It is a common question whether the most famous of all precious metals will burn when subjected to extreme heat. The simple answer is no; real gold does not burn or combust in the air like wood or paper. Gold is classified as a noble metal, a group of elements highly resistant to chemical reactions like oxidation, even when very hot. While heat affects gold, causing it to change its physical state, it remains chemically unchanged as the element gold (Au) throughout the process.
Gold’s Resistance to Chemical Reaction
The reason gold cannot burn lies in the chemical process of combustion. Burning is a rapid oxidation reaction that releases heat and light, requiring a substance to readily combine with an oxidizing agent, usually oxygen in the air. Most materials and metals burn because their atomic structure allows them to easily lose electrons and form new compounds, such as oxides, when exposed to oxygen and heat.
Gold, however, is chemically stable due to its unique electron configuration, which makes its outer electrons tightly bound and less available for bonding. Gold’s noble metal status means it is one of the least reactive elements on the periodic table, resisting combination with oxygen, water, or sulfur. Even when heated to high temperatures, gold does not form an oxide layer or tarnish like iron or copper. The only chemical processes capable of dissolving gold are highly specialized, involving extremely corrosive mixtures like aqua regia or cyanide solutions, not simple burning.
The Physical Effects of Extreme Heat
While gold is chemically unreactive to heat, it will undergo a physical change when the temperature is raised high enough. When gold is heated to 1,064 degrees Celsius (1,947 degrees Fahrenheit), it reaches its melting point and transitions from a solid to a liquid state. Achieving this extremely high temperature requires specialized equipment, such as powerful furnaces or industrial-grade torches.
The molten gold remains the same element, Au, simply changing its physical phase, similar to how ice turns into water. The liquid metal is often poured into molds for casting or refining, demonstrating its malleability. If the temperature were raised further, gold would reach its boiling point at about 2,807 degrees Celsius (5,084 degrees Fahrenheit), causing it to vaporize into a gaseous form. This wide temperature difference between the melting and boiling points allows manufacturers to work with the liquid metal without fear of it evaporating.
Practical Applications of Heating Gold
The high melting point and chemical inertness of gold are utilized in several important industrial and artistic processes. In metal refining, high heat separates gold from impurities and other metals, but the gold itself is not consumed. A classic technique is the fire assay, which involves heating a sample in a porous cupel at temperatures around 1,100 degrees Celsius. During this process, base metals within the sample oxidize and are absorbed into the cupel, while the gold remains behind as a metallic bead.
In jewelry making, heat is applied for both casting and soldering, relying on the metal’s ability to melt without oxidizing. Gold is often alloyed with other metals like copper or silver to increase its durability, which can lower the overall melting point of the material. If gold jewelry shows minor discoloration upon heating, the less-noble alloying metals are reacting with the air, not the gold itself. The intentional heating of gold is a controlled process that takes advantage of its stability to maintain its form and purity.