Bronze Coatings

Surface Alterations and the Need for Bronze Coatings

Outdoor bronzes often undergo chemical changes driven by rain, irrigation, pollution, biological growth, and fluctuations in temperature and relative humidity. In the case of Little Girl, the most visible alteration was the accumulation of calcareous deposits across large areas of the surface. These whitish, crust-like accretions commonly form when hard water is used in garden irrigation systems. Calcium and magnesium salts dissolved in the water precipitate onto the metal, gradually masking the original patina and creating a dull, uneven appearance.

Surface deposits are not merely aesthetic issues. They can trap moisture, create micro-environments that promote corrosion, and interfere with the proper adhesion of bronze coatings. For that reason, safe, controlled cleaning is a necessary first step before any protective layer is applied.

Case Study: Conservation Treatment of “Little Girl” by Lynn Chadwick

1. Removing Calcareous Deposits

To eliminate the mineral deposits, a 10% solution of sodium hexametaphosphate in distilled water was used. This chelating agent is particularly effective for breaking down calcium-based encrustations without damaging well-established patinas. The application was carried out gradually, allowing the solution to soften the deposits so they could be removed mechanically with minimal intervention.

Because chelators can leave residues that interfere with future coatings or cause unwanted surface reactions, a thorough rinse with distilled water was essential. The sculpture was rinsed several times to ensure complete removal of any remaining sodium hexametaphosphate.

2. Addressing Unstable Corrosion in Crevices

Some recessed areas showed early signs of unstable corrosion, likely linked to trapped moisture and environmental contaminants. These areas were carefully cleaned and treated to halt further deterioration. Although the corrosion was not extensive, stabilizing these micro-environments was critical to prevent deeper structural issues over time.

For most outdoor bronze sculptures, the most appropriate and widely recommended coating is wax. Among all available types of bronze coatings, wax offers several advantages:

• It forms a flexible protective barrier that accommodates the expansion and contraction of metal exposed to thermal fluctuations.
• It is easy to apply, even during routine maintenance.
• It can be renewed frequently without removing all previous layers.
• It provides an effective barrier against moisture, pollutants, and mild abrasion.

Wax also works well as a topcoat over many acrylic or solvent-based lacquers, providing an additional layer of UV and weather protection.

Microcrystalline Waxes as the Gold Standard

Microcrystalline wax is the preferred option among conservators due to its inertness, stability, and resistance to yellowing over time. Unlike natural waxes, microcrystalline formulations have a finer crystalline structure, making them less prone to cracking or flaking under outdoor conditions.

When applied to a properly degreased and clean surface, a thin, even layer of microcrystalline wax can be buffed with soft cotton rags and bristle brushes to achieve a subtle sheen that enhances the sculpture’s visual depth while preserving the original patina.

Maintenance Practices for Long-Term Protection

Even the best bronze coatings require consistent maintenance to remain effective. Outdoor bronzes should receive a yearly or twice-yearly waxing, depending on climate. Sculptures in coastal regions, near sprinklers, or under dense foliage may require more frequent care due to the higher presence of airborne salts, organic material, or water exposure.

Routine inspections can identify areas where the coating has thinned or where moisture has accumulated. Early detection of changes in appearance, color, or texture helps prevent avoidable damage and reduces the need for intrusive treatments later.

Conclusion: Bronze Coatings as Essential Preservation Tools

Wax-based coatings, especially microcrystalline waxes, remain the most reliable and reversible solution for preserving outdoor patinated sculptures. When combined with appropriate cleaning methods and scheduled maintenance, they effectively safeguard surfaces from environmental wear, corrosion, and aesthetic alteration. Implementing a consistent care routine helps preserve both the cultural significance and the material integrity of bronze artworks for generations to come.