Philadelphia Museum of Art

Scientists at the Philadelphia Museum of Art (PMA) bring an eclectic background to the relatively young field of art conservation and authentication. Chemistry, art history, studio art, and historic preservation go hand in hand with expertise in pigments and varnishes, metal corrosion, and biochemistry. Add to that forensics – as it relates to ancient artifacts – and an interest in researching artists’ techniques through the ages, and you’ll have an idea of what a typical research project at the PMA requires of its scientific personnel.

“This work draws on so many different specialties,” Senior Scientist Beth Price says. “The Museum collection includes everything from chocolate to plastics.” For example, Naum Gabo’s Construction in Space with Two Cones (1927) is made of degraded or deacetylated cellulose acetate, an early plastic. A Dieter Roth portrait is a bust made of chocolate (1960s).

Compositions – Revealing the Secret Ingredients in Works of Art

Working with colleague Dr. Ken Sutherland and a department of art conservators, Beth’s analysis of the Museum’s collection has included painted, carved, sculpted, fabricated, woven, or printed works of art. These works are from many different time periods, locations, and schools of art.

Some artists used vibrant tempera paints whose composition included egg yolk. Tin and silicate were used to add weight to silk. Photographers printed richly detailed photographs on albumen and gelatin papers. Other artists used specific pigments known to have been used for thousands of years or, in the case of pigments such as emerald green, only since the 19th century.

Often artworks have undergone restoration or alteration in the past. Many factors are considered and many minute details revealed, such as the repositioning of an ear in Portrait of an Elderly Gentleman painted in the 1400s by Renaissance artist Vincenzo Foppa. He also left his fingerprints in the paint.

Combining Analytical Techniques

While Beth and Ken each have their specialties, they employ a variety of analytical techniques and often look at the same piece together. They are also co-authors on several papers.

Ken primarily uses mass spectrometry in his work, and recently examined varnishes on the Portrait of a Lady in Black by the artist William Merritt Chase, which incorporate the insect resin shellac.

“It is unusual to find this material as a picture varnish,” Ken explains.

Beth and Ken both work with SEM, and have imaged starch grains used for different types of matte finishes on photographic prints from the late 19th and early 20th centuries.

Beth has analyzed the metal composition of a Germain silver soup tureen owned by Catherine the Great.

The pair has examined paint layers on Pontormo’s Portrait of Alessandro de’ Medici, completed between 1534-35.

Their primary tools are Fourier transform infrared microspectroscopy, gas chromatography mass spectrometry, x-ray diffraction, and scanning electron microscopy using secondary and backscattered electron imaging and energy and wave dispersive spectroscopy.

Stewards for 247,000 Works of Art

The PMA is the third largest art museum in the United States, comprising 200 galleries. It is one of only 18 U.S. art museums that can boast its own scientific lab. It houses over 247,000 works of art, ranging from medieval arms, armor, and tapestries to Flemish and Dutch paintings and an entire Chinese reception hall from the Ming Dynasty. Each piece is exhibited carefully and tended by the Conservation Department.

Scientific research helps guide the Museum in authenticating potential acquisitions, restoring damaged artwork without compromising the original materials, learning about an artist’s materials and techniques, and preserving the collections for generations to come.

Exposure to the environment and even time takes its own toll, altering the chemical composition of the materials. “Changes in material composition over time makes the study of works of art challenging,” Beth adds.

130 years ago last May (2007), the Museum permanently opened its doors in response to the enthusiasm generated during the great 1876 Centennial Exposition. Like a massive Greek temple, the dolomitic limestone building sits on hill overlooking the Schuylkill River and Benjamin Franklin Parkway, one of the main avenues into the heart of Philadelphia.

Priceless Sample Extraction Made Easier In House

To support its extensive conservation treatments, the Museum purchased the JEOL SEM model JSM-6460LV in 2003 with funds provided by The Neubauer Family Foundation. The SEM lab is situated on the main floor of the massive building, down a long hallway behind the exhibition galleries. Ken’s and Beth’s work is time consuming, meticulously done, and carefully archived. A fleck of paint, barely noticeable on the JEOL sample stub, is the result of careful extraction from a priceless work of art.

