Analytical study of traditional decorative materials and techniques used in Ming Dynasty wooden architecture. The case of the Drum Tower in Xi’an, P.R. of China

Journal of Cultural Heritage 5 (2004) 273–283 www.elsevier.com/locate/culher

Original article

Analytical study of traditional decorative materials and techniques used in Ming Dynasty wooden architecture. The case of the Drum Tower in Xi’an, P.R. of China Rocco Mazzeo a,*, Darinn Cam b, Giuseppe Chiavari a, Daniele Fabbri c, He Ling d, Silvia Prati c a

Department of Chemistry “G. Ciamician”, University of Bologna, Via Selmi 2, 40126, Bologna Italy b Environmental Research Centre, Via Ciro Menotti, 48, 48023, Marina di Ravenna (RA), Italy c Laboratory of Chemistry, C.I.R.S.A. University of Bologna, via S.Alberto 163, Ravenna, Italy d Chemistry Department, Jaotong University, Xi’an (Shaanxi), P.R. China Received 20 January 2004; accepted 7 June 2004

Abstract Only few published information are available in the conservation literature on materials and techniques used by ancient Chinese artists to decorate wooden architectural buildings. This paper presents the results of a joint research aimed at collecting technical information through an historical survey and studying the results of the scientific examinations carried out on the paint samples collected from the decorated surfaces of the Drum Tower in Xi’an, a Ming Dynasty monument built up in 1380 AC. Optical microscopy of the cross-sections, scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), X-ray diffraction as well as pyrolysis-gas chromatography– mass spectrometry have been used to both characterise the inorganic pigments composition and the binding media used. The analytical results showed that the materials composition and technique used to plaster the wooden surface are in good agreement with the information gathered through the historical survey. In fact, clay, lime, siccative oil, probably tung oil and fabrics’ strips are the main plaster components. At the same time the plaster represents the priming material for the painted decorations whose pigments composition, indicates that they are both original and applied on the occasion of a past restoration procedure carried out in the XVIII century even though the binding medium used follows the ancient tradition. © 2004 Elsevier SAS. All rights reserved.

1. Research aims Very few publications are available on materials and techniques used by ancient Chinese artists to decorate wooden architectural buildings [1]. On the contrary, the nowadays restoration of decorated Chinese wooden architectural structures makes extensive use of modern materials whose performance, when exposed to outdoor environments, has not been yet fully evaluated. This research is aimed at contributing to a better understanding of the original

materials used in the past so that the implementation of further research studies make take advantage of this knowledge when studying the most appropriate restoration materials and methods to be adopted. In this research the results of scientific examinations carried out on the paint samples collected from the decorated surfaces of the Drum Tower in Xi’an have been compared with information collected through historical survey on ancient decoration techniques. 2. Introduction

* Corresponding author E-mail addresses: [email protected] (R. Mazzeo), [email protected] (D. Cam), [email protected] (G. Chiavari), [email protected] (D. Fabbri), [email protected] (H. Ling), [email protected] (S. Prati). 1296-2074/$ - see front matter © 2004 Elsevier SAS. All rights reserved. doi:10.1016/j.culher.2004.06.001

The Drum Tower (Fig. 1), so called because of the presence of a huge drum used to tell the time at dusk, is a magnificent wood monument built in 1380 AC (thirteenth

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year of Hong wu in the Ming Dynasty) in Xi’an. Decorations are present on the wooden structure of both stories and can be assigned to the “geometric and scrolls” category that was mainly used to decorate official important buildings. Actually the remains of the external decorations are in very bad conditions as they suffer flaking and blistering phenomena that are much more evident on the west side façade (Fig. 2). A partial previous restoration intervention carried out at the end of the seventeen and the first half of the eighteenth century on the painted decorations has been documented as well as the repainted decorations done by Russians in 1953 and nowadays visible on the ceiling of the first floor. Furthermore, small parts of the decorated beams of the first floor have been completely repainted with acrylic pigments in 1996 in order to show how the final restoration would look like by its completion. The available information concerning the ancient techniques used to paint decorations on wooden architectural

