The Technical Analysis of a Known Forgery - American Chemical

Chapter 1

Downloaded by 41.143.255.77 on April 18, 2016 | http://pubs.acs.org Publication Date (Web): July 10, 2012 | doi: 10.1021/bk-2012-1103.ch001

What’s Wrong with this Picture? The Technical Analysis of a Known Forgery Gregory D. Smith,*,1 James F. Hamm,2 Dan A. Kushel,2 and Corina E. Rogge2 1Indianapolis

Museum of Art, 4000 Michigan Road, Indianapolis, IN 46208 2Art Conservation Department, 1300 Elmwood Avenue, Buffalo State College, Buffalo NY 14222 *E-mail: [email protected]

Robert Lawrence Trotter was convicted in federal court in 1990 of producing and selling fake American primitive style folk art. A methodical ‘reverse engineering’ of one of his confiscated paintings, Village Scene with Horse and Honn & Company Factory, was undertaken to determine what telltale signs might exist to identify this work as a forgery. Currently 39 other Trotter fakes are yet unaccounted for and are potentially circulating on the art market or belong to private or institutional collections. A crescendo approach to the critical examination of this painting began with a simple visual assessment followed by diagnostic imaging using X-ray, near infrared, and UV radiation sources. Non-sampling chemical analysis with X-ray fluorescence and Raman microspectroscopies was conducted next to determine specifically the forger’s materials. Finally, additional information was gathered from invasive sampling approaches including cross section analysis, FTIR microspectroscopy, and pyrolysis-gas chromatography-mass spectrometry. Copious clues to the work’s inauthenticity exist at every level of investigation. Although simple visual examination would raise questions as to the artwork’s genuineness, diagnostic imaging and chemical analysis prove beyond a doubt that the work is a modern fake. Anachronistic pigments and improbable construction techniques are evidence that this is not an authentic piece of 1860s folk art. © 2012 American Chemical Society Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Introduction In 1990, Robert Lawrence Trotter was sentenced to ten months in federal prison for a decade long scheme that involved the production and sale of fake American 19th-century primitive style paintings (1–3). By his own admission, Trotter conducted fifty-two sales of his fakes and forgeries from 1981 to 1988 involving six art dealers and twenty-nine auction houses in eleven states. His ill-gotten gains were in excess of $100,000 (1), although some of his earliest fakes sold for paltry sums, one for only $36 (1, 2). The actual crime to which he pled guilty was wire fraud related to these transactions (2). Trotter’s familiarity with the art and antiques market in the early 1980s made him aware of the innumerable fakes that exist, especially in the primitive or folk art style. Being an amateur artist himself, he joined in the production of bogus artworks in order to augment his income. Initially these generic, anonymous folk art pieces fetched only modest sums at auction and attracted little attention. His works included typical folk art scenes and sitters, and he utilized a pastiche of the physical characteristics admired in many styles of folk art to enhance the appeal of his forgeries. In 1988 Trotter, being impatient with the trivial earnings of his fakes up to this point, left the relatively safe confines of low value, anonymous primitive art and began directly imitating the styles of well-known 19th-century folk artists such as M. W. Hopkins, Ammi Phillips, and Noah North, and finally the artist best known for his trompe l’oeil paintings, John Haberle. These more ambitious attempts came to the attention of the community of scholars and collectors specializing in these artists’ works, and their authenticity began to be questioned. Because of suspicions regarding Trotter’s fake ‘Haberle,’ the FBI established a sting operation that ultimately caught him red-handed. Dan Hingston, an auction manager caught up in the scheme, noted, “We’re lucky Trotter raised the stakes. If he’d stayed at this level [anonymous, generic folk art], he could still be doing it (2).” Of the fifty-five fakes he produced, only sixteen of these works were located by the FBI in their investigation (1). Moreover, only five of these identified works were seized by the Bureau or turned over to it as part of Trotter’s compensation settlement. One of these paintings, known as Village Scene with Horse and Honn & Company Factory, which was signed “Sarah Honn,” and dated “May 5, 1866 A.D.,” was actually painted by Trotter in 1985 and ultimately was given to the Art Conservation Department at Buffalo State College by the courts in 1991 to be used for study and research (1). This landscape painting is shown in Figure 1(a). With thirty-nine of Trotter’s fake paintings still unaccounted for and likely circulating on the art market or part of private or institutional collections, the Buffalo State College faculty decided to undertake a comprehensive study of the work to determine what signs might point a conservator or curator to question its authenticity. This is particularly important since the current condition of the Village Scene painting is poor and has noticeably worsened in the intervening years, likely the result of the techniques used by Trotter to enhance its aged appearance. Based on this observation, it is reasonable to assume that others of Trotter’s oeuvre will likely be brought to conservators for stabilization, cleaning, 2 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


