Science and Justice 54 (2014) 465–469
Contents lists available at ScienceDirect
Science and Justice journal homepage: www.elsevier.com/locate/scijus
Technical note
Scientific analysis and historical aspects as tools in the legal investigation of paintings: A case study in Brazil Patricia Schossler a,b,⁎,1,2, João Cura D'Ars de Figueiredo Júnior b,3, Isabel Fortes a,2, Luiz Antônio Cruz Souza b,3 a b
Departamento de Química, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil Laboratório de Ciências da Conservação (LACICOR), Escola de Belas Artes, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil
a r t i c l e
i n f o
Article history: Received 27 May 2013 Received in revised form 22 June 2014 Accepted 26 June 2014 Keywords: Pictorial materials Scientific analysis Historical aspects Art technological studies Authenticity
a b s t r a c t The faker makes use of several strategies to give credibility to his work, as for example by copying artist's style or by using artificial aging techniques. The characterization of artistic materials, such as pigments, binding media and supports through chemical and/or physico-chemical analysis, coupled with art historical information is essential to establish the non-authenticity of works of art. This paper presents a contribution in a legal case regarding paintings attributed to important Brazilian and European artists such as Candido Portinari, Juan Gris, Camille Pissarro, and Umberto Boccioni, among others. In the investigation, modern synthetic painting materials were identified in all the ground layers of the suspected paintings. The use of diverse instrumental analytical techniques such as Fourier transform infrared spectroscopy, polarized light microscopy and pyrolysis-gas chromatography/mass spectrometry enabled this characterization. The results demonstrated the presence of titanium dioxide, calcium carbonate and kaolin as inorganic components of the paints, and polyvinyl acetate copolymerized with vinyl versatates or diisobutylphtalate as binding media in the ground layers of the paintings. The results obtained, along with art historical information and art technological studies, were very important in the judicial process, due to the possibility to use titanium dioxide and polyvinyl acetate copolymerized with vinyl versatates as chronological markers. © 2014 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction and research aims Collections of artworks and antiquities are exposed to the risk of forgeries [1,2]. To fake a work is to give it a worth that does not originally belong to it, such as the authorship, the style to which it belongs and even the painting materials. The knowledge of styles and techniques of artists allows forgers to produce a copy that is difficult to distinguish from the original. In addition, the authentication of art or historic objects is frequently a subjective process, strongly based on the knowledge and expertise of the art expert assigned to the task. To overcome these difficulties, the authentication of artworks becomes increasingly an interdisciplinary undertaking. Some recent judicial cases involving suspected artworks have highlighted the need
⁎ Corresponding author at: Departamento de Química, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil. Tel./fax: + 55 31 3409 5262. E-mail address: [email protected] (P. Schossler). 1 Present Address: Technische Universität Braunschweig, Pockelsstraße 14, 38106 Braunschweig, Germany. 2 Tel./fax: +55 31 3409 5720. 3 Tel./fax: +55 31 3409 5262.
of multidisciplinary approach [3]. In a first step of an authentication procedure, an art historian can be asked to study a work of art. In the cases where some aspects of the work of art lead to the questioning of authorship, and if the knowledge of the materials can provide helpful information, physicochemical analysis are conducted by scientists. The results can be contrasted with the previous art technological research studies if available. This paper describes and details an investigation of a group of 10 paintings involved in a legal dispute (Process 175/95, Delegacia de Defraudações — Rio de Janeiro, Brazil) between the State of Rio de Janeiro and a private Marchand [4,5]. These paintings were for sale at Marchand's shopping as masterpieces from several very important artists (please see Table 1). The authenticity of two of these works attributed to the Brazilian artist Candido Portinari, was questioned by the “Projeto Portinari” which is devoted to catalog the production of the artist. Candido Portinari is an important and well known Brazilian artist, therefore there is a substantial amount of information available with the “Projeto Portinari” team members and also at project's website http://www.portinari.org.br. These two paintings were the initial focus of an interdisciplinary study involving art historical knowledge, art technological research and material analysis in order to investigate the suspected paintings listed in Table 1.
http://dx.doi.org/10.1016/j.scijus.2014.06.013 1355-0306/© 2014 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
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P. Schossler et al. / Science and Justice 54 (2014) 465–469
2. Materials and methods 2.1. Samples The paintings listed in Table 1 were examined by a conservator and a chemist. Afterwards, they were photographed to produce the initial documentation analysis. Micro-samples were removed with great care from places showing painting losses and/or lateral sides that are found easier for sampling. The discussion with the conservator during the sampling procedure was conducted in order to identify original areas of the paintings that were not subjected to prior conservation/restoration interventions. One micro-sample was removed from an original area of each of the paintings under study, which corresponds to a total of 10 collected fragments. The collected fragments were stored in appropriate vials and labeled according to the standard procedure of the Laboratório de Ciências da Conservação (LACICOR).
