In the fall of 1939, the Philadelphia Museum of Art, under the direction of its curator of painting and sculpture, Henri Marceau, established its first on-site conservation laboratory. Prior to that period, freelance restorers would perform such work on pieces entrusted to the Museum. As Marceau noted in the January 1940 Bulletin, this practice gave the Museum little or no control over the person hired and the resulting work. The new laboratory not only allowed for monitored conservation work but also for technical research that encouraged a scientific approach to the problems of authenticity and identification. Using a variety of photographic methods, including infrared, ultraviolet and X-ray imaging, curators collected evidence about the authenticity of objects owned or considered for acquisition by the Museum, as well as works on loan for special exhibit. Photographic records also allowed for a thorough documentation of an object's condition and all steps of conservation work performed. Other technical shops within the laboratory were equipped for working with wood, metal and stone, and for tasks such as cleaning, relining and restoring paintings on various supports.
The Museum's commitment to a more regimented program of conservation and technical research came at a time when such issues were receiving worldwide attention. Credited with having a profound impact on the approach to object conservation, the Fogg Art Museum established its Conservation Department in 1928 as a center for such work in the field of fine arts. During the 1930s, Marceau, as curator of the John G. Johnson collection of European paintings, was in close contact with the Fogg Museum's head conservator George L. Stout. During that period the Fogg performed much of the conservation work done to many paintings in the Johnson collection. In 1950, the International Institute for the Conservation of Museum Objects was incorporated with headquarters in London. As director of the Museum, Marceau became a fellow member of IIC by at least 1956, and both he and Theodor Siegel, the Museum's conservator, were invited to review journals for one of the institute's publications, IIC Abstracts.
In setting up the Museum's laboratory, Marceau recruited David Rosen to serve as technical adviser. Born in Russia, Rosen studied sculpture and painting in Paris before coming to the United States in 1913 to practice as an art restorer. In 1937 he participated in a meeting of art experts in Paris to discuss the detection of frauds in paintings with the use of scientific methods. Rosen's relationship with the Philadelphia Museum of Art began in 1936 with his conservation of works of art in the Wilstach Collection. He also worked on paintings in the Elkins and McFadden Collections as well as the John G. Johnson. By 1946, Rosen restored 234 paintings in the Johnson Collection and a combined total of 150 works from the other collections. Earning an international reputation as a pioneer in the scientific examination and preservation of art, Rosen also served as technical adviser at the Walters Art Gallery in Baltimore, the Worcester (Mass.) Art Museum and other institutions, as well as private collections such as the George Blumenthal Collection and the Morgan Library in New York. He collaborated with Stout at the Fogg Museum and was a charter fellow of IIC. Rosen had an art conservation and research laboratory in New York City, where he resided as well. At his death in 1960, Rosen was described as the "greatest expert in the field in the Western World." "[T]he daddy of all of them." Measured against today's principles and practices, Rosen's conservation techniques have been criticized for being too intrusive and sometimes incorrect, requiring some of his projects to be reversed.
In the spring of 1955, the Museum expanded its Department of Conservation and Restoration. In addition to increasing its workspace and equipment, the Museum also hired a conservator, Theodor Siegl. The following year an assistant joined the staff, and during the 1956-1957 season, a total of 253 paintings were treated. Again, compared to today's practices, such a heavy workload, apparently supervised by Rosen, would be considered overly ambitious. By 1964, the department consisted of Siegl, an assistant and two volunteers, and a total of 139 objects in all categories were treated. Siegl continued to head the department until his death in 1976.