structures, refer to the one used in Qing Dynasty. Qi Yingtau [2] mentions that the technique was characterised by a first application on the wood of a plaster aimed at both protecting and concealing the wooden surface faults. At the same time the plaster, made of tung oil, brick powder, lime, flour and pig blood represents the priming material for the painted decorations. The application of fabric strips, fixed to the wooden support with iron nails, follows. The decorations were painted, over the fabric strips, using pigments with tung oil as binding medium. In ancient time the use of donkey glue, bone glue and/or tung oil is reported as well. The use of blood in order to improve the plasters’ adhesive qualities is already attested in western countries. Davey [3] mentions bullock’s blood as organic additive used in England since earlier times and during the Italian “stucco revival”. Furthermore Bostock and Riley [4] gave an explanation as to why ox blood is preferred over the other. In Asia, an oral source refers to the use of blood as binder for plastering the wooden structure of the Amarbayasgalant Monastry (1727– 1735) in Mongolia [5]. 3. Experimental section 3.1. Sampling

Fig. 1. The Drum Tower, Xi’an, (P.R. of China).

In order to characterise both the original scheme of polychromy and the materials used, six paint samples (DR1, DR2, DR3, DR4, DRgold and DR6) were collected from the decorations of the second level of the west side façade. After a careful examination of the fragments under a binocular stereo microscope they have been cross-sectioned and submitted to different analytical investigations. Optical and scanning electron microscopy coupled with electron beam

Fig. 2. Flaking phenomena of the painted decorations.

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Fig. 3. Cross-section of sample Drgold: (a) optical photomicrograph (50× original magnification): (1) first layer of plaster, (2) cotton fabric embedded into an organic material, (3) second layer of plaster, (4) green layer, (5) yellow layer, (6) brown varnish layer with gold leaf on the top; (b) SEM-BSE micrograph: the presence of heavier chemical elements below the gold leaf can be observed.

microprobe analysis using an energy-dispersive X-ray detector (SEM-EDX) were employed in order to characterise the stratigraphic morphology and determine the elemental composition of each paint layer. X-Ray diffraction was used to confirm the composition of some pigments and pyrolysis-gas-chromatography mass spectrometry was performed in order to characterise the nature of the organic binding media used. The latter was also

used to characterise the chemical nature of a reference sample of tung oil, which was spread over a glass support and left curing for three years (1995–1998) in China under normal laboratory environmental conditions. To this regard it has to be pointed out that no air conditioning system was available at that time in the laboratory of the Xi’an Centre for conservation, so that both temperature and relative humidity fluctuations were very high.

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Fig. 4. Sample DR3: cotton textile fibres embedded into the brown organic layer (SEM).

3.2. Methodologies 3.2.1. Pyrolysis–Gas chromatography–Mass Spectrometry In this study, analytical pyrolysis [6–12] experiments were performed using an integrated system consisting of a CDS Pyroprobe 1000 heated filament pyrolyser (Chemical Data System, Oxford, PA, USA) and a Varian 3400 gas chromatograph coupled to a Saturn II ion-trap mass spectrometer (Varian Analytical Instruments, Walnut Creek, CA, USA). A DB-5MS J&W capillary column (30 m × 0.25 mm; i.d.: 0.25 µm film thickness) was programmed from 50 to 300 °C at 5 °C/min, holding the initial temperature for 2 min. The samples, less than 1 mg, were pyrolysed without treatment in duplicate through a quartz sample holder at 700 °C for 10 s. The pyrolysis experiments were carried out in the methylating conditions adding 5 µl of an aqueous solution of 25% of tetramethyl ammonium hydroxide (TMAH) to the sample before pyrolysis; in this way it is possible to obtain the methylation of carboxylic and hydroxyl groups. This procedure is called thermally assisted hydrolysis and methylation (THM), TMAH thermochemolysis or more simply pyrolysis-methylation. PY-GC interface was kept at 250 °C and the injection port at 250 °C. Injection mode was split (1:50 split ratio). The carrier gas was Helium at a flow rate of 1.5 ml/min. Mass spectra (1 scan/s) were recorded under electron impact at 70 eV from 40 to 450 m/z. 3.2.2. Optical microscopy (OM) Samples were embedded in a resin support, then crosssectioned and polished according to conventional methods. Dark field observation of cross-sectioned samples has been performed using a LEITZ LABORLUX S microscope equipped with fixed ocular of 10× and objective of 10×.