and treatment if they haven’t already been restored – many of his works were immediately taken by their new owners to restorers (2). This investigation brought together the combined expertise of paintings conservators, conservation scientists, and imaging specialists. The approach to the examination began with the simplest form of exploration, namely close critical observation of the painting’s composition and obvious physical construction. This level of investigation is available to all conservators, curators, and collectors. Next, macroscopic imaging techniques familiar to art conservators and forensic investigators were used to capture images of the artwork using X-ray, near-infrared, and UV radiation sources. These images provide complementary information on the artist’s working methods, the condition of the artwork, and hidden aspects of its construction. Finally, scientific analysis, first using only non-destructive methods and later techniques that required sampling from the artwork, were utilized to explore the materials used by the forger and to compare them to what would be expected for a true 1860s folk art painting. This level of investigation is only possible at the most technologically sophisticated cultural heritage institutions, although motivated clients could arrange for contract analysis of their paintings.

Experimental Section Imaging Techniques Color photographs were acquired using a Sinar view camera with a Better Light digital scanning back CCD trilinear array with 3200 K incandescent illumination. Ultraviolet-induced visible fluorescence images of the painting were captured with a Nikon D100 digital camera (CCD array) with Wratten 2E and CC40Y filters. The camera was adjusted to white balance 7000 K and Adobe Camera Raw® tint +11. The source of UVA radiation (315 to 400 nm) was a pair of high-pressure mercury lamps filtered of their visible emission lines. A near infrared (NIR) image in transmission mode was acquired with the digital scanning back mentioned above, but modified with a Wratten 87C visible blocking filter, thus restricting the camera sensitivity to 850 to 1000 nm. The painting was exposed to NIR radiation from incandescent photo lamps directed onto the verso with the camera capturing the radiation transmitted through the painting. A radiograph of the painting was recorded on Kodak Industrex Rapid 700 radiographic paper. The Philips X-ray tube voltage was 30 kV and exposure was 525 mA•sec at a 60 in. film-focus distance. The radiograph of the experimental canvas mock-up discussed below was recorded on Kodak Industrex M100 film using the same experimental parameters. Digital versions of all images were adjusted in Adobe Photoshop for color correction, tint, exposure, mosaicking, and sharpness as necessary. Microfocus X-ray Fluorescence (XRF) X-ray fluorescence spectra were collected using a Bruker ARTAX energy dispersive X-ray spectrometer system. The excitation source was a molybdenum 3 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

target X-ray tube with a 0.2 mm thick beryllium window, operated at 50 kV and 600 mA current. The X-ray beam was directed at the painting through a masked aperture of 0.65 mm diameter. X-ray signals were detected using a Peltier cooled XFlash 2001 silicon drift detector. Helium purging was used to enhance sensitivity to light elements. Spectra were collected over 60 sec live time.


Raman Microspectroscopy Raman spectra of pigments were acquired using a Bruker Senterra microscope suspended on a Z-axis gantry. The ‘Z-stage’ allowed the entire artwork to be placed directly under the 50X ultra-long working distance objective of the microscope. Excitation at 785 nm and 1.1 mW power at the laser focus was used to stimulate Raman scattering from an area of approximately 1-2 μm diameter. To reduce the interference due to fluorescence, an area of agglomerated pigment particles was chosen in an exposed fissure in the paint film. The resulting spectrum was measured at 3-5 cm-1 spectral resolution with several hundred seconds of spectral coaddition. The pigment’s identity was ascertained by comparing its spectrum to those of likely reference materials. Sampling and Cross Section Preparation Paint samples were acquired from the painting under a stereomicroscope at low magnification using chemically etched tungsten needles and a surgical scalpel. Sampling was limited to existing areas of damage, abrasion, or cracks. Disperse samples of pigments and media were collected as surface scrapings or small paint flakes from a specific area or paint passage, and these were stored on glass well slides under cover slips until analyzed. Cross section samples were acquired by cutting vertically through the varnish, paint, and ground layers to the underlying canvas substrate using a 500 μm tip microchisel (Ted Pella). The sectioned sample was generally less than 100 μm in the long dimension. These samples were mounted in Ward’s Bio-plastic™ polyester resin. Once the embedding medium fully cured, the plastic block was cut and polished on a series of Micromesh™ cloths to expose the painting’s cross section. Darkfield images of the sectioned samples were acquired on a Zeiss AxioImager A1m compound microscope with a 20X objective using an MRc5 digital photomicrography camera. The same area was then examined under UV irradiation for signs of visible luminescence. A DAPI filter cube set allowed narrowband excitation between 325 and 375 nm with observation throughout the visible spectrum (λ > 412 nm). Fourier Transform Infrared (FTIR) Microspectroscopy Infrared spectra were collected using a Continuum microscope coupled to a Magna 560 FTIR spectrometer (Thermo Nicolet). Samples were prepared by flattening them in a diamond compression cell (Thermo Spectra Tech), removing the top diamond window, and analyzing the thin film of sample in transmission mode on the bottom diamond window. An approximately 100 μm square 4 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

microscope aperture was used to isolate the sample area for analysis under a 15X Schwarzschild objective. The spectra are the average of 32 scans at 4 cm-1 spectral resolution. Correction and subtraction routines were applied using the instrument’s Omnic software as needed to eliminate interference fringes, sloping baselines, or peaks from interfering spectral components. Sample identification was aided by searching a spectral library of common conservation and artists’ materials (Infrared and Raman Users Group, http://www.irug.org).


Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) A small scraping of paint was analyzed by Py-GC-MS after derivatization of the sample using tetramethylammonium hydroxide (TMAH). The sample was analyzed using a Frontier Lab Py-2020D double-shot pyrolyzer system with a 320°C interface to an Agilent Technologies 7820A gas chromatograph and 5975 mass spectrometer detector. An Agilent HP-5ms capillary column (30 m x 0.25 mm x 0.25 µm) was used for the separation with 1 mL/min of He as the carrier gas. The split injector was set to 320°C with a split ratio of 50:1. The GC oven temperature program was 40°C for 2 min, ramped to 320°C at 20°C/min, followed by a 9 min isothermal period. The MS transfer line was at 320°C, the source at 230°C, and the MS quadrupole at 150°C. The mass spectrometer was scanned from 33-600 amu at a rate of 2.59 scans/sec with no solvent delay. The electron multiplier was set to the auto-tune value. Samples were placed into a 50 µL stainless steel Eco-cup, and 3 µL of a 25% methanolic solution of TMAH were introduced for derivatization. After 3 min the cup was placed into the pyrolysis chamber where it was purged with He for 3 min. Samples were pyrolyzed using a single-shot method at 550°C for 6 sec. Sample identification was aided by searching the NIST MS library and by comparison to pyrograms of authentic samples.

Results and Discussion Visual Examination On the surface, the painting has all the hallmarks of a highly desirable piece of American folk art from the 19th-century. The scene, Figure 1(a), is a typical primitive style landscape showing a small village surrounded by pastures. The artist appears to be an amateur based on the naïve sense of perspective. The careful observer is rewarded by recognizing a nearly obscured signature in the lower right hand corner of the painting. The autograph, in clear block lettering in brown paint, reads “Sarah Honn May 5, 1866 A.D.” The signature is interesting on several levels. First, folk art paintings are rarely signed, and this picture would be especially valuable because the artist is presumably a woman. History has recorded very few female folk art painters outside of the well known Susan Waters and Grandma Moses. When viewed under the stereomicroscope, it is obvious that the aging cracks run through the artist’s paint as well as the signature, indicating that the two were contemporary and that the entire painting with its autograph aged together. 5 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


The village scene composition might well be a nod to the historical practice of itinerant painters of the mid-19th century who traveled the country drawing or painting a client’s land holdings in return for a small payment or even a place to stay. In this instance, the presence of a small sign over the door of the red brick factory, which reads “Honn & Co.,” adds an interesting twist in that the artist is presumably recording her own family’s property. All attempts to identify a Sarah Honn living in late 19th-century America or a Honn & Co. business were fruitless. This anonymity reveals the forger’s cleverness. Sarah Honn as a person is more believable because of the existence of her place name, and yet being purely fictitious, there are no potential inconsistencies to be discovered by a studious researcher. The verso of the painting, Figure 1(b), provides additional ‘badges of authenticity’ for a gullible collector. The back of the canvas is lined onto a piece of blue-striped mattress ticking, partly obscured by a dark stain, presumably due to mold. Mattress ticking has occasionally been used as a cheap canvas material by itinerant painters and folk artists. However, in this instance the mattress ticking is not the artist’s canvas, but rather a glued relining fabric, which is unique in the experience of the authors. Relining of a worn canvas is a preservation intervention performed when the original is structurally too compromised or weakened to support the paint. Careful examination of the paint surface in raking light showed a friable, undulating paint layer, but no indication of tears or holes in the canvas that would have necessitated relining. The presence of the mattress ticking as a lining fabric is perhaps the most telling outward clue that the artwork has been at least embellished to enhance its desirability. Figure 2 shows a detail shot of the bottom tacking margin, i.e. the lower flap of canvas that is used to tack the painting onto a rectangular wooden stretcher. The upper layer of fabric, the original canvas, is frayed and reveals the blue-striped ticking underneath. The metal tacks, which were removed from their original locations (dashed circles) during the relining, present an improbable situation. The artist’s white priming layer runs over top of both the original tack holes and the tack heads in their current position, suggesting the canvas was removed from the stretcher, lined, re-tacked to the stretcher, and then primed and painted. This necessitates that the painting was relined before the surface image was painted, a situation that makes no logical sense in terms of a painter’s normal practice. Imaging Techniques UV-induced visible fluorescence imaging is a useful survey technique to gauge the condition of an artwork (4, 5). Artists’ paints and varnishes tend to develop fluorophores as they age, giving old paintings a characteristic luminescence when irradiated with long wavelength UVA lamps. Recent areas of retouching over damages or paint losses will not have had the time to develop the same level of fluorescence, thus appearing as darker patches in the fluorescence image. In describing his last criminal endeavor, Trotter mentioned that on the ‘Haberle’ painting he, “. . . used a thin coat of copal varnish. It’s browner and thinner and with a blacklight it tends to throw that even overall glow that can fool people not used to using a blacklight (2).” 6 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 1. Color images of the front (a) and verso (b) of “Village Scene with Horse and Honn & Company Factory,” 40.8 cm x 51.1 cm. Courtesy of Buffalo State College. 7 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 2. Detail of the lower tacking margin showing former tack holes (dashed circles). Courtesy of Buffalo State College.

