patina

Patina is a film or surface alteration that develops on materials through aging and exposure. It results from chemical and physical changes such as oxidation, hydration, mineral deposition, and the accumulation of oils and dirt. Patina can form naturally over time or be artificially created to simulate age in art, metalwork, and furniture.

On metals, patina often reflects specific reactions with air, moisture, and pollutants. Copper and bronze can develop green or brown verdigris as copper salts form; iron and steel may acquire a protective oxide layer that ranges in color from brown to blue-gray. Silver tarnish appears as a dark layer of silver sulfide. In stone, wood, and leather, patina denotes a mellowed sheen, deeper color, and wear patterns produced by handling, use, and environmental exposure.

Causes of patina include oxidation, dehydration and hydration cycles, exposure to pollutants, and the deposition of minerals. Natural patinas typically take years to form, while artisans can hasten or tailor patination with chemical treatments to achieve particular hues and textures.

Cultural and practical significance varies. Patina is often valued in antiques and sculpture as a sign of age and authenticity, contributing to perceived character and value. In conservation, patina may be preserved to retain historical integrity, or removed if it obscures original details. Some processes intentionally apply patinas to create a desired decorative effect.

Preservation considerations depend on material and context. Patina can offer some protective benefits but may also indicate material deterioration, so cleaning or polishing is usually performed with material-specific methods to avoid inadvertent damage.