How It’s Applied
PVD is applied in a similar method to electroplating of gold where a current is passed through the part to be coated. While there are many methods for PVD, the vacuum coating process is probably the one used by most watch parts manufactures. The parts are sealed in an air tight chamber where a vacuum is created, negative voltage attracts the positive ions and inert gas is introduced which create the environment necessary for the deposition process to occur. The coating compounds are made up of various elements such as carbides, nitrides, borides and silicides. The makeup of the compound varies some depending on what the application necessitates. For example graphite and titanium are often used when friction and temperature reduction are necessary.
In the early 1980’s and 90’s powder coating and black oxide anodization were the methods of choice for blacking watch parts. Tag Heuer in particular with its Black Coral 1000 series professional watch used a base black anodization with a top powder coating. Powder coating is essentially a bake on paint that is sprayed on to the metal and heat bonded by placing the part in an industrial oven. Powder coat finishes are generally very smooth and hard; however they are thick and chip off over time. Thus the reason for anodizing the parts before powder coat so when the powder coating chips off the bare metal isn’t exposed. Black oxide is similar to anodization and has been used by gunsmiths for over a century to blacken barrels giving that dark matte black finish. Black oxide is generally simple to apply and inexpensive. It requires very few chemicals to apply black oxide however it doesn’t penetrate deep into the metal like PVD or even some types of anodization. Therefore black oxide would not be appropriate for high wear areas on watches such as clasps, and bezel surrounds. Many watch parts manufactures still use black oxide for small parts such as crowns and screws, however anodization is much more common.
Newly powder coated watch band.
Powder coated watch band after 6 years of daily wear.
Table – Comparison of Similar Metal Coating Processes (click the chart below for a larger version)
PVD Finishes & Results
Most PVD is black in color however the underlying finish of the metal can affect the reflective properties. Thus a bead blasted finish will produce a dull deep black appearance, whereas a rough brushed finish may produce a semi glossy finish, as seen on the Blackout EvoGrip™ 10 Swiss Army Knife. The method of metal surface finishing is where you will see a great deal of variance between watch manufactures. Therefore buying an aftermarket Hadley Roma PVD watch bracelet for example will likely look nothing like your Wenger Sea Force 0641.107 Swiss watch.
Brushed finished stainless steel.
A semi glossy PVD finish is the result of a brushed finish on the base stainless steel.
Picture of the inside of a clasp before and after PVD plating. Notice the semi polished finish produces a semi matte/ reflective PVD appearance. *The light blue haze is result of a less than clean prep work.
Read the original Nicholas Time article.