3.2.3. Scanning Electron Microscopy–Energy Dispersive X-Ray spectroscopy (SEM-EDX) In this study, a Scanning Electron Microscope, Philips XL 20 model SEM-EDX equipped with an Energy Dispersive X-ray Analyser was used on the same cross-sectioned samples already prepared for the optical microscopy observations. The elemental composition was carried out at an acceleration voltage of 25–30 KeV, lifetime > 50 s, CPS ≈ 2000 and working distance 34 mm. 3.2.4. X-ray diffraction A Philips 1015 with a CuK radiation, 40 KV and 40 mA, Ni filter radiation was used to characterize the pigment composition. Diffraction patterns were interpreted by comparison with JCPDS data. 3.3. Analytical results 3.3.1. Preparation layers All analysed samples are characterised by two preparation layers with, in between, the presence of fabric strips, embedded into an organic matrix (Fig. 3a). The fabric strips are made of cotton as confirmed by microscopic observation and comparison with standard cotton fibres (Fig. 4). Furthermore, differences in fabric weft and colour were observed. Sample DR1 in fact presents a wider fabric weft which has a brownish colour if compared with all other samples were the weft is smaller and the fabrics colour is white, indicating the use of a less amount of organic material applied before their application above the underneath plaster layers. In all samples, a similar elemental composition (Table 1) of the two preparation layers was detected, showing the presence of silicon, aluminium, iron, potassium and sodium, which are all indicative of the use of clay as filler. Calcite and quartz Inclusions were also present in all samples.

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Table 1 Results of the Py-GC-MS and SEM-EDX analyses (in brackets elements detected in trace amount) Sample DR1

DR2

DR3

DR4

DRgold

DR6

a

Py-GC-MS Main fragments Azelaic acid Palmitic acid Stearic acid Benzoic acid Phtalic acid Dimethyl ester Azelaic acid Palmitic acid Stearic acid

Material identification Siccative oil Anthraquinone dye or alkoid resin

Siccative oil

Azelaic acid Palmitic acid Stearic acid Pirrole Azelaic acid Palmitic acid Stearic acid As4 Azelaic acid Palmitic acid Stearic acid As4

Siccative oil and Animal glue

Azelaic acid Palmitic acid Stearic acid As4

Siccative oil

Siccative oil

Siccative oil

OM Stratigraphy

Thickness (µm)

SEM-EDX Elemental composition identification

1 Superficial layer a Red 18 Brown plaster 30 Brown organic layer with traces of brown plaster

Ba, S, Si, Ca (Al, K, Fe) C, Ba, Ca, S (Si, Al) Si, Ca, Al, (Ba, S, Mg, Fe, K, Na) C, Si, Ca, Al, (Fe, K, Na)

Red 1 Blackish organic layer 1 Orange/Red 2 Brown plaster 5 Brown organic layer with traces 15 brown plaster Blue 5 Brown plaster 15–20 Brown organic layer 10 White cotton fibres 30–40 Green 2–5 Brown plaster 40 Brown organic layer 20–25 Brown plaster 40 Gold leaf Varnish Yellow 2 Green 3–4 Brown plaster 15–30 Brown organic layer 20–30 Brown plaster 20 Grey 2 Brown plaster 15 Brown organic layer 20 Brown plaster 35-40

