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Also sometimes referred to as gold-dipping, gold anodizing is a process by which base metals are coated to produce a gold color, but are not necessarily dipped in real gold. This can be performed in a couple of different ways. The most common gold anodizing method is a two-part process that first anodizes a base metal and then coats it in a gold dye. The color can also be produced in the coating film by mixing the sulfuric acid electrolyte with an organic acid.
Anodizing is an electrochemical process that creates an oxide film on a base metal, in an electrolytic solution. The metal being treated becomes the anode, or positive electrode, and current is passed between it and a cathode, or negative electrode. Sulfuric acid is commonly used as the electrolytic solution. As direct current is passed through the solution, an anodic film is formed. When aluminum is used as the base metal, the film is called aluminum oxide.
The anodizing process can be performed on a variety of base metals, with aluminum being one of the most common. Titanium, zinc, and magnesium can also be used as a base metal. Using titanium can produce a gold coating without the use of any dyes. With titanium, a nitride coating can be formed, which can produce the golden color and still maintain corrosion resistance. Gold anodizing on titanium is often used to create jewelry and artwork.
With regular anodizing processes, the electrical current is applied at a steady, constant rate. The same gold color can also be produced as part of the anodic film in a different process, however. This is done using a mix of an organic acid and a sulfuric electrolyte, and a pulsed current is applied, creating a golden, anodic film.
Inorganic methods can also be used in gold anodizing. Using ferric ammonium sulfate as an electrolytic solution produces black or gold colors on the base metal. Gold anodizing created by an inorganic method produces a stronger coating that is not as likely to lose its color. When inorganic dyes are used, they are normally sealed to protect the finish.
Metals are anodized to help protect them from corrosion. Andodizing changes the surface texture of a metal. Corrosion resistance can be achieved with a sealing process. Base metals can become harder than the original metal, but may lose some resistance to wear. Increasing the thickness of the anodized coating, or applying a sealant, can increase the durability of the outer layer.