Song et al. Herit Sci (2018) 6:18 https://doi.org/10.1186/s40494-018-0182-5 RESEARCH ARTICLE Open Access A technical study of the materials and manufacturing process used in the Gallery wall paintings from the Jokhang temple, Tibet Yan Song1* , Feng Gao1, Austin Nevin2, Juwen Guo1, Xiao Zhou1, Shuya Wei3 and Qianqian Li3 Abstract Wall paintings from the Jokhang temple, Lhasa, Tibet, China cover over 4000 m2. In order to protect these valuable paintings and to provide more conclusive information regarding the date of the painting scheme from the outer north Gallery, painting materials and techniques have been studied using optical and scanning electron microscopy, X-ray difraction and raman spectroscopy. Organic materials were analysed with pyrolysis-gas chromatography– mass spectrometry. The wall painting technique is typical of Tibetan paintings and includes multiple layers of locally sourced materials. Analytical results demonstrate the presence of natural and synthetic pigments, including cinnabar (HgS), malachite ­(CuCO Cu(OH) ), azurite ­(2CuCO Cu(OH) ), orpiment ­(As S ), red lead ­(Pb O ), synthetic ultramarine 3· 2 3· 2 2 3 3 4 blue ­(Na3CaAl3Si3O12S) and emerald green (Cu(C2H3O2)2 3Cu(AsO2)2) which allow us to date the paintings from the mid to late nineteenth century. The binding media is a kind· of animal glue which is likely to be bovine or yak glue, the traditional medium used in Tibet. Gilding was applied as gold powder or gold foil. In the past a sealing material or varnish containing drying oil (maybe tung oil) and pine resin was applied to the surface to protect the paintings. Keywords: Tibet, Jokhang temple, Wall painting, Pigment, Binding media Introduction have gradually increased to more than 4000 m2 [4, 5]. Te Te Jokhang temple, also known as “Zula Kang” is located themes depicted in the paintings involve various aspects in the old city center of Lhasa. It has been the most of Tibet’s political, economic, historical, literary, religious important Tibetan Buddhist monastery since it was built and social life [6–12]. Tey are physical evidence of the in 647 C.E. (Tang Dynasty) by Songzain Gambo (the frst evolution of painting technology, and the long history of king of Tubo Dynasty). Today, with an area of 25.1 thou- Tibetan wall paintings. At present, most wall paintings sand square meters, it is dedicated to Buddha, Bodhisat- preserved in Jokhang temple belong to the “Men Tang” tva, deities, patriarchs, and Dharma gods of Bonpo, style which was created by Menla Dondub (a Tibetan Nyingma, Sakya, Kagyu and Gelug sects of Tibetan Bud- master who lived between the 15 and sixteenth century) dhism [1, 2]. In 1961 the Jokhang temple was listed as a [13, 14]. Paintings are generally sophisticated and beauti- State-level key heritage site of China and included in the ful with rich colours (especially red, yellow, orange, green, UNESCO World Heritage List in 2000. blue and gold are most frequently used) [15–19]. Tey Since the establishment of Jokhang temple, wall paint- provide convincing solid evidence for study of Tibetan ings have been an important part of the buildings [3]. wall paintings. However, deterioration is apparent in the Developed over more than thirteen centuries (from the wall paintings due to the aging of historic buildings, long Tubo dynasty to modern times), the wall painting areas and strong exposure to light, severe fuctuations in tem- perature and humidity, and other natural or human fac- tors. Major deterioration is manifested in deformation of *Correspondence: [email protected] walls, cracking, collapse, detachment of paint and plas- 1 Chinese Academy of Cultural Heritage, No. 2 Gaoyuan Street, North Fourth Ring Road, Chaoyang District, Beijing, China ter, faking of paint, smoke accumulation due to pollution Full list of author information is available at the end of the article from butter burning, and abrasions, all of which pose a © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Song et al. Herit Sci (2018) 6:18 Page 2 of 13 threat to the long-term preservation of the paintings. In wall paintings. Tis work aims to study the techniques, order to protect these valuable wall paintings, the Chi- pigments, binding media and varnish materials from nese Academy of Cultural Heritage (CACH) carried out fragments collected as part of conservation work carried the conservation of various schemes from 2012 and work out by CACH on the outside Gallery. at the temple