Summarize

Radioaktīvā oglekļa datēšana ir metode organiskā materiāla saturoša objekta vecuma noteikšanai. Kopš metodes izstrādes 20. gadsimta vidū to galvenokārt ir izmantojuši arheologi senlietu datēšanai. Rakstā Dr. Irka Hajdas, jonu staru fizikas laboratorijas eksperte Cīrihē, apraksta ne tikai metodes vēsturisko attīstību, bet arī tās iespējamu netiešu, bet spēcīgu ietekmi, kuru varētu ļaunprātīgi izmantot, atbalstot nelegālu tirgu. Ņemot vērā temata nozīmīgumu, autore iesaka ekspertiem (analīzes veicējiem) ievērot noteiktus minimālus standartus, lai izvairītos no kultūras priekšmetu nelikumīgas tirdzniecības atbalstīšanas.

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Raksts tiek publicēts oriģinālvalodā

Dr. Irka Hajdas,

ETH Laboratory of Ion Beam Physics in Zurich

Radiocarbon dating of antique objects — how can we avoid analysis for the illicit market?

Foundation for the radiocarbon dating method has been set in the first half of the last century. A team around Willard Libby has shown that radioactive isotope of carbon (14C or radiocarbon) can be used as a clock to measure the time that elapsed from the point of formation of material in question [1]. Interestingly, to do so, they chose antique objects such as wood, textile and a rope from Zoser (Djoser) tomb, which were of known historical age. They were intrigued to find the right relation between measured remaining ¹⁴C activity of the material and their historic date. One can say that archeology was among the very first disciplines that recognized the power of the method and remind one of the leading and vital applications relying on radiocarbon ages [2].

Furthermore, those are archeologists, specifically archeologists working in Africa SAFA (https://safa.rice.edu/)[1], who in 2012 issued a warning: radiocarbon dating cannot be used for dating antique objects of unknown origin. One must say that despite close collaborations with archeologists, the radiocarbon community was not aware of the problem addressed and discussed by archeologists. The situation can be seen as such that each community was looking from a different perspective. Early radiocarbon laboratories were mostly established by chemists and physicists and have always focused on providing as accurate and precise ages as possible, therefore not interfering with the research behind the samples, unless these were part of research collaboration projects. Historically, radiocarbon laboratories provide so-called “research service or analysis” to external users. A considerable share of the users are public institutions such as state archeology offices, universities but also profit-oriented institutions. In 1977, when a technique of Accelerator Mass Spectrometry (AMS) was invented, measuring ¹⁴C in a tiny amount of material became a reality. Soon after, the famous analysis of the Shroud of Turin has been performed [3] and possibly triggered the interest of the antiquities market. Here was a method that could prove if an object is old or if it is a recent copy.

In decades that followed, that power of the method has been employed by the antiquity market. In general, laboratories did not inquire about the origin of the material submitted for analysis. However, as described by Huysecom et al., [4], analysis of samples from antique objects has to be carefully considered because their origins might be questionable. Moreover, radiocarbon ages showing how old the objects are, increase their monetary value, and make them desirable. This, in turn, amplifies the need for more of such objects and triggers mechanisms of looting. Looting is an act of destruction of cultural heritage, often even if objects are later recovered, their unique context is lost[2].

Archeologists around the world are the most involved community fighting the illicit trade and looting, but they need support from other stockholders: museums, law representatives, police and customs forces, international organizations and researchers who often study antique objects. Among those researchers are radiocarbon specialists and their laboratories. Therefore, following the signals from the SAFA representatives, the first steps have been undertaken by the radiocarbon community to find a common approach to the analysis of antiquities that are in the private sector.

The first meeting at ETH Zurich [5] gathered a small but dedicated group representing thirteen¹⁴C laboratories, archeologists, museum conservators, researchers into the illicit art market. The proposed procedure has been summarized in a short letter [6]. These include reviewing the following documents before a potential acceptance of the sample:

a. Pictures of the object

b. A signed declaration of origin (country of origin, provenance) for antique objects.

c. A declaration that the submitter is the owner or acting for the owner.

Laboratories, which followthe suggested protocol, are listed on the official web page of the Radiocarbon journal http://radiocarbon.webhost.uits.arizona.edu/node/11. It can be stated with certainty that the procedure sends a clear signal to potential customers. Numerous inquiries about potential analysis remain silent after the request of (a-c) documents. Sometimes, arguments are used, such as the customer is a respected dealer but does not possess any papers for the object. Frequently, family history is involved implying origin as discovery in old inherited property. In the last years, analysis of old manuscripts was requested frequently. A review of the cases pointed to an origin from Syria, highlighting an urgent need for a broader support for radiocarbon laboratories, which are dealing with such cases. Important questions here are: what can be done in case of suspicious objects? What are the obligations of researchers, and what are their options?

Presently, no clear regulations or guidelines are available for research communities, which can be facing issues similar to the described problem of radiocarbon dating being misused by the grey market of antiquities trade.Recent years place the dangers to cultural heritage in the spotlight and numerous communities are working together to increase protection of the remains of ancient cultures. Science has always been viewed as holding the ‘candle in the dark’ and protecting humanistic values. Moreover, radiocarbon dating method is the technique, which was invented to serve the mankind [7], therefore radiocarbon community is working to ensure that due diligence in dealing with antique objects will be part of our legacy.

1.         Arnold, J.R. and W.F. Libby, Age Determinations by Radiocarbon Content - Checks with Samples of Known Age. Science, 1949. 110(2869): p. 678-680.

2.         Renfrew, C., Before Civilization. 2011: Random House.

3.         Damon, P.E., D.J. Donahue, B.H. Gore, A.L. Hatheway, A.J.T. Jull, T.W. Linick, P.J. Sercel, L.J. Toolin, C.R. Bronk, E.T. Hall, R.E.M. Hedges, R. Housley, I.A. Law, C. Perry, G. Bonani, S. Trumbore, W. Woelfli, J.C. Ambers, S.G.E. Bowman, M.N. Leese, and M.S. Tite, Radiocarbon Dating of the Shroud of Turin. Nature, 1989. 337(6208): p. 611-615.

4.         Huysecom, E., I. Hajdas, M.-A. Renold, H.-A. Synal, and A. Mayor, The “Enhancement” of Cultural Heritage by AMS Dating: Ethical Questions and Practical Proposals. Radiocarbon, 2017. 59(2): p. 559-563.

5.         Radiocarbon dating and the protection of cultural heritage, 16-​17 November 2017, ETH Zurich. Available from: https://ams.ethz.ch/LIPServices/radiocarbon-dating-and-protection-of-cultural-heritage.html.

6.         Hajdas, I., A.T. Jull, E. Huysecom, A. Mayor, M.-A. Renold, H.-A. Synal, C. Hatté, W. Hong, D. Chivall, and L. Beck, Radiocarbon dating and the protection of cultural heritage. Radiocarbon, 2019. 61(5): p. 1133-1134.

7.         Libby, L.M. Banquet speech. NobelPrize.org. Nobel Media AB 2020. . 1960 Thu. 2 Jan 2020.; Available from:https://www.nobelprize.org/prizes/chemistry/1960/libby/speech/.