Rhodium Plating

Rhodium plating is an electroplating process in which an extremely thin layer of rhodium, one of the rarest platinum-group metals, is deposited onto a piece of jewellery, a coin or a component. The result is a mirror-bright, silvery-white and cool surface with high scratch resistance and excellent resistance to tarnishing.

Why plate with rhodium?

White gold often contains nickel or palladium in its alloy to neutralise the yellow tint of gold, but it rarely reaches the cool, brilliant white that customers expect. Rhodium plating fully masks the slightly yellow or grey natural colour of the alloy and gives the piece the visual appearance of platinum. Sterling silver is occasionally plated too, to slow down tarnishing caused by sulphur compounds.

How the process works

1. Cleaning: grease, oxides and fingerprints are removed with an ultrasonic bath and degreaser.
2. Activation: a brief acid pickle ensures a reactive, oxide-free metal surface.
3. Electroplating: the workpiece serves as the cathode in a rhodium sulphate or rhodium phosphate bath; direct current deposits rhodium ions as a metallic layer.
4. Rinsing & drying: thorough rinsing prevents bath contamination.

Layer thickness is typically between 0.05 and 0.5 microns, rising to about 1 micron on heavily worn items such as rings. Thinner coatings are cheaper but wear away faster.

Durability and renewal

Because rhodium is only deposited on top rather than alloyed in, the layer wears away through contact with skin, sweat and mechanical stress. Rings and bracelets need re-plating every 1 to 5 years, while pendants and earrings last considerably longer. A goldsmith or jeweller can renew the coating easily after cleaning and re-activating the surface.

Rhodium plating on coins

Some collector coins in proof quality are rhodium-plated to protect the polished mirror surface permanently. Note that the rhodium layer does not change the fineness of the coin, though during a coin authenticity check by X-ray fluorescence analysis it can distort the surface signal. A melt assay or the melt value calculator always reflects the base value of the core metal.

Rhodium as a precious metal

Rhodium is one of the most expensive and rarest metals in the world; over recent years its price has swung between a few hundred and more than USD 20,000 per troy ounce (its record high in 2021). The amount of material in a plating layer is so tiny (fractions of a milligram), however, that it carries no meaningful intrinsic value; the cost comes primarily from the manual work and bath preparation.

In a nutshell

Rhodium plating is a well-established electroplated surface treatment that visually enhances jewellery and coins and protects them from tarnishing, but it requires regular renewal. It does not affect the actual precious metal content of the underlying piece.