Gold plated employs a base metal which is then electroplated with gold. Usually a brass item dipped into a bath of electroplating solution that deposits a thin layer of gold on the jewelry. The gold layer is less than gold filled, quite thin and will wear off faster than gold-filled.
Electroplating is a process by which a thin layer of gold, silver, palladium and other metals are deposited on a conductive material to improve appearance and value. Utilizing an electrical current, positive metal ions travel through the electrolyte and deposit in a negatively charged metal.
The metal being plated is located at the anode and the item to be plated at the cathode, both are immerse in a solution that contains a dissolved metal salt and other ions that allow the flow of electricity. A direct current is applied to the anode oxidizing the metal atoms and dissolving them in the electrolyte. The metals ions are reduced at the cathode, plating the metal. The current is such that the rate the anode is dissolved is equal to the rate the cathode is plated.
In electroplating, is used an inert anode, where metal is not dissolved away, and control the concentration of the depositing metal in the electrolyte solution by direct additions of the appropriate metal as a salt to the electrolyte.
The electrolytes can be classified into cyanide and non-cyanide based and may contain small alloying additions to control color and other properties. All cyanide-based electrolytes are based on the use of gold potassium cyanide salt, KAu(CN)2, which contains about 68% gold. Some electrolytes are acid, others neutral and others are alkaline.
The amount of metal – in our case gold – deposited is governed by Faraday’s law which says that: The weight of metal deposited is proportional to the quantity of electricity passed.
The quantity of electricity is defined as the current in amps, multiplied by the time in seconds. The weight of metal deposited for a given quantity of electricity will be different for different metals which are related to their atomic number and valence through a factor called the electrochemical equivalent (atomic mass/valence).
M=Weight of metal deposited, Z=Electrochemical equivalent, I=Current in amperes, t=time in seconds
This Faraday law is very useful in calculating and controlling the thickness of metal deposited on a piece of jewelry. Obviously, at a constant electroplating current and salt concentration in the electrolyte, thickness of the electroplate is directly proportional to the plating time. Double the plating time and you double the thickness.
The most commonly plated materials are cooper, bronze, aluminum and silver.
Types of gold plating
24K yellow for fine jewelry, 18K yellow, 18K green, 18K rose and 14K yellow with a wide range of color tints and hues. The 14K is the most used in the jewel industry.
The thickness of gold plating ranges from 0.175 microns (7 micro inches) to 7.5 microns (300 micro inches).
Electroplating standards are regulated by the Federal Trade Commission (USA).
-Gold flash-Gold washed, is an electroplating of minimum 10K and thickness of less than 0.175 microns (7 micro inches)
-Gold electroplated (GEP), is an electroplating of fine gold (14K, 18K or 24K) with minimum thickness of 0.175 microns (7 micro inches)
-Gold plated (GP), is fine gold deposited by any means with minimum thickness of 0.5 microns (20 micro inches). Recommended minimum 1 microns (40 micro inches) for handling jewelry.
-Heavy gold electroplated (HGE), is electroplating fine gold with minimum thickness of 2.5 microns (100 micro inches). For items exposed to chemicals and abrasives.
Gold plated jewelry is most often marked with identification that is stamped on the jewelry. This can include HGE or RGP which are both common markings for jewelry that is plated with gold rather than made of pure gold. HGE is used to mark gold electroplate and RGP is used to mark rolled gold plate.
Gold plated jewelry example
Gold plated copper bracelet
I will continue the explanations for each metal.
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