Naturwissenschaften und Technologie in der Kunst; Akademie der bildenden Künste Wien; Schillerplatz 3; 1010 Wien
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Conservation of Wall Painting from the Ming Dynasty Temple, China

The Ming Dynasty wall painting of Dazhao Temple in Inner Mongolia.

In the frame of the cooperation project ‘Rescue and Conserve the Endangered Wall Paintings in the Museums of China’, systematic investigations concerning the materials and techniques used in the wall paintings detached from a Ming Dynasty (1368-1644) temple, Dazhao Temple in Hohhot, Inner Mongolia of China, as well as the previous conservation intervention materials have been carried out. X-ray Fluorescence Analysis (XRF), X-ray Diffraction (XRD), Scanning Electron Microscopy in combination with Energy Dispersive X-ray microanalysis (SEM/EDX) were used for the identification of inorganic materials in the wall paintings, while Pyrolysis in combination of Gas Chromatography Mass Spectrometry (Py-GC-MS) was applied for the characterization of binding media.

Identification of proteinaceous materials by Py-GC-MS
Ten of the samples with different colour were analyzed by Py-GC-MS techniques. Reference materials including bone glue, egg and casein were analyzed by using the same Py-GC-MS parameters as the samples.

The Ming Dynasty wall painting of Dazhao Temple in Inner Mongolia.  

One of the results is depicted in figure 1, the total ion chromatogram (TIC) of sample DZS 6 obtained by Py-GC-MS. The marker pyrolysis products for animal glue including pyrrole (m/z 67), 3-methyl-1H-pyrrole hexahydro-pyrrolo[1,2-a]pyrazine-1,4-dione (m/z 154), 1H-isoindole-1,3(2H)-dione and toluene were detected in the samples. Comparing to the reference material of animal glue, it can be concluded that animal glue is present in all the ten samples.

Fig. 1: TIC of sample DZS 6 obtained by Py-GC-MS analysis, 1: Pyrrole, 2: Toluene, 3: Furfural, 4: 3-methyl-1H-pyrrole, 5: 2-methyl-1H-pyrrole, 6: Benzonitrile, 7: 1-(1H-pyrrol-2-yl)-ethanone, 8: 1H-pyrrole-2-carbonitrile, 9: Azulene, 10: 1H-isoindole-1,3(2H)-dione, 11: Benzofuro[3.2-d]pyrimidin-4(3H)-one, 12:Hexahydro-pyrrolo[1,2-a]pyrazine-1,4-dione, 13: Phthalic a Stearic acid cid butyl undecyl ester, 14: Oleic acid, 15: Stearic acid

The identification of consolidation materials used in the painting by Py-GC-MS  

In order to find out consolidation materials used in the previous conservation, the five samples taken from the conservation intervention areas (DZS A-E) were subjected to Py-GC-MS analysis. The chromatograms of the five samples obtained by Py-GC-MS are similar, the dominant peak in the chromatograms is phthalic anhydride (RT 23.44 min), which indicates that alkyd resins are present in the five samples, for all alkyd resin, phthalic anhydride was the main peak detected by pyrolysis and was therefore used as the diagnostic peak for alkyd resin. One of the chromatograms is depicted in figure 2.  Styrene and vinyl toluene were detected in the chromatogram also. They are the copolymers of alkyd, since alkyds were often modified with these compounds to improve certain properties. Dibutyl phthalate and dipropyl phthalate are the plasticizers normally used in alkyd for desired flexibility and durability.

Fig. 2: TIC of sample DZS-D obtained by Py-GC-MS analysis; 1: propanal, 2: 2-propen-1-ol , 3: toluene, 4: styrene, 5: vinyl toluene, 6: benzoic acid 2-propenyl ester, 7: Phtalic anhydride, 8: 2-(hydroxymethyl)-1H-isoindole-1,3(2H)-dione, 9: dipropyl phthalate, 10: dibutyl phthalate  

No surprise, animal glue was identified as binding medium, which was also found in other Chinese wall paintings. The conservation materials used in the wall painting are the copolymer of alkyds with styrene and vinyl toluene. This information will definitely be essential for making proper conservation strategies for this valuable object.

Poster

Papers:

S. Wei, M. Schreiner, H. Guo, Q. Ma:
Scientific investigations about the materials in a Ming Dynasty wall painting
Journal of International Conservation Science, 3 (2010) 99-112