The National Gallery of Art's outdoor sculpture garden was opened to the public in 1999, with 16 modern sculptures by artists such as Alexander Calder, Sol LeWitt, Ellsworth Kelly, and Claes Oldenburg.

​Today the 16 sculptures currently in the garden are a mixture of stainless steel, bronze, aluminum, and stone, with a variety of patinas and painted surfaces. While it is understood that these works of art will age differently than those displayed inside the museum, every effort is made to care for, preserve, and protect the sculptures.  As part of a general preservation plan, each sculpture is treated once or twice per year, most often during the summer months. Objects conservator Katy May is the main conservator in charge of the outdoor sculpture. Under her supervision, objects conservators wash the sculptures with water or a dilute detergent, using sponges or soft brushes.  After very thorough rinses with water, depending on their composition, the sculptures are either dried or coated with a protective material like wax.