Conservation of Henry Moore’s Outdoor Bronze Sculptures

The British artist Henry Moore (1898–1986) is well known for his monumental outdoor sculptures and was an influential artist in the mid-20th century. His distinct style of modernism was distinguished by abstract forms and figures. Primarily a sculptor, Moore started working in stone by direct carving and moved towards making plaster models and employing bronze foundries to create castings. Influenced by the craft of foundrywork, he experimented with chemical patinas to color the surface of his bronzes that ranged from subtle golden hues to vibrant greens and blues. The Henry Moore Foundation, established in 1977, works to preserve his legacy and support the visual arts.

The colors, or ‘patina’ on a bronze surface are the result of a chemical application that reacts to form copper oxides and minerals. The alteration includes a range of colors, lowers the reflective nature of the bronze metal, and can be applied to a hot or cold surface. Coatings are often applied to a new patina to saturate and protect the layer, yet the patina continues to react over time. Some of the chemical formulations produce stable and even slightly protective layers on the surface, while others may be more unstable and unpredictable.

Moore was known for coloring his bronze sculpture with patinas and wrote about the inevitable change that would happen when they were exposed to an outdoor environment. He asked the foundries to apply chemical patinas to produce brown, green, or reddish colors – ultimately followed by brushing on a protective wax coating. Moore often intentionally created lights and darks in his compositions as a result of patination, but also loved how his static compositions would change as the sunlight cast additional highlights and shadows throughout the day. Some works have dark patinas that he polished away selectively to create contrast. Moore’s assistants and foundry patinators each had their own skilled (and often secretive) techniques to create the formulations, and to control the mixtures with different means of application and heat.

In 2006, the Getty Museum acquired 28 outdoor sculptures from the Fran and Ray Stark Revocable Trust. Three of these were created by Moore – Bronze Form, Seated Woman, and Draped Reclining Mother and Baby. The department of Decorative Arts and Sculpture Conservation oversees the objects’ maintenance with special consideration to their exposure to the elements.

The patina on Moore’s sculptures at the Getty Center have protective coatings such as hot wax or a clear acrylic coating. Waxes can oxidize and change from the heat, so they must be re-applied yearly. Acrylic coatings are more durable and can protect the metal for several years before having to be replaced. Adding wax over an acrylic coating can extend the lifetime. Conservators monitor the coatings and locally repair any minor damages. If corrosion or uneven changes to the patina occur on a larger scale, conservators must formulate a plan to replace the protective coatings.

There are challenges to stabilizing or restoring the surface of patinas, regardless of protective coatings. The golden, transparent patina on Bronze Form is particularly delicate and prone to uneven darkening over time. At 14 feet high and mounted over a pool, the scale of the sculpture adds to the difficulty of re-applying coatings uniformly and in situ. Golden patinas are also difficult to restore locally and any irregularity to the surface, such as welds, porosities, or alloy variation will change at different rates.

Regular maintenance to clean and replenish protective coatings will help to protect surface patinas. Due to the size of Bronze Form, coating treatments need to happen in situ, and an enclosure with scaffolding can keep the worksite clean. Seated Woman and Draped Reclining Mother and Baby, on the other hand, are de-installed and brought to the conservation laboratory to fully clean and re-apply coatings in a controlled environment. Conservators have researched coatings and application methods to improve the performance, such as using the correct air supply for spray guns and testing for adhesion prior to use. Developing a better chemical patina for Bronze Form has also provided a more stable surface that will make maintenance easier in the long-term.

Museum conservators have combined archival resources, foundry specialists, and technical surface analysis to discover options for maintaining Bronze Form and other Moore sculptures in the collection. With curatorial guidance, studying the timeline of Moore’s stylistic changes in relation to the works in our collection has clarified our options and approach to their preservation. In addition, taking advantage of the Henry Moore Foundation archives, oral interviews, and correspondence have provided information about the fabrication of Moore’s sculpture, and approaches to conservation in Moore’s lifetime.

Getty’s approach to understanding patinas on sculpture includes using surface analysis on the sculpture, such as X-ray fluorescence spectroscopy (XRF). Analyzing the bulk of the metal alloy in comparison to the surface helps identify elements that remain from chemical treatments, such as iron from a ferric nitrate patina. Surface analysis of Bronze Form prior to the 2022 repatination treatment showed no difference in alloy between a polished and unpolished surface, for example, indicating that there was no extant chemical patina.

Getty also tests the performance of wax and acrylic coatings which can be affected by different patinas. Monitoring coatings in use on the Stark Collection is ongoing. Numerous coating studies on bronze samples that are naturally or artificially aged allow conservators to choose more appropriate protective coatings related to the bronze surface on sculpture. Coatings are evaluated using Electrolytic Impedence Spectroscopy, Gas-chromotography Mass Spectroscopy, and ASTM standards for evaluating adhesion.