Does Gold Turn Black When Heated?

The age-old question of whether gold turns black when heated has sparked numerous discussions and debates among scientists and enthusiasts alike. It’s important to understand the nuances involved in the behavior of gold and its alloys upon heating, as well as the factors that might contribute to a change in color.

Properties of Pure Gold

Pure gold, specifically 24-karat (24k) gold, is a stable metal that retains its golden hue even at high temperatures. This is due to its high resistance to corrosion and oxidation. When 24-karat gold is heated, it remains unchanged and does not exhibit any color transformation.

Gold Alloys and Heating

While pure gold remains stable, gold that has been alloyed with other metals such as nickel or copper may exhibit different behaviors when heated. These alloys can tarnish or oxidize under certain conditions, which can lead to darkening or discoloration. Additionally, surface treatments like rhodium plating can wear off or react to heat, potentially creating a darker appearance on gold jewelry.

Heating Gold at High Temperatures

When gold alloys are heated to very high temperatures, changes can occur in their surface finish or the appearance of any attached materials. However, the gold itself will not turn black. Instead, it may display a pink tinge due to the absorption of gold atoms by the crucible in certain experimental conditions.

Heating Gold Alloys to High Temperatures

When gold alloys like 9-karat, 10-karat, and 14-karat gold are heated to a red-hot temperature in open air, they usually become discolored, often blackened. This is because these alloys contain copper and other metals that react with oxygen to form oxides in the air. The lower the gold content and the hotter and longer the heating process, the more pronounced and darker the discoloration will be.

Factors Contributing to Color Changes

The color change is primarily due to the presence of these other metals in the alloy and their interaction with atmospheric oxygen. An alloy with a lower karat value (i.e., less gold content) is more susceptible to oxidation and discoloration when exposed to heat and air.

Resistant to Oxidation

Pure gold, when heated to its melting point of approximately 1,064 degrees Celsius, remains a glowing liquid and retains its golden color upon cooling. The absence of change in appearance is due to gold's inherent resistance to corrosion and oxidation under these conditions.

Conclusion

In summary, pure gold does not turn black when heated, provided it remains pure. However, gold alloys, particularly those with lower karat values, can become discolored, usually blackened, when exposed to high temperatures and air. Understanding the composition of the gold and the conditions under which it is heated is crucial in predicting any potential color changes.