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Published: June 28, 2011
Most any old object provokes questions: What is it? Who made it? When and why? What is it made of? Is it authentic? Other questions arise as to condition and possible restoration. The answers have long been found in traditional resources, such as research, documented history, family lore, examination and comparison with similar objects.
Each of these resources has great value, but none is precise. Recent advances in technology, however, now permit much more accurate assessments and deeper understanding of material and culture. State-of-the-art scientific conservation facilities have sprung up at museums around the world. One such site is the Scientific Research and Analysis Laboratory (SRAL) at Winterthur.
It is a serendipitous convergence in which science and art have met at Winterthur, Henry Francis du Pont’s Nineteenth Century country estate in the Brandywine Valley. Back in the 1930s, du Pont’s family’s corporation, DuPont, advertised itself with the slogan “Better Living Through Chemistry.” Around the same time, du Pont, collector and family scion, established the Winterthur Corporation, a nonprofit, educational organization based at his family’s home. His goal was to create a museum to house his formidable collections.
By 1941, Winterthur was open to limited view and by 1951 it was up and running as a museum. Today, the collections number some 90,000 objects in the museum and another 100,000-plus rare books and prints in the library. Such a vast collection requires care and conservation and the museum’s SRAL responds readily to those requirements.
Dr Jennifer L. Mass, director and senior scientist of the Winterthur SRAL, outlines the questions posed by objects in conservation. She likens the process to a detective story. Briefly, there is decay, which presents mystery, sometimes deception, and then analysis, sometimes comparison, leading to understanding. Dr Mass explains that in some restoration processes, information may be lost; in forensic study, however, something is always gained.
She notes that a piece of furniture from about 1710‱720 can have 15 to 25 layers of surface. Study of Nineteenth Century weathervanes indicates that not all gilded objects were stripped to facilitate re-gilding. Some vanes may have up to seven or eight layers of gilding or paint decoration, one on top of another. Dr Mass has also observed many kinds of prior “restorations” †actually, false patinations †that involved painted-on “verdigris.”
A conservation scientist is a chemist, geologist, physicist, biologist and engineer who is engaged in the preservation of our cultural heritage. They operate under the medical axiom, “First, do no harm.” The goal is minimal intervention. The essential function of the scientific conservation laboratory is to assess age, condition, method and materials of construction, and the history and authenticity of irreplaceable objects in the least invasive way possible. No small task.
From these findings, appropriate conservation methods are formulated, and these are meant to be reversible, as future discoveries in scientific conservation may bring new treatment methods.
Winterthur’s SRAL is unique among other scientific conservation laboratories in that it is also a teaching and research facility. In conjunction with the University of Delaware, it is part of the art conservation department that awards master’s and doctoral level degrees in art conservation and preservation studies, in addition to the American material cultural program.
One of the best-equipped facilities in the country, Winterthur’s SRAL boasts an impressive array of equipment worth several million dollars: two x-ray fluorescence spectrometers, a scanning electron microscope with x-ray microanalysis capabilities, a Fourier transform infrared microspectrometer, a Raman microspectrometer, a liquid chromatograph mass spectrometer and a gas chromatograph-mass spectrometer. The devices allow analysis of the surface layers of an object, identifying and often dating any restorations or enhancements.
It is in this laboratory that chemistry, the goose that laid the golden DuPont egg, comes full circle. The tools are several. X-ray fluorescence spectrometers (XRF) permit the noninvasive identification of the elemental components of pigments, metals, glass and ceramics and stone.
Raman microspectrometry allows for the molecular identification of materials of manufacture. Pigments can be analyzed and age can be determined.
The Fourier transform infrared microspectrometer (FTIR) allows scientists to determine the molecular composition of pigments, metal corrosion products, varnishes, adhesives and paint binders, which allows a more precise dating of objects. It is also used to make accurate identification of restoration materials.
The gas chromatograph-mass spectrometer identifies trace molecules thought previously to have disintegrated beyond recognition. It can identify the presence of a specific organic material, such as dammar resin or linseed oil.
When dirt of the centuries clings to an object, cleaning is required. Now technology allows conservation scientists to identify paint pigments and their components and recommend the least invasive, least detrimental method of cleaning an object.
Winterthur’s SRAL also prepares objects for exhibition, affirming their authenticity and helping undo prior restorations. As an example, Dr Mass notes that a Meissen tureen from the Campbell collection bore a decorative pattern from the 1730s. Analysis proved, however, that the overglaze was of a Nineteenth Century composition and the tureen was relabeled. Such discoveries always lead to a correction of exhibit labels.