2.2. Analytical procedure The analytical procedure involves investigations employing stereomicroscopy, Fourier transform infrared spectroscopy (FTIR), polarized light microscopy (PLM) and pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS). A trinocular stereo microscope Olympus SZ-1, fitted with an AxioCam ICc3 digital camera for photomicrography, was used to closely examine the samples. The transmission FTIR analyses were carried out using a Bomem MB100 FTIR spectrophotometer with a MCT detector cooled by liquid nitrogen. To avoid a large signal of CO2, the system was purged with nitrogen before the analyses. A 1 mm micro-diamond compression cell was used for sample preparation. The fragments were observed under a stereomicroscope Olympus SZ-11 at up to 80 × magnification in handling of the samples, which were carefully positioned in the diamond window. Spectra were acquired in a spectral range between 4000 and 450 cm−1 performing 64 scans at 4 cm−1 resolution. Dispersions of the samples were prepared in Meltmount Cargile resin, with a known refraction index of 1.662, followed by examination using a polarized light microscope Olympus BX 50 at up to 200× magnification. The dispersions were observed under crossed and parallel polarizers using transmitted and reflected light. Standard procedures for the identification of the pigments and fillers described in the literature were applied [6]. Pyrolysis analyses were carried out based on the previously developed methodology in the same research group [7]. The pyrolysis of the samples was performed under inert atmosphere using a Curie Point Pyrolyzer PSC 1040 (Fischer GSG, Bruchsal, Germany) directly connect to the gas chromatograph injector. The volatile products were analyzed using a gas chromatograph (Hewlett Packard 5890 II) coupled to a quadrupole mass spectrometer (Hewlett Packard 5890 A). The capillary column used was a HP-5 MS (25 m × 0.2 mm × 0.32 μm). Helium
was used as carrier gas at a constant flow of 0.8 ml min−1. Approximately 70 μg of the samples was placed on the pyrolysis filament (Fe/Ni and Ni/Co alloy, GSG Mess- und Analysengeräte) and pyrolysed at 670 °C during 8 s. The pyrolysis chamber was set at 200 °C and the gas chromatograph injector temperature was adjusted to 250 °C. The analyses were carried out in a splitless mode (1.0 min) using an oven temperature program as follows: 40 °C (2 min) and ramp at 10 °C/min to 280 °C (10 min). The mass spectrometer used electron impact ionization at 70 eV and scanned in the range 40–500 m/z. The source temperature was of 250 °C, whereas the quadrupole was set at 100 °C. 3. Results and discussion A white common ground layer was observed in all paintings (see Fig. 1 for P10) and considered as an important starting point for the analytical investigation since the ground layers could be compared. Fig. 2 presents the FTIR spectra of the common white ground layer from the paintings under study. It was possible to observe a similar pattern in most of the collected FTIR spectra, with the exception of samples P3 and P5 in which a strong influence of absorption bands related to inorganic substances was observed. According to the FTIR analysis most of the ground layers are composed of calcium carbonate (CaCO3) filler and titanium white (TiO2) pigment. The presence of CaCO3 in sample P1 (see Fig. 3 for a detailed analysis) is indicated by the appearance of a broad absorption between 1390 cm− 1 and 1490 cm− 1 and a strong and sharp absorption at 875 cm− 1 and less strong, but still sharp bands at 1794 cm− 1 and 2515 cm− 1 [8,9]. The broad absorption between 430 cm− 1 and 700 cm−1 is a strong indicator of the presence of TiO2 in the analyzed samples [8]. All the other collected samples presented absorptions bands attributed to CaCO3,~1390 cm− 1–1490 cm− 1; ~ 875 cm− 1 (Fig. 2). It is also possible to observe the TiO2 characteristic broad absorption (~ 430 cm− 1–700 cm− 1) in most of the studied samples, with the exception of the samples collected from the paintings P3 and P5. Pigments and fillers identified in the samples were submitted to PLM analysis for further verification/confirmation of their composition. The results indicated the presence of TiO2 as pigment and CaCO3 and kaolin as fillers in all the samples. Calcium carbonate particles are anisotropic and showed a refractive index of 1.662. Titanium white particles were tiny round, same size and pseudo opaque in transmitted light. Pseudo opaque particles have refractive index greater than 1.662 and appear black in transmitted light. Translucent particles with low birefringence were attributed to kaolin. The presence of CaCO3 was confirmed
Table 1 List of suspected paintings involved in the judicial case. Painting
Artist
Technique
Date of birth and death
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10
Candido Portinari Candido Portinari Juan Miró Antônio Gomide Georges Rouault Frank Kupka Henri Matisse Juan Gris Umberto Boccioni Camille Pissarro
Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas
1903–1962 1903–1962 1893–1983 1895–1967 1871–1958 1871–1957 1869–1954 1887–1927 1882–1916 1830–1903
Fig. 1. Photomicrograph under visible light of fragments from Painting P10: dark surface layer and white ground layer.
P. Schossler et al. / Science and Justice 54 (2014) 465–469
2515 2871
1240
1430
1739
450
1023
875
1119
2965 2928
% Transmittance
by qualitative microchemical analysis with the addition of HCl and observation of gas effervescence (CO2) in all the samples collected from the paintings described in Table 1.