Figure 3(a) shows a color image of the front of the Village Scene painting when exposed to UVA. It is obvious that Trotter implemented a similar coating technique, since the entire surface of the painting emits an uneven, striated cool fluorescence suggestive of a natural resin coating, although not necessarily a copal varnish, partially obscured by UV blocking dirt and grime. Conservators, however, are very used to utilizing a blacklight, and this image is startling to a highly trained eye for a painting that purports to be nearly 100 years old, has already undergone a relining, and bears extensive mold growth suggesting years of exposure to moist conditions. There are no dark patches in the fluorescence image that would indicate a history of retouching, structural repair, or restoration. Such a homogenous surface fluorescence is unusual unless a forger or dealer is trying to be duplicitous by adding an intentionally concealing surface coating. Figure 3(b) shows the same imaging technique applied to the verso of the artwork. The heavy, seemingly brush applied mold stains are faintly fluorescent, which is not atypical for molds. However, the relining fabric, best seen in the upper right corner, is far more luminescent. Optical brighteners are applied to modern fabrics or are included in laundry detergents to give textiles a ‘whiter-than-white’ appearance. Fluorescent brighteners are a post-WWI invention (6), providing a clear indication that this lining fabric was applied in the 20th-century.

Figure 3. UV-induced visible fluorescence images of the (a) front and (b) verso of the painting. Courtesy of Buffalo State College. 8 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Transmitted NIR photography relies on the transparency of many artists’ materials to long wavelength radiation thus allowing imaging of underlying structures or compositions that include infrared opaque materials (7). Most often NIR examination is conducted to visualize underdrawings or preparatory cartoons executed in graphite or charcoal. In the transmitted NIR detail photograph of the white building on the horizon, Figure 4, there is no indication of a carbon-based underdrawing. The opaque passages are simply those surface features that utilize a carbon containing black paint. It is obvious that the artist painted in the landscape prior to placing the buildings since the horizon line is clearly running behind the central white building. These construction details evidenced by NIR imaging are not an indication of fakery for a primitive-style painting since it is easy to imagine the amateur folk artist painting what they saw in a very spontaneous way without significant planning or sketching.

Figure 4. Transmitted NIR image detail showing the horizon line running through the building and the fine craquelure pattern. Courtesy of Buffalo State College. More importantly, the transmitted NIR image highlights in stark contrast the islands of paint separated by a scaly craquelure. This significant cracking and its evenness across the surface of the painting deviates from the typical age-induced crack patterns observed in old oil paintings. Naturally occurring cracks create a pattern perpendicular to radiating lines of stress originating in the restrained canvas corners, which are often exacerbated by low relative humidity or low temperatures (8). The cracking in Village Scene is similar to cracking that occurs when paint is dried by heat, causing rapid, simultaneous contraction of the entire paint surface (9). Trotter again has provided some clues to the techniques used to simulate aging. He reportedly used “. . . lots of driers [siccatives] …” and would age his finished paintings for a week under a sunlamp (2). No doubt the 9 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


chemical accelerators coupled with the heat from the lamp contribute to the small, even cracking observed in this forgery. In another work by Trotter, a conservator observed under the microscope that the age cracks had actually been scratched into the paint using a sharp stylus (2). X-radiography is often utilized by conservators to image the distribution of heavy metal pigments in a painting. Until the commercialization of a synthetic route to ultrapure TiO2 pigment in the late 1910s, the most common white artists’ pigment was basic lead carbonate [2PbCO3•Pb(OH)2] (10), being the principle white paint, but also mixed into other colors to adjust their value. As a result of this widespread use of lead white pigment, most X-ray images of historic artworks show a ghost-like image of the surface painting, but also reveal underlying artist’s changes as well as abandoned compositions or reused canvases.

