Sterling silver, an alloy composed primarily of silver with a small percentage of other metals, notably copper, is susceptible to tarnish, a surface discoloration. This phenomenon is often mistaken for oxidation, leading to inquiries about whether this precious metal alloy corrodes in the same manner as iron-based materials.
The presence of copper in the alloy makes it more durable and workable than pure silver. However, copper also reacts with sulfur-containing compounds in the air, forming silver sulfide, the dark, often blackish, layer known as tarnish. This surface alteration is not structural degradation in the same way that the oxidation of iron causes it to disintegrate. The base metal present in the alloy is not as reactive and it prevents the disintegration.