Cubic zirconia (CZ) is a popular, colorless synthetic gemstone used widely as a diamond simulant. Its appeal lies in its affordability and visual similarity to natural diamond. The CZ stone itself is fundamentally free of nickel. The concern for nickel arises not from the stone, but from the metallic setting that holds the CZ gem. Since nickel is a common alloy in many jewelry metals, its presence depends entirely on the material used to create the jewelry piece.
The Chemical Makeup of Cubic Zirconia
Cubic zirconia is defined by its chemical structure, which is zirconium dioxide (\(\text{ZrO}_2\)) in a cubic crystalline form. This material is synthesized in a laboratory using a process that requires extremely high temperatures. To stabilize the cubic structure, small amounts of other oxides, such as yttrium oxide or calcium oxide, are added during growth.
The final synthetic crystal is a ceramic material composed of zirconium and oxygen. Nickel is not a component of this chemical formula, nor is it introduced as a stabilizing agent during the manufacturing process. Therefore, the CZ stone itself does not contain nickel, meaning cubic zirconia stones are nickel-free.
Why Nickel is Found in CZ Jewelry Settings
The issue of nickel arises because the CZ stone must be mounted into a metallic setting. Nickel is frequently used as an alloy in jewelry metals because it is inexpensive and adds hardness and strength to softer precious metals like gold and silver.
In white gold, nickel is a primary component mixed with yellow gold to achieve the characteristic silvery-white color. For instance, an 18-karat white gold alloy contains 75% pure gold, with the remaining 25% often including a substantial amount of nickel. Although palladium can whiten gold, nickel is often chosen for its lower cost and superior hardening effect.
Nickel is also present in many base metals used for costume jewelry, sometimes called “nickel silver” or “German silver.” These alloys use nickel, copper, and zinc to create a bright, silvery appearance. Even sterling silver (92.5% silver) can occasionally contain trace amounts of nickel in the remaining alloy, though copper is the traditional addition.
Nickel’s widespread use is the source of allergic reactions for many people, often causing a rash known as contact dermatitis. The reaction occurs when nickel atoms leach out and react with the skin’s sweat. If a piece of jewelry is plated, and that plating wears down, the nickel-containing base layer can come into direct contact with the skin.
How to Ensure Your Jewelry is Nickel-Free
For individuals with nickel sensitivity, the focus must be on the metal setting. A reliable way to ensure safety is to purchase items that comply with the European Union’s (EU) Nickel Directive. This standard limits the amount of nickel that can be released onto the skin, which is distinct from the total nickel percentage in the alloy.
When shopping, look for metals that are naturally nickel-free or meet strict manufacturing standards. Platinum and titanium are excellent choices, as they are highly biocompatible and do not require nickel for strength. High-karat yellow gold (18-karat or higher) is also safer because the high proportion of gold means alloying metals are less likely to contain nickel.
Surgical stainless steel, particularly grade 316L, is often considered safe because the nickel is tightly bound within the alloy, minimizing its release. Always be cautious with white gold and sterling silver unless they are explicitly certified as nickel-free. The term “hypoallergenic” is not regulated in the United States and may still contain trace amounts of nickel, but consumers can use home testing kits to check for leachable nickel on existing jewelry.