Royal Institute for Cultural Heritage

Radiocarbon and stable isotope measurements.

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Royal Institute for Cultural Heritage web based Radiocarbon database

Mark Van Strydonck,  Edwin De Roock

From 1995 onwards IRPA/KIK’s Radiocarbon laboratory started to publish its dates in small publications, continuing the numbering of the preceding lists in Radiocarbon. The first booklet in this series was “Royal Institute for Cultural Heritage Radiocarbon dates XV” (Van Strydonck et al. 1995), followed by three more volumes (XVI, XVII, XVIII). The next list (XIX, 2005) was no longer printed but instead handed out as a PDF file on CD-rom.

The ever increasing number of dates and the difficulties in handling all the data, however, made us look for a more permanent and easier solution. In order to improve data management and consulting, it was thus decided to gather all our dates in a web-based database. List XIX was in fact already a Microsoft Access database that was converted into a reader friendly style and could also be printed as a PDF file. However a Microsoft Access database is not the most practical solution to make information publicly available. Hence the structure of the database was recreated in Mysql and the existing content was transferred into the corresponding fields. To display the records, a web-based front-end was programmed in PHP/Apache. It features a full-text search function that allows for partial word-matching. In addition the records can be consulted in PDF format.

Old records from the printed date-lists as well as new records are now added using the same Microsoft Acces back-end, which is now connected directly to the Mysql database. The main problem with introducing the old data was that not all the current criteria were available in the past (e.g. stable isotope measurements). Furthermore since all the sample information is given by the submitter, its quality largely depends on the persons willingness to contribute as well as on the accuracy and correctness of the information he provides. Sometimes problems arrive from the fact that a certain investigation (like an excavation) is carried out over a relatively long period (sometimes even more than ten years) and is directed by different people or even institutions. This can lead to differences in the labeling procedure of the samples, but also in the interpretation of structures and artifacts and in the orthography of the site’s name. Finally the submitter might change address, while the names of institutions or even regions and countries might change as well (e.g.Zaire - Congo)

At the moment the database contains about 5000 results and new dates are introduced at regular intervals, with the provision that an embargo of at least one year is maintained between the delivery of the report to the submitter and the introduction of the results in the database. Please note that the database shows the data as they were at the time they were entered [e.g. a sample from Zaire isn’t renamed later as from Congo].   

Figure 1: Search form. The featured criteria can be divided in:

a)      Criteria concerning the geographic localisation of the sample, from general (country) to very specific (site name);

b)      Name of the sample, although this is often not known by people who are not directly involved in the concerned dating project;

c)      Dated material. One can select from a list with all the different sample materials;

d)     Period. This can be a specific period (Iron Age, Preboreal, Gothic, etc.) or a date range (between 2000 and 3000 BP). The archaeological or geological period is only mentioned if this information was provided by the submitter;

e)      Laboratory code.

Figure 2: Display of a record. Empty cells are not shown, except for the name of the site (9). If the site name is unknown or if the information is irrelevant, it is referred to as “Provenance: Not defined site at…”. 

The information on the printout contains the following cells:

1) Research field. This can be Archaeology, Geology, History of the Arts, Other;

2) Name of the country;

3) Unique sample name;

4) The radiocarbon date BP ± 1 standard deviation (Stuiver and Pearson 1977). If the radiocarbon content indicates that the sample is younger than 1950 AD, the result is given in PMC (% Modern Carbon) ± 1 standard deviation. In case a sample has a radiocarbon content that is too low to be statistically different from the background the result is specified as “>X BP”, X being the maximum age that can be measured;

5) Indicates the measurement technique. This can be AMS (Accelerated Mass Spectrometry) or b-decay counting, either by Liquid Scintillation Counting (LSC) or by Gas Counting (GC); 

6) d ¹³C expressed in ‰ can be measured by MS or AMS. If measured by AMS the value includes the effects of fractionation during graphitisation and in the AMS-system. Therefore it cannot be compared with d¹³C values obtained per mass spectrometer on CO₂. In the early years of our laboratory this value was not measured;

7) d ¹⁵N (‰) and C/N (carbon nitrogen ratio) are measured for bone samples. In the early years of our laboratory these values were not measured;

8) The uppermost number is the KIK sample number. This code did not exist in the early years of our laboratory. The lowermost number is the laboratory number. This code identifies the laboratory that measured the sample [e.g.: IRPA (KIK-IRPA, Brussels); UtC (R.J. van de Graafflaboratorium, Departement Natuur- en Sterrenkunde, Universiteit Utrecht - NL); KIA (Leibniz Labor für Altersbestimmung und Isotopenforschung, Christian-Albrechts-Universität, Kiel - D); RICH (AMS at IRPA/KIK, Brussels) etc.];

9) Site name;

10) Locality. If possible and useful the geographical coordinates are given as well;

11) Name of the collector and name and address of the submitter;

12) Sample material;

13) Sample position. The sample position can be noted as “cm below surface” or “cm TAW”[1]. The latter is only valid for Belgian samples. In the example this cell is not depicted because it is empty;

14) Associated culture. This information is in most cases provided by the submitter;

15) Context. This field informs about the location of the sample. In fact this can be any type of site description such as a geological layer or an archaeological feature but also a specific area of a painting, cloth or sculpture;

16) This field refers to the common sample pre-treatments such as the AAA-method (Alkali-Acid-Alkali) for charcoal, the Longin-method for bones, etc. No references are given and the specialised literature concerning these pre-treatments should be consulted for further information;

17) This field contains an overall appreciation of the sample quality. During pre-treatment the lab technician notes on the work sheet whether the sample resists very well to the pre-treatment or whether the pre-treatment had to be weak, e.g. because of, sample size, decomposition, etc. The lab technician also notes whether the pre-treatment could be considered as successful according to several parameters tested during the pre-treatment;    

18) Comment. In this field all information can be written down that does not fit into one of the other fields;  

19) Literature references.

The calibrated radiocarbon date is not included because it is already an interpretation of the data. The outcome of a calibration depends on the calibration program as well as on the calibration curve used. Furthermore dates can be calibrated using the Bayesian approach (stratigraphical models, wiggle matching, etc.), which may influence the outcome of the calibration as well.

Conclusion

Although the maintenance of a radiocarbon database is an elaborate and meticulous work, it is the only way to ensure the accessibility of older dates over a long period.   

References

A.N. Shreurs. 1968. Institut royal du Patrimoine artistique Radiocarbon Dates I. Radiocarbon 10: 29-35.

M. Stuiver, H.A. Polach. 1977. Discussion: Reporting 14C data. Radiocarbon 19(3): 355-363.

M. Van Strydonck, L. Forest, M. Landrie, V. Hendrix, K. van der Borg, A. De Jong, 1995.  Royal Institute for Cultural Heritage Radiocarbon Dates XV, ed. IRPA/KIK: 48.