Short abstract

The European project Ancient Charm used non-destructive neutron-based techniques and studied a number of cultural heritage objects from Hungary, Italy and The Netherlands. The goal of the physicists in the project was to develop a 3-D imaging technique based on epithermal neutron absorption and the archaeologists wanted to use the various methods to characterize the heritage objects and, in one case, suggest methods for preservation or restoration.

Project description

The study of cultural heritage objects tries to answer a number of questions like ‘what is it?’, ’how old is it?’, ‘how was it made?’, ‘where does it come from?’ and ‘how do we preserve it?’. Scientific analyses of archaeological and historic objects can help to answer these questions, and suggest methods for restoration and conservation. A large variety of chemical and physical techniques are currently employed for the characterization of objects of cultural significance. Some examples of methods are X-ray fluorescence (XRF), Particle Induced X-ray Emission (PIXE), and photon emission and absorption spectroscopy. Most conventional methods are, however, either invasive (i.e. require removal of a sample, even if a very small one) or are limited to analysis of the object surface. Such methods are widely accepted and appropriate for a whole range of materials; i.e. surface analysis will provide the best insight into the decoration of ceramic and glass vessels, and the patina and minor corrosion phases and residues on metal objects. Sampling of materials such as, for instance, production residues (e.g. slag) and building fabric is normally not a problem.

When it comes to metal artefacts however, cutting/drilling to get samples is not often permitted. Surface analyses will give an idea of the corrosion but tell us little about the composition (and microstructures) of the metal underneath. Neutrons can penetrate materials deeply and therefore thick objects can be examined in neutron-based methods. These methods are also non-destructive; it is not necessary to treat objects before measurements, to clean surfaces, or to take samples by drilling or cutting as is necessary in many other methods. This makes neutrons an ideal probe for non-destructive bulk chemical and crystallographic analysis and imaging of metal objects. The only problem one should consider with some care is the possibility that very small amounts of some elements occurring in an artifact can be activated by neutron absorption. This does not change the chemical properties, but some nuclei having absorbed neutrons can be unstable. Most of the produced radioactivity in neutron-based methods will disappear after a short waiting time. However, in cases where radioactivity with long live times can be produced, it is advisable to limit the neutron fluency to a level such that waiting time is not unacceptable long before the activity is less than internationally accepted levels below which an artifact is not considered to be a radioactive object.

Neutron methods are relevant, too, in cases where bulk analysis is needed for large intact ceramic, glass or stone artefacts, and the decision has been made not to remove samples or to disassemble the object. The constraint of carrying out work at large-scale neutron and x-ray synchrotron facilities is that the methods are non-portable: the objects must be transported to the facility.

The European project Ancient Charm used non-destructive neutron-based techniques and studied a number of cultural heritage objects from three European countries. Ancient Charm stands for Analysis by Neutron resonance Capture Imaging and other Emerging Neutron Techniques: new Cultural Heritage and Archaeological Research Methods.

The results of research to characterize objects can help to answer questions about an artefact's historical and cultural importance. These questions can be about provenance, technology, authenticity, function - functional or ceremonial -, etc. The results can also suggest methods for preservation or restoration. The Ancient Charm collaboration selected a number of objects suitable for the development of the new imaging technique but also with research questions belonging to the list above. Six objects from Italy, Hungary and The Netherlands were chosen, two from each country. Here we will limit ourselves to the objects from the RMO, the Dutch National Museum for Antiquities.

Two presumably ceremonial swords from the Netherlands were analysed. The first, the bronze sword or dirk from Jutphaas, dates from the Bronze Age, more precisely between the 15th to 14th century BC. It is 42 centimetres long, rather thin and flat, the edges are not sharpened and it is perfectly symmetrical. It is believed to be a ceremonial sword of extra-ordinary high quality and without doubt a masterpiece of bronze working. The workshop where it was fabricated was presumably located in Brittany or South England, so it travelled over 800 km. The sword was found in 1947 during dredging activities for a harbour near Jutphaas. The finder, Giel Smidt, gave it to two boys who hung it on the wall of their bedroom. In 2004 the Dutch National Museum of Antiquities in Leiden acquired it.

