The ancient Greeks were known to gold plate items mechanically by attaching a gold plate to other metals via applying intense heat to the base metals and placing them together, then rapidly cooling the combination. These gold-plated jewelry pieces were then hammered into shape and worn as adornments by them.
The modern version of gold plating jewelry, called electroplating, relies on a chemical process to combine different metals together into a solid piece with a layer of gold resting on the jewelry's surface.
When gold plating, the professional plater begins by polishing the jewelry's base metal and cleaning it as thoroughly as possible before the plating process begins. The gold plate will look uneven and smudged if the jewelry's surface is dirty, oily, scratched, or otherwise damaged.
Next, modern gold plating services create a metal salt using the base metal (usually brass or silver). These salts form when an acid and a base combine, creating a neutralization reaction. Metal salts form from a metal's positively charged ions combining with an acid or non-metal. Then, the salt is placed into a plating solution.
Then, the jewelry's base metal is gold plating by immersing it in a plating bath, where an electrical current is applied. The electrical current is directed to the base and dissolves the metal salts as it moves through the bath. The gold deposits ride the current and deposit themselves onto the base metal. How long the professional plater leaves the gold deposited onto the metal to soak in plating baths determines the thickness of the gold-plated layer. The plater may redo this process as many times as needed.
There can be many layers of plating done on a single gold-plated piece; for example, a gold-plated silver article is usually a silver substrate with layers of copper, nickel, and gold on top of it.