Pure rhodium, a rare and precious metal, does not contain nickel. Rhodium is an element found in the platinum group of metals, and its pure form is inherently nickel-free. The metal is valued for its bright, silvery-white color and high resistance to corrosion and tarnish. Concerns about nickel exposure arise not from the rhodium itself, but from how it is utilized in consumer products.
Rhodium and Nickel as Distinct Elements
Rhodium (Rh) and Nickel (Ni) are entirely separate elements with distinct positions on the periodic table. Rhodium is a noble metal with the atomic number 45, placing it in the platinum group alongside metals like palladium and iridium. It is one of the rarest and most expensive metals, known for its exceptional hardness and reflectivity.
Nickel, in contrast, is a base metal with the atomic number 28, often used in alloys to add strength and whiteness. Unlike rhodium, nickel is a common contact allergen, causing skin irritation for a significant portion of the population. Pure rhodium is hypoallergenic and contains no nickel content.
Rhodium’s properties make it highly resistant to chemical attack and oxidation, allowing it to maintain its brilliant luster without tarnishing. Using solid rhodium for jewelry is cost-prohibitive and impractical due to its rarity and brittle nature when applied too thickly. This stability and purity make the metal a sought-after outer layer in manufacturing.
The Role of Rhodium in Consumer Products
The public primarily encounters rhodium as an ultra-thin coating known as rhodium plating. This process applies a layer, often between 0.75 and 2.0 microns thick, to the surface of other metals, such as white gold, sterling silver, or brass. The purpose of this coating is to provide a final finish that is bright, durable, and highly reflective.
For white gold, which naturally has a slightly yellowish tint, rhodium plating provides the brilliant, pure white look consumers expect. For sterling silver, the rhodium acts as a protective barrier to prevent tarnishing. This thin layer enhances the jewelry’s overall appearance and improves its resistance to scratching and wear.
The electroplating process involves immersing the piece in a rhodium solution and applying an electric current, chemically bonding the rhodium to the underlying metal. This plating method allows manufacturers to benefit from rhodium’s desirable surface properties without the prohibitive cost of using solid rhodium.
Nickel Exposure in Rhodium-Plated Items
Despite pure rhodium being nickel-free and hypoallergenic, nickel exposure can occur when wearing rhodium-plated items. This happens because nickel is often present in the layers of metal beneath the rhodium coating. For example, white gold is frequently alloyed with nickel, and some manufacturers use a nickel layer as an undercoating on silver or base metals.
This nickel underlayer serves a technical function, acting as a barrier to prevent the base metal’s components from migrating into the rhodium layer and improving plating adhesion. Over time and with daily wear, the thin rhodium plating naturally wears down due to friction and contact with skin, sweat, and chemicals.
Once the rhodium layer is breached, the underlying nickel comes into direct contact with the skin, triggering an allergic reaction in sensitive individuals. The nickel ions leach out, causing symptoms of contact dermatitis like redness, itching, and a rash. Consumers with sensitivities should inquire about using nickel-free base metals or barrier layers, such as palladium, beneath the rhodium plating.