In total there are five largely similar dirks known. Two originate from The Netherlands (Jutphaas and Ommerschans), two from France (Plougrescant and Beaune) and one from the UK (Oxborough). They are all very similar to each other and too large to handle and too thin to use. They are clearly ceremonial items. It is assumed that they all come from the same workshop. The Jutphaas dirk, however, is much smaller compared to the other four and because of that has been seen by some researchers as a falsification. Results from a NRCA analysis at the GELINA facility in Geel (Belgium) show that the composition of the Jutphaas dirk is very similar to two other dirks (Oxborough and Beaune. The upper part of the Beaune dirk differs in composition but this is a modern repair made from brass. The analysis demonstrates that, notwithstanding its size, the Jutphaas dirk belongs to the group of Ploughrescant-Ommerschans dirks and that the dirk is not a falsification. Moreover it demonstrates that all of the dirks were probably made in one workshop. This, in combination with their wide distribution and extraordinary shape and size demonstrates the special, symbolic character of these weapons.

The bronze sword from Buggenum dates to the Middle Bronze Age between 1300-1100 BC. It can be classified as a Vollgriffschwert, due to the solid grip, of the type Vielwulstschwert, due to the multiple ribs. It is 68 cm long and its blade is 4 cm wide and was originally fabricated in Bavaria, Southern Germany or Austria. The sword does not appear to have been used; it has a fully decorated hilt (cire perdue-casting?) and a blade with a mid-rib and sharp edges.

Based on these characteristics, it was labelled as ceremonial. The object is a very rare object within the Dutch Bronze Age assemblages. It was dredged from an old bedding of the river Meuse near Buggenum in the province of Limburg, the Netherlands in 1964. The finder, Mr. Peters, kept it in his possession until 1999 when it was purchased by the National Museum in Leiden.

The main questions for this object were if the hilt and the blade were produced separately or not and if the sword was a potentially functional weapon.

Three types of analysis were performed on the Buggenum sword, NRCA at the Geel Electron LINear Accelerator (GELINA) in Geel (Belgium) on 13 locations of the sword, neutron diffraction experiments on ENGIN-X of the ISIS facility of the Rutherford-Appleton Laboratory on comparable positions, and neutron tomography at FRM II in Munich. Figure 10 shows the sword at the GELINA facility in Geel in Belgium. Figure 11 shows some of the results from GELINA. It clearly demonstrates the differences in tin and copper weight ratios and the density between the blade and the hilt. They are without doubt separately produced. A radiographic picture show the way blade and hilt are connected. This was confirmed by neutron tomography in Munich.

Neutron diffractions and the Munich data furthermore indicate that the tin contents in the edges differ from the mid-rib of the blade. The edges are homogenized and hardened. The sword was thus manufactured as a potentially functional weapon. This casts some doubts on the label ceremonial with respect to the design of the weapon. In contrast to the Jutphaas dirk mentioned above, the Buggenum sword was not necessarily intended to be a ritual or symbolic object from the moment is was made.

The Ancient Charm project has been successful on all archaeological applications. It shows that the methods used can give answers for cultural heritage objects on topics like characterization (the Hungarian objects), provenance, technology, authenticity (Jutphaas) and functional or ceremonial use (Buggenum). It can also suggest methods for preservation or restoration.

Selected literature:

Giorini G. & Kamermans H. (2011), Neutron-based Analysis for Cultural Heritage Research.Results of the Ancient Charm project. In: Börner W., Uhlirz S. (Eds.) Workshop 14. Archäologie und Computer. Kulturelles Erbe und Neue Technologien.. Vienna: Museen der Stadt Wien – Stadtarchäologie. 211-233.

Postma H., Amkreutz L.W.S.W., Borella A, Clarijs M., Kamermans H., Kockelmann W., Paradowska A., Schillebeeckx P. & Visser D. (2010), Non-destructive bulk analysis of the Buggenum sword by neutron resonance capture analysis and neutron diffraction, Journal of Radioanalytical and Nuclear Chemistry 263(3): 641-652.

Postma H.L., Amkreutz L, Bom V., Borella A, Clarijs M., Eijk C.W.E. van, Fontijn D.R., Kamermans H. & Schillebeeckx P. (2011), Neutron Resonance Capture Analysis (NRCA), elemental compositions of bronze age objects. In: Börner W., Uhlirz S. (Eds.) Workshop 14. Archäologie und Computer. Kulturelles Erbe und Neue Technologien. Vienna: Museen der Stadt Wien – Stadtarchäologie. 659-665.

• 3-d imaging
• characterization
• cultural heritage
• neutron study
• non-destructive analysis

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