With exception of the samples collected from the paintings P3 and P5, the FTIR analyses presented absorption bands characteristic of vinyl resins [10,11]: CH2 stretching at frequencies around 2955 cm−1, 2928 cm−1 and 2871 cm− 1, the carbonyl stretching band at around 1739 cm−1 and strong bands in the fingerprint region around 1240 cm−1 (C\O stretching), 1119 cm−1 and 1023 cm−1. However, due the similarity of the FTIR spectra of some synthetic resins and the overlapping of organic and inorganic substances present in the paints, the samples were submitted to Py-GC/MS analyze for an unequivocal characterization of its binding medium. The two peaks observed at lower retention times on the pyrogram belonging to the ground layer of P1 (see Fig. 4) were identified by their mass spectra as acetic acid (m/z 43, 45 and 60) and benzene (m/z 78). These compounds are characteristic products of the thermal degradation of polyvinyl acetate (PVAc), since vinyl resins undergo the “side group elimination” pyrolytic process [12]. The presence of benzene, in combination with acetic acid, is a strong indicator of the use of PVAc as resin in the paints [13]. The same pyrogram profile, with the presence of acetic acid and benzene at lower retention times, was observed in the white ground layers present in all the analyzed samples. Despite the strong influence of the inorganic compounds in the FTIR spectra of the samples collected from the paintings P3 and P5, it was possible to observe in the pyrograms the presence of acetic acid and benzene at lower retention times, suggesting the presence of PVAc as binding medium. Diisobutylphtalate (DiBP) was identified as plasticizer in the samples P1, P2 and P7, while the isomeric mixture of vinyl versatates was the internal plasticizer found in the white ground layers from paintings P3, P5 and P8. The remaining samples (P4, P6, P9 and P10) presented peaks at higher retention times of their pyrograms, which could correspond to plasticizers. However, due to the poor resolution of the mass spectra, the identification was not possible. Plasticizers are known to be ubiquitous contaminants in the environment [14], but in this case a contamination due to the previous interventions could be discarded since all the analyzed samples were part of the paintings ground layers. This layer, denominated also as “base preparation”, is the first layer over the canvas and below the painting layers. Any kind of varnish, repainting or other kinds of intervention cannot alter them because they were all below other layers. After stereomicroscopic observation of the samples and identification of the ground layer, historical and art technological aspects were compared and contrasted to the analytical results. Paintings attributed to Candido Portinari presented a suspect authentication stamp at the back (see Fig. 5) which, according to the Projeto Portinari, has never
1794
Fig. 2. FTIR spectra of the white ground layers from fragments of the paintings under investigation.
467
Wavenumber (cm-1) Fig. 3. FTIR spectrum of the white ground layer of a fragment from painting P1.
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P. Schossler et al. / Science and Justice 54 (2014) 465–469
A
B
Fig. 4. Pyrogram (Total Ion Current, TIC) at 670 °C of the white ground layer from painting P1 (A) and from painting P3 (B). Characteristic fragments and compounds are described.
been used [15]. In addition to the authentication stamp, some other aspects concerning the paint composition were in disagreement. The recent studies related to artist's materials and techniques (a field also denominated “Art Technological Studies”) pointed out the presence of a white ground layer in Candido Portinari's paintings, however it was composed of animal glue, calcium sulfate and/or calcium carbonate and, in some cases, of lead white and oil [16,17]. The use of synthetic modern paints by the artist is until now not documented. In contrast, the preference of Portinari for traditional oil painting materials and techniques when painting on canvas was mentioned by the artist and is well known [16,18]. Analytical results and historical data of the paintings presented in Table 1 were put together and other disagreements were identified. One of the paintings was attributed to Camille Pissarro, who died in 1903 and, consequently, lived years before the use of the vinyl resins by artists. Polyvinyl acetate was first synthesized in 1912 and its patent dates from 1913 [19]. Only in the late 1940s, after PVAc being available as emulsion house paint, it was commercialized in considerable amounts and also used by artists [20]. Since PVAc as pure resin is too hard to form a coherent film, it needs to be plasticized. External plasticizers like phthalates were commonly used until the 1960s, when internal plasticizers including other vinyl and acryl monomers and also highly branched C9 and C10 vinyl esters called vinyl versatates (VeoVa) were copolymerized with PVAc. VeoVa were developed by Shell International B.V in 1966 and commercialized since this date [21]. Thus, the presence of VeoVa in the paintings P5 and P8 increased the suspicions of non-authenticity of these works. Another identified material that could have not been used by Camille Pissarro is the pigment TiO2. The particles observed by PLM presented a
characteristic profile of TiO2 in the synthetic form which is reported to be invented in 1916 and widely used as pigment in the 1930s [22]. 4. Conclusions The combined used of microscopic techniques, infrared spectroscopy and analytical pyrolysis enabled the identification of both inorganic (TiO2, kaolin and CaCO3) and organic (PVAc plasticized with VeoVa or DiBP) painting materials utilized in the white ground layer of the paintings described in Table 1. Combining the knowledge of art historians and conservation scientists, allied to information from technical art research, it was possible to access and understand particular aspects of the suspected paintings. Regarding to the paintings attributed to Candido Portinari (P1, P2) the various findings, inferred from the stylistic analysis by art historian, as well as the presence of materials not usually used by the artist and, at least, by the presence of an authentication stamp, were of enormous importance in the judicial process. Considering the technical literature on the chronological availability of the pigment TiO2 and the synthetic binding medium, a date of manufacture before 1912 is not acceptable for painting P10 attributed to Camille Pissaro. The same conclusion can be drawn to the paintings attributed to Georges Rouault (P5) and Juan Gris (P8) due to the chronological impossibility of the use of a paint containing VeoVa as internal plasticizer by these artists. Legally, at least in Brazil, the chemical or material analysis is essential to verify the authenticity of works of art in specific cases, because the analytical results are considered material evidences. In this case, using FTIR, PLM and Py-GC/MS, material evidences related to the nonauthenticity of the paintings P1, P2, P5, P8 and P10 were found. These scientific results, together with art historical and technological
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Acknowledgments Financial support from Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG - Brazil) is gratefully acknowledged. P. Schossler would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Brazil) for a research fellowship. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scijus.2014.06.013. References
Fig. 5. Front (A) and back sides (B) of painting P1 attributed to Candido Portinari.