Pb C, O Pb Si, Al, Mg (Fe, K, Na) C, Si, Al, (Mg, Fe, K, Na) Si, Al, S, Na, (Ca, Fe, K) Si, Al, Mg (Fe, K, Na) C, O C, O As, Cu Si, Al, Ca, (Mg,Fe, K, Na) C (S, Ca, Si, Al, Na, Fe) Si, Al, Ca (Mg, Fe, K, Na) Au (Cu, As, Fe) C, O Ba, S, Pb (Cr, As, Cu) As, Cu Si, Al, Ca, (Mg,Fe, Cl, As) C (Ca, Si, Al, Na, Fe) Si, Al, Ca,Mg,(Fe) C,O (Si, Al, Ca, Fe) Si, Al, Ca, (Mg,Fe, K, Na) C (Ca, Si, Fe) Si, Al, Ca, (Mg,Fe, K, Na)

Visible in cross-section under UV illumination and in SEM-BSE micrograph (Fig. 6c).

3.3.2. Paint layers: pigments Electron beam microprobe analyses showed that two kinds of red pigments have been used (Table 1). Minium (Pb3O4) is present in both the red layers of sample DR2 even though the inner one shows an orange tonality if compared with the deep red characteristic of the surface. It was not possible to characterise the thin black layer that can be observed in cross-section (Fig. 5) between the two paint layers. In spite of this, the large amount of carbon detected with microprobe analysis can be indicative of an organic material applied as a varnish. The red layer in sample DR1 does not contain any chemical element that could be related with the presence of an inorganic red pigment. In fact the presence of barium, calcium and sulphur may be attributed to barium and calcium sulphate that have been used as mordant in connection with lake paints since about the beginning of the XIX century [13]. These elements are much more concentrated at the bottom of the red layer as showed in the back-scattered photomicrography (Fig. 6a). The presence of a red lake is clearly visible under microscopic examination of the cross-section that shows also how it penetrates into the

ground layer (Fig. 6b). In addition, a thin layer that fluoresces yellow under the excitation of UV light is clearly visible on the top of the red layer (Fig. 6c). It shows an elemental composition similar to the underneath red layer and correspond to the external whitish thin layer visible in the Scanning Electron Microscope–Back Scattered Electron micrograph (Fig. 6a). This layer may represent a further superficial thin application of red lake. The blue pigment (sample DR3) resulted to be constituted of lapis lazuli (Fig. 7), the main component of the semiprecious stone lazurite, a sodium aluminosilicate mineral with sulphur radical anions residing in the aluminosilicate crystal lattice (Table 1). Its presence has been confirmed by X-ray diffraction analysis. In fact, a part from a large amount of quartz, the X-ray diffraction data (Table 2) present a good match to those obtained from a blue paint from a fresco at Bamiyan, Afghanistan that was identified as natural ultramarine [14]. Lazurite has been ascribed to various sources in Persia, China and Tibet. The best quality lazurite comes from Badakhshan in northeastern Afghanistan and was first iden-

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present a good match to the standard ICDD data for copper acetate arsenite (Table 3). The gilding technique (sample DR gold) used gold leaf made adhering to the paint layer with a varnish whose composition remains unknown (Fig. 3a) in spite of its elemental chemical composition which is characterised by a great amount of carbon (Table 1). The gold leaf has been applied over a yellow paint layer characterised by the presence of barium with secondary amounts of lead and sulphur. These results, together with the trace amount of chromium, could be indicative of the presence of a mixture of yellow and white pigments such as barium sulphate, barium chromate and lead oxide (PbO). The green layer, which is observed below the yellow, seems to have the same composition of the emerald green found in sample DR4.

