Radiocarbon dating of twentieth century works of art

Appl. Phys. A (2016) 122:983 DOI 10.1007/s00339-016-0501-1 Radiocarbon dating of twentieth century works of art F. Petrucci1,2,3 • L. Caforio1,4 • M. Fedi4 • P. A. Mandò4,5 • E. Peccenini6 V. Pellicori1 • P. Rylands7 • P. Schwartzbaum8 • F. Taccetti4 • Received: 15 July 2016 / Accepted: 12 October 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract The atmospheric tests of nuclear weapons caused a sudden increase in the radiocarbon concentration in the atmosphere from 1955, reaching its maximum value in 1963–1965. Once the nuclear tests in the atmosphere were halted, the 14C concentration started to decrease. This behavior of the radiocarbon concentration is called the ‘‘Bomb Peak’’, and it has successfully been used as a tool for high-precision radiocarbon measurements, in forensic sciences and biology. In the art field, the possibility of dating canvas, wood and paper, widely used as supports for paintings, may be an invaluable tool in modern art studies. 1 Introduction The principle of radiocarbon dating consists in the comparison between the 14C content of the sample and the atmosphere concentration. The 14C concentration in any living being is in equilibrium with that of the atmosphere during its life, due to metabolic exchanges. Following the death of the animal or plant, the radiocarbon concentration decays with the rate of the isotope, halving in 5730 years. This is the basis of radiocarbon dating of organic remains of archaeological interest: the measurement of the isotopic fraction 14C/12C in a biological remnant gives the time elapsed from the end of its life. The nuclear tests in the atmosphere resulted in the doubling of the atmospheric concentration of 14C (Fig. 1), which reached its peak in the northern hemisphere in 1963 [1]. Such tests were banned in 1963, as a consequence of the signing of the Partial Test Ban Treaty. The ‘‘Bomb Peak’’ has allowed dating of recent documents in forensic sciences [2, 3]. In the art field, this paper shows that it can be used to date organic materials used as supports for works of art from the second half of twentieth century and may be an effective tool for authentication, capable of identifying forgeries made after 1955 of artworks purported to have been made prior to that date. & F. Petrucci [email protected] 2 A twentieth century forgery 1 Department of Physics and Earth Science, University of Ferrara, Ferrara, Italy 2 INFN - Sezione di Ferrara, Ferrara, Italy 3 TekneHub, Ferrara, Italy 4 INFN, Sezione di Firenze, Sesto Fiorentino, Italy 5 Dipartimento di Fisica e Astronomia, Università di Firenze, Sesto Fiorentino, Italy 6 Dipartimento di Fisica Università and INFN, Bologna and Centro Fermi, Rome, Italy 7 Peggy Guggenheim Collection, Venice, Italy 8 Solomon R. Guggenheim Foundation, New York, NY, USA A painting bearing a signature of Fernand Léger, and purported to date from 1913 (Fig. 2), is conserved in the repository of the Peggy Guggenheim Collection (PGC) in Venice, as its authenticity had been questioned by some art historians. Radiocarbon dating was performed on a sample of excess unpainted canvas, part of a tacking edge folded on the painting’s reverse. The response of the radiocarbon measurement, performed by Accelerator Mass Spectrometry (AMS) at INFN-LABEC (Laboratorio di tecniche nucleari per l’Ambiente e i Beni Culturali) in Florence, was conclusive: The level of detected concentration was inconsistent with 123 983 Page 2 of 4 Fig. 1 Radiocarbon concentration in the atmosphere since 1950. Data are reproduced from [1]. The concentration is expressed in ‘‘percent of Modern Carbon’’ (pMC), setting to 100 the 14C concentration in the fifties F. Petrucci et al. Since many such paintings still have their tacking edges folded around the backs of their stretchers, the necessary sample, which is destroyed in the analysis, can be removed without damage to the artwork. Moreover, thanks to the sensitivity of AMS, the withdrawn material can be reduced to a few milligrams: in practice a few yarns of a few tens of millimeters of canvas. However, the dating of canvases is not necessarily straightforward. In the course of the twentieth century, artificial and synthetic fibers such as rayon and nylon, produced from hydrocarbons, were often mixed with natural fibers. Hydrocarbons, derived from organic compounds formed millions of years ago, no longer contain radioactive carbon, so that the measured concentration leads to incorrectly ancient dates. The synthetic fibers can be quite easily recognized and distinguished from natural ones by optical or electronic microscopy. Thus, each time a canvas sample is examined for dating, a good practice is first to check whether the origin of the fibers is natural or not, in order, eventually, to date only the natural ones. Figure 3 shows measurements of radiocarbon concentrations obtained on natural cotton canvases, labeled by the date painted on the artwork. This date is clearly subsequent to the year of the ‘‘death’’ of the cotton plant of which the canvas is made. We may notice that there is a lapse of some years, from 2 up to 10, between the date inscribed on the artwork and the measured one: This corresponds to a delayed use of the canvas. The only exception is the painting indicated by the red square. The date on it claims that it was painted 5 years before the production of its canvas. This anachronism signals a possible counterfeit and indicates the need for further investigation. 