information and the experience of the conservator, were extremely important to prove the non-authenticity of the paintings P1, P2, P5, P8 and P10 during the judicial process. Confronting the analytical results with historical information about the other paintings (P3, P4, P6, P7 and P9), it was not possible to reach quick unequivocal conclusion, despite the suspected use of the same paint materials by different artists, some of them living in different countries and working in different periods. These evidences led the team members of LACICOR to discuss the possibility of a further research project that should take into account the characterization of the materials present in the other painting layers as well as bibliographical research related to art technological studies of the different artists listed in Table 1.
[1] D.R. Chartier, W.C. McCrone, R.J. Weiss, Society of Photo-optical Instrumentation Engineers, Scientific detection of fakery in art II: 20-21 September 1999, Boston, Massachusetts, The Society, Bellingham, Wash, 2000. [2] P.T. Craddock, Scientific Investigation of Copies, Fakes and Forgeries, 1st ed. Elsevier/ Butterworth-Heinemann, Oxford; Burlington, MA, 2009. [3] S. Frenzel, Den Fälschern auf der Spur in: Monopo, Ringier Publishing GmbH, Berlin, 2012. 56–61. [4] A. Pimenta, Pilantras do Pincel, in: Revista Veja, Editora Abril, São Paulo, 1996. pp. 102–105. [5] L. Antunes, "Marchand" processado por vender telas falsas é acusado de nova falsificação, in: O Globo, Editora Globo, Rio de Janeiro, 1996. [6] W.C. McCrone, The microscopical identification of artist's pigments, J.Int. Inst. Conserv. Can. Group 7 (1982) 11–34. [7] P. Schossler, I. Fortes, J.C.D.A. de Figueiredo Júnior, F. Carazza, L.A. Cruz Souza, Acrylic and vinyl resins identification by pyrolysis-gas chromatography/mass spectrometry: a study of cases in modern art conservation, Anal. Lett. 46 (2013) 1869–1884. [8] F.A. Miller, C.H. Wilkins, Infrared spectra and characteristic frequencies of inorganic ions — their use in qualitative analysis, Anal. Chem. 24 (1952) 1253–1294. [9] R.A. Nyquist, R.O. Kagel, Infrared Spectra of Inorganic Compounds: 3800–45 cm−1, Acad.Pr, New York, 1971. [10] T. Learner, The Use of a Diamond Cell for the FTIR Characterisation of Paints and Varnishes Available to Twentieth Century Artists, in: B. Pretzel (Ed.), Second International Infrared and Raman Users Group Conference, Victoria & Albert Museum, London, 1995, pp. 7–20. [11] M.R. Derrick, D. Stulik, J.M. Landry, Infrared Spectroscopy in Conservation Science, Getty Conservation Institute, Los Angeles, 1999. [12] W.J. Irwin, Analytical pyrolysis — an overview, J. Anal. Appl. Pyrol. 1 (1979) 89–122. [13] T. Learner, The analysis of synthetic paints by pyrolysis-gas chromatography–mass spectrometry (PyGCMS), Stud. Conserv. 46 (2001) 225–241. [14] C.J. Weschler, Changes in indoor pollutants since the 1950s, Atmos. Environ. 43 (2009) 153–169. [15] J.C. Portinari, Personal communication, in, Rio de Janeiro, 1999 [16] A. Rosado, História da Arte Técnica: um Olhar Contemporâneo Sobre a Práxis das Ciências Humanas e Naturais no Estudo de Pinturas Sobre Tela e Madeira, in: Escola de Belas Artes, Universidade Federal de Minas Gerais, Belo Horizonte, 2011. 289. [17] A. Rosado, L.A.C. Souza, E. Motta JR, C.V. Teixeira, J.C. Portinari, I.C. Mendes, Candido Portinari: Materials and Techniques of a Brazilian Modern Painter — Part I, in: J. Bridgland (Ed.), ICOM-CC 16th Triennial Conference, Critério – Produção Gráfica Ltda, Lisbon, 2011, pp. 1–9. [18] M. Moreira, Candido Portinari, Editora Três, São Paulo, 1974. [19] [19] Journal and patent literature, Journal of the Society of Chemical Industry, 34 (1915) 600-640. [20] T. Learner, Getty Conservation Institute, Modern Paints Uncovered: Proceedings From the Modern Paints Uncovered Symposium, Getty Conservation Institute, Los Angeles, 2007. [21] S.C. Limited, Our History, Shell Chemical Limited, England, 2013. [22] W.C. McCrone, A history of titanium white pigments, Microscope 45 (1997) 41–46.
