Silver and gold have been valued for millennia, often compared for their use in jewelry or coinage. The question of which metal is harder is not simple, as both pure elements are relatively soft. When examining their elemental states, pure silver is generally considered slightly harder than pure gold. The practical durability of items made from these metals depends almost entirely on the other metals mixed with them, a process known as alloying.
Measuring Hardness: The Scientific View
Hardness in material science refers to a metal’s resistance to permanent deformation, such as scratching or indentation. When considering the elements in their pure form, gold is one of the softest metals known. Pure gold, often called 24-karat gold, scores approximately 2.5 on the Mohs scale of mineral hardness, which measures scratch resistance.
A score of 2.5 means pure gold can be scratched by a copper penny or even a fingernail. Pure silver, while still quite soft, is slightly firmer than gold. The Mohs scale gives pure silver a rating of 2.5 to 3.0, indicating a marginally higher resistance to scratching.
More precise methods, such as the Vickers hardness test, confirm this difference by measuring resistance to indentation. This test involves pressing a diamond pyramid into the metal’s surface under a specific load. Although the Mohs scale values are similar, the Vickers scale shows that pure silver requires slightly more force to deform than pure gold.
The Importance of Purity and Alloying
In commerce, both gold and silver are almost never used in their pure forms because they would be too easily scratched and damaged during daily wear. Their practical hardness is dramatically increased by alloying, the process of mixing them with a harder base metal. The final hardness is determined by the percentage and type of the added metal, often making the alloy far harder than the pure base metal.
For gold, purity is measured in karats; 24K is pure, while 18K contains 75% gold and 14K contains 58.3% gold. The remaining percentage in these alloys is typically copper, silver, nickel, or zinc, which significantly increases the overall hardness. For instance, 14K gold is harder than 18K gold because it contains a greater proportion of these strengthening alloy metals.
Silver is commonly alloyed with copper to create sterling silver, which is 92.5% silver and 7.5% copper. This addition of copper brings the Mohs hardness of sterling silver up to around 2.7 to 3.0, making it suitable for jewelry. While 14K gold can achieve a Mohs rating of 3.5 to 4, sterling silver usually remains softer than the harder gold alloys used in jewelry. The comparison is between the specific alloy formulations, rather than the base metals themselves.
Practical Durability and Long-Term Wear
Durability encompasses more than just initial hardness, relating to a material’s resistance to damage over time and its long-term stability. While silver is slightly harder than gold in its pure state, gold has a significant advantage in chemical stability. Gold does not react with oxygen or common chemicals, meaning it is highly resistant to corrosion and does not tarnish.
Silver readily reacts with sulfur compounds in the air, a process known as sulfidation, which causes a dark layer to form on the surface. This visible corrosion, commonly called tarnish, does not affect the metal’s structural integrity. However, it requires regular cleaning and maintenance to restore the item’s appearance.
Gold’s chemical inertness means that gold items, even those made from softer alloys, maintain their appearance without this constant upkeep. This superior resistance to environmental factors is a primary reason gold is often considered more durable for items intended for everyday, long-term wear.