Figure 5. Radiograph of “Village Scene”. Figure 5 shows the radiograph of Village Scene. It is immediately obvious that no heavy metal pigments, at least none containing lead, were used to create the surface image as there is hardly any indication of the landscape. A palette devoid of lead white is inconsistent with a 1860s provenance. Moreover, one sees only amorphous, high contrast passages with blurred, indistinct borders unrelated to any figure or structure in the surface painting. In the investigation of the Trotter case, the FBI found that the forger often visited antique shops where he would buy inexpensive period paintings (1, 2). Trotter confessed that these paintings provided him with the old canvas support necessary to produce a convincing 10 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


fake. The application of commercial paint strippers removed the painted image on the authentic canvas, allowing Trotter to prepare his fakes without any telltale underlying textures. The radio-opaque indistinct passages in the X-ray image of Village Scene suggested that remnants of an old lead white containing ground were not removed by the paint stripper, perhaps because the ground was pushed into the canvas weave. The authors produced a mock-up using period canvas with a lead white oil ground which was removed using Zip-Strip® purchased at a local hardware store. After softening the oil paint and scraping it from the canvas with a putty knife, a radiograph of the mock-up, reproduced in (11), was captured using identical instrumental parameters to those used to collect the radiograph in Figure 5. The two images show a clear similarity, thereby confirming Trotter’s reuse of canvas from an old painting for the creation of Village Scene. Noninvasive Scientific Analysis Sophisticated scientific analysis is available to many conservators and curators at larger institutions employing conservation scientists. Even at smaller institutions and in private practices, the availability of a limited number of scientific instruments, optical microscopes, and microchemical testing equipment is common. If such instrumentation is accessible, then the investigator can gain a specific knowledge of the materials used by an artist. For the sake of authentication, or more accurately ‘inauthentication,’ one is typically looking for anachronistic or otherwise undocumented materials or methods for a particular artist, style, or time period being employed in the creation of the suspect artwork. X-ray fluorescence (XRF) spectroscopy is one technique that is widely available, either as a laboratory based microanalytical instrument or as the growingly popular handheld XRF units. The power of XRF lies in its non-invasive nature and the fact that the resulting elemental spectrum can be used to infer the inorganic or organometallic pigments used by the artist. Village Scene was subjected to an exhaustive analysis of the forger’s palette using a microfocus lab-based instrument. When creating his last forgery, i.e. the trompe l’oeil style ‘Haberle’ painting, Trotter is reported to have used standard tube oil colors from an art supply store and synthetic bristle brushes. He is quoted as saying, “I limited my palette to colors Haberle would have had (2).” XRF analysis of the present painting shows that Trotter was less exacting in selecting his paints for this work. Many anachronistic colorants were detected. Figure 6 shows the XRF analysis of the white paint used in the central white structure on the horizon (inset detail). Although one would expect lead white or perhaps ZnO to be used in the 1860s, the latter pigment being available at least since 1803 (10), the strongest peak in the XRF spectrum is in fact titanium. Trotter’s use of TiO2 white explains the transparency of the surface image in the radiograph in Figure 5. Based on this evidence alone, one could confidently rule out the signature date of 1866. Other colorants inferred from XRF data included Prussian blue [Fe4[Fe(CN)6]3•14-16H2O] in the blue window sills, yellow ochre in the yellow buildings and sunset [FeOOH + silicates], and red ochre in the central red building [Fe2O3 + silicates], all of which would have been available to 19th-century folk artists. 11 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 6. XRF spectrum with major element peaks identified for the white paint from the central white building. The inset shows a detail photo of the analysis spot.

In addition to these colorants, XRF revealed low levels of Co in all paints and the ground, Pb in varying amounts throughout the painting, and often concomitant peaks for Ba and Zn. The ubiquitous Co signal may represent a cobalt linoleate or naphthenate siccative added to accelerate the drying of the oil paints as confessed by Trotter. The relatively weak Pb signals in each spectrum are probably due to residual lead white ground left from stripping the reused canvas. When peaks associated with Ba and Zn occur together, this is often indicative of the use of lithopone, a co-precipitated mixture of ZnS and BaSO4 that has been used since 1874 as an inexpensive filler in many paints (10). Although XRF analysis provided potential pigments for most of the colors used in the painting, elemental spectra taken of the green hills showed only the omnipresent Co, Pb, Fe, Ba, and Zn. No metal could be clearly associated with a green pigment. To clarify the nature of the green colorant, the entire painting was placed under a gantry-mounted Raman microspectrometer, and vibrational spectral analysis was performed on the green pasture near the horse. The resulting Raman spectrum, shown in Figure 7(a), reveals numerous sharp spectral features indicative of an organic or organometallic pigment. The spectrum is compared to that of (b) phthalocyanine green, PG7, a chlorinated copper phthalocyanine complex first synthesized in 1938 (12), and a high degree of correlation is observed. However, under the microscope copious intermixed yellow particles were also visible, although they did not give as clear a Raman spectrum as the green component under the experimental conditions utilized. 12 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 7. Raman spectra of (a) green pigment particles and (b) reference phthalocyanine green, PG7.

