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CIRAM Corp. Head office: c/o Constantin – 575 Madison Avenue, 25th Fl., Mobile: +1-917-509-5616 New York, NY 10022, USA E-mail: [email protected]

This document has been protected with CIRAM Track® process

Dr. Armel Bouvier for CIRAM Corp. New York, June 26th 2016 (1)

information given by the applicant. (2)

sample was taken by CIRAM Corp. (3)

conclusions given by CIRAM Corp. are based on the study of a single micro-sample, which is not necessarily representative of the whole object. In addition, they concern the dating of the constitutive material of the object and not its manufacturing.

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SCIENTIFIC REPORT 0516-OA-32N-2

DESCRIPTION OF THE OBJECT

Object and raw materials (1): Wooden Bowl Presumed origin and period (1): Congo, Kuba people, 18

th – 19

th century AD

Sizes: H.: 13 cm w.: 54 cm

P1: Wood sample from the base

SAMPLE (2)

Sample P1 has been analysed by C14 method associated with a mass spectrometer (AMS-system), in order to date the raw material.

Conventional Age: 220 ± 20 BP After calibration (2 σ): 1646 – 1679 AD (40.8% probability) (95.4% confidence) 1764 – 1800 AD (43.9% probability)

1938 – 1950 AD (10.7% probability)

This dating range is consistent with the presumed attribution. The wood has most probably been cut between the end of the 17th century and the first half of the 20th century.

The dating of the wood is consistent with the presumed period of this object (3)

.

Abstract of analysis results

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AIMS

EXPERIMENTAL METHODS

SAMPLE

The aim of the radiocarbon dating is to provide information on the consistency of the cutting of the tree with its supposed attribution.

The wood sample was mechanically and chemically cleaned, in particular with Soxhlet extraction system, erasing modern or ancient pollutions. Then, the CO2 was extracted. The different carbon isotopes were separated using a mass spectrometer, and the 14C content has been determined by comparing the simultaneously collected 14C, 13C and 12C beams with those of reference products (Oxalic Acid, CO2, charcoal).

The 14C conventional age was calculated according to the method described by Stuiver and Polach (Radiocarbon 19/3 (1977), 355); it takes into account the 13C correction for isotopic fractionation, based on the comparison between the concentration measurements of 13C/12C and 14C/12C. The measuring uncertainty (standard deviation ) was evaluated from both the counting statistics of the residual 14C measurement, the variability of the interval results and the substraction of the background. Due to the location of the provenance country, the calendar age was calculated using the following calibration procedure: OxCal v4.2.4 (Bronk Ramsey, 2013, Radiocarbon 51, vol. 4 337 – 360) IntCal13, northern hemisphere calibration (Reimer et al., 2013, Radiocarbon 55, vol.4, 1869 – 1887). The sample gave enough carbon, and produced sufficient ion beam during the AMS measurement. The 13C value is in the normal range and insofar the results are reliable.

The study was carried out on a single sample (Fig. 1):

P1: Wood sample from the base.

Fig. 1: Detailed view of the object and localization of the sample (arrow).

P1

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RADIOCARBON DATING - P1

Fraction Corrected pMC Conventional Age 13

C (‰)

Wood, alkali residues 97.35 ± 0.27 220 ± 20 BP - 25.65

After calibration (2 σ): 1646 – 1679 AD (40.8% probability) (95.4% confidence) 1764 – 1800 AD (43.9% probability)

1938 – 1950 AD (10.7% probability)

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CONCLUSIONS

The radiocarbon dating of the wooden bowl showed that:

Sample P1 has been analysed by C14 method associated with a mass spectrometer (AMS-system), in order to date the raw material.

Conventional Age: 220 ± 20 BP After calibration (2 σ): 1646 – 1679 AD (40.8% probability) (95.4% confidence) 1764 – 1800 AD (43.9% probability)

1938 – 1950 AD (10.7% probability)

This dating range is consistent with the presumed attribution. The wood has most probably been cut between the end of the 17th century and the first half of the 20th century.

The dating of the wood is consistent with the presumed period of this object. The analysis and the report have been performed by Dr. Armel Bouvier.