Contents lists available at ScienceDirect
Science and Justice journal homepage: www.elsevier.com/locate/scijus
Technical note
Scientific analysis and historical aspects as tools in the legal investigation of paintings: A case study in Brazil Patricia Schossler a,b,⁎,1,2, João Cura D'Ars de Figueiredo Júnior b,3, Isabel Fortes a,2, Luiz Antônio Cruz Souza b,3 a b
Departamento de Química, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil Laboratório de Ciências da Conservação (LACICOR), Escola de Belas Artes, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil
a r t i c l e
i n f o
Article history: Received 27 May 2013 Received in revised form 22 June 2014 Accepted 26 June 2014 Keywords: Pictorial materials Scientific analysis Historical aspects Art technological studies Authenticity
a b s t r a c t The faker makes use of several strategies to give credibility to his work, as for example by copying artist's style or by using artificial aging techniques. The characterization of artistic materials, such as pigments, binding media and supports through chemical and/or physico-chemical analysis, coupled with art historical information is essential to establish the non-authenticity of works of art. This paper presents a contribution in a legal case regarding paintings attributed to important Brazilian and European artists such as Candido Portinari, Juan Gris, Camille Pissarro, and Umberto Boccioni, among others. In the investigation, modern synthetic painting materials were identified in all the ground layers of the suspected paintings. The use of diverse instrumental analytical techniques such as Fourier transform infrared spectroscopy, polarized light microscopy and pyrolysis-gas chromatography/mass spectrometry enabled this characterization. The results demonstrated the presence of titanium dioxide, calcium carbonate and kaolin as inorganic components of the paints, and polyvinyl acetate copolymerized with vinyl versatates or diisobutylphtalate as binding media in the ground layers of the paintings. The results obtained, along with art historical information and art technological studies, were very important in the judicial process, due to the possibility to use titanium dioxide and polyvinyl acetate copolymerized with vinyl versatates as chronological markers. © 2014 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction and research aims Collections of artworks and antiquities are exposed to the risk of forgeries [1,2]. To fake a work is to give it a worth that does not originally belong to it, such as the authorship, the style to which it belongs and even the painting materials. The knowledge of styles and techniques of artists allows forgers to produce a copy that is difficult to distinguish from the original. In addition, the authentication of art or historic objects is frequently a subjective process, strongly based on the knowledge and expertise of the art expert assigned to the task. To overcome these difficulties, the authentication of artworks becomes increasingly an interdisciplinary undertaking. Some recent judicial cases involving suspected artworks have highlighted the need
⁎ Corresponding author at: Departamento de Química, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil. Tel./fax: + 55 31 3409 5262. E-mail address: [email protected] (P. Schossler). 1 Present Address: Technische Universität Braunschweig, Pockelsstraße 14, 38106 Braunschweig, Germany. 2 Tel./fax: +55 31 3409 5720. 3 Tel./fax: +55 31 3409 5262.
of multidisciplinary approach [3]. In a first step of an authentication procedure, an art historian can be asked to study a work of art. In the cases where some aspects of the work of art lead to the questioning of authorship, and if the knowledge of the materials can provide helpful information, physicochemical analysis are conducted by scientists. The results can be contrasted with the previous art technological research studies if available. This paper describes and details an investigation of a group of 10 paintings involved in a legal dispute (Process 175/95, Delegacia de Defraudações — Rio de Janeiro, Brazil) between the State of Rio de Janeiro and a private Marchand [4,5]. These paintings were for sale at Marchand's shopping as masterpieces from several very important artists (please see Table 1). The authenticity of two of these works attributed to the Brazilian artist Candido Portinari, was questioned by the “Projeto Portinari” which is devoted to catalog the production of the artist. Candido Portinari is an important and well known Brazilian artist, therefore there is a substantial amount of information available with the “Projeto Portinari” team members and also at project's website http://www.portinari.org.br. These two paintings were the initial focus of an interdisciplinary study involving art historical knowledge, art technological research and material analysis in order to investigate the suspected paintings listed in Table 1.
http://dx.doi.org/10.1016/j.scijus.2014.06.013 1355-0306/© 2014 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
466
P. Schossler et al. / Science and Justice 54 (2014) 465–469
2. Materials and methods 2.1. Samples The paintings listed in Table 1 were examined by a conservator and a chemist. Afterwards, they were photographed to produce the initial documentation analysis. Micro-samples were removed with great care from places showing painting losses and/or lateral sides that are found easier for sampling. The discussion with the conservator during the sampling procedure was conducted in order to identify original areas of the paintings that were not subjected to prior conservation/restoration interventions. One micro-sample was removed from an original area of each of the paintings under study, which corresponds to a total of 10 collected fragments. The collected fragments were stored in appropriate vials and labeled according to the standard procedure of the Laboratório de Ciências da Conservação (LACICOR).
