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 deposited onto a piece of jewellery, a coin, or a component. The result is a mirror-bright, cold silver-white surface with high scratch resistance and excellent tarnish protection.

Why Is Rhodium Plating Used?

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

The Plating Process

1. Cleaning: Grease, oxides, and fingerprints are removed using an ultrasonic bath and degreasing agent.
2. Activation: A brief acid etch 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 used items such as rings. Thinner layers are more cost-effective but wear down faster.

Durability and Renewal

Since rhodium is only deposited on the surface rather than alloyed into the metal, the layer wears away through contact with skin, sweat, and mechanical stress. Rings and bracelets typically need re-plating every 1 to 5 years, while pendants and earrings require it far less frequently. A goldsmith or jeweller can easily renew the layer after 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 can distort the surface signal when testing authenticity by X-ray fluorescence analysis. 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; its price has fluctuated in recent years between a few hundred and over 20,000 USD 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 does not represent any notable material value — the costs arise primarily from the craftsmanship and bath preparation involved.

In Brief

Rhodium plating is a proven electrochemical surface treatment that enhances the appearance of jewellery and coins and protects them from tarnishing, but requires periodic renewal. It does not affect the actual precious metal content of the underlying piece.