Before the sealing stage of anodization, the oxide surface of a metal can be dyed. This is done when the exterior appearance of the product is significant. There are countless dye colors in color anodization. The colors range from light to dark, although lighter colors may be more difficult to manufacture on certain alloys.
Color anodizing is a popular process because it allows for the creation of products in a wide range of colors. Such an enhancement of appearance can make a product more appealing to a potential customer. Buyers of color anodized metals should keep in mind the limitations of the color anodizing process, though.
For example, some colors fade more easily than others. Black and gold dyes are made by inorganic means; namely they are the result of combining a chemical mixture called ferric ammonium oxalate to an anodized product. This inorganic dye tends to be more lightfast than other colors. Organic colors, which are much more varied, have the downside of being prone to fade. Metallic colors are limited to metallic hues, but remain bright longer then either of the first two processes.
Customers should consult professionals before making decisions about the color of their anodized products. What type of product is being produced will also play a part in what color a customer chooses. For example, the architecture industry tends to use mostly metallic color processes, while organic dyes, used in the electronic and construction fields work best with aluminum.
The actual dying techniques vary depending on the dye being used as well as the metal. Some metals do not require the additional step of dying to create a variety of colors. Anodized titanium naturally produces color, what hue depending on the amount of electrical current used to anodize the piece. Many metal accessories such as body piercing studs, wedding rings and costume jewelry are made from titanium.
However, the most commonly employed color anodization comes from organic and chemical dyes applied directly after the anodizing treatment. Because anodizing increases the pore size of the chemical body at the surface of a metal, it soaks up and retains color well. Once a metal has been dyed, hot water or steam, often mixed with nickel acetate, is used to seal the surface and to convert the oxide into its hydrated form.
This process decreases bleed out and can improve corrosion resistance. Whether the color is a result of the process of anodizing or added, it is just one more reason anodized products are in such high demand.