CIRAM laboratories carry out carbon-14 (or radiocarbon) dating of your art objects in wood, ivory, bone, textiles... but also of organic materials in general. Discover CIRAM's protocols for dating ivory objects: dating method, calibration of results and interpretation. Our scientists interpret the results with the utmost precision, so you get the results you expect.
Carbon-14 dating techniques for ivory from CIRAM laboratories
Radiocarbon (carbon-14) dating quantifies the time that has elapsed since the death of an organism. The technique is based on measuring the amount of carbon 14 remaining in an organism after death. 14C is a radioactive carbon isotope that decays progressively according to a known exponential law. Its concentration is halved every 5,730 years. Beyond 60,000 years, the quantity of carbon 14 is too small to be measured. This is the dating limit.
Collagen extraction, the first step to precise dating
Ivory is composed of a mineral part, bioapatite, and an organic part, collagen. Collagen is the most suitable fraction and is normally used for radiocarbon dating. The first step in the dating process is therefore collagen extraction. To this end, samples are treated with hydrochloric acid (HCl, 1 M), then treated with sodium hydroxide (0.1 M) at room temperature and again treated with cold hydrochloric acid, to avoid absorption of atmospheric carbon dioxide. After washing with demineralized water, the samples are boiled to dissolve and recover the collagen.
Collagen analysis, a crucial step in ivory dating
The extracted collagen undergoes combustion at 920°C and is transformed into gas. During this stage, an initial check of the C/N ratio is carried out using an elemental analyzer (Elementar Vario ISOTOPE Select). This step is essential, as it constitutes a quality control. A C/N value between 2.9 and 3.6 indicates that the collagen is well preserved and will provide reliable dating. If the C/N ratio is outside this range, the collagen will not be C14 dated. In this case, the mineral part of the ivory can be used to date the bioapatite. Stable carbon and nitrogen isotope analysis will then be carried out using IRMS. These values will provide information on the terrestrial or marine origin of the ivory. At the same time, carbon dioxide from combustion is separated from other residues using a zeolite trap. This carbon dioxide is then catalytically converted into graphite using an automated system (AGE 3, Ion Plus).
Mass spectrometry for radiocarbon measurement
For radiocarbon measurement, we use mass spectrometry coupled to a particle gas pedal (AMS). This method requires very little material (1 mg of pure carbon compared with 1g previously), a minimum of time (around 1 hour of counting instead of several days or weeks in the past) and a more accurate result.
Gross age and calibrated dating: the importance of calibrating results
To obtain reliable and relevant data, it is important to calibrate the results based on :
- Gross age: expressed in BP years (before present, or before 1954), based on the assumption that carbon-14 concentration has been constant in time and space.
- To obtain calibrated dates, calibration curves are used, which take into account variations in carbon-14 content in space and time. These calibrated dates, combined with probability percentages, are used to verify the authenticity of an ivory object.
The problem of recent dating (after 1954)
It is possible to tell whether objects were made before or after 1954 by their carbon-14 content, but how?
This artificial "boundary" was man-made, as atomic bombs and atmospheric nuclear testing in the 50s and 60s doubled the amount of carbon-14 in the atmosphere.
In recent objects, our scientists have detected abnormally high levels of carbon 14. However, since the end of atmospheric nuclear testing in the mid-1960s, we have seen a steady decline in the quantity of C14. This phenomenon makes it possible to provide very precise dating of recent years (to within one or two years in the best case), used for dating wine, for example.
Carbon-14 dating in Tribal Art
Radiocarbon dating is relevant to Tribal Art, because carbon 14 can absolutely differentiate between objects made from materials that lived before and after 1954. Carbon 14 clearly identifies copies and fakes. The analysis is equally effective for older cultures.
But these scientific "tests" must be combined with a historical and stylistic study of a work. It is important to maintain a global and comprehensive approach to deliver accurate and reliable results. Carbon-14 dating must be used as an objective aid to decision-making.
Filing a CITES dossier with radiocarbon dating
Carbon-14 dating of ivory is also useful for filing a CITES dossier, to prove that the animal died before 1947. The 1975 UNESCO Convention restricts the sale and possession of elephant tusks.
Whether for the art market or archaeology, carbon-14 dating is a major advance. Over the years, this analysis has become a precious and indispensable tool for CIRAM laboratories.
