What Is Coloring?
Coloring, in this context, is based on the same principle as a rainbow appearing in the sky after summer rain. When sunlight passes through lingering water droplets, the light is refracted and dispersed—creating a prism effect that the human eye perceives as a spectrum of colors.
In stainless steel, a similar effect occurs when an oxide film is grown on the surface. Depending on the thickness of the film, light interference creates visible colors such as brown, blue, yellow, red, or green. This is what we refer to as “coloring.”
Unlike painting, printing, or plating—where pigment or coating is applied to the surface—coloring is achieved through optical interference. It is not an added layer but a result of how light interacts with the material itself.
Common surface treatments for coloring stainless steel include the following methods:
| Treatment Methods | Main Objectives |
|---|---|
| [Painting] Spray coating, electrostatic coating, electrodeposition coating, powder coating |
Corrosion Resistance, Aesthetic Finish |
| [Wet Plating] Electroplating, chemical plating (electroless plating) |
Decoration, Corrosion Resistance, Wear Resistance |
| [Anodizing] Anodizing for steel, anodizing for non-ferrous metals (aluminum) Corrosion Resistance, Wear Resistance, Coloring |
Corrosion Resistance, Wear Resistance, Coloring |
| [Dry Plating (Vapor Phase)] Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD) |
Wear Resistance, Frictional Properties, Optical Properties |
However, the surface treatments mentioned above tend to have poor adhesion to stainless steel, making them prone to peeling.
To address this drawback, a new approach was developed: coloring through oxide film formation. This method creates color as part of the material’s surface, not as an added layer—resulting in improved durability and a more stable finish.
The surface of stainless steel is naturally covered by a transparent passive film—an oxide layer primarily composed of chromium. When this film is precisely thickened in increments of 1/100 microns, light interference begins to produce visible color on the metal surface.
Because the oxide film is extremely thin, it allows the natural texture of the material to show through, unlike paint or plating. The finish retains dimensional accuracy while delivering vibrant color. In addition, growing the oxide layer enhances the stainless steel’s inherent corrosion resistance.
The Challenge of Achieving a Uniform Black Finish
Among these challenges, achieving a deep and uniform black color is particularly difficult. However, this has been successfully realized with Abel Black®.