Fig. 5. Cross-section of sample DR2: optical photomicrograph (100× original magnification). (1) Cotton fabric embedded into an organic material, (2) second layer of plaster, (3) orange-red layer, (4) varnish layer, (5) red layer.

tified on fifth-century wall paintings from Kizil in Chinese Turkestan. As far as the green paint layers (sample DR4) is concerned (Fig. 8) the elemental composition is mainly characterised by the presence of arsenic and copper (Table 1). The presence of arsenic has been also confirmed by pyrolysis analysis that gives evidence of As4 deriving from pyrolitic decomposition of an arsenic-containing compound (Fig. 9). The contemporary presence of arsenic and copper could be indicative of the use of both emerald green [Cu(CH3COO)2.3Cu(AsO2)2], an artificial copper aceto-arsenite pigment, first formulated in Germany in 1814, that, as stated by Yu Feian, was widely used in China as watercolour on pith paper works and on scroll paintings since the 1850s [15], and Scheele’s green [(CuHAsO3)], an acid copper arsenite artificially produced by a Swedish chemist in 1778. On the attempt to distinguish emerald green from Scheele’s green microprobe analysis were performed on the cross-sectioned sample. The arsenic-to-copper weight ratio, resulting from 10 replicates, was equal to 1. Scientific literature reports 1.76 for emerald green and values between 0.59 and 2.36 for Scheele’s green. This makes the use of the As/Cu ratio unable to distinguish between them [16] and pointed out the need to use specific methods such as X-ray diffraction. Therefore, being not possible to determine the carbon content due to the contamination deriving from the presence of the organic binding medium, the sample was submitted to X-ray diffraction analysis, which allowed the identification of the green pigment as emerald green [17]. A part from the major lines that can be attributed to gypsum (7.65, 4.27, 3.06) and quartz (3.34, 4.27, 1.81) those at 9.91, 3.06 and 2.68

Carbon is the main element detected in grey-brown paint layer (DR6) with traces of the same elements constituting the underneath plaster (Table 1). The SEM observation revealed, between the two plaster layers, the presence of a large area, which appears black in BSE condition (Fig. 10), whose chemical composition is characterized by a great amount of carbon that can be attributed to the organic material used for the application of the fabric strips. 3.3.3. Paint layers: binding media The analyses so far carried out have been performed on the bulk samples without any separation among the different layers identified microscopically. The chromatograms obtained from analytical pyrolysis of all the samples were dominated by peaks associated to the methyl esters of long chain aliphatic monocarboxylic acids, such as palmitic and stearic acid. These are typical compounds derived from the TMAH thermochemolysis of lipid materials containing fatty acid derivatives, such as eggs, natural waxes and drying oils [18,19]. The detection of high concentrations of the dimethyl ester of the azelaic acid (nonanedioic acid) together with the presence of suberic acid (octanedioic acid) dimethyl ester, suggest the use of a siccative oil as binding medium. All these results are comparable with those obtained from the analysis of a reference sample of aged Tung oil (Fig. 11) where the presence of both aliphatic monocarboxylic acids and azelaic and suberic acid were detected. Dicarboxylic acids, such as azelaic and suberic acid, are formed during polymerisation and ageing of siccative oils. Nevertheless, being the detection of these acids a common finding of different aged siccative oils analysed with Py-GC-MS in the presence of TMAH, it is not possible to assign unambiguously the results to a specific siccative oil. In this particular case the possible assignment to tung oil, a siccative and though drying oil obtained from the seeds of the tung trees (Aleurites fordii, A. cordata and A. monatana) [20], that are indigenous to the mountain regions of China, can be made just on the basis of historical information [2] and by considering that there is neither scientific nor historical

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Fig. 6. Cross-section of sample DR1. (a) SEM-BSE micrograph (82× original magnification). The BSE observation highlight the presence of heavier element both on the surface and on the bottom of the red layer, (b) optical photomicrograph (100× original magnification): (1) plaster layer, (2) red layer, (c) optical photomicrograph under UV fluorescence (200× original magnification): a thin layer that fluoresces yellow is visible on the top of the red.

