Bringing the shine back to the iconic sculpture Bronze Form

Gleaming golden in the California sunshine, Henry Moore’s sculpture Bronze Form welcomes visitors to the J. Paul Getty Museum in Los Angeles with its imposing structure.

At more than 4 m tall and weighing nearly 2 metric tons, it’s one of the first things visitors see once they ascend from the museum’s underground parking structure. The play of shadow and light on the bronze sculpture’s undulating form changes dramatically throughout the day. Although Bronze Form is abstract, its orientation suggests a human with a curvaceous figure.

Last year, Getty conservator Julie Wolfe and her colleagues refinished Bronze Form’s surface by adding a patina and coating it with lacquer. Although that might seem like a standard activity for conservators, adding this finish was, in fact, an unusual intervention. It also turned out to be something of a chemistry experiment.

“We try and spend most of our energy on preventative care,” Wolfe says. That normally involves washing the sculpture to remove dirt and grime and clearing the droppings from birds that like to sun themselves atop it. But Bronze Form needed more than cleaning. The sculpture had begun to darken and discolor from corrosion.

“When Bronze Form started to change in a way that the appearance no longer represented what it looked like originally, or even just like what the artist would intend his bronze sculptures to look like, that’s when we really had to jump in and start to act as an advocate for the artist,” Wolfe says.

Knowing how Moore would have wanted Bronze Form to be treated wasn’t straightforward. Morris Singer Foundry, in the south of England, cast seven Bronze Form sculptures between 1985 and 1986. Moore was ill at the time. He died in 1986, and it’s unlikely that he ever saw the completed works.

The artist Bernard Meadows, who was Moore’s assistant from 1936 to 1940 and acting director of the Henry Moore Foundation when Bronze Form was fabricated, stood in for Moore during the fabrication. Meadows decided not to apply a patina to the sculptures and instead directed the foundry to polish them to a bright, golden color.

A patina is a thin layer of controlled oxidation, achieved on bronze sculptures through a hot or cold treatment with chemicals. The color a patina gives a sculpture can vary depending on the chemicals and how they are applied, says Andrew Baxter, president of the company Bronze et al and an expert in bronze sculptures. Getty consulted him for the restoration of Bronze Form.

Not applying a patina to Bronze Form was a departure from how Moore’s previous outdoor works were treated. Earlier bronze sculptures received a cold wash of patinating chemicals, according to Katrina Posner, a private object conservator. The washes included ferric nitrate and liver of sulfur—a mix of potassium sulfide, potassium polysulfide, potassium thiosulfate, and potassium bisulfide. Posner worked with Bronze Form when she was a conservator at the Getty, from 2005 to 2013.

“The vast majority of Moore’s artwork is indoors, and so there’s a longevity that can be maintained,” Posner says. But outdoor sculpture is a different beast. Because of corrosion, “it’s impossible to maintain an unpatinated bronze sculpture outdoors,” she says.

The original decision not to patinate Bronze Form meant that the seven sculptures—now at locations including the Kawamura Memorial DIC Museum of Art and the Wellington Botanic Garden—required treatment to prevent corrosion just a few years after they were fabricated.

Getty’s Bronze Form was originally in the personal collection of philanthropist Fran Stark and film producer Ray Stark. It arrived at the Starks’ home near Santa Barbara, California, directly from the foundry. But the sculpture was already showing signs of corrosion, presumably from exposure to ocean air during its overseas journey. The sculpture was sanded, patinated (although the precise chemicals used were not recorded), and coated with acrylic urethane and wax.

The sculpture was donated to the Getty in 2005, a year after Ray Stark’s death. When it was installed in 2007, its acrylic urethane coating had begun to break down, and the sculpture showed signs of corrosion.

This type of coating deterioration happens with large, smooth sculptures like Bronze Form, says James Copper, sculpture conservator at the Henry Moore Foundation. “There’s nothing for the lacquer to grip onto, so that all the lacquer is doing is holding onto itself,” he says. Scratches compromise the coating and allow moisture to get beneath it. Once this happens, Copper says, “there’s nothing to hold the rest of the lacquer on, and it just literally unpeels like an orange.”

In 2012, after several years of research, Getty conservators treated Bronze Form again. But by 2021, that treatment was already starting to break down. That’s when Baxter and his partner, Steve Roy, were brought in.