Invasive Scientific Analysis Small loose fragments of the green paint analyzed above were extricated for analysis by transmission FTIR microspectroscopy. The green paint layer was separated from the other layers under the stereomicroscope prior to preparation for analysis. The resulting spectrum is shown in Figure 8(a) along with reference spectra of (b) polymerized linseed oil, and (c) hide glue. The sample spectrum shows a large oil component as revealed by methylene CH stretching bands at 2923 and 2852 cm-1 as well as the prominent νCO of the triglyceride esters at 1734 cm-1. The broad νOH peak centered at 3420 cm-1 indicates that the oil binder, presumably linseed oil, is well-cured and significantly hydrolyzed. Although Trotter did reveal that he used standard tube oil colors, he never mentioned the addition of a proteinaceous component, which can be presumed present due to the weak Amide I, II, and III bands at 1651, 1533, and 1450 cm-1. There are some verbal indications that Trotter did not always work in oils. At least one fake painting, an image of a ship at sea, is described by the Maine Antique Digest as being “tempera,” suggesting an egg binding medium, and Trotter himself in an interview with the Digest after sentencing cryptically described his first fake as being a “buttermilk paint,” presumable containing a casein binder (2). At this point the rationale for the protein in the green paint, whether intentional or accidental, could not be known. With no clear indicator of the pigments used in the green paint passage based on the FTIR spectrum in Figure 8(a), a spectral subtraction was attempted to remove the overwhelming spectral features of the binding media. After scaled 13 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


subtraction of the reference spectra for linseed oil and hide glue, the resulting residual spectrum is shown in Figure 9(a). Although this spectrum appears quite noisy, a spectral library search yielded a high quality match with the spectrum of Hansa Yellow, PY3, first available in 1928 (12). The spectrum of the pure colorant is shown in Figure 9(b). Because of its high tinting strength, this strongly colored yellow pigment is often mixed with a barium sulfate (BaSO4) filler, which is evidenced here by the sulfate stretching band triplet between 1235 and 1035 cm-1 and the sharp associated peak at 984 cm-1. The spectrum of pure barium sulfate is shown in Figure 9(c) for comparison.

Figure 8. FTIR spectrum of (a) green paint sample compared to reference spectra of (b) polymerized linseed oil and (c) hide glue.

Through a combination of FTIR and Raman analyses, the green paint used for the landscape appears to be a mixture of phthalocyanine green and Hansa yellow, which incidentally is often given the paint color name Permanent Green Hue in the modern artist’s palette (10). Permanent Green was originally a mixture of chrome oxide green with zinc yellow (ZnCrO4), which in fact would theoretically have been available to Haberle in the 1860s (10). It is possible that Trotter may not have been aware that the modern variant no longer uses the toxic chromate containing pigment. 14 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 9. FTIR residual spectrum of (a) green paint after subtraction of linseed oil and hide glue reference spectra. Comparison is made to reference spectra of (b) Hansa Yellow (PY3) pigment and (c) barium sulfate.

To assess the nature of the surface coating, a thin scraping was carefully removed from the area of the horse’s pasture without disturbing the underlying green paint layer. FTIR analysis (not shown) provided surprisingly an almost perfect match to well-aged shellac. Although Trotter had specifically mentioned copal as the coating of choice for his last forgery (2), the ‘Haberle,’ it would appear that an insect resin rather than a tree resin was used in this instance. The expected role of the shellac, which can be difficult to apply thinly and evenly by brush, in producing a convincing fake is not known. The detection of shellac required further investigation as it typically fluoresces bright orange when unbleached, unlike the cool, milky fluorescence observed in the UVA-induced visible fluorescence image in Figure 3(a).

15 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Further analysis of the binding media and varnish was performed using PyGC-MS of surface scrapings. The pyrogram of the TMAH-derivatized sample taken from the horse’s green pasture is shown in Figure 10(a). For comparison, pyrograms for (b) linseed oil and (c) very light shellac (unbleached) are included. The major marker peaks for various artists’ materials are identified in Table I (13, 14). Py-GC-MS confirms the results from FTIR analysis by revealing the simultaneous presence of oil, protein, the Hansa Yellow pigment, shellac, and trace amounts of pine resin (colophony). The shellac is most likely unbleached due to the lack of chlorinated marker compounds that have recently been reported to occur in shellac that has been decolorized by the addition of a chlorine bleach (15). Copal varnish, which was reportedly used in other Trotter fakes, is shown not to have been used in this work due to the absence of methyl sandaracopimarate, the marker compound for Manila copal, at detectable levels (16).