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Fig. 7. Cross-section of sample DR3: optical photomicrograph (100× original magnification): (1) traces of cotton fibres, (2) organic material that embeds the cotton fibres, (3) plaster layer, (4) blue layer.

Table 2 X-ray diffraction data for sample DR3 and a blue paint sample from a fresco at Bamiyan, Afghanistan [12] Paint sample Bamiyan Freer F1444

DR3

Paint sample Bamiyan Freer F1444 (continued)

DR3 (continued)

D (A)

I

d (A)

RIa (%)

d (A)

I

D (A)

I

d (A)

7.64 6.42 4.82 4.57 4.29 4.06 3.82 3.71 3.62 3.50 3.35 3.22

64 17 34 57 96** 66 69 100+ 61 39# 49** 31+

7.55 6.45 b

2 2

24 3 5 13

64 17 34 57 96** 66 69 100+ 61 39# 49** 31+

24 3 5 13

3.19 3.07 2.97

36 72* 21+

3.19 3.07 2.97

36 72* 21+

2.88 2.80 2.69

42 13 21

2 100 32 19 15 4 14 9 7.5

7.64 6.42 4.82 4.57 4.29 4.06 3.82 3.71 3.62 3.50 3.35 3.22

4.26 4.02 3.80 3.71b

3.47 3.34 3.27 3.21 3.18 3.06 2.99 2.95 2.868 b

42 13 21

2 100 32 19 15 4 14 9 7.5

2

2.88 2.80 2.69

3.47 3.34 3.27 3.21 3.18 3.06 2.99 2.95 2.868 b

2.688

39 16+ 17 21 29+ 34 31* 13 19 21*# 25+ 34+ 9+# 4+ 13**+ 9** 21 17*+ 5+ 4

7.55 6.45b

4.26 4.02 3.80 3.71b

2.62 2.50 2.44 2.28 2.22 2.14 2.09 2.00 1.90 1.87 1.82 1.78 1.74 1.68 1.67 1.65 1.62 1.61 1.57 1.56

RIa (%) 2 2

2.688

2

Paint DR3 sample (continued) Bamiyan Freer F1444 (continued) d (A) I 2.62 2.50 2.44 2.28 2.22 2.14 2.09 2.00 1.90 1.87 1.82 1.78 1.74 1.68 1.67 1.65 1.62 1.61 1.57 1.56

39 16+ 17 21 29+ 34 31* 13 19 21*# 25+ 34+ 9+# 4+ 13**+ 9** 21 17*+ 5+ 4

* Probably caused by presence of calcite in sample. ** Probably caused by presence of quartz in sample. + Probably caused by presence of diopsite in sample. # Probably caused by presence of forsterite in sample. a Relative Intensity (%) b d-spacing of lazurite.

evidence of the use of other type of siccative oil, such as linseed oil, in ancient time in China.

The chromatogram of DR1 (Fig. 12) was characterised by the presence of high levels of the methyl esters of benzoic

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Fig. 8. Cross-section of sample DR4: optical photomicrograph (100× original magnification).

The coupling of reflected light microscopy, SEM-EDX, XRD and Py-GC-MS applied on cross-sectioned paint samples taken from the Ming Dynasty monument of the Drum Tower provides a useful tool for the contemporary characterisation of the original scheme of polychromy and the identification of the nature of the pigments and the organic binding media used. The scientific results of this study are quite in agreement with the few historical information available. Fig. 9. Reconstructed ion chromatogram arising from pyrolysis methylation of sample DR4; the presence of As4 deriving from pyrolitic decomposition of an arsenic-containing compound is detected.

acid and 1,2-benzenedicarboxylic acid (o-phthalate) as well as phthalic anhydride, not detected in the chromatograms of the other samples. The very source of phthalic acid is still under investigation. Phthalic acid derivatives are components of alkyd resins, which have been used as varnishes for woodworks, and occasionally found by restorers on paintings. Antraquinones occurring in madder dyes are also known to produce dimethyl phthalate in the pyrolysates when subjected to pyrolysis/methylation [21]. 4. Conclusions In this study, the analyses are not only meant to assist in the assessment of the authenticity of the materials used but also aimed at guiding conservators and conservation scientists in taking into account materials and methods used in the past by Chinese artists.

