Rhodium Plating

Rhodium plating refers to an electroplating process in which an ultra-thin layer of rhodium – one of the rarest platinum-group metals – is applied to a piece of jewellery, a coin or a component. The result is a mirror-bright, silvery-white cold surface with high scratch resistance and excellent tarnish resistance.

Why is rhodium plating done?

White gold often contains nickel or palladium in its alloy to neutralise the yellow colour of gold – but rarely achieves the cold, radiant white tone that customers expect. Rhodium plating completely masks the slightly yellowish or grey inherent colour of the alloy and gives the piece the visual appearance of platinum. Sterling silver is also occasionally rhodium-plated to delay tarnishing (from sulphur compounds).

Process sequence

1. Cleaning: Grease, oxides and fingerprints are removed by ultrasonic bath and degreaser.
2. Activation: A short acid pickle ensures a reactive, oxide-free metal surface.
3. Electroplating: The workpiece is immersed as a 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.

The layer thickness is typically between 0.05 and 0.5 µm – up to 1 µm for heavily stressed items such as rings. Thinner layers are cheaper but wear out faster.

Durability and renewal

Since rhodium is only deposited on, not alloyed in, the layer wears off through contact with skin, sweat and mechanical stress. Rings and bracelets must be re-plated every 1 to 5 years, pendants and earrings much less frequently. A goldsmith or jeweller can easily renew the layer after cleaning and reactivation.

Rhodium plating on coins

Some collector coins in proof quality are rhodium-plated to permanently protect the polished mirror surface. It should be noted that the rhodium layer does not change the fineness of the coin, but during coin authenticity checking 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 among the most expensive and rarest metals in the world; its price fluctuated in recent years between a few hundred and over USD 20,000 per troy ounce (record high in 2021). However, the material content of a rhodium-plating layer is so small (fractions of a milligram) that it represents no significant material value – the costs arise primarily from the manual effort and bath preparation.

In brief

Rhodium plating is a proven electroplating surface treatment that visually enhances jewellery and coins and protects against tarnishing, but requires regular renewal. It does not affect the actual precious-metal content of the underlying piece.