While pure gold does not tarnish, 18 karat gold can turn black under certain conditions due to the presence of other metals in the alloy.
Here's a breakdown:
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Pure Gold (24 Karat): Gold in its purest form is highly resistant to corrosion and oxidation. It doesn't react easily with air or moisture, meaning it won't tarnish or turn black.
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18 Karat Gold Composition: 18 karat gold is made up of 75% pure gold and 25% other metals. These other metals are typically silver, copper, and zinc, which are added to increase the gold's durability and alter its color.
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Tarnishing and Blackening: The non-gold metals in 18 karat gold can react with substances in the environment, such as:
- Sulfur: Exposure to sulfur compounds (found in air pollution, some cosmetics, and even some foods) can cause the other metals to tarnish, creating a dark or black layer on the surface.
- Chlorine: Chlorine (found in swimming pools, cleaning products) can also react with the alloy metals.
- Acids: Acids from sweat, lotions, and perfumes can corrode the other metals in the alloy.
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The Process: When these metals react, they form compounds like silver sulfide or copper oxide, which are often dark in color. This surface discoloration is what appears as "blackening."
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Factors Influencing Blackening:
- Body Chemistry: Individual body chemistry plays a significant role. Some people's sweat is more acidic or contains more sulfur compounds, which can accelerate tarnishing.
- Environment: Exposure to polluted air, humidity, and chemicals in cosmetics or cleaning products increases the likelihood of blackening.
- Metal Composition: The specific alloy used in the 18k gold will impact how susceptible it is to tarnishing. Higher copper content may lead to a quicker darkening.
In summary, while the pure gold in 18 karat gold is inert, the other metals present can react with environmental factors and cause a dark or black tarnish to form on the surface. Regular cleaning with a jewelry cleaner can help prevent or remove this tarnish.