Figure 10. GC-MS pyrogram of TMAH-derivatized (a) green paint sample, (b) linseed oil, and (c) very light shellac.

The excessive craquelure of the paint in Village Scene provided numerous opportunities to prepare cross sections of paint passages without causing a noticeable lacuna in the painting’s surface. Although an invasive approach, cross section analysis is one of the only ways to explore the working methods of an artist. To understand the layered structure of this painting, selective areas were sampled and cross sections prepared for analysis by optical microscopy. 16 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 11(a) shows a photomicrograph of one section taken from the hindquarters of the horse in the painting’s foreground. Figure 11(b) shows the same section under UV irradiation. The stratigraphy of the section revealed in the two images records the process by which Trotter created the fake. At the lowest level, a chunky, fragmented white ground layer with carbon inclusions shows the incomplete removal of paint from the reused canvas. This layer is best viewed in a previously published cross section (11), but can be faintly seen in the lowest area of Figure 11(a). On top of this are two thinner, homogeneous modern white ground layers applied by the forger to prepare the reused canvas for painting. The lower of these two is only partly preserved to the far right in the cross section shown here. A translucent layer seen in Figure 11(a) separates these two grounds, and it is shown to be highly luminescent in Figure 11(b). This blue fluorescence is typical of proteinaceous materials (17). On top of the modern grounds are two green paint layers, a dark green and an upper yellow-green (the Permanent Green Hue paint layer discussed above), again interleaved with a fluorescent material consistent with a proteinaceous layer. The paint of the brown horse overlays the landscape colors, again sandwiched between fluorescent layers, the topmost of which appears to be a mostly continuous blue fluorescent layer with occasional orange fluorescent components.

Figure 11. Visible light photomicrographs of a cross section sample from the horse’s hindquarters in (a) normal illumination and (b) UV irradiation. Lower right scale = 100 μm.

It is interesting to note in the cross section the numerous thin separations that exist in all of the oil paint and ground layers. It is believed that Trotter intentionally violated the painter’s “fat over lean” rule, using a fast drying medium like animal glue overtop of a slower drying medium like linseed oil (9). This type of construction inevitably leads to the oil paint being pulled apart into small islands by the rapid contraction of the surrounding protein layers, especially when heated, thus inducing nearly instantaneously the evenly random craquelure observed in Village Scene. 17 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Table I. Major pyrogram peaks, their identification, and associated artists’ material source of the TMAH derivatized compound Retention time (min)

Peak Identity

Origin

1.2-1.3

TMAH

derivatizing agent

3.04

pyrrole

protein

3.31

methyl methoxyacetate

oil

3.63

2-methoxyacetic acid, methyl ester

oil

4.22

N-N-dimethylglycine methyl ester

protein

4.76

styrene

protein

4.84

glycerol, trimethylester

oil

4.59

1,3-dimethoxy-2-propanol

oil

5.11

hexanoic acid, methyl ester

oil

6.09

heptanoic acid, methyl ester

oil

6.20

butanedioic acid, dimethyl ester

oil

6.96

octanoic acid, methyl ester

oil

7.52

3-methoxy-2,2’-bis(methoxymethyl)-1-propanol

oil

7.62

2-chloro-N-methylbenzamine

Hansa yellow

7.75

nonanoic acid, methyl ester

oil

8.65

heptanedioc acid, dimethyl ester

oil

8.68

8-methoxyoctanoic acid, dimethyl ester

oil

9.34

octanedioic acid, dimethyl ester

oil

9.46

dimethyl phthalate

plasticizer?

9.98

nonanedioic acid, dimethyl ester

oil

10.59

decanedioic acid, dimethyl ester

oil

11.01

tetradecanoic acid, methyl ester

oil

11.16

undecanoic acid, methyl ester

oil

12.09

hexadecanoic acid, methyl ester

oil

12.33

siloxane

column

12.76

unidentified, but occurs in reference

shellac

13.06

octadecanoic acid, methyl ester

oil

13.22

derivative of aleuritic acid

shellac

13.37

butylated hydroxytoluene (BHT)

antioxidant?

13.50

tetramethyl derivative of jalaric acid

shellac Continued on next page.



