FTIR in the service of art conservation - ACS Publications - American

weakened support. The conservator may periodically be called uponto re- move the uppermost layer of discol- ored varnish to allow a proper viewing...
0 downloads 0 Views 6MB Size
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

.---------------_-_

I

~~

~

~~~

~

~

~

p

~~~~~~

~

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.

~~~

-----------------8781

corner

Apenure: 120pm: scans: 512

There are dozens of journals devoted to chemistry, but only ONE magazine devoted to chemists CHEMTECH. This stimulating monthly magazine reports on world concerns and personal ones - technology, economics, energy, environment, and much more - a s they concern chemists. And it covers the field of chemistry itself with insight, perspective, a flair for selecting what‘s important and packaging it in authoritative, readable form.

-

too0

2oM)

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

WITH OVER 400 JARRELL-ASH ICP'S INSTALLED WORLDWID TO BE AN APPLICATION If you have a difficult applications problem, you may not care that larrell-Ash has the broadest line 6f ICP spectrometers. What you want to know is whether one of ours can be set up and runjust to handle your individual analysis problem That's where experience counts. Jarrell-Ash experience. And technical expertise. Here's a sample of a few of our installations. See how close we come to yours. GEOLOGICAL MAPPING. For the USGS, ICP analysis of mountain streams maps t tion of mineral depocitq

10

Oil companies measure the levels of nickel and vanadium which inhibit the cracking process in crude oil SEWAGE. The State of New York looks for toxic metals in sewage and sludge using ICE DRY CELL BATTERIES. Manganese poisons nickellcadmium and lead dry cells. Prest-0-Lite uses ICP to make sure that starting materials are manganese-free. OIL EXPLORATION. Anaiysis of surface samples indicates the presence of oil hundreds of feet below the surface. NUTRITION. ICP analysis of h a r can diagnose the nutritional state of human subjects.

40 5

6

7 "

of micronutrients in soil samples.

17 PLATrNG BATHS. ICP '18 measure the level of precious metals in plating

measure mercury levels in fish,

can

CHEMICAL QUALITY 1 0 CONTROL Monsanto, Dow and Union Carbide check

baths.

0

BABY FOOD QUALITY. 1 9 When Mead-Johnson certifies the nutritional element

the purity of laboratory and industrial chemicals. MEDICAL IMPLANTS. The FDA makes sure there there are no toxic metals in cardiac pacemakers, catheters and other implantables. EXHAUST EMISSIONS. 0 ICP helps engineers reduce the toxicity of exhaust at Ford,

cohtent of their baby foods, it's ICP results that stand that guarantee. PHOTOO ~ H I C MATERIALS. Kodak uses ICP to measure the levels of silver metal in film and paper.

A 211

Mines use our IC to assay minerals and ores.

3

DRUG EVALUATION. Hoffman-LaRoche checks drug -.uuritv. with ICP. INDUSTRIAL.EMISSIONS. The EPA tests air quality with ICP.

SOIL EVALUATION. Farmer's coopera8 tives measure the level

k

20-

12

and General Electri analysis of engine lubricants

h

insects by measuring the trace element composition of their

1

are wearing. of Starting materials for s ceramic, epoxy and glassy carbon production can be measured for fracture-inducing elements. SULFUR IN COAL. Steel mills assay coke for sulfur and other elements that

15

L

OUT PLASMA

and

.

applications notes in your area of interest, please call or write Jarrell-Ash Division, Fisher Scientific company, 590 Lincoln Street, Waltham, MA 02254. (617) 890-4300.

4

Jarrell-Ash An&ED

Company

C l R W 110 ON READER SERVICE CARD

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

chemical technicians

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-

MODERN CHEMICAL TECHNOLOGY is a unique, hands-on, practice-oriented program developed and newly updated by the American Chemical Society. It’s a concise, seven-volume practical approach to chemistry for both students and on-the-job, degreed technicians and a valuable set of reference manuals as well. Students and technicians focus on a wide range of practical applications of theoreticat concepts...and cover sampling, analytical, and instrumentation techniques.

01

0

441

15

Wavenumber (cm’) ... ..

Cost effective. Thorough. Unique. For complete information, write or call collect: AMERICAN CHEMICAL SOCIETY Division of Education 1155 Sixteenth St.,’N.W. Washington, D.C. 20036

Wavenumber (an-’)

gure 3. Spectra of core sample

PHONE: 202/872-4588

878 A

ANALYTICAL CHEMISTRY,

white layw-pwture: Red layer-ertue:

VOL.

55,

NO. 8.

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

r

"The

Project SEED summer program gave me a chance to learn about research

This summer, thanks to Project SEED, over 130 economically disadvantaged high school students like Angela Odom had a chance to work and learn in a number of academic research labs throughout the U S .

4 400

Your contributions, which are ised 100% for student sti>ends, are needed for SEED ;o continue helping students prepare for making vitally important decisions about their Future education and work. 1111111111

Project SEED ACS. 1155 16th St., N.W. Washington, D.C. 20036

Yes, I'd like to help these students learn what is required for success as college students.

... 15M) Wavenumber (cm-')

loo0

,

(1

400

Name: 4ddress -

Eontribution: 1850 0 5 2 0 0 5 1 0 1Other 1111111111

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.

I

I

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

National Water Quality Laboratory 5 2 9 3 Ward Road, Arvada, CO 80002 (303) 2 3 4 - 4 9 9 2

I

Registration Deadline: July ZG, 1983

880A

Dr. Tom Zamis Colorado School of Mines __ Chemistry/Geochemistry Department Golden, CO 8040 I , (303) 273 - 3 6 3 9 * / t includes r e g i s t r a t i o n to t h e 25th Rocky M o u n t a i n Conference

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.