“The samples are taken with a surgical scalpel or tungsten needle from an area near a loss, or a damaged area. One needs a very steady hand!” Beth explains. “We typically split the sample: one half is reserved for chemical analysis and the other half for examination by SEM as a cross-section in polyester-polystyrene matrix.” When they are done with the sample it is logged into a database and remains carefully stored for future analysis.

Database Management Crucial to Analysis

Through the years, Beth and Ken have created their own collection of ideas, discoveries, and information garnered from their careful analysis of priceless artworks. They have collected numerous reference materials to significantly supplement their subset of the historic Forbes Pigment Collection housed at the Fogg Art Museum.

Juxtaposed to this set of colorful reference materials shelved on the wall in their office are the computers, where Beth logs onto the Infrared and Raman Users Group website (www.IRUG.org). Here, she accesses an IR spectral database of artist’s materials that provides a central, searchable, readily accessible compilation for the museum and academic communities. Beth serves as a chair for the organization, which encourages sharing of data and information throughout the art world.

“Museum scientists are not able to purchase all the commercial IR libraries that are out there,” she explains. Accessing the information can be cost prohibitive because the range of materials they analyze is so broad. Moreover, the commercial libraries do not cover aged artists materials.

“The growing IRUG database contains almost two thousand spectra of materials specific to the world’s cultural heritage. The data have been contributed by over a hundred and ten institutions worldwide.”

EDS Detection: From Atget’s Gold-toned Photographic Prints to Details on a Tibetan Altar

A combined project resulting in a book published by the PMA concerns the albumen and gelatin prints of Eugène Atget’s photographs. Atget perfected a technique for printing images of Paris streetscapes, parks, and people between 1890 and the 1920s, producing unparalleled sharpness and clarity. Among Atget’s admirers was Berenice Abbot, who later reprinted many of Atget’s negatives.

The range of materials used by Atget and Abbot has been a topic of Beth’s and Ken’s careful research and publication. They determined the structures of the papers and the composition of the binders, some of which were formulated with rice starch to attain different degrees of matte finish. These can be seen in low kV SEM images at 2000X magnification. While the photographic images that are carefully preserved speak volumes about time and place, the SEM images speak of technique and composition of a different nature,.

Atget’s use of gold toning for his albumen prints in the Museum’s collection was confirmed by EDS. In the 19th century, the process of treating a photographic print with a solution of gold chloride (AuCl) resulted in partial replacement of silver image particles, lending the images a deep, rich sepia tone.

A more recent project is of a quite different nature. A 19th century wooden Tibetan altar over 10 feet in height and six feet in width arrived at the Museum in 2004 in 76 pieces, covered with soot from countless burnt offerings. The goals of conserving this piece included reconstruction to reveal the brilliant red, green, blue, and white colors of the distemper paint underneath the soot and grime, and examination of the paint structure and hidden decorations.

For this project, Beth had the assistance of Xian Zhang, an intern from Boston University, whose research studies for her Ph.D. focused specifically on yellow flavonoid colorants. Xian determined that the yellow coating applied over flake brass and tin leaf to imitate gold was berberine from Berberis tibetacae.

The Tibetan altar was washed in a thin base coat of red pigment under its bold overall coloring and brightly painted, ornate panels. Red paint often denotes a religious context. SEM of paint layers revealed hidden details in the decoration while EDS helped detect emerald green and synthetic ultramarine pigments thus suggesting that the decoration originated in the mid 19th to early 20th century.

The altar conservation is a work in progress that is now spotlighted in the Museum’s Asian art gallery while the pigment research is part of an ongoing PMA project to establish a database for the dating of Tibetan painted artifacts, and to explore the introduction of western pigments into Tibet.

Following Inspiration

Prior to purchasing the JEOL microscope, Beth and Ken used one at the corporate research laboratories of nearby Rohm & Haas Company, which has a long-standing commitment to allocate scientific resources to the PMA.

It’s now easier to have the SEM at hand in the Museum where inspiration can follow its own path down the hallway to the laboratory, for quick analysis of an infinitesimal fleck of an artistic masterpiece.

To see more on conservation at the PMA, visit www.philamuseum.org/conservation.