engleski

Radiocarbon dating of cultural heritage objects – case studies of regional importance

Radiocarbon (14C) dating is a convenient and accurate method of absolute dating of organic materials. Radiocarbon is a cosmogenic isotope formed in the upper atmosphere and after oxidation to CO2 it becomes involved in the carbon cycle together with other carbon isotopes (12C, 13C). Equilibrium between radioactive 14C decay and its replenishment is established in all living organisms. After death the replenishment stops while the radioactive decay continues. By measuring the 14C remained in the organic material we can determine the time elapsed since the death of the organism. Various organic materials can be 14C dated, such as wood, charcoal, bone, seeds and grains, paper, parchment, hair, etc. Here we present details of two recent studies of the Croatian culture heritage dated in the Zagreb Radiocarbon Laboratory. Dating of several other cultural heritage objects from the neighboring countries will be also briefly described. All the results were obtained by AMS (accelerator mass spectrometry) measurement technique [1] that enables analysis of very small samples containing a few milligrams of carbon, and is therefore applicable to various objects of cultural heritage. The conventional radiocarbon age expressed in years Before Present (BP) were calibrated by OxCal software using the IntCal13 calibration curve [2]. The calibrated ages and age spans are expressed as "cal AD". The Cathedral of St. Domnius in Split received a massive gilded wooden door on the Feast of St. George in 1214. The doors (Figure 1), made by the local craftsman Master Andrija Buvina, are 530 cm high and the two wings are 360 cm wide. The doors contain 28 scenes from the life of Jesus Christ. Five wood samples (oak and walnut) from the Buvina’s door were taken, as well as 2 samples from the choir benches from the Cathedral [3]. At least two wooden pieces belong to the original doors from AD 1214 (Figure 2) with the calibrated age spans cal AD 1155 – 1210 (Z-5720) and cal AD 1054 – 1191 (Z-5721). Two samples (Z-5719, Z-6037) are somewhat younger (cal AD 1245 – 1272 and cal AD 1225 – 1266) and one sample is considerably younger (cal AD 1481 – 1650) indicating that they could not have been built into the original doors. The sample Z-6605 from the choir benches was dated to the second half of the 13th century (cal AD 1266 – 1281, Figure 2), as expected, while the other was probably placed into the benches during the repair in the second half of the 20th century. The Old olive tree (Olea europaea L.) on the Veli Brijun Island, National Park Brijuni, Istria, Croatia, was expected to be 1600 years old (Figure 3). However, the inner and oldest part of the trunk in olive trees usually rots, making the radiocarbon analysis of material from the first years of life of the tree impossible. The inside of the Old olive tree was hollow so that the central, older wood was missing. Five samples were taken from the inner side of the trunk. Four of them resulted in conventional radiocarbon ages of up to 150 BP. After calibration it was found that the wood was not older than 300 years. This is in agreement with most other radiocarbon dates of internal wood from living olive trees, rarely older than 300 years [4]. The last sample clearly indicated a younger branch dated to the period cal AD 1979 – 1981, showing thus the complexity of the olive trunk structure.

14C ; dating ; Old olive tree ; Brijuni ; Buvina door ; Split

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