To understand how a metal can be dyed black, the basic process of anodization should be understood. Anodizing involves using a corrosive chemical and electrical current to alter the chemical body of certain metals and make them stronger in the process. There are many types of anodizing acids, including sulfuric and chromic as the major anodizing contenders. However, some acids such as organic and boric are used in custom anodizing situations because they can offer more control in smaller settings.
Metals commonly anodized are aluminum, titanium, magnesium and zinc. The new characteristics of an anodized metal are increased strength and corrosion resistance, a thicker and smoother protector then regular paint or metal plating. However, the process does make the metal more brittle, so extreme temperatures can cause damage. Depending on the style of anodizing and the type of metal, dying the product is possible.
Because the basic black dye is made from an inorganic substance, a chemical mixture called ferric ammonium oxalate, dyes used in black anodizing tend to be more lightfast. The same chemical is used to produce gold dye. To be lightfast means that the colors tend not to fade as quickly. This is true of any inorganic dye used during an anodizing process.
Black anodizing is produced in the same basic fashion that all colors for anodizing are produced, although there are a couple alternative processes too. Most anodizing processes, such as the sulfuric acid, make the surface of a metal more porous and therefore able to soak and retain the color of dyes. So directly after the major chemical shift in the metal’s crystal structure, a dye can be applied.
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 the potential of bleeding and can improve corrosion resistance. A black anodized product can also be made by way of metal dyes, which are electrolytically deposited in the pores.
Organic dyes are actually used during the chemical immersion of a product. The dying process is utilized in almost every industry and application non-colored anodized products are. A couple examples include the electronic field, which sells colored Mp3 players, flashlights and cameras, and the cooking industry, which often markets two-toned cookware.