to change its color is transformed into a vapor. It is then transported to the item to be covered and then deposited on the surface. The big difference is that this all happens at an atomic level. Understanding the details of physical vapor deposition can be very useful when buying a watch. This knowledge will help you make more educated decisions by asking key questions.
Watch cases are generally manufactured from stainless steel. A variety of stainless steels are used, but generally, the higher quality watches will use 316L stainless steel. As part of the manufacturing process, the watch case is finished with one or various surface finishes. These can be polished, brushed, hammered, etc. The final surface finish will reflect the finish on the initial workpiece, sometimes called the substrate. As we will see later, the coating applied through physical vapor deposition is very (very) thin.
Physical Vapor Deposition is sometimes referred to as Vacuum Plating or Plasma Vapor Deposition. All are accurate descriptions of part of the process, but none of them capture all the details. The objective is to adhere a thin coating or film of material to the substrate (watch case) to change the finish color. The process to achieve this occurs in a vacuum and at a very high temperature. The combination of temperature and vacuum is adjusted so that the coating material is vaporized. The vapor of the coating material is transported through the vacuum to the substrate. Magnetic fields control the movement of the plasma in the vacuum. When the plasma hits the substrate, it condenses and adheres to the workpiece surfaces at an atomic level.
Let’s Get Physical
It is important to note that this is a physical process instead of a chemical process or reaction. Electroplating would be an example of a chemical process that differs from PVD as there is a ballast through which the application of an electric current transports the plating material. In the PVD process, the coating material is transported through the vacuum to the workpiece as a vapor in its final chemical composition. When the coating material vapor comes into contact with the work piece, the vapor condenses and adheres to the surface of the work piece at an atomic level creating a robust and consistent coating.
There are several advantages that plasma vapor deposition has over the processes that were used historically. First and foremost, it is infinitely more environmentally friendly than chemical plating. Electroplating uses toxic and corrosive chemicals, so the PVD process is safer for workers as they are not exposed to dangerous chemicals. The coating applied through the PVD process is tougher, more dense, uniform, and has better corrosion resistance than other plating processes. Furthermore, it can be easily customized to change the color, durability, or other characteristics of a coating. The beautiful, tough finishes explain why physical vapor deposition is the only plating process used in watchmaking today.
At The Atomic Level
A surface that has received a coating by physical vapor deposition has received an extremely thin coating material layer. But how thin? So thin that it is measured in microns (a micron is one-thousandth of a millimeter); therefore, as we noted earlier, if the finished surface is to be brushed, then the workpiece must have a brushed finish prior to the PVD process. The PVD process will not change the finish of the workpiece except its color and hardness, so the PVD process is always the last in the preparation of any component.
The joy of PVD is that many colors can be achieved. Each color has specific details on how it is applied, but there are commonalities between them. Let’s have a look at the details of the most popular colors. For watches, the most popular are black, gold, and rose gold. Technically these are referred to as Ion Plating Black (“IPB”), Ion Plating Gold (“IPG”), and Ion Plating Rose Gold (“IPRG”), respectively. Each color is achieved by changing the coating material.
Going for Gold
For IPG and IPRG, there needs to be an initial base layer applied. This is because the final coating material, either gold or a gold/copper alloy, will not adhere to the workpiece sufficiently, or the coating material is too soft, so it needs to have a hard base. This will increase the durability of the finished piece. For a gold-based coating, an initial layer of Titanium Nitride (TiN) is applied. This is a gold color, so it reduces the thickness of the final surface material that needs to be applied and increases the final surface’s adhesion and hardness.
A substrate layer of Titanium Nitride is necessary, and it is usually applied to a thickness of approximately 0.6 microns. The final finish layer is then deposited to a thickness of 0.1 ~ 0.2 microns of gold for a gold finish or an alloy of gold and copper for a rose gold finish.
The Little Black Watch
Titanium Carbide is deposited on the surface of the workpiece to make it black. This is a much simpler process as it is extremely hard and will adhere to the workpiece directly. Usually, it will be applied to a thickness of approximately 0.7 microns is deposited directly on the workpiece. Titanium Carbide is an extremely hard and wear-resistant material – so hard it is used to harden the tips of high-speed tools for drills and cutting blades.
Hardness and Durability
The PVD process has advantages over and above, creating a beautiful finish. Both Titanium Nitride and Titanium Carbide increase the hardness of the finish improving the durability of the surface. To illustrate this, the hardness of stainless steel is approximately 6.5 Moh. The hardness of Titanium Nitride is 7, and that of Titanium Carbide is 9 Moh, and for comparison, Diamond is 10Moh.
The conclusion is that if you are going to wear a watch in a rough environment, you would be well advised to choose black and thus hardened by a Titanium Carbide coating. Be sure to inquire about the thickness of the application for a premium watch, and it should be no less than 0.5 microns and ideally towards 1 micron.
The astute among you will have noticed that we only have one single piece of a SNGLRTY watch that sports a PVD coating. Our blue OHI hand is made out of rhodium – it is stronger and less dense than stainless steel, so it requires less torque from the movement to turn the hand. The hand is coated with zirconium oxide through the PVD process to create the deep blue color on our blue OHI hand.
We expect to add many additional PVD-coated options in the future. If there is a particular color you would like to see in our range, please do let us know in the comments below, and Daniel will get to work on it!
Need More Information
There is always more to learn about watches. These masterful pieces of precision engineering use a huge range of technologies. Technologies that have been discovered over the last few hundred years have been progressively integrated into watch manufacture to improve looks and accuracy. Keeping up with all this is a challenge, but that is what Daniel has done! He was responsible for over 100 watch designs in the market and multiple patents. He can keep you straight and narrow.
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