Long lives the Isotop...

14C is a radioactive carbon isotope in the atmosphere surrounding us. Plants e. g. absorb it continuously during photosynthesis, and via the food chain it is taken in by living beings. Consequently 14C exists in the hair of animals, the thread of silk worms and in plants like flax and cotton etc. The process of accumulating 14C is stopped only when an organism dies.

...and it fades away very slowly

As 14C is an unstable isotope its amount in an organism starts to diminish from this moment on – very slowly though, as the so called radioactive half life adds up to 5730 years. Because the remaining amount of the carbon-14 isotope can be determined we can calculate the time when an organism ceased accumulating this isotope – i. e. an animal died or a plant was harvested. Since it is unlikely that, for example, much time passed between the shearing of a sheep and the processing of the wool, this method can often date the production of a textile to within one or two hundred years.

Mind the time range - and the calendar!

The result of this dating method, however, is not a precise date but a relatively broad range of years, due to uncertainty of measurements (the so called standard deviation, indicated as the 1- and 2-σ value). Also, what we receive first is the so called 14C-age which not yet is corresponding to the historical time specification of our calendar. This 14C-age is named as y BP – years Before Present, which is according to convention the year 1950. Therefore, the 14C-age has to be calibrated (i. e., most of all, to be brought in concordance with dates gained by the dendrochronological measurements) which is another complex calculation process. This gives us the actual calendar age.

OxCal

There are different programs for this calibration. To guaranty an optimum of comparability we calculate all incoming dates once again with one and the same calibration program, in this case OxCal version 4.1.

Bibliography

The explanation given above is a simplifying description of an actually highly complicated matter. For thorough description and information, please turn to articles as, for example:

• Horst Willkomm, Alterbestimmungen im Quartär. Datierungen mit Radiokohlenstoff und anderen kernphysikalischen Methoden (München 1976).
• Georges Bonani, Radiocarbon Dating of Milligram Samples of Anatolian Kilims by Accelerator Mass Spectrometry, in: Jürg Rageth (ed.) Anatolian Kilims and Radiocarbon Dating. A new
• Approach to Dating Anatolian Kilims (Riehen 1999) 15/22.
• Mark Van Strydonck / D. E. Nelson / P. Crombe et al. What's in a 14C Date, in: J. Evin / C. Oberlin et al., 3rd International Symposium 14C et Archéologie, Lyon 1998 (Lyon 1999) 433/48.
• Antoine De Moor / Mark Van Strydonck / Chris Verhecken-Lammens, Radiocarbon Dating of two Sasanian coats and three post-Sasanian Tapestries, in: Cäcilia Fluck / Gilian Vogelsang
• Eastwood (ed.), Riding Costumes in Egypt. Origin and Appearance = Studies in textile and costume history 3 (Leiden 2004) 181/7.
• Paula J. Reimer et a., IntCal104 terrestrial radiocarbon age calibration, 0-26 cal kyr BP, in: Radiocarbon 46 (2004) 1029/58
• Antoine De Moor, Radiocarbon dating of ancient textiles. State of research, in: De Moor / Fluck 2007, 99/111.
• Mark Van Strydonck, How accurate are 14C dispersion diagrams in estimating a cultural period in the 1st millennium AD?, in: De Moor / Fluck 2007, 112/4.