The question of whether real gold turns green is a common one, often fueled by seeing jewelry that appears to have a greenish discoloration. The short answer is: pure gold itself does not turn green. However, the appearance of green on what appears to be gold jewelry often stems from other factors, making it crucial to understand the properties of gold and the potential causes of discoloration.
Why Doesn't Pure Gold Turn Green?
Gold's resistance to tarnishing and corrosion is legendary. Its inherent chemical stability means it doesn't readily react with oxygen, water, or most other substances in the environment. This is why it's valued as a precious metal and why it's often used in jewelry and other applications where durability and resistance to discoloration are paramount. Its inertness is the key.
So, What Causes That Greenish Discoloration?
The green hue on what seems to be gold jewelry is usually not the gold itself changing color, but rather a reaction involving other metals or substances. Here are the most common culprits:
1. Alloying Metals: What are the alloys in gold?
Gold jewelry is rarely made from 100% pure gold (24 karat). Pure gold is very soft and easily damaged. To increase its durability and hardness, it's often alloyed with other metals like copper, silver, or zinc. These alloying metals are significantly more reactive than gold and can tarnish or corrode, resulting in a green discoloration—especially copper, which can form verdigris (a green patina). The percentage of gold in the alloy (karat) determines the color; lower karat gold will have a more noticeable discoloration over time.
2. Reactions with Chemicals: How do chemicals react with gold?
Exposure to certain chemicals can also cause a green discoloration, particularly near areas with high concentrations of sulfur or chlorine. For example, swimming in a chlorinated pool or wearing gold jewelry while working with certain chemicals can accelerate the tarnishing of the alloying metals, leading to a greenish film.
3. Environmental Factors: Can the environment affect gold?
Environmental conditions play a role too. High humidity or exposure to pollutants can accelerate the tarnishing process. This is particularly relevant in coastal areas or places with high levels of air pollution.
4. Poor-Quality Gold Plating: Is it plated gold or real gold?
Items plated with gold might appear golden initially but, over time, the plating can wear off, revealing the base metal underneath which may tarnish or corrode, giving a greenish or other discoloration.
How Can You Tell if It's Real Gold?
Several methods can help you determine if a piece of jewelry is genuinely gold or a gold-plated item:
1. Acid Test: What is an acid test for gold?
A jeweler can perform an acid test, applying a small amount of acid to a discreet area to check its purity. This method is reliable and widely used in the jewelry industry. However, this should be done by a professional.
2. Hallmarks: Where do I check for hallmarks?
Look for hallmarks stamped on the piece. These are official markings that indicate the karat of gold (e.g., 14K, 18K). The presence of a hallmark does not guarantee authenticity but significantly increases the likelihood that it's real gold.
3. Density Test: How is the density of gold measured?
While less accessible, a density test can accurately determine the density of the item to verify if it matches the density of pure gold. This test requires specific equipment and expertise.
In Conclusion
While pure gold itself resists tarnishing and will not turn green, the presence of a green discoloration on what appears to be gold jewelry typically indicates a reaction involving alloying metals or external factors. Understanding these factors helps to distinguish between genuine gold that may show surface discoloration due to its alloying metals and counterfeit or plated gold. If you are concerned about a piece of jewelry's authenticity, consulting a qualified jeweler is always the best option.
