Gold is one of the most precious metals on Earth, prized for its beautiful yellow color and resistance to corrosion. However, some people claim that real gold can turn black over time. Is this really true? Let’s examine the facts.
Why Does Gold Change Color?
Pure gold is chemically very stable and does not normally change color. The yellow color of gold comes from the atomic structure of the metal itself. However, most gold jewelry and artifacts are not made of pure gold. They contain other metals added to the gold to increase the hardness, known as alloying.
When gold is alloyed with metals like copper, nickel, silver, zinc, etc., the alloys can undergo color changes over time when exposed to certain environmental conditions. This is especially true for low-karat golds, which have higher percentages of other metals mixed in. So when people claim that their “gold” jewelry turned black, it is likely due to the other alloys in the gold mixture, not the gold itself.
Common Reasons Gold Alloys Can Turn Black
Here are some of the most common reasons gold alloys can turn black over time:
- Tarnishing – When exposed to air and moisture, some metals in gold alloys like copper and silver can react and tarnish to a dark appearance.
- Sulfide Reactions – Hydrogen sulfide in the air or exposure to sulfur compounds can cause a chemical reaction turning the alloys black.
- Corrosion – Low-karat gold alloys with more base metals can corrode overtime, especially in acidic or damp conditions.
- Heat Damage – High heat when soldering or casting can discolor some gold alloys to a dark tone.
Will Pure Gold Turn Black?
Pure gold is very resistant to tarnishing and corrosion. The conditions that cause gold alloys to turn black do not affect pure 24K gold the same way. So technically, real pure gold will not normally turn black.
However, there are a few rare scenarios where even pure gold can change color:
- Thin Oxidized Layer – Pure gold can develop an extremely thin, invisible layer of gold oxide on the surface when exposed to air. This could make the surface appear darker, but it is not a true black tarnish.
- Gold Nanoparticles – Tiny gold nanoparticles appear black or dark brown due to quantum effects, even though the bulk gold is still yellow. These nanoparticles can form in gold alloys under certain conditions.
- Radiation Damage – Pure gold can turn a grayish color when exposed to alpha particles or high energy ion radiation, which displaces gold atoms from the structure.
In most cases though, pure 24K gold will remain its signature yellow color and not turn black even after many years. The black discoloration is usually due to other factors like alloys, tarnish, or corrosion.
How to Clean Blackened Gold
If your gold jewelry has turned black or dark over time, don’t panic – in many cases you can restore the original gold color. Here are some tips:
- Use a good quality gold jewelry cleaner or dip. These contain mild acids like citric acid to dissolve tarnish and discoloration.
- For stubborn tarnish, let the gold soak for 10-30 minutes in the cleaner to fully dissolve it.
- Gently scrub with a soft brush or cloth to remove any remaining residue after cleaning.
- Avoid abrasive scrubbers or toothbrushes, which can scratch the gold surface.
- Baking soda or aluminum foil methods can also help lift tarnish off gold via a chemical reaction.
- Store gold properly after cleaning to prevent new tarnish – keep it in sealed bags or boxes away from air and sulfur.
If discoloration remains after thorough cleaning, then the gold may be permanently corroded or damaged. In that case, re-plating the item may be required to restore the original appearance.
Conclusion
While pure gold does not normally turn black, gold alloys with other metals can tarnish and change color over time when exposed to air or chemicals. Cleaning and polishing can often remove this discoloration. But permanent corrosion is also possible in low-karat gold alloys. To keep gold jewelry looking its best, proper care and storage is essential. So while real gold itself does not blacken, many factors can cause gold jewelry to turn black as it tarnishes.