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X-ray Radiography Applied to the Study of the Ancient Manufacturing Technique and the State of Conservation of Cultural Relics Junchang Yang Xi'an Center for the Conservation and Restoration of Cultural Relics 12 Xing Shan Si East Road, 710061 Xi'an, P. R. China Yanli Duan Xi'an Air Force Engineering University, 1 Feng Hao Lu, 710077 Xi'an, P. R. CHINA Contact

Summary

X-ray radiography (XR) is a non-destructive testing technology. This paper presents some practical cases in which X-ray radiography is used and X-ray films are highly informative in the state of conservation and the ancient manufacturing techniques. These cases show that X-ray radiography is available in the study of cultural relics, which is made of varieties of materials.

Introduction

The use of X-ray Radiography (XR) to study historical objects started in 1996 in Xi'an Center for the Conservation and Restoration of Cultural Relics (XCCR) with the three-year-term cooperation project between P. R. China and Italy. The X-ray radiography is a photography using x-ray as a light source and it is a non-destructive testing technology, so it is available to be used in the study of cultural relics because of its non-destructibility. Objects whose restoration work has not been made before are mainly from some local museums, for example, Shaanxi History museum, Banpo museum and other county museums. These objects include bronzes (ancient ritual vessels, mirrors and weapons, etc.), irons (vase, etc.), pottery and ceramics and so on. The examination is made, using X-ray radiography, firstly to reflect the state of ancient objects and secondly to get some manufacturing information for the study of ancient manufacturing techniques.
Usually X-ray film is made before restoration in order to reveal the state of conservation of objects. For the ancient technical problems it is better to make x-ray during and after restoration because in this way some special parts can be aimed at and some disturbed factors can be cut off. The x-ray films produced in X-ray laboratory are highly informative. From x-ray films we made, the state of conservation, the past repairs, jointing techniques, structure characteristics, etc., can be clearly shown. It is more important to know the state of conservation and the past repairs because it is the basis to draw up the restoration plan. Jointing techniques, structure characteristics, and other technical traces are the important clue to make the further study of ancient manufacturing techniques.

Case 1: bronze mirror, Han dynasty
Figure 1 shows a one-fourth-bronze mirror, its radius being 56.3mm or so. From Figure 1 we can see that the mirror is mostly covered with patina and some soil, and therefore the decorative pattern on the surface is also blurred. X-ray radiography is made in order to understand the state of its preservation and to get a clear information of its decoration. In the practical work 3 x-ray films have been taken due to different thickness of the mirror. X-ray films produced show clearly the distribution of cracks and micro-cracks inside (fig.2, left), and the decorative pattern and 2 writings (Fig. 2, right). The state of conservation of object is the foundation of working out the restoration plan, and the writings and the decorative pattern provide the evidence of dating for the bronze mirror belonging to Han dynasty.

Fig 1: The one-fourth-bronze mirror before making restoration.	Fig 2: The x-ray films of the mirror, reflecting the distribution of cracks and micro-cracks inside, and the clear writings and the decorative pattern.

Case 2: Bronze He, Western Zhou
Figure 3 is the bronze He which was used for drinking wine in ancient time, belonging to the Western Zhou and from the Fufeng country museum. X-ray films produced reflect the good state of conservation, but the inside morphology of the coiling dragon on the lid and the relationship between the animal and the body are more interesting. The radiograph in Fig. 4 (left) shows clearly that the animal handle are cored, and at two joints of the handle there are two bosses which were cast integrally with the vessel. Obviously the handle was pre-cast and installed in the outer mold, and then it was jointed together with the body by casting. From the same radiograph the clay spacers (black square block) on the inside core mold of the animal handle can be seen. The radiograph of the lid (fig.4, right) reveals that some clay protrusion on the core mold inside the coiling dragon also exists, which serve the function of as same as the chaplet (spacer) usually being found and used in Chinese ancient bronzes.

Fig 3: The bronze He, Western Zhou.	Fig 4: The x-ray film of the jointing structure between the animal and the body (left),and the x-ray film of the lid (right).

Case 3: Iron sward with jade, Han dynasty
The iron sward (Figure 5) was excavated from a tomb, its length being about 856mm. From its surface we can see it was corroded, but we can not know its corrosion situation. Before restoration the x-ray radiographic examination is carried out and it shows the corrosion morphology of the sword (Fig.6), it's maximum thickness being about 5mm. As we know, when iron is corroded, its base become porous and loose and for x-ray it is easy to penetrate the loose part. Therefore the surviving body of the sward and the corroded layer can be easily distinguished from the x-ray film and the conclusion about corrosion situation can be got. Understanding the corrosion situation is very important for a restorer because he can work out the conservation plan according to the state of preservation of it.

Fig 5: The iron sward with jade, Han dynasty.

Fig 6: The drawing of x-ray, which shows the corrosion morphology inside the iron sward

Conclusion

Radiography produced in our work is highly informative. As a non-destructive scientific method, x-ray radiography can be employed in varieties of cultural relics to get some direct concealing information about the state of the conservation, past restoration works, ancient repairs and technical problems. Here also it is necessary to point out that if objects need to do TL dating analysis, x-ray radiography must be done after TL dating.
The portability is one of the most important factors in the examination of ancient objects, for in many cases an object is not allowed to be taken to a laboratory even for researchers and the examination must be done in situ with a simple equipment.
For an operator, the experience of operating x-ray instrument is necessary, but it is of great importantance to have some basic knowledge about ancient manufacturing technology to varieties of materials, for example, pottery and terracotta objects, bronze vessels, etc. Like this there is a determined purpose in the practical work when a x-ray film is made in laboratory.
Using some assistant tools, for example, optical magnifier is necessary and useful when the radiographs are observed and read. In this way some information in details can be taken and at the same time some drawing and notes must be done.
About image processing of x-ray films is another more important thing. The use of computer makes both the qualities of x-ray films better and also this process simpler and more convenient.

References

1. ARTURO GILARDONI, 'X-rays in Art' (second edition), Grafica & Arte Bergamo (1994).
2. JUNCHANG YANG, 'X-ray radiography applied to the study of the ancient manufacturing
   technique and the state of conservation of cultural relics', Xi'an Center for the Conservation
   And Restoration of Cultural Relics, Xi'an (1998).
3. JUNCHANG YANG, 'X-ray radiography applied to the study of Chinese ancient bronzes', Studies
   Of Bronze Culture 1 (1999) 151-154.

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