In fact the presence between clay based plaster layers of fabric strips treated with a siccative oil, probably tung oil was confirmed. In addition both the brownish colour and the wider weft of the cotton fabric observed in sample DR1 seems to be original, while the red lake, which penetrates onto the underneath plaster layer, was applied on the occasion of past restoration interventions. The emerald green and the composition of the yellow layer found in samples DR4 and DR gold can certainly be ascribed to a later restoration procedure carried out in the late XVIII century which corresponds to the time of introduction in China of the above mentioned pigments. To the same period of time can be dated the external red layer found in sample DR2. In this case the presence of an underneath varnish, which appears black under cross-section, can be a further confirmation. A siccative oil, probably tung oil, seems to have been used not only as a waterproof agent but also as binder for the plaster layersand pigments, even though the blue decoration shows the possible use of animal glue. It was not possible to confirm the hypothesis about the presence of blood binder even though it can be sustained thanks to the available bibliographic data [3,4].

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Table 3 X-ray diffraction data for sample DR4 and Copper acetate arsenites (Emerald green): ICDD 1-51 and 31-448 (15) Copper acetate arsenite ICDD Copper acetate arsenite 31-448 C4H6As6Cu4O16 ICDD 1-51 D (A) I D (A) I 10.0 100 9.71 100 6.76 25 5.36 5 4.86 9 4.55 12 4.70 11 3.99 12 4.53 100 3.48 8 3.93 95 3.71 5 3.30 4 4.48 80 3.06 20 3.38 55 2.68 24 3.28 70 2.40 4 3.18 8 3.09 45 3.07 60 1.69 8 3.06 80 1.62 4 2.98 10 1.55 8 2.73 55 1.45 4 2.71 80 2.69 19 2.68 100 a b

DR4 D (A) 9.91b 7.65

RIa(%) 45 22

4.91 4.27 4.04 3.34 3.19

13 57 9 100 68

3.06b

38

2.98 2.87

22 20

2.68b

17

Copper acetate arsenite ICDD 31-448 (continued) D (A) I 2.67 20 2.63 9 2.62 40 2.58 20 2.55 35 2.49 25 2.48 2 2.46 9 2.43 5 2.41 60 2.38 12 2.36 6 2.31 7 2.26 14 2.25 65 2.18 17 2.15 5 2.12 10 2.11 16 2.07 12 2.00 16

DR4 (continued) D (A)

RIa(%)

2.49

17

2.45

15

2.28 2.13 2.08 1.97 1.87 1.81 1.77 1.66

5 19 4 4 6 12 10 5

Relative Intensity (%). d-spacing of emerald green.

Fig. 10. Cross-section of sample DR6:SEM-BSE micrograph (39× original magnification), a large black area due to the presence of an organic material is visible on the upper left side.

Acknowledgements

The authors would like to express their gratitude to the Shaanxi Bureau of Cultural Relics and the Xi’an Center for

the Conservation and Restoration of Cultural Relics in Xi’an for having provided the samples for analysis. A special thanks has to be paid to Dr. Giuseppe Falini (University of Bologna, Chemistry Department) for having performed the X-ray diffraction analyses.

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Fig. 11. Reconstructed ion chromatogram arising from pyrolysis methylation of a reference sample of tung oil.

283

[2]

Q. Yingtau, Protection and maintenance of ancient Chinese buildings, Zhongguo Gudai Jianzhu de Baohu yu WeixiuWenwu edition, Beijing, 1986 p. 77.

