Edited by Jeanette G. Grasselli
FTIRin 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. I t is
the traditional function of the art restorer, also known as a conservator, to etabilize 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 n a y 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. Photomicrographs of core sample 874A
ANALYTICAL CHEMISTRY. VOL. 55, NO. 8, JULY 1983
W03-2700183/0351-874A$O 1.5010
Q 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 Hoeplner Travers Newton '
Detail of Virgin and Chi keeping with the period of the artwork. 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 conservator may use gas chromatography (GC) and infrared (IR) spectroscopy. While GC is limited to the examination 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 pigments, binding media, and waxes, applications of IR spectroscopy in the museum field have been extremely limited (14).Such investigations clearly have been hindered by cost, equipment availability, problems of sensitivity and resolution, the limita-
Williamstown Regional Art Conservation Laboratory, Inc. 225 South St. Williamstown,Mass. 01267
tions of sample size imposed by the art object, and the extreme complexity of the samples. Until the advent of Fourier transform infrared (FTIR) technology, the minimum sample size required for IR analysis was 0.5 pg. Now, powerful FTIR spectrophotometers measure samples that are three orders of magnitude smaller. Advantages of these instruments include increased optical throughput, a modulated IR beam at the sample (which dramatically reduces sample heating by the IR beam and eliminates the effect of stray light a t the detector), and the capacity for fast signal averaging. These instruments allow the user to quickly analyze nanogram-size samples with little sample preparation and a simple beam condensor (7).Further, these analyses may now be made a t a reasonable cost, as FTIR technology has entered the mid- to low-priced end of the spectrophotometer market. We are now beginning to explore the potential application 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 collection of the Clark Art Institute, the Virgin and Child. The work was unattributed hut presumed to be of the 15th century. This painting came to the Williamstown Regional Art Conservation Laboratory, Inc. for conser-
ANALYTICAL CHEMISTRY, VOL. 55, NO. 8. JULY 1983 * 875 A
CHEmTECH...
3OoO
because a chemist leads so many lives
Figure. z.Spectrum of red material from lower left
vation treatment because the paint layers were flaking from the wooden support. Preliminary examination raised doubts, on the hasis of style, regarding the painting’s authenticity. The manner in which the features were drawn, particularly those of the Christ Child, was not in keeping with practices of the 15th century. The characteristics of the paint surface did not correspond with known qualities of egg tempera painting. The randomness of the punch-work in the halo was For a clear-eyed view of a// the not in keeping with standards of facets of a chemist’s life - subcraftsmanship of the time (8). scribe to CHEMTECH now1 I t was becoming apparent that the painting lacked the quality and CALL TOLL FREE 800-424-6747ru.~aiy1 craftsmanship of a 15th-centurywork. It seemed more likely that the paiutCHEYTECH 1983 ing was a 19th-centurycopy or a reAmerlcan Chemical Soclely 1155 18th Street, N.W. Washington, D.C. 2WM I worked fragment of an original composition. One possible course of acSign me up lor a one-year subscription lo CHEM-I TECH magazine. Ihave indicated subscription cat- I tion, in addition to X-radiography, egov and payment preferences below. I would have been to open up “winUS. Fomign.. I dows” in the surface paint layer to ACS Members‘ os22 OS28 I look for indications of an older work Nan-members (Personal) 0 S 33 0 $ 39 I Inrilutionr, Companies 0 $155 0 $161 1 beneath. This was not desirable, how0 Bill me 0 Bill mmpany I ever, because the now visible painting, 0 Payment BrrlDsBd (Make C m k payable b herican 1 which in its present state has a unique Chemral society) I value to the collection as a study C h a w my: J MaoterCard 7 VISA I piece, would be altered. Card Number 1 Experimental lnlerbank Number-. ExpreDale -I I (MasIwCardonly) At this point we examined paint I Sinat”rrt_~ I samples with FTIR microspectropboNamB I tometry. Using a stereo zoom