2.2. Analytical procedure The analytical procedure involves investigations employing stereomicroscopy, Fourier transform infrared spectroscopy (FTIR), polarized light microscopy (PLM) and pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS). A trinocular stereo microscope Olympus SZ-1, fitted with an AxioCam ICc3 digital camera for photomicrography, was used to closely examine the samples. The transmission FTIR analyses were carried out using a Bomem MB100 FTIR spectrophotometer with a MCT detector cooled by liquid nitrogen. To avoid a large signal of CO2, the system was purged with nitrogen before the analyses. A 1 mm micro-diamond compression cell was used for sample preparation. The fragments were observed under a stereomicroscope Olympus SZ-11 at up to 80 × magnification in handling of the samples, which were carefully positioned in the diamond window. Spectra were acquired in a spectral range between 4000 and 450 cm−1 performing 64 scans at 4 cm−1 resolution. Dispersions of the samples were prepared in Meltmount Cargile resin, with a known refraction index of 1.662, followed by examination using a polarized light microscope Olympus BX 50 at up to 200× magnification. The dispersions were observed under crossed and parallel polarizers using transmitted and reflected light. Standard procedures for the identification of the pigments and fillers described in the literature were applied [6]. Pyrolysis analyses were carried out based on the previously developed methodology in the same research group [7]. The pyrolysis of the samples was performed under inert atmosphere using a Curie Point Pyrolyzer PSC 1040 (Fischer GSG, Bruchsal, Germany) directly connect to the gas chromatograph injector. The volatile products were analyzed using a gas chromatograph (Hewlett Packard 5890 II) coupled to a quadrupole mass spectrometer (Hewlett Packard 5890 A). The capillary column used was a HP-5 MS (25 m × 0.2 mm × 0.32 μm). Helium
was used as carrier gas at a constant flow of 0.8 ml min−1. Approximately 70 μg of the samples was placed on the pyrolysis filament (Fe/Ni and Ni/Co alloy, GSG Mess- und Analysengeräte) and pyrolysed at 670 °C during 8 s. The pyrolysis chamber was set at 200 °C and the gas chromatograph injector temperature was adjusted to 250 °C. The analyses were carried out in a splitless mode (1.0 min) using an oven temperature program as follows: 40 °C (2 min) and ramp at 10 °C/min to 280 °C (10 min). The mass spectrometer used electron impact ionization at 70 eV and scanned in the range 40–500 m/z. The source temperature was of 250 °C, whereas the quadrupole was set at 100 °C. 3. Results and discussion A white common ground layer was observed in all paintings (see Fig. 1 for P10) and considered as an important starting point for the analytical investigation since the ground layers could be compared. Fig. 2 presents the FTIR spectra of the common white ground layer from the paintings under study. It was possible to observe a similar pattern in most of the collected FTIR spectra, with the exception of samples P3 and P5 in which a strong influence of absorption bands related to inorganic substances was observed. According to the FTIR analysis most of the ground layers are composed of calcium carbonate (CaCO3) filler and titanium white (TiO2) pigment. The presence of CaCO3 in sample P1 (see Fig. 3 for a detailed analysis) is indicated by the appearance of a broad absorption between 1390 cm− 1 and 1490 cm− 1 and a strong and sharp absorption at 875 cm− 1 and less strong, but still sharp bands at 1794 cm− 1 and 2515 cm− 1 [8,9]. The broad absorption between 430 cm− 1 and 700 cm−1 is a strong indicator of the presence of TiO2 in the analyzed samples [8]. All the other collected samples presented absorptions bands attributed to CaCO3,~1390 cm− 1–1490 cm− 1; ~ 875 cm− 1 (Fig. 2). It is also possible to observe the TiO2 characteristic broad absorption (~ 430 cm− 1–700 cm− 1) in most of the studied samples, with the exception of the samples collected from the paintings P3 and P5. Pigments and fillers identified in the samples were submitted to PLM analysis for further verification/confirmation of their composition. The results indicated the presence of TiO2 as pigment and CaCO3 and kaolin as fillers in all the samples. Calcium carbonate particles are anisotropic and showed a refractive index of 1.662. Titanium white particles were tiny round, same size and pseudo opaque in transmitted light. Pseudo opaque particles have refractive index greater than 1.662 and appear black in transmitted light. Translucent particles with low birefringence were attributed to kaolin. The presence of CaCO3 was confirmed
Table 1 List of suspected paintings involved in the judicial case. Painting
Artist
Technique
Date of birth and death
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10
Candido Portinari Candido Portinari Juan Miró Antônio Gomide Georges Rouault Frank Kupka Henri Matisse Juan Gris Umberto Boccioni Camille Pissarro
Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas Painting on canvas
1903–1962 1903–1962 1893–1983 1895–1967 1871–1958 1871–1957 1869–1954 1887–1927 1882–1916 1830–1903
Fig. 1. Photomicrograph under visible light of fragments from Painting P10: dark surface layer and white ground layer.
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2515 2871
1240
1430
1739
450
1023
875
1119
2965 2928
% Transmittance
by qualitative microchemical analysis with the addition of HCl and observation of gas effervescence (CO2) in all the samples collected from the paintings described in Table 1.
