Annual Maintenance of the Bronze, Iron, and Stone Monuments

A major aspect of the internship each year is the routine maintenance of the bronzes. This involves assessing damage from the environment as well as chemical corrosion from reactions with atmospheric gases.

Many of the park monuments are made up of two main parts- a stone base and a cast metal sculpture. These materials require different treatments and exhibit distinct deterioration patterns, with varied vulnerabilities to common cleaning materials.

Location:

Central Park, New York City, NY

Issues:

  • Protective coatings on Bronze and Cast Iron are sacrificial and need to be removed and redone annually

  • Granite and Marble bases are the perfect surface environment for biological growth and need to be cleaned of this growth to prevent it from eventually becoming a hard to remove biofilm/crust.

  • All monuments must be condition checked every year to track any active corrosion.

Treatments Carried Out:

  1. Wet cleaning using a low concentration of non-ionic soap and a pressure washer

  2. Wax treatments for the metal components- hot wax, warm wax, and cold wax treatments are used depending on which monument is being treated.

Cleaning and Caring for Stone

In Central Park there are a number of specific types of stone used in monument base construction. Marble and granite are the two most common stones used as base stone material, however there is a variety in the hardness in the stones used in the park. Tennessee Pink Marble, used as a base material for the U.S.S. Maine Monument, is technically a limestone, and thus softer and porous. Identifying which stone was used was important to assess the optimal cleaning pressure.

The cleaning process, once the stone has been identified, is rather straight forward- a low concentration of Vulpex, a gentle nonionic soap developed for restoration work, is used with natural fiber brushes to clean off any loose surface residue before a power washer is used to clean off any soapy residue and stubborn surface dirt.

Cleaning and Waxing Bronze

The bronzes are treated similarly, but a lower water pressure is used to avoid damaging the coating on the bronze surface. The bronzes are scrubbed by hand using natural fiber brushes with water and Vulpex. They are then pressure washed to remove the rest of the dirt, loose corrosion, and encrustations. Once dry, a protective wax coating is reapplied. After 24 hours, the wax can be buffed into a consolidated protective layer. Some monuments, like the Monumental Women, the Three Bears, and Frederick Douglass require the use of a propane torch to heat the surface of the bronze and melt the wax on application.

Washing and applying a sacrificial wax layer to protect the park’s sculptures provides a holistic approach to conservation, safeguarding the works without replacing or altering the original material. This approach respects the artist’s intent while aligning with the CPC’s core values of upholding sound, ethical principles and developing expertise. Minimizing intervention is a guiding principle widely shared across the conservation field.

Figure 2- Being an outdoor collection, mud was a common work hazard. Here I am directing the stream of a hot-water pressure washer with precision, sacrificing the cleanliness of my work pants for that of the project.

Figure 4- My colleague Sarah and I using a propane torch to apply a warm Getty wax treatment to a cleaned and dry cast bronze. Due to the scale of some of the monuments, we were trained on the operation of boom lifts.

Figure 5- Here we are as a team caring for the Monumental Women Monument by applying a warm Getty wax treatment using propane torches.

Figure 1- The kickback of the power washer meant that safety and balance were a team effort.

Figure 3- Here I am applying renaissance wax to a cleaned and dried bronze.