4 Dating wood Fig. 2 After F. Léger, Contrastes de formes oil on canvas, 92 9 74 cm. Venice, Peggy Guggenheim Collection (Solomon R. Guggenheim Foundation) the period of the artist’s life. The cotton of the canvas, indeed, was found to have a radiocarbon concentration only consistent with a plant still alive in 1959, i.e., after the death of Léger in 1955 [4]. 3 Dating canvas Dating of canvases used as supports of paintings of the second half of the twentieth century may be one of the most obvious applications of this method. 123 Wood has been used in the art of the twentieth century, and still is, to create sculptures as well as stretchers for paintings. Examining here the possibility of radiocarbon dating of contemporary artworks, we cannot disregard the difficulties that this material poses. A common problem in the radiocarbon dating of wooden artworks, not necessarily of the twentieth century, is encountered when consolidation has been performed with acrylic resins (e.g., Paraloid B76) that contain no radiocarbon. In this case, a significant backdating is obtained, due to the contamination of the consolidant. Contamination must first be removed, and the general interest in this regard is feeding studies at various laboratories. Radiocarbon dating of twentieth century works of art Fig. 3 Radiocarbon concentrations measured on nine dated canvas paintings of the Bomb Peak period. The year painted on the canvas, the measured radiocarbon concentration and the corresponding calibrated age, at 95% confidence level, are reported. Due to the Page 3 of 4 14 Calendar age (AD) Sample code Year on painting EA2/58 1958 177.60 ± 0.50 1963 or 1965 Can1962 1962 109.19 ± 0.76 1956-1957 Can1965 1965 167.55 ± 2.18 1965-1966 EA1/65 1965 170.30 ± 0.74 1963 or 1965-66 Can1966B 1966 109.09 ± 0.38 1956-1957 Can1966N 1966 171.1 ± 1.09 1965-1966 Can1971A 1971 172.98 ± 0.55 1965-1966 Can1971C 1971 121.83 ± 0.80 1959-1962 Can1980 1980 112.76 ± 0.64 1957-1958 C conc. (pMC) 983 shape of the peak and to fluctuations, two or more calendar periods are given. Here, the most recent one has been dropped since it conflicted with other documented evidence, such as the presence of the painting in a public collection Currently, the sample pre-treatment with chloroform, tested at the LABEC in Florence [5], looks promising. 5 Dating paper Fig. 4 Radiocarbon determinations on 28 daily newspapers, published in Italy from 1938 to 2009. The dashed curve plots the moving average of radiocarbon concentration in atmosphere over 15 years, delayed of 2 years The radiocarbon concentration of newspaper samples (Fig. 4) shows significantly lower values than those detected in the Bomb Peak, because this is low-quality paper obtained from trees specially grown for periods from 15 to 30 years. The radiocarbon concentrations are then averaged over such periods, and the relevant fluctuations are in part due to the different collection intervals [6]. The situation is different for drawing papers, from linen or cotton plants, with annual harvest. In this case (Fig. 5), the 14C/12C ratio is typical of the year of plant life and the Sample name Printing year Carma60 1960 14 C conc. (pMC) Calibrated age (AD) 102.80 ± 0.63 1954-1956 Abe61 1961 111.75 ± 0.79 1957-1958 or 1993-2000 Far63 1963 111.45 ± 0.68 1957 or 1993-1999 Seve65 1965 117.41 ± 0.82 1958-1959 or 1986-1990 Cobra68 1968 147.66 ± 0.80 1962-1963 or 1970-1973 Mac70 1970 101.60 ± 0.59 1953-1956 Moore71 1971 137.29 ± 0.98 1962 or 1974-1977 Candi76 1976 131.69 ± 0.36 1962 or 1977-1979 Papa80 1980 132.01 ± 0.63 1961-1962 or 1977-1979 Fig. 5 Radiocarbon concentrations measured on nine samples of fine paper for art and drawing, manufactured in the Bomb Peak period. The year of printing, the measured radiocarbon concentration and the corresponding calibrated age, at 95% confidence level, are reported 123 983 Page 4 of 4 measurements are directly related, although not necessarily coincident, to the year of production. 6 Conclusions Radiocarbon dating of twentieth century paintings with the Bomb Peak is an innovation for the contemporary art field, being the only absolute dating method for works from 1955 to the present. It has obvious authentication applications and may also contribute to chronological studies of artistic oeuvres. Acknowledgements This work was supported by INFN Cultural Heritage Network (CHNet) and by INFN 5th Commission (Application Technology). 123 F. Petrucci et al. References 1. Q. Hua, M. Barbetti, A.Z. Rakowski, Radiocarbon 55, 2059 (2013) 2. D. Zavattaro, G. Quarta, M. D’Elia, L. Calcagnile, Forensic Sci. Int. 167, 160 (2007) 3. U. Zoppi, Z. Skopec, J. Skopec, G. Jones, D. Fink, Q. Hua, G. Jacobsen, A. Williams, Nucl. 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