With exception of the samples collected from the paintings P3 and P5, the FTIR analyses presented absorption bands characteristic of vinyl resins [10,11]: CH2 stretching at frequencies around 2955 cm−1, 2928 cm−1 and 2871 cm− 1, the carbonyl stretching band at around 1739 cm−1 and strong bands in the fingerprint region around 1240 cm−1 (C\O stretching), 1119 cm−1 and 1023 cm−1. However, due the similarity of the FTIR spectra of some synthetic resins and the overlapping of organic and inorganic substances present in the paints, the samples were submitted to Py-GC/MS analyze for an unequivocal characterization of its binding medium. The two peaks observed at lower retention times on the pyrogram belonging to the ground layer of P1 (see Fig. 4) were identified by their mass spectra as acetic acid (m/z 43, 45 and 60) and benzene (m/z 78). These compounds are characteristic products of the thermal degradation of polyvinyl acetate (PVAc), since vinyl resins undergo the “side group elimination” pyrolytic process [12]. The presence of benzene, in combination with acetic acid, is a strong indicator of the use of PVAc as resin in the paints [13]. The same pyrogram profile, with the presence of acetic acid and benzene at lower retention times, was observed in the white ground layers present in all the analyzed samples. Despite the strong influence of the inorganic compounds in the FTIR spectra of the samples collected from the paintings P3 and P5, it was possible to observe in the pyrograms the presence of acetic acid and benzene at lower retention times, suggesting the presence of PVAc as binding medium. Diisobutylphtalate (DiBP) was identified as plasticizer in the samples P1, P2 and P7, while the isomeric mixture of vinyl versatates was the internal plasticizer found in the white ground layers from paintings P3, P5 and P8. The remaining samples (P4, P6, P9 and P10) presented peaks at higher retention times of their pyrograms, which could correspond to plasticizers. However, due to the poor resolution of the mass spectra, the identification was not possible. Plasticizers are known to be ubiquitous contaminants in the environment [14], but in this case a contamination due to the previous interventions could be discarded since all the analyzed samples were part of the paintings ground layers. This layer, denominated also as “base preparation”, is the first layer over the canvas and below the painting layers. Any kind of varnish, repainting or other kinds of intervention cannot alter them because they were all below other layers. After stereomicroscopic observation of the samples and identification of the ground layer, historical and art technological aspects were compared and contrasted to the analytical results. Paintings attributed to Candido Portinari presented a suspect authentication stamp at the back (see Fig. 5) which, according to the Projeto Portinari, has never
1794
Fig. 2. FTIR spectra of the white ground layers from fragments of the paintings under investigation.
467
Wavenumber (cm-1) Fig. 3. FTIR spectrum of the white ground layer of a fragment from painting P1.
468
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A
B
Fig. 4. Pyrogram (Total Ion Current, TIC) at 670 °C of the white ground layer from painting P1 (A) and from painting P3 (B). Characteristic fragments and compounds are described.
been used [15]. In addition to the authentication stamp, some other aspects concerning the paint composition were in disagreement. The recent studies related to artist's materials and techniques (a field also denominated “Art Technological Studies”) pointed out the presence of a white ground layer in Candido Portinari's paintings, however it was composed of animal glue, calcium sulfate and/or calcium carbonate and, in some cases, of lead white and oil [16,17]. The use of synthetic modern paints by the artist is until now not documented. In contrast, the preference of Portinari for traditional oil painting materials and techniques when painting on canvas was mentioned by the artist and is well known [16,18]. Analytical results and historical data of the paintings presented in Table 1 were put together and other disagreements were identified. One of the paintings was attributed to Camille Pissarro, who died in 1903 and, consequently, lived years before the use of the vinyl resins by artists. Polyvinyl acetate was first synthesized in 1912 and its patent dates from 1913 [19]. Only in the late 1940s, after PVAc being available as emulsion house paint, it was commercialized in considerable amounts and also used by artists [20]. Since PVAc as pure resin is too hard to form a coherent film, it needs to be plasticized. External plasticizers like phthalates were commonly used until the 1960s, when internal plasticizers including other vinyl and acryl monomers and also highly branched C9 and C10 vinyl esters called vinyl versatates (VeoVa) were copolymerized with PVAc. VeoVa were developed by Shell International B.V in 1966 and commercialized since this date [21]. Thus, the presence of VeoVa in the paintings P5 and P8 increased the suspicions of non-authenticity of these works. Another identified material that could have not been used by Camille Pissarro is the pigment TiO2. The particles observed by PLM presented a
characteristic profile of TiO2 in the synthetic form which is reported to be invented in 1916 and widely used as pigment in the 1930s [22]. 4. Conclusions The combined used of microscopic techniques, infrared spectroscopy and analytical pyrolysis enabled the identification of both inorganic (TiO2, kaolin and CaCO3) and organic (PVAc plasticized with VeoVa or DiBP) painting materials utilized in the white ground layer of the paintings described in Table 1. Combining the knowledge of art historians and conservation scientists, allied to information from technical art research, it was possible to access and understand particular aspects of the suspected paintings. Regarding to the paintings attributed to Candido Portinari (P1, P2) the various findings, inferred from the stylistic analysis by art historian, as well as the presence of materials not usually used by the artist and, at least, by the presence of an authentication stamp, were of enormous importance in the judicial process. Considering the technical literature on the chronological availability of the pigment TiO2 and the synthetic binding medium, a date of manufacture before 1912 is not acceptable for painting P10 attributed to Camille Pissaro. The same conclusion can be drawn to the paintings attributed to Georges Rouault (P5) and Juan Gris (P8) due to the chronological impossibility of the use of a paint containing VeoVa as internal plasticizer by these artists. Legally, at least in Brazil, the chemical or material analysis is essential to verify the authenticity of works of art in specific cases, because the analytical results are considered material evidences. In this case, using FTIR, PLM and Py-GC/MS, material evidences related to the nonauthenticity of the paintings P1, P2, P5, P8 and P10 were found. These scientific results, together with art historical and technological
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Acknowledgments Financial support from Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG - Brazil) is gratefully acknowledged. P. Schossler would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Brazil) for a research fellowship. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scijus.2014.06.013. References
Fig. 5. Front (A) and back sides (B) of painting P1 attributed to Candido Portinari.
