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Cleaning of Grant Memorial

Outdoor sculpture and monument preservation is a field of museum conservation that focuses on care and treatment of outdoor installations. Sculptures and monuments are permanent or semi-permanent, and they are often erected for artistic or memorial purposes. They can be made from a variety of materials, including bronze, steel, fiberglass, wood, marble, granite, stone, or combinations of materials. Preservation activities are typically carried out by conservators or museum staff, though routine cleaning and maintenance may be performed by city workers or contractors.

Potential Damage

Sculptures showing weathering and green patina

Outdoor sculptures and monuments are constantly exposed to a number of potentially damaging elements and activities. Sculptures and monuments may be damaged by everyday activities, such as rain, bird droppings, and people touching, to much more consequential events, such as natural disasters and war. These activities could result in the sculpture or monument becoming discolored, eroded, cracked, broken, or vandalized. A sculpture or monument’s inherent vice could also contribute to damage.

Human Activity

Examples of human activity that can have an impact on outdoor sculptures and monuments include, but are not limited to:

• Touching or sitting
• Graffiti
• Food and drink spills
• Vehicular damage
• Relocating or moving
• Pollution
• War or conflicts

Natural Damage

Examples of damage that may occur due to natural forces include, but are not limited to:

• Rain
• Snow and sleet
• Wind
• Inherent vice
• Animal guano
• Animal destruction
• Natural disaster
• Fungus and mold

Treatment Methods

In order to preserve outdoor sculptures and monuments, conservators have developed treatment methods for the different construction materials. When working on a particular piece, conservators have to consider the cultural significance and aesthetics of each piece, which may influence which treatment method is used.

Metal

Outdoor metal sculptures, such as bronze statues, can be treated with organic waxes and resins that help retain color and luster. Sculptures and monuments are cleaned to get rid of any dirt, guano, or pollution that has accumulated. Once the piece is ready, a thin layer of wax is applied to help seal and protect it. The wax is diluted with different solvents to make application easier and can be removed from the piece at a later date. There are different types of wax, such as microcrystalline and carnauba, that apply differently and give differing results over time.

Conservators may also treat metal sculptures with chemicals that remove corrosion, soil, and calcareous accretions to bring back the original form and detail. However, care must be taken by the conservators to protect both themselves and the piece from exposure to these chemicals. Protective gear must be worn at all times. Treatment with these chemicals should be kept at a minimum because overexposure can do more damage to a sculpture or monument’s surface.

Another, more contemporary, treatment method for metal sculptures is laser cleaning. Lasers can break through the accumulation of dirt and debris to restore the original luster of a piece.

Stone

Stone sculptures and monuments may erode or discolor over time due to environmental, mechanical, or applied decay. For treatment, conservators may apply potassium silicate paints that act as a toning material to give a stone-like appearance while protecting the sculpture from further damage. For broken or eroded pieces, composites may be fabricated to fill in the missing parts. These composites can be made of polyurethane and stainless-steel to give structural stability and support to a piece.

Wood

Totem pole showing weathering and fading

Wood sculpture and monuments, such as totem poles, can be especially vulnerable to damage due to the material’s inherent vice. It is recommended to place outdoor wooden objects under the protection of a shelter, if at all possible. This will help slow deterioration and prevent damage. However, if a shelter or covering is not possible, wood sculptures and monuments may be treated with water repellents and preservatives. Borate preservatives are odorless, don’t discolor wood, and aren’t toxic to humans, though their water-solubility may cause them to leach from treated wood. In this case, commercial water repellents can be used to help protect the wood and the preservative.

It is a prefered practice that paints not be applied to wood sculptures and monuments because they trap moisture and may cause more damage. However, if paint needs to be applied, the borate should be applied first, followed by paints, and finished with water repellent.

No Treatment

“No treatment” is a method that has been gaining traction in recent years. By choosing not to treat an outdoor sculpture or monument, aesthetics such as weathering and patinas will be retained. This helps preserve a monument’s history and cultural significance without relying on a pristine appearance.