Color Anodizing
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. Another problem that may occur is lightfastness, or the fading of certain colors. Because black and gold dyes are made by inorganic means, they tend to be more lightfast.
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.