information and the experience of the conservator, were extremely important to prove the non-authenticity of the paintings P1, P2, P5, P8 and P10 during the judicial process. Confronting the analytical results with historical information about the other paintings (P3, P4, P6, P7 and P9), it was not possible to reach quick unequivocal conclusion, despite the suspected use of the same paint materials by different artists, some of them living in different countries and working in different periods. These evidences led the team members of LACICOR to discuss the possibility of a further research project that should take into account the characterization of the materials present in the other painting layers as well as bibliographical research related to art technological studies of the different artists listed in Table 1.
[1] D.R. Chartier, W.C. McCrone, R.J. Weiss, Society of Photo-optical Instrumentation Engineers, Scientific detection of fakery in art II: 20-21 September 1999, Boston, Massachusetts, The Society, Bellingham, Wash, 2000. [2] P.T. Craddock, Scientific Investigation of Copies, Fakes and Forgeries, 1st ed. Elsevier/ Butterworth-Heinemann, Oxford; Burlington, MA, 2009. [3] S. Frenzel, Den Fälschern auf der Spur in: Monopo, Ringier Publishing GmbH, Berlin, 2012. 56–61. [4] A. Pimenta, Pilantras do Pincel, in: Revista Veja, Editora Abril, São Paulo, 1996. pp. 102–105. [5] L. Antunes, "Marchand" processado por vender telas falsas é acusado de nova falsificação, in: O Globo, Editora Globo, Rio de Janeiro, 1996. [6] W.C. McCrone, The microscopical identification of artist's pigments, J.Int. Inst. Conserv. Can. Group 7 (1982) 11–34. [7] P. Schossler, I. Fortes, J.C.D.A. de Figueiredo Júnior, F. Carazza, L.A. Cruz Souza, Acrylic and vinyl resins identification by pyrolysis-gas chromatography/mass spectrometry: a study of cases in modern art conservation, Anal. Lett. 46 (2013) 1869–1884. [8] F.A. Miller, C.H. Wilkins, Infrared spectra and characteristic frequencies of inorganic ions — their use in qualitative analysis, Anal. Chem. 24 (1952) 1253–1294. [9] R.A. Nyquist, R.O. Kagel, Infrared Spectra of Inorganic Compounds: 3800–45 cm−1, Acad.Pr, New York, 1971. [10] T. Learner, The Use of a Diamond Cell for the FTIR Characterisation of Paints and Varnishes Available to Twentieth Century Artists, in: B. Pretzel (Ed.), Second International Infrared and Raman Users Group Conference, Victoria & Albert Museum, London, 1995, pp. 7–20. [11] M.R. Derrick, D. Stulik, J.M. Landry, Infrared Spectroscopy in Conservation Science, Getty Conservation Institute, Los Angeles, 1999. [12] W.J. Irwin, Analytical pyrolysis — an overview, J. Anal. Appl. Pyrol. 1 (1979) 89–122. [13] T. Learner, The analysis of synthetic paints by pyrolysis-gas chromatography–mass spectrometry (PyGCMS), Stud. Conserv. 46 (2001) 225–241. [14] C.J. Weschler, Changes in indoor pollutants since the 1950s, Atmos. Environ. 43 (2009) 153–169. [15] J.C. Portinari, Personal communication, in, Rio de Janeiro, 1999 [16] A. Rosado, História da Arte Técnica: um Olhar Contemporâneo Sobre a Práxis das Ciências Humanas e Naturais no Estudo de Pinturas Sobre Tela e Madeira, in: Escola de Belas Artes, Universidade Federal de Minas Gerais, Belo Horizonte, 2011. 289. [17] A. Rosado, L.A.C. Souza, E. Motta JR, C.V. Teixeira, J.C. Portinari, I.C. Mendes, Candido Portinari: Materials and Techniques of a Brazilian Modern Painter — Part I, in: J. Bridgland (Ed.), ICOM-CC 16th Triennial Conference, Critério – Produção Gráfica Ltda, Lisbon, 2011, pp. 1–9. [18] M. Moreira, Candido Portinari, Editora Três, São Paulo, 1974. [19] [19] Journal and patent literature, Journal of the Society of Chemical Industry, 34 (1915) 600-640. [20] T. Learner, Getty Conservation Institute, Modern Paints Uncovered: Proceedings From the Modern Paints Uncovered Symposium, Getty Conservation Institute, Los Angeles, 2007. [21] S.C. Limited, Our History, Shell Chemical Limited, England, 2013. [22] W.C. McCrone, A history of titanium white pigments, Microscope 45 (1997) 41–46.
