Bronze sculptures are prized for their durability and timeless beauty, but over time, they often develop surface discoloration due to environmental and chemical factors. The most common causes include oxidation, patina formation, pollution exposure, and improper handling.

1. Oxidation and Patina: Bronze naturally reacts with oxygen and moisture, forming a green or brown patina. While some patina is desirable for artistic effect, excessive buildup can obscure details. Treatment involves gentle cleaning with specialized solutions or controlled mechanical methods.

2. Pollution and Acid Rain: Urban environments expose bronze to sulfur dioxide and acidic compounds, leading to black or blotchy stains. Professional conservators use chemical cleaners or laser ablation to remove corrosive layers without damaging the metal.

3. Chloride Corrosion: Exposure to saltwater or de-icing salts causes pitting and bright green spots. Treatment includes rinsing with distilled water and applying corrosion inhibitors.

4. Organic Stains: Bird droppings, algae, or fingerprints can leave unsightly marks. Mild detergents or enzymatic cleaners are effective for removal.

Preventive measures like wax coatings and indoor display can minimize discoloration. For valuable artworks, consult a professional conservator to ensure safe restoration. Understanding these causes and treatments helps preserve bronze sculptures for future generations.