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RADIOCARBON DATING PRINCIPLES

The Carbon 14 dating is based on the measurement of the radiological activity of the 14C contained on all the organic materials. It permits to determine the time passed since the death of the organism to be dated (cut of the tree, for instance). Historical information

At the end of the 1940’s, US works tried to evaluate the potentialities of using the natural radioactivity properties of the Carbon 14, for the dating of organic materials [1]. Then, during the 1950’s, Willard Frank Libby began to perform experiments on Egyptian samples, successfully, and obtained the Nobel Prize of Chemistry for the development of this method [2-3]. From this moment, with the evolution of measurement techniques and the increasing of their reliability, it appeared that the initial principle had to be revaluated, that led to elaborate a “calibration procedure” of the results based on, in particular, the comparison with information given by other dating methods (dendrochronology, for instance) [4]. Method principle The carbon 14 (14C), or radiocarbon, is a radioactive isotope of the Carbon element, with a radioactive period (or half-time) equal to 5730 years. A living organism incorporates carbon, without any isotopic distinction, the 14C content against total carbon (12C, 13C and 14C) being the same as the one existing in the current atmosphere. The radiocarbon dating is based on the presence, in all living organism, of a little content of radiocarbon (about 10-12 for the C14/total C ratio). When the organism dies, the exchanges with the environment are stopped, and the quantity of internal radiocarbon decreases with time according to a defined exponential law (natural decay of Carbon 14 atoms). An organic material sample extracted from this organism can be dated by measuring the 14C/total C ratio.

Exponential decay curve of 14C

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REFERENCES FOR RADIOCARBON DATING

Antiquity evaluation To date a sample of organic material consists on the measurement of the C

14/total C ratio and the

deduction of its age. The 14C/total C ratio is measured indirectly by the measurement of the specific activity due to the natural radiocarbon, proportional with the 14C/total C ratio, or directly by mass spectrometry (AMS-system). Nowadays, the direct measurement of the 14C/total C ratio using the second method is the most frequently performed because it permits to date smaller samples (less than one milligram against several grams of Carbon before) and with a minimal time (less than one hour against several days or weeks). In practice, the carbon extracted from the sample is first changed into graphite, then into ions that are accelerated by a tension generated by a mass spectrometer coupled with a particle accelerator. The different carbon isotopes are separated, that allows counting the Carbon 14 ions. Note that the samples older than 50,000 years cannot be dated with radiocarbon method, because the 14C/total C ratio is then too low to be measured by actual techniques. Conventional Age and calibrated Age The conventional Carbon 14 age of an organic material sample, given in years “before present” (BP), is calculated by considering the two following elements: - the carbon 14 decay period was measured by Libby, around 1950, at 5568 years ; but more recent

and more precise experiments were carried out, giving a period of 5730 years; - the reference date from which the time passed since the death of the organism is measured was

fixed at 1950 by Libby.

Furthermore, as early as the beginning of 1960’s, systematic divergences were observed, on the same samples, between the 14C age and the one estimated from archaeological considerations or dendrochronological approach. Indeed, it appears that consecutively to the variations of the magnetic field of the Earth, the production of the natural radiocarbon has varied during time. Climatic changes and important dumping of fossil carbon in the atmosphere due to industry and transports modified also the total content of carbon, and so carbon 14. In addition, during the 1950’s and the 1960’s, nuclear bomb tests caused the doubling of the radiocarbon quantity in the atmosphere.

Consequently, the conventional principles defined by Libby being not satisfying and the total content of carbon 14 in the biosphere being not equal during time, it became necessary to build calibration curves by comparing 14C dates and results obtained with other dating methods, like dendrochronology. Then, using these curves, we apply a correcting factor to the BP age, and we change it in a calibrated or calendar age, given in chronological intervals associated with a percent of probability [5-6].

[1] G. Marlowe, 1999, « Year one: radiocarbon dating and American archaeology, 1947-1948 », American Antiquity, LXIV/1, p. 9-32.

[2] W.F. Libby, 1955, Radiocarbon dating, 2nd edition, University of Chicago Press, Chicago. [3] G. Marlowe, 1980, « W.F Libby and the Archaeologists, 1946-1948 », Radiocarbon, XXII/3, p. 1005-1014. [4] R.E. Taylor, 1987, Radiocarbon dating: an archaeological perspective, Academic Press, London, chap. 6. [5] M. Stuiver et al., 1998, « CALIB rev 4.3 (Data set 2) », Radiocarbon, vol. 40, p. 1041-1083. [6] A.J.T. Jull, 2003, Radiocarbon, vol. 46, 18th conference, Wellington.

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