The laboratory also accepts analysis projects from area museums and private collections, usually those related to the Winterthur collections. A case in point is an assessment of the degradation of cadmium yellow pigments in Henri Matisse’s “Joy of Life” with the goal of appropriate restoration.
Another example was the assessment of the Liberty Bell before it was moved to a new pavilion at Independence National Historical Park in 2003. The SRAL was commissioned to analyze the metal of the 2,000-pound piece and found that it was made of 70 percent copper, 25 percent tin and smaller amounts of lead, zinc, arsenic, gold and silver. It is the high tin count that renders the bell brittle and susceptible to cracking when rung.
In the case of the Matisse painting, the SRAL staff made use of XRF, Raman spectroscopy, infrared spectroscopy and scanning electron microscopy to identify the yellow pigments and to study the cause of their deterioration. The project was undertaken for the nearby Barnes Foundation, which owns the picture the artist painted in the winter of 1905-1906. The SRAL study found that the cadmium sulphide used by the artist was not processed correctly †it needs to be heated to 600 degrees in order to be stable. Chemists were only just learning to make synthetic pigments at this time and did not always use the best methodologies. Matisse and other artists of the time did not always have the money to purchase unadulterated best paints. Substandard materials are a frequent element in deterioration. Research continues to find a way to halt the degradation and to stabilize the painting.
SRAL also facilitated the discovery of N.C. Wyeth’s dramatic illustration of “The Mildest Mannered Man,” executed for a 1919 edition of Everybody’s Magazine. Analysis revealed that Wyeth had reused the canvas, and that the illustration lay beneath a study for a family portrait. The process used by the department revealed patterns of pigments not visible on the surface, but that are consistent with other known images. Dr Mass reports that roughly one in ten canvases has another painting beneath the surface image.
Winterthur’s SRAL has also examined colonial American silver to understand the provenance and methods of manufacture. Eighteenth Century American silver pieces often exhibit buried fire-scale that emerges over time, resulting in a layer of copper oxide that cannot be easily polished out. SRAL metallurgy studies continue and soon sound procedures to more easily date metals will be in place.
Dr Mass is a highly trained chemist with a doctorate in inorganic chemistry. But, growing up outside New York City, she made frequent visits to the city’s museums and was drawn to what she saw. Although she concentrated on science in college, she also studied art history and was hooked. For her, the SRAL post is the perfect combination of art and science.
Over the course of her career at Winterthur some of the most interesting objects she has assessed are painted furniture. Protein-based paint, often misnamed milk base paint, was used in New England painted furniture from Taunton and Saybrook, and was a traditional method probably imported from England.
Pennsylvania painted furniture is more likely to have oil paint, although distemper decoration, brought there by German craftsmen, has also been identified.
Dr Mass has also conducted studies on ancient Roman and Egyptian glassmaking practices at the Metropolitan Museum of Art.
XRF analysis of a rare glass beaker produced by John Amelung at Maryland’s Eighteenth Century New Breman Glass Manufactory was conducted. Interestingly, the analysis revealed a high potassium and high manganese content, and the absence of lead. The analysis established a “map” of the chemical components of the products produced at one of America’s most important glass factories. Because of the rarity of Amelung pieces, keepers of collections all over the country are interested in authenticity, says Dr Mass.
Several objects in this year’s “Paint, Pattern and People: Furniture of Southeastern Pennsylvania” exhibition, organized by Winterthur curators Wendy A. Cooper and Lisa Minardi, were studied in the SRAL. XRF analysis was carried out on five Winterthur pieces of Mahantongo furniture, determining that the primary color in the blue and green fields is Prussian blue. The presence of lead and chromium in the yellow areas indicated the use of chrome yellow, which was commercially available only after 1818. Copper was found in two green areas, confirming the presence of a copper green pigment.
More recent studies by Dr Mass of the origins of chrome yellow and green paint (chrome yellow and chromium oxide green) often seen on Nineteenth Century Pennsylvania painted furniture revealed that they came from deposits of chromite ore in the Bare Hills and Soldiers Delight sections of Baltimore.
When the SRAL studied a group of Taunton chests, it was found that the chests had been covered with an iron-based, red-brown stain before being decorated inventively in vermillion, copper green, lead white pigments and azurite, a blue pigment that appears black because of its oil base.
The information gleaned from scientific and technological study of objects leads to greater understanding of their makers and owners, and the period and purpose for which a piece was used. From these studies, much is unearthed about our cultural heritage.
Winterthur is on Route 52, five miles south of Route 1. For general information, www.winterthur.org , 800-448-3883 or 302-888-4600.
5 Church Hill Road / Newtown, CT 06470
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