microJob Tine - I scope to view the work, a minute chip I of a red colorant was removed from Employer -~ .I the lower left corner of the painting Mdress I with a dissecting needle and scalpel. CIII From the upper right quadrant a stale,zIP~ ~ _ _ _ _ _“core” sample (Figure 1) was removed, I ’MembBr tat88 are lor wrsmsl “88 only. permitting the analysis of each layer .lnl(lm11li~on~lmonByoIder, .Foreign pymenl must UNESCOcoupmn8. be made in U.S. s ~ ~ r e o cbyy I of paint from the surface down to the U.S.bank I dren Worderthrovgh y~urrubrcnpbnagsoc”.Aiioow EO 1 wood panel. Artists routinely use muldays lor first copy 10 8vive. 2WSN 1 tiple layers of different colors to
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achieve the desired textures and to produce luminous effects, leading to a three-dimensional appearance. Samples were placed in dimpled microscope slides and covered. They were then taken to the Analect applications laboratory in Utica, N.Y.,for analysis. Samples were prepared for FTIR analysis by the method of Cournoyer, Shearer, and Anderson (7).In this method, individual specks of material, down to 1ng or less, are supported on a salt crystal and placed over an aperture 20-200 wm in diameter. The samples were examined in an Aualect fX6201 FTIR spectrophotometer equipped with an fXK-635 high-sensitivity, wide-band mercury-cadmiumtelluride detector and an fXA-510 aspheric beam condenser. The resulting IR spectra are presented in Figures 2 and 3. If greater sensitivity or a higher signal to noise ratio (S/N) had been desired, a narrow-band mercury-cadmium-telluride detector could have been used. This would yield a factor of 5 to 8 improvement in S/N,hut the useful spectral range would end around 700 wavenumhers. Use of this detector provides faster data aquisition (by reducing the signal-averaging requirements), allows the use of apertures down to 20 @min diameter, and permits subnanogram sample detection. The limitation on spectral range (700 wavenumhers), however, could limit the ability to characterize inorganic components, many of which exhibit spectral features beyond 700 wavenumhers.
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corner
Apenure: 120pm: scans: 512
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 8. JULY 1983
Analysis and Discussion The binding medium in the paint layers for this type and style of painting should have been predominantly
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ANALYTICAL CHEMISTRY, VOL. 55. NO. 8, JULY 1983 * 877A
tempera (9). Investigations of this ure, however, must take into acint the possibility of pollutants m later restorations, The painting ild have been treated many times b a variety of materials. Until reitly, few records were kept on the atments applied to paintings, so ijecture about modifications to a !cific work is based on the practices nmon to specific historical periods. I example, it would have been comIn practice during the 19th century remove the varnish and apply new ers of varnish or oil, either singly or combination. In addition, bide glues gelatin may have been used to conidate flaking paint. I t is also reaiahle to assume that surface d a n may have been retouched or areas vorked in varnish, oil, or tempera,e paint. A sample of red media from the sur:e of the painting’s lower left corner
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gave a spectrum (Figure 2) similar to shellac. This material was in common use in the 15th century and is mentioned in treatises of the time (IO). The “core” sample (Figure 1) from the upper right quadrant included both the ground or priming layer and the paint layers. The white ground layer was applied to the wood panel to make the surface smooth and to provide a proper surface for the paint layers. It also provided a white base layer to reflect light hack through the various paint layers, The priming normally would he composed either of shell white (calcium carbonate) or, more typically for an Italian painting, gesso (calcium sulfate) with an animal skin glue as a binding medium (11). The spectrum in Figure 3a clearly shows the presence of calcium sulfate dihydrate, but the identity of the hinder is uncertain. The paint layer that lies immediate-
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878 A
ANALYTICAL CHEMISTRY,
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JULY 1983
