Gold-plated means a thin coat of gold laid over the surface of a different metal. Watch cases can be finished this way. Because the coat is thin, its thickness matters. How long gold plating holds up in use depends on how many microns of gold there are.
How is a watch case gold plated?
In watchmaking, electroplating means dipping a part into a chemical bath that holds ions of the coating metal. An electric current runs through the bath while the part sits in it, and this lays the coating on the surface. Watch cases can be given several decorative electroplated finishes, and gold is one of them. Electroplating is not the only route. Swiss precious-metals rules allow the precious-metal layer on plated articles to be applied by mechanical, electroplating, chemical or physical means.
How thick is gold plating?
It is very thin. Under one grading scheme, a gold layer counts as gold plated once it is at least half a micron thick. Thickness decides how the finish behaves in use. How long the plating holds up depends on how many microns of gold were applied. Vintage Omega cases show this in the metal itself. Their gold-plated cases carry no hallmarks and are often stamped 20M. The mark means 20 microns of plating.
Where it comes from
Electroplating was invented in 1805 by the Italian chemist Luigi Valentino Brugnatelli. A later step came from John Wright of Birmingham. He found that potassium cyanide worked as an electrolyte for plating gold and silver. In plating, the electrolyte is the chemical bath that carries the metal ions while the current runs. Gold-plated watch cases made by electroplating follow the same basic principle.
Not to be confused with
Gilding is the word for decorating an object with a gold covering. It is kept apart from modern plating methods, so the two terms are not interchangeable. A gold cap is different again. Swiss precious-metals rules treat it as a separate category. A gold cap is a layer of gold at least 200 microns thick, permanently fixed to the watch case. That is far thicker than the half-micron threshold for plating.
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