Table I. (Continued). Major pyrogram peaks, their identification, and associated artists’ material source of the TMAH derivatized compound Retention time (min)

Peak Identity

Origin

13.70

tetramethyl derivative of shellolic acid

shellac

13.97


shellac

14.19

dehydroabietic acid, methyl ester

pine resin, trace

14.21


shellac

14.34

siloxane

column

14.47


shellac

14.64

7-methoxy-tetrahydroabietic acid, methyl ester

pine resin, trace

15.18

7-oxo-dehydroabietic acid, methyl ester

pine resin, trace

15.21

7,15-dimethoxytetradehydroabietic acid, methyl ester

pine resin, trace

In numerous cross sections the penultimate surface layer was found to show traces of an inhomogeneous orange luminescent coating. This is consistent with the presence of unbleached shellac, which fluoresces a characteristic bright orange under UV excitation (15, 17). These cross sections confirm the FTIR and PyGC-MS analyses that also indicated shellac along with pine resin. The presence of the coating largely in the penultimate surface layer, rather than the uppermost one, explains the cool fluorescence in the UV-induced visible fluorescence image, Figure 3(a), rather than a warm orange fluorescence typical of unbleached shellac. A topmost surface coating of glue and dirt filters the UV radiation and prevents fluorescence from the largely underlying shellac. The presence of shellac as a picture varnish is unusual (17) aside from a few notable examples (15), although it may have been added here to the uppermost layers to induce hardness to the paint surface that could not easily be achieved in a young oil paint (9) or to enhance the craquelure through shrinkage. This combination of surface layers containing glue, shellac, and pine resin is surprisingly identical to the layering found in another fake, a purported 15th century portrait group acquired in 1923 by the National Gallery in London (18).

Conclusion A careful investigation of the artistic composition, materials, and construction techniques of one of Trotter’s forgeries, namely Village Scene with Horse and Honn & Company Factory, has revealed numerous ‘red flags’ indicating that the work is not a genuine piece of 19th-century folk art. Upon casual observation, the painting appears to have all the hallmarks of a great piece of primitive-style art. This is in fact one of the indicators of its ersatz nature – it has nearly all of the most prized physical characteristics of the folk art genre in one painting: a 19 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


quaint composition, naïve sense of perspective, female autograph, visible mattress ticking, heavy patina and fine craquelure suggestive of aged paintings, and mold stains commensurate with years of hanging on uninsulated parlor walls. Several curious and in some instances inexplicable clues are evident with merely a close visual examination. Foremost, the use of mattress ticking as a canvas lining fabric is unique in the authors’ experience, especially when no obvious canvas defects are visible to suggest relining was warranted. The applied nature of the mold and the uniform, dense surface cracking are also atypical of true primitive style paintings. Finally, the tacking margins reveal an implausible situation where the artist’s ground layer and painted composition appear to have been applied after the canvas was relined. Advanced imaging techniques also reveal several indicators of the painting’s speciousness. Again, for a relined canvas, there are no signs in the UV, NIR, or X-ray images of damages, losses, or structural deficits that would explain the lining fabric, which is shown to contain anachronistic optical brighteners. Furthermore, radiography revealed that no heavy metal pigments were used in this work, which is only feasible with a purely modern palette, although amorphous radio-opaque remnants of the original ground layer from a reused “stripped” canvas are detectable. In the event that scientific analysis is possible, a Trotter fake can be definitively identified as a 20th-century product due to the presence of numerous synthetic organic and inorganic pigments that were unavailable in the previous century or by the unconventional artistic technique of interleaving animal glue and paint as seen in fluorescence microscopy of cross sections. Since leaving prison, Robert Trotter has continued to paint 19th-century style artworks, but this time ‘genuine’ fakes that are sold legitimately to buyers of contemporary folk art (2, 3). When asked about the convicted forger’s new career, Arthur Riordan, one of the art dealers previously fooled by Trotter and owed compensation under the court sentencing, declared, “Good, I hope he makes a million dollars because we get the first $62,000 (2).” For the remaining thirty-nine unidentified Trotter fakes, compensation to their owners seems unlikely. Still, it is hoped that for the sake of art history and the reputations of gallery owners and collectors that the indicators revealed here might help to unmask others of Trotter’s oeuvre. The consistency of the forger’s methods is not at present known. However, four additional Trotter fakes confiscated by the FBI are now part of the Yale University Art Gallery’s study collection. Future work will hopefully subject these forgeries to the same level of scientific scrutiny in order to establish the reliability of the ‘red flags’ discovered here in the condition, construction, and materials of Village Scene.

Acknowledgments This work was completed at Buffalo State College and first appeared in a summary version as a presentation at the 2007 Annual Meeting of the American Institute for Conservation (11). The faculty recognizes the exhaustive research of the Trotter trial by graduate student Jennifer DiJoseph from the Class of 2010 and prosecutor Peter Jongbloed, former U.S. District Attorney in Connecticut, 20 Lang and Armitage; Collaborative Endeavors in the Chemical Analysis of Art and Cultural Heritage Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

for information regarding the case and ultimately the transfer of the Village Scene painting to Buffalo State College. GDS and CER acknowledge the financial support of the Andrew W. Mellon Foundation.

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The Technical Analysis of a Known Forgery - American Chemical

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