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Gold electroplating is a process in which an electric current is used to bond an extremely thin coating of gold to an object made of some other metal. Circuit elements called cathodes and anodes and an acidic solution called an electrolyte solution, containing dissolved gold compounds and catalyst chemicals, are used to create the coating, which may be mere microns in thickness. A tank of an inert material like glass or plastic is used to contain the solution.
The process of electroplating begins with the preparation of the electrolyte solution. For gold electroplating, the chemical bath will consist mostly of water, acidified by the addition of phosphoric acid. Gold, in the form of gold chloride is added to the solution. Catalysts such as potassium cyanide may also be used. They aid in the transference of gold ions to the object to be plated and increase the conductivity of the solution, which is important, as it is the flow of current through the solution that creates the reaction that bonds the gold to the target object.
The object to be plated is connected to one part of an electric circuit, called a cathode. The cathode is analogous to the positive terminal on a battery. As the gold salt compounds in the electrolyte solution deposit gold onto the target object, they lose electrons which form the electric current.
The other end of the circuit is called an anode and is made of metal. The anode is the analog of the negative terminal on a battery and the current flows from the anode into the electrolyte solution. For many types of electroplating, the anode is made of the same metal being deposited on the target object. For gold electroplating, anodes are usually stainless steel, graphite, specially treated titanium, or a metal called columbium, although other metals may sometimes be used. The cathode with the target object and the anode are submerged in the electrolyte solution and the current is introduced.
Gold electroplating typically only takes a few minutes. Thicker layers of gold may take longer. As an item plated with gold ages, atoms of the underlying metal may gradually mix with and migrate through the layer of gold to the surface, a process that can take many years. Copper and silver are known for this phenomenon. For this reason, objects made of copper or silver that are to be electroplated with gold are often electroplated with another metal first, such as nickel, which prevents the base metal from migrating into and through the gold layer at the surface.