Longevity in precious metals is determined by two qualities: chemical stability and physical resistance to wear. Consumers interested in materials for jewelry, coinage, or heirlooms must compare a metal’s tendency to react with its environment against its capacity to withstand daily physical damage. The comparison between silver and gold is a balance between these two factors.
Gold’s Chemical Inertness
Gold’s exceptional longevity is a direct result of its chemical classification as a noble metal, meaning it resists chemical reactions under standard conditions. Unlike iron (which rusts) or copper (which forms a patina), pure gold does not react with oxygen in the air or water. This resistance is rooted in the unique structure of the gold atom, which holds its electrons very tightly.
The metal’s stability is so profound that it remains unaffected by most common acids, sulfur, or corrosive agents found in the environment. This inherent chemical inertness is the primary reason gold retains its metallic luster and does not degrade or lose material over centuries. Gold only dissolves in aqua regia, a highly corrosive mixture of nitric and hydrochloric acids, far outside normal environmental exposure.
Why Silver Tarnishes
Silver’s chemical stability is significantly less robust than gold’s due to the common phenomenon of tarnishing. Tarnish is a reaction called sulfidation, occurring when silver comes into contact with sulfur compounds in the air. These sulfur-containing gases, such as hydrogen sulfide, are present in air pollution, certain foods, and even rubber.
This reaction forms a thin, dark layer of silver sulfide (\(\text{Ag}_2\text{S}\)) on the metal’s surface, which diminishes its reflective shine. While this layer is superficial and does not compromise the structural integrity of the metal like rust, it necessitates frequent cleaning and polishing. Polishing removes the silver sulfide, but it also takes away minute amounts of the underlying silver metal each time, resulting in constant material loss.
Physical Durability and Scratch Resistance
When considering physical durability, the comparison shifts to mechanical properties like hardness and scratch resistance. Both pure gold and pure silver are extremely soft, scoring between 2.5 and 3.0 on the Mohs hardness scale, making them too malleable for practical daily use.
For this reason, both metals are mixed with others to create alloys, such as sterling silver (92.5% silver) or 14-karat gold (58.3% gold). The alloying process significantly changes their physical strength, and gold alloys generally surpass silver alloys.
Common 14-karat gold alloys typically have a Vickers hardness ranging from 150 to 200, making them resistant to scratching. In contrast, sterling silver alloys often have a Vickers hardness between 60 and 100, making them softer and more susceptible to dents and scratches during routine wear.