The Analytical Approach Edited by Jeanette G. Grasselli
FTIR in the Service of Art Conservation The problem of separating the authentic from the imitative is one of the great pleasures of art history. Traditionally, it has been the human eye, appraising with a certain educated feeling of the connoisseur, that determined whether a painting was autograph, derivative, or merely fraudulent. It is sometimes difficult, however, to judge the style of a painting due to alterations of the varnish and paint surfaces. Museum paintings of a certain age are often obscured by discolored varnish and old restorations. It is
the traditional function of the art restorer, also known as a conservator, to stabilize any deterioration within the art object such as flaking paint or a weakened support. The conservator may periodically be called upon to remove the uppermost layer of discolored varnish to allow a proper viewing of the colors and forms in a painting. Old, discolored retouchings or repainted areas are removed, missing passages in the composition may be reconstructed, and the painting given a new coat of varnish. Frequently, the conservator needs
information about constituent materials in a painting prior to treatment. Some of the methods now routinely used by the art conservator to examine the object include microscopic examination of the media, wet chemical testing, and X-radiographs (which help reveal hidden damage to a painting). Other analytical techniques may be required if the authenticity of a painting is questioned. Polarized light microscopy, X-ray diffraction, X-ray fluorescence, and electron microprobe analysis will identify the component pigments to determine if they are in
Figure 1 . P h o t o m i c r o g r a p h s of c o r e s a m p l e
874 A · ANALYTICAL CHEMISTRY, VOL. 55, NO. 8, JULY 1983
0003-2700/83/0351-874A$01.50/0 © 1983 American Chemical Society
James C. Shearer J. Shearer Consulting, Inc. 81 Lakeshire Rd. Rochester, N.Y. 14612
David C. Peters Analect Instruments 1231 Hart St. Utica, N.Y. 13502
Gerald Hoepfner Travers Newton Williamstown Regional Art Conservation Laboratory, Inc. 225 South St. Williamstown, Mass. 01267
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Detail of Virgin and Child keeping with the period of the art work. These techniques are well suited to the characterization of inorganic pigments, but they are generally not useful for studying the binding media and organic colorants. To verify the identities of these compounds the con servator may use gas chromatography (GC) and infrared (IR) spectroscopy. While GC is limited to the examina tion of the organic components of
media, IR spectroscopy can be used to characterize both organic and inorgan ic materials. Although some research has been conducted to identify pig ments, binding media, and waxes, ap plications of IR spectroscopy in the museum field have been extremely limited (1-6). Such investigations clearly have been hindered by cost, equipment availability, problems of sensitivity and resolution, the limita
tions of sample size imposed by the art object, and the extreme complexity of the samples. Until the advent of Fourier trans form infrared (FTIR) technology, the minimum sample size required for IR analysis was 0.5 μg. Now, powerful FTIR spectrophotometers measure samples that are three orders of mag nitude smaller. Advantages of these instruments include increased optical throughput, a modulated IR beam at the sample (which dramatically re duces sample heating by the IR beam and eliminates the effect of stray light at the detector), and the capacity for fast signal averaging. These instru ments allow the user to quickly ana lyze nanogram-size samples with little sample preparation and a simple beam condensor (7). Further, these analyses may now be made at a reasonable cost, as FTIR technology has entered the mid- to low-priced end of the spectro photometer market. We are now be ginning to explore the potential appli cation of FTIR spectroscopy to the analysis of art objects, with particular attention to paintings. A Case in Point Our initial investigation centered on an Italian panel painting in the collec tion of the Clark Art Institute, the Virgin and Child. The work was unattributed but presumed to be of the 15th century. This painting came to the Williamstown Regional Art Con servation Laboratory, Inc. for conser-
ANALYTICAL CHEMISTRY, VOL. 55, NO. 8, JULY 1983 · 875 A
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