What Is Rhodium Plating on White Gold?

Rhodium is one of the most reflective and dazzling metals.

White gold is pure gold alloyed with palladium or nickel. White gold is graded by its whiteness, and to improve its brightness and reflective quality, white gold is commonly plated with rhodium. Rhodium is a platinum-like metal that alone is too brittle and difficult to work into jewelry, but provides a brilliant white reflective plating.

Rhodium

Rhodium is an extremely rare metal that has some qualities similar to platinum. It has a high melting point (1963 degrees Celsius) and is brittle in the solid state, so it is difficult to work into pieces of jewelry. Rhodium is used industrially in catalytic converters. Rhodium is typically two to 10 times more expensive than gold.

White Gold

White gold is an alloy of yellow gold (pure gold) and either palladium or nickel. White gold made with nickel may cause allergic reactions, so this cheaper alloy is usually found only in older pieces. Palladium is a platinum-group metal that is about 1/5 the price of gold. "Whiter" gold is more precious.

Rhodium Plating

Rhodium is dissolved in a strong acid solution such as aqua regia, dried and re-suspended in a solution containing phosphoric or sulfuric acid. This solution is used for electroplating white gold and other precious metals. The white gold is attached to an electrode, and when a current is passed through the solution, elemental rhodium is deposited in a thin coating on the white gold.

Qualities of Plated Rhodium

Rhodium is usually applied at a thickness of 20 to 30 thousandths of an inch. Thicker rhodium plating can develop fractures or a crystalline structure unless extremely stringent plating conditions are maintained. Rhodium is extremely hard and corrosion-resistant.

Wearability and Re-plating

Depending on how heavily worn the piece is, rhodium is commonly re-plated. Flash plating applies only a very thin layer of rhodium to the white gold, and may have to be repeated annually for the piece to retain its shine and luster. Other pieces such as brooches may not ever have to be re-plated.

References

• Chemicool; Rhodium
• Proplate: Rhodium Plating