Oxidation in watchmaking is not a defect to prevent at all costs: it is a chemical phenomenon that, depending on the material and the control with which it is applied, can be an enemy, a working tool, or the desired result of years of wear. Distinguishing between these three cases is the first task of anyone working at the bench.
On the front of controlled treatments, titanium is the material that has opened the most interesting possibilities. De Bethune has built much of its chromatic vocabulary on thermal oxidation of grade 5 titanium: heat modifies the thickness of the oxide layer on the surface, and that thickness determines the color perceived through optical interference. Yellow emerges first, then orange, violet, and finally the deep blue that the brand has made recognizable. The same principle has been applied to Muonionalusta meteorite. Ming used an oxyacetylene torch by hand on titanium to achieve color gradients on the 37.06 Lightning dial, with extremely high production scrap: about one dial in three does not pass quality control. Montblanc adopted the laser to induce localized and precise oxidation on titanium, achieving permanent colors without varnishes or enamels. Anodized aluminum follows the same logic but through electrochemical oxidation: a layer of oxide is grown in a controlled manner, making the surface harder and dyeable.
Rhodium plating on movement components, on the other hand, responds to the opposite logic: it is a physically inert layer that blocks oxidation of the underlying metals, typically brass or nickel silver. Rhodium is chemically stable, reflects light well, and does not alter the mechanical properties of the pieces on which it is deposited.
Bronze introduces a third category: oxidation as a slow and individual process. Bronze in contact with oxygen, moisture, and carbon dioxide develops a patina that changes over time and differs from specimen to specimen. Traditional alloys tend to develop greenish and irregular tones. Copper-aluminum, used for example by Bremont, instead produces a more uniform patina with golden and reddish hues. The sandblasted bronze of some Bulgaris evolves differently compared to polished bronze. There is no right patina: there is the patina of that watch, worn by that person, in that climate.
The case of the Daytona Patrizzi is instructive for different reasons: the oxidation of the subdials was not sought, but was the result of a defect in the protective Zappon varnish layer. Today that production weakness has become the reason why certain examples are sought after in the vintage market. Uncontrolled oxidation, in that context, has produced value. On the opposite front, Montblanc built the "0 Oxygen" concept by hermetically sealing the case to prevent oxygen from reaching the inside, protecting the movement in conditions of extreme temperature fluctuation. It is the same chemical reaction, managed at the two extremes of possible control.