ART+Science FIG. 9: Post-bomb calibration curve (blue) and interval of calibrated dates (grey peak). Radiocarbon date: post 1954. Calibrated dates: 1963–1964 (95.4% probability). Q&A Carbon-14 is useless for tribal art! False. First of all, carbon-14 testing allows for unequivocal differentiation of objects made before or after 1954. Moreover, it is highly accurate for objects from ancient cultures such as those of the Dogon, Tellem, and Djenneke. It also provides multiple date intervals that express the most probable period of an object’s manufacture. The conditions in which an object is preserved (sediments, water, cave environment) will alter its date. Absolutely not, because it is a date of death that is being identified. By definition, death marks an end to an organism’s carbon-14 exchange with the environment. After this, carbon-14 disappears at a rate that has nothing to do with the environment. Scanning or intentional irradiation will alter a carbon-14 date. Not at all. The organism is dead, and it cannot be “recharged” with carbon-14. Nor can carbon-14 be extracted or removed to age an object artificially. Given a piece of wood, ivory, paper, or textile of identical age, for which will carbon-14 testing yield the most accurate result? There will be no difference in the accuracy. These materials have integrated the same concentrations of carbon-14 and their disintegration will proceed at the same rate regardless of the environment. The dating of ivory requires large samples, however, because we are dating the collagen in it, which represents only about ten to twenty percent of its mass. A minimum sample size is 200 milligrams. Can patinas on wood (such as blood, millet, oil, egg, etc.) be dated using the carbon-14 method? In principle, yes, because these are organic substances, but in practice, the results are not generally very convincing because such materials might have been applied repeatedly and at different times. The dating obtained will thus represent an average of periods that is not very useful. Nevertheless, the study and analysis of the composition of patinas can supply interesting technical information. Will a sample taken from the center of a mask or sculpture differ in age from one taken at the edge? Yes, and this represents one of the method’s limitations. In most cases, there is a difference of between the date of a tree’s felling and the date of the death of its heartwood (duramen). We call this the “old wood” effect, and for this reason, we always take our samples from the outer areas of objects so that we can identify the event closest to its date of manufacture. OLD BUT NEW It is vital to remember that carbon-14 dates the death of an organism and not an object’s date of manufacture. One can easily imagine a recently sculpted object being made of wood that is two or three hundred years old. The date of the material must conform to the style of the object. As examples, we cite a copy made of 35,000-yearold mammoth ivory that was preserved in continually frozen permafrost or a copy of an Egyptian Late Period (first millennium BC) statue made of wood harvested in the 15th century AD. Astonishing! THE PLACE OF SCIENCE Carbon-14 dating has constituted a major advance for archaeology and art history. Over time, it has become an important tool for the art market. In the words of noted tribal art dealer Bernard Dulon, “Carbon-14 testing is perfectly suited to the detection of fakes, particularly in the tribal art field.” It supplies objective information that contributes to the study of an object, just as thermoluminescence does for terracotta and micro-analysis does for metal. On the other hand, these scientific “tests” are not a substitute for the historical and stylistic evaluation of art works. They are rightly seen as aids to decision making, as indicators of risk, and as tools used in connection with buying. BIBLIOGRAPHY E. C. Anderson, W. F. Libby, S. Weinhouse, A. F. Reid, A. D. Kirshenbaum, A.V. Grosse, 1947, “Radiocarbon from cosmic radiation,” Science 105: 576–577. P. Craddock, 2009, Scientific Investigation of Copies, Fakes, and Forgeries, Butterworth-Heinemann, Oxford, p. 628. A. J. T. Jull, 2003, Radiocarbon, vol. 46, 18th conference, Wellington. W. F. Libby, 1955, Radiocarbon Dating. 2nd ed., University of Chicago Press, Chicago. G. Marlowe, 1980, “W. F. Libby and the Archaeologists, 1946–1948,” Radiocarbon, XXII/3, pp. 1005–1014. G. Marlowe, 1999, “Year One: Radiocarbon Dating and American Archaeology, 1947–1948,” American Antiquity, LXIV/1, pp. 9–32. M. Stuiver, et al., 1998, “CALIB rev 4.3” (Data set 2), Radiocarbon, vol. 40, pp. 1041–1083. R. E. Taylor, 1987, Radiocarbon Dating: An Archaeological Perspective, Academic Press, London, chap. 6.
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