120 pm: sans: 512. (b) 61- layer--apenure: 150 pm: scans: 512. 120 pm: sans: 512. (d) Gold laye+peRure: 80 pm: scans: 1536
ly on top of this white ground layer is Finally, above the red is an excomposed of brilliant blue particles tremely thin layer of gilding. We suspended in a medium. The blue pigwould expect this material to consist ments commonly available to artists in of elemental gold deposited on a sup the 15th century were azurite and natport. The spectrum of this layer, ural ultramarine (lapis lazuli, sodium shown in Figure 3d, is rather weak, aluminum silicates, and sulfides) (E). but hands are clearly evident indicat The spectrum of the blue layer in ing the presence of kaolin clay, wbicl Figure 3h is obviously not that of was a common support used in this lapis lazuli. The prominent band a t period. Gold has no absorption band 2091 cm-' leads us to conclude that in the IR, and its presence must be the pigment is iron(II1) ferrocyanide, confirmed by other techniques. commonly known as Prussian blue. Conclusion Other features in the spectrum appear similar to aged natural resins. There is no solid evidence of an eg: Above the blue layer is a red layer. tempera-type binding medium in tht The spectrum of this red material various samples tested. This is the (Figure 3c) indicates the presence of type of binder that an Italian artist a kaolin clay and an unidentifiedorganthe early or mid-15th century would ic binder. This type of coloring matter, have used. Instead, resin or oil medir sometimes referred to as Lake red, is appear to he the predominant bindir produced by depositing an organic red materials within the paint layers. Oil ,materialonto an inorganic support, did not supersede egg tempera as a then mixing this with a binder. significant medium in Italy until the
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 8, JULY 1983
879A
etropolitan State College, Colorado August 13- 14,1983 STATISTICAL METHODS FOR CHEMISTS: An introduction t o a wide variety of statistical methods in chemistry Faculty: Dr. Robert A . Crovelli, Mathematical Statistician, Resource Appraisal Group, U.S. Geological Survey, i s Project Chief of Probabilistic and Statistical Methodology for Petroleum Resource Appraisal.
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assumptions and applications of statistical methods in chemistry. The student will learn how t o use statistical methods and the appropriate formulas without an emphasis on proofs and arithmetic. Topics are probability distributions, descriptive statistics. sampling theory. statistical estimation, tests of hypotheses, nonparametric statistics, analysis of variance, design of experiments, factorial experiments, linear regression and correlation, multiple linear regression, and statistical computer packages. This intensive course is designed for the chemist who is a beginner in the application of statistical methods. The course text and lectures are carefully coordinated so that the student finishes the course with a complete printed guide for future referencte. FEE*: ACS Members, $ 2 9 5 ; Nonmembers, $ 3 2 5 ; Reduced Rates/Students &. Retirees
LABORATORY AUTOMATION: Micro-, Mini-, or Midi-Computers: How t o choose ...and use ...the right automation equipment Faculty: Dr. Raymond E. Dessy, Professor of Chemistry, Virginia Polytechnic Institute and State IJniversity, is an international authority on minicomputers and microprocessors and their applications to chemical research. He is the author of over IO0 publications. Assisting Professor Dessy will be members of the VPI and SU Chemistry Department Instrument Design and Automation Research Group. Course Synopis: The course shows, through the use of governmental and industrial examples, how t o decide on proper laboratory automation equipment under specific circumstances and how data acquisition and utilization can be accomplished. Your staff scientists will learn the basic philosophies and jargon involved, from ziimple data logging through fully implemented real-time foreground/background computer systems involving multi-programming and multi-taslting. Utilization of dedicated microprocessors and minicomptuters as intelligent nodes with minimum configuration to hierarchical networks involving maximum system configuration is covered. The course is intended for scientists who are involved with laboratory automation at either the bench or managerial level. Some exposure to programming a computer in any language is helpful but not essential. Participants are encouraged to bring their own automation problems with them for discussion with the staff and other course participants. FEE*: ACS Members. $ 4 9 5 ; Nonmembers, $ 5 2 5 . Reduced Rates/Students &. Retirees