[3]

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[4]

J. Bostock, H.T. Riley, The Natural History of Pliny, vol III. Henry G. Bohn, MDCCCLV, London, 1855 p. 79.

[5]

R. Lujan, Conservation of mural paintings, Amarbayasgalant Monastery, ICCROM mission report, January, 1988.

[6]

W.J. Irwin, “Analytical Pyrolysis”Marcel Dekker Inc, New York, 1982.

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G. Chiavari, S. Prati, Analytical pyrolysis as diagnostic tool in the investigation of works of art, Chromatographia 58 (9/10) (2003) 543–554.

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G. Chiavari, G.C. Galletti, G. Lanterna, R. Mazzeo, The potential of pyrolysis gas chromatography-mass spectrometry in the recognition of ancient painting media, Journal of Analytical Applied Pyrolysis 24 (1993) 227–242.

[9]

G. Chiavari, P. Bocchini, G.C. Galletti, Rapid identification of binding media in paintings using simultaneous pyrolysis methylation, Science and Technology for Cultural Heritage 1 (1992) 153–158.

[10] G. Chiavari, D. Fabbri, R. Mazzeo, P. Bocchini, G.C. Galletti, Pyrolysis gas chromatography-mass spectrometry of natural resins used for artistic objects, Chromatographia 41 (5/6) (1995) 273–281. [11] G. Chiavari, N. Gandini, P. Russo, D. Fabbri, Characterization of standard tempera painting layers with pertinacious binders by pyrolysis (methylation) gas chromatography/mass spectrometry, Chromatographia 47 (1998) 420–426. [12] G. Chiavari, A. Colucci, R. Mazzeo, M. Ravanelli, Organic content evaluation of corrosion patinas in outdoor bronze monuments, Chromatographia 49 (1/2) (1999) 35–41. [13] H. Trillich, Das Deutsche Farberbuch, Parts I–III, Part II, B. Heller, Munich, 1923 pp.45–46. [14] J. Plester, Ultramarine blue, natural and artificial, in: Ashok Roy (Ed.), Artists’ Pigments, A Handbook of Their History and Characteristics 2 (1993) 37–65. [15] Y. Feian, Chinese painting colours: studies of their preparation and application in traditional and modern times (trans., J. Silbergeld and A. McNair)University of Washington Press, Washington, 1988. [16] I. Fiedler, M. Bayard, Emerald and Scheele’s green, in: E. West FitzHugh (Ed.), Artists’ Pigments, A Handbook of their History and Characteristics 3 (1998) 249–250. [17] A. Scott, David, Copper and bronze in art. Corrosion, colorants, conservation, Getty Conservation Institute, 2002.

Fig. 12. Reconstructed ion chromatogram arising from pyrolysis methylation of sample DR1. The presence of benzenoic acid methyl ester and phthalic acid dimethyl ester is detected.

[18] G. Chiavari, D. Fabbri, S. Prati, Analysis of Fatty Materials Used in Painting Layers by in situ Pyrolysis and Silylation, Chromatographia 53 (5/6) (2001) 311–314.

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[19] S. Prati, S. Smith, G. Chiavari, Charaterisation of Siccative Oils, Resins and Pigments in Art Works by Thermochemolysis coupled to Thermal Desorption and Pyrolysis GC and GC-MS, Chromatographia 59 (2004) 227–231.

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[20] R.J. Gettens, G.L. Stout, Painting Materials, A Short EncyclopediaDover Publication, Inc, New York, 1966.

Zhang Zhuangzhi, Sauvegarde des monuments historiques en bois en Chine. Yansui Ge: Pavillon de la Longue Paix du Monastère Yonghe Gong. Thèse en vue de l’obtention d’une maîtrise en Conservation des Monuments Historiques, Année académique 1987–1988, Katholieke Universiteit Leuven.

[21] D. Fabbri, G. Chiavari, He Ling, Analysis of anthraquinoid and indigoid dyes used in ancient artistic works by thermally assisted hydrolysis and methylation in the presence of tetramethylammonium hydroxide, J. Anal. Appl. Pyrolysis 56 (2000) 167–178.