Naturwissenschaften und Technologie in der Kunst; Akademie der bildenden Künste Wien; Schillerplatz 3; 1010 Wien
Research > Projects > Material Analysis > Identification of Natural Organic Materials Print

Conservation Project of Wall Painting from Tang Dynasty Royal Tombs

 

The archaeological discoveries of Tang tomb murals in Xi’an, China have brought to light unprecedented data for the study of the art of the Tang Dynasty (618-907 AD).They are like an inexhaustible encyclopedia, which provides first-hand material for the study of the history, social life and painting techniques in the Tang Dynasty. After their excavation the murals were detached from the tomb chambers and stored in Shanxi History Museum, amounting to about 1000 m2 of painted area, collected from nearly twenty Tang tombs by taking the layer of the upper 0.5-1 cm of the murals off the tomb walls. In the frame of the cooperation project ‘Rescue and Conserve the Endangered Wall Paintings in the Museums of China’, the systematic analytical investigation described in this report has been carried out.
Figure 1a-c are the wall paintings which were investigated in this study.

 

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a) The wall painting of Weishi’s tomb (B185), b) The wall painting from prince Zhanghuai’s tomb (B113) and c) The wall painting from Li Shuang’s tomb (B31).

Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and gas chromatography-mass spectrometry (GC/MS) were applied for the characterization of the binding media in the paintings. The combination of these analytical techniques is ideal methodology to identify binding media in unknown samples, which covers wide range of substances, such as synthetic resins, natural resins, drying oils and proteinaceous materials. The two-step derivatization procedure for GC/MS analysis: In the first step, samples are derivatized with trimethylsulfonium hydroxide (TMSH) reagent for the identification of oils, resins . The procedure enables for the quantitative analysis of fatty acids, which subsequently makes the classification of various types of oil possible based on A/P (aezlaic acid to palmitic acid) and P/S (palmitic acid to stearic acid) ratios. Although terpenic resin compounds contain hydroxyl groups, that cannot be derivatised with TMSH reagent, the procedure enables identification of the marker compounds of resins. In the second step of the analytical procedure, the sample residue from the first step analysis is evaporated to dryness, hydrolyzed and then derivatized with ethyl chloroformate (ECF) reagent for the quantitative analysis of amino acids. Based on the relative composition of amino acids, classification of different proteinaceous materials can be achieved.

Peach gum, animal glue, linseed oil and pine resin were identified in different samples. Peach gum is the material normally used for consolidation purpose during detaching the painting from wall. Animal glue was found in two paintings from two tombs (in samples B31, B113), which could be the original binder of the paintings, according to historical literature. It is the first time that linseed oil and pine resin are found in Tang Dynasty wall paintings (in samples B185-2, B31-1, B31-2). They could either be the original binding media or components of later conservation intervention, which needs further investigation.

Papers:

S. Wei, M. Schreiner, E. Rosenberg, H. Guo , Q.  Ma:
Identification of the binding media in Tang Dynasty Chinese wall paintings by using Py-GC/MS and GC/MS techniques
Journal of International Conservation Science, 2 (2011) 77-88