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, cool surface with high scratch resistance and excellent tarnish resistance.

Why Rhodium Plate?

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

The Process Step by Step

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

The layer thickness is typically between 0.05 and 0.5 µm — up to 1 µm for heavily worn pieces such as rings. Thinner layers are cheaper but wear away more quickly.

Durability and Renewal

Since rhodium is only applied on top and not alloyed in, the layer wears away through contact with skin, perspiration, and mechanical stress. Rings and bracelets must be re-plated every 1 to 5 years, pendants and earrings considerably less often. A goldsmith or jeweller can easily renew the layer after re-cleaning and re-activation.

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 alter the fineness of the coin, but 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 among the most expensive and rarest metals in the world; its price has fluctuated in recent years between a few hundred and over USD 20,000 per troy ounce (record high in 2021). The material content of a rhodium plating layer, however, is so small (fractions of a milligram) that it represents no appreciable material value — the costs arise primarily from the craftsmanship involved and the bath preparation.

In Brief

Rhodium plating is a proven electroplated 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.