The purity of gold is measured using the karat system, where 24 karat (24k) represents 99.9% gold content. Pure gold is rarely used for jewelry because its physical properties require mixing it with other metals in a process called alloying. This alloying creates a material more suitable for everyday wear. The presence of nickel depends entirely on the specific alloy recipe used by the manufacturer. The karat stamp indicates the proportion of gold to these companion metals.
Why Gold Needs Companions
Pure 24k gold is a very soft and malleable metal that easily bends, scratches, and deforms under the stresses of daily life. This softness makes it impractical for crafting durable items like rings or gemstone settings that require structural integrity. Gold must be blended with stronger metals to increase its hardness and overall durability, which also helps manage the material cost.
The addition of companion metals, such as copper, silver, or zinc, changes the gold’s physical characteristics and lowers the overall proportion of pure gold. For instance, 14k gold contains 58.3% pure gold, with the remaining 41.7% being the alloy mix. The specific combination of these non-gold metals allows jewelers to manipulate the final color and working properties of the metal.
The Role of Nickel in Specific Gold Alloys
Nickel is a common metal used in gold alloys, primarily due to its ability to act as a “bleaching agent” to counteract gold’s natural yellow color. It is a traditional component in the creation of white gold, alloyed with gold, copper, and zinc to produce a significantly whiter metal. Nickel-based white gold is exceptionally hard and strong, making it ideal for items like pins and rings that require high wear resistance.
A common formulation for nickel white gold might contain approximately 10% by weight of nickel. Nickel is also sometimes used in lower-karat yellow gold (10k or 14k) to increase the alloy’s strength and reduce the overall material cost. However, because of known reactions, some manufacturers use palladium, which is more expensive, as an alternative to produce white gold that is typically softer and more pliable.
Health Implications of Nickel Content
The main concern regarding nickel in gold alloys is its potential to cause nickel contact allergy, known as allergic contact dermatitis. This is a common sensitivity, affecting an estimated 10% to 20% of the population. The allergy is triggered when nickel ions are released from the alloy and come into direct, prolonged contact with the skin, often accelerated by sweat.
Once released, the nickel ions penetrate the skin and trigger a delayed-type hypersensitivity reaction from the immune system. Symptoms typically appear as a localized, itchy rash, redness, swelling, or small blisters at the point of contact. Once a person is sensitized, subsequent contact can provoke a reaction within a day or two.
Identifying and Avoiding Nickel Exposure
The most effective way to avoid nickel exposure is by inquiring directly with the jeweler about the alloy composition before purchase. While a piece of jewelry may be labeled “nickel-free,” there are no federal standards in the United States to verify this claim. For a quick check on existing jewelry, consumers can use a home testing kit containing dimethylglyoxime solution, which turns pink when swabbed onto metal that is releasing nickel ions.
Regulations on nickel content vary widely across the globe. The European Union, through its Nickel Directive, enforces strict limits on the rate at which nickel can be released from products intended for prolonged skin contact. The limit for these items is set at 0.5 micrograms per square centimeter per week, while jewelry for newly pierced skin has an even lower limit.
For individuals with a known sensitivity, the safest alternatives are high-karat yellow gold (18k or 24k), platinum, or palladium white gold alloys, as these do not rely on nickel for their properties.