Baxter and Roy had previous experience with Moore’s work. In 2014, the pair worked on Moore’s Mirror Knife Edge at the National Gallery of Art in Washington, DC. But Bronze Form was something new. “It is uncommon that we fully repatinate a sculpture,” Baxter says. If possible, he and Roy try to work with the artist’s original patina so that they’re not inserting their aesthetic into the artist’s work.

That wasn’t an option in this case because Getty’s Bronze Form had no original patina and had weathered poorly. But Baxter says that with some experimenting, he felt confident he could make it look like Moore would have wanted it to appear.

The first decision was one of temperature. The pair decided to apply a hot patina by painting on a chemical oxidant and then heating it. Hot patinas are generally easier to control and apply to large, smooth, vertical surfaces than cold patinas, Baxter says, although the process is not trivial. “You’re essentially standing in front of a waffle iron in August with a blowtorch, so it’s pretty tough work,” he says.

The next decision was what chemical mix to use, and that took a lot longer to puzzle out. Although the conservators did some experimenting with sample pieces of bronze, they ultimately had to test various patinating chemical solutions directly on Bronze Form. That’s because the sculpture was cast from a bronze alloy of copper, tin, zinc, and lead that’s no longer used because of the tin and lead content.

After sanding the entire surface of the artwork, the conservators tested the patinas in large patches on Bronze Form and then let them age for several months to see if they changed. Understanding patination is a fine art and a specialized skill, Getty conservator Wolfe says. “Depending on the alloy, you’re going to get different results.”

Testing alone involved three visits from Baxter and Roy. Baxter says they struggled with the sculpture’s high lead and tin content. “They don’t like to take a patina, those two metals. And they had migrated to the surface in very specific ways,” Baxter says.

Lead and tin can sweat out during the casting process, Wolfe explains. This sweating creates areas of different chemical composition in the sculpture, but “when it’s highly polished, you don’t see that difference in color,” she says.

The chemical composition can cause discoloration when a patina is applied. Baxter recalls that the patinating would be going well, and then they would treat a region of high lead or tin, and the patina would make that part of the sculpture turn black. When the patinas started to turn black, the conservators used X-ray fluorescence spectroscopy to see what was happening with the underlying work. And then they’d try a different patina treatment.

Ultimately, the team settled on a mixture of cupric nitrate and ferric nitrate with a top layer of ferric nitrate. This coating helped the underlying golden bronze shine through. Although it took years to research the treatment, it took only 2 weeks to do the restoration work once a course of action was set. Restoration was completed in July 2022.

Baxter also says he had some trouble getting the correct hydrate of cupric nitrate. The chemical supplier he used for this material when he worked on Moore’s Mirror Knife Edge at the National Gallery had gone out of business. And cupric nitrate from a different supplier couldn’t reproduce the effects he had seen previously.

Fortunately, Baxter had an old container of the chemical in the back of his truck and, using its CAS number, he was able to find another supplier for the correct hydrate of this material.

This type of reproducibility problem is common for conservators, Wolfe says. As companies merge or formulation requirements change—because of regulations for volatile organic compounds, for example—materials that conservators once found to be useful can vanish from the market. “There are changes in formulations constantly,” she says.

Vanishing varnish also became a problem after patination was complete and the team wanted to protect its hard work. The acrylic lacquer the Getty conservators planned to use wasn’t in stock when they needed it because of supply chain issues. So they were forced to coat Bronze Form after patination with a lacquer they had never used before.

While the patina may have been a chemistry challenge, applying the lacquer was an engineering challenge, Wolfe says. Because the sculpture is large and outdoors, the conservators had to build a large scaffold around it to protect it from collecting dirt and dust during the lacquering process.

Only time will tell how the treatment holds up—whether the patina and lacquer will weather uniformly or if further treatment will be needed. “Things are continually changing,” Copper of the Henry Moore Foundation says. “The patina is always going to change. However much you control it, it will continue to oxidize. All you can do is keep on top of the maintenance.”

For Bronze Form, maintenance involves a semiannual cold wax treatment, which Wolfe says has kept the piece looking lustrous. A year after the conservators finished the project, Getty’s Bronze Form still shines brightly.