ORGANIC CHEMISTRY OF WATER A N D WASTEWATER: An authoritative treatment of organic solutes in water-their origins and reactions Faculty: Dr. E. Michael Thurman. Research Hydrologist, Organic Research Group, U.S. Geological Survey, Denver, Colorado, is active in organic geochemistry, analysis of organic: substances in natural and polluted waters. and the movement of organic pollutants in ground water. Course Synopsis: ‘The course discusses the amount of organic solutes in natural and polluted waters with special emphasis on ground waters. The classes of organic compounds are described including: carboxylic acids, amino acids, carbohydrates, humic substances, and hydrocarbons. Pollutant organics are discussed and their interactions with sediment, water, and aquifer materials, The role of geochemical processes such as adsorption, oxidation/reduction, precipitation, and metal complexation is addressed. ‘The methods of analysis of organic substances, liquid and gas chromatography, mass spectroscopy, nuclear magnetic resonance, as well as other spectroscopic methods are explained. The final session includes problem solving by various analytical approaches A B A / B S degree in chemistry is required. FEE*: ACS Members, $ 2 9 5 ; Nonmembers. $ 3 2 5 ; Reduced Rates/Students &. Retirees Registration: For registration or more information contact: Mr. Carlos Arozarena U.S. Geological Survey
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 8 , JULY 1983
beginning or middle of the 16th century (13).In addition, the Virgin Mary’s robe is entirely painted in Prussian blue, a pigment that was invented in Germany around 1704 and not widely used by artists until a considerably later time (14). Thus the FTIR analysis of the paint materials supports the judgment of the art conservator; i.e., the painting is either a very heavily reworked fragment or an imitation of an early work. As we have demonstrated, FTIR is a practical method for analysis of both organic and inorganic painting materials. Although further testing of this painting would be necessary to arrive at a final statement regarding authenticity, FTIR can quickly provide information on complex painting materials in extremely small samples. The painting remains intact for further study by scientists, historians, and students. It is our hope that further research will be conducted to classify typically used artists’ pigments, oils, varnishes, and other media according to their IR spectra. FTIR may also help the conservator identify modern substances applied to art objects and provide an understanding of the alteration of materials as they age. Acknowledgment
We would like to thank Jean Rosston, former intern at the Williamstown Regional Art Conservation Laboratory, Inc., currently Mellon Fellow in the Paintings Conservation Department of the Philadelphia Museum of Art, for her work in collecting reference materials on this project. References (1) Olin, J. S.Instrum. News 1966,17,1.
(2) Kuhn, H. Stud. Conseru. 1970,15, 12-36. (3) Mills, J. S.“Conservation in the TropICs,’’ Proceedings of the Asian Conference on ConserGation of Cultural Property; 1972, pp. 159-170. (4) Van’t Hul-Ehrnreich, E. H. Stud. Conseru. 1970,15, 175-82. (5) Baer, N. S.; Indicator, N. J.Coat. Technol. 1976,48,58-62. (6) Low, M.; Baer, N. Stud. Conseru. 1977, 22,116-28. (7) Cournoyer, R.; Shearer, J. C.; Anderson, D. H. Anal. Chem. 1977,49,2275. (8) Frinta, Mojmir S. State University of New York a t Albany, personal communication. (9) Johnson, M.; Packard, E. Stud. Conseru. 1971,16,145-64. (10) Cennini, Cenino. “I1 Libro dell’Arte”; Thompson, D. V., Ed.; Dover Publications Inc.: New York, 1933; p. 26. (11) Gettens, R.; Fitzhugh, E.; Feller, R. Stud. Conseru. 1974,19,157-84. (12) Gettens, R.; Stout, G. “Painting Materials: A Short Encyclopaedia”; Dover Publications Inc.: New York, 1966, p. 95 and p. 165. (13) Johnson, M.; Packard, E. Stud. Conseru. 1971,16,145-64. (14) Harley, R. “Artist’s Pigments c. 1600-1835”; Butterworths: London, 1970, pp. 65-68.