is ongoing. Before restoration, the materials According to the records in “History of the Jokhang and techniques of the wall paintings were studied and are Temple”’: in 1783, the Dalai Lama VIII (1758–1804) the focus of this work. Figure 1 shows a scene from the invited painters to draw the wall paintings on the out- Jokhang temple murals. side Gallery and courtyard [12]. Tus, wall paintings Tere are relatively few published studies on wall paint- on the outside gallery were likely frstly executed in the ings from Tibet, and most research has focused on the late eighteenth or early nineteenth century. However the history, iconography, techniques of painting, and reli- paintings have been extensively repaired and repainted, gious and aesthetic value of depictions. Limited research so the exact date of the scheme is unknown. A multi- has focused on the constituent of materials and tech- analytical approach was chosen for the analysis of sam- niques of Tibetan wall paintings. For example, Xiang ples based on published methods used for the study of studied the contents, characters and the iconography of wall paintings [25–33]. Cross-sections were prepared the wall paintings from the Gallery of Jokhang temple and studied using optical microscopy, Raman spectros- [20]; others have studied the compositions of pigment, copy, and scanning electron microscopy–energy disper- plaster layer and base layer of wall paintings samples sive x-ray spectroscopy. Fragments were also analysed by from Jokhang temple [21–23]. Te pigments present in X-ray difraction for a complete characterisation of the the wall paintings from the Potala Palace, Norbulingka ground materials. Binding media and varnish analysis and Sakya Monastery have also been reported [24]. Data was carried out with pyrolysis gas chromatography–mass from these studies suggest that Tibetan murals have spectrometry. unique national characteristics in terms of their build- up or stratigraphy and the methods employed for their Methods execution. Instrumentation However, there is little literature about the varnishes 1. Optical microscopy was carried out using a Leica and surface fnishes which were routinely applied to the DM4000 M (Germany) and samples were observed paintings and the binding media employed in Tibetan under various magnifcations. Te stereo microscopy Fig. 1 Part of wall paintings on north outside Gallery wall of Jokhang temple Song et al. Herit Sci (2018) 6:18 Page 3 of 13 was carried out using a Keyence VHX-900 (Japan) Sampling information and samples were observed under various magnifca- All samples were taken from damaged parts or fragments tions. that had fallen of. Te samples, including three larger 2. Scanning electron microscopy (SEM) was carried out fragments and some smaller fragments and powder sam- using ZEISS EVO18, equipped with a SmartSEM sys- ples, were all taken from the outside Gallery of Jokhang tem for data collection. Sample cross-sections were temple. coated with gold prior to analysis. Te range of mag- 6 Sample preparation nifcation is 5–10 ×. Focused working distance is 2–145 mm. Te excitation voltage is 20 kV, and scan- Some paint samples were observed directly under the ning time is 60 s. Energy spectrum analysis was car- optical microscope and examined by Raman spectros- ried using Bruker Nano XFlash Detector 5010 Energy copy. Local soil samples were ground into powder and Spectrometer (EDS). analysed by XRD. Te ground layer (including coarse clay 3. Raman spectroscopy was carried out on cross-sec- layer and fne clay layer) were scraped from the samples tions with a HORIBA (JY Company, France) instru- and ground into powder which was analysed by XRD. ment equipped with Olympus BX-41 microscope at Other samples were prepared as cross-sections using an 50×. Te grating is 1200T (line/mm). Te spectrom- epoxy resin and polished before examination. eter is calibrated by monocrystalline silicon. Te laser wavelengths employed were 532 and 785 nm, with an Results and discussion acquisition time of 20–30 s, and 4–6 acquisitions per Stratigraphy of the wall paintings spectrum. Red, yellow and black pigments were ana- Trough the results of feld investigations and sample lysed with the 785 nm laser. While blue, green and analysis, the Jokhang temple wall painting is basically white pigments were tested with 532 nm. Te power composed of fve parts (from inside to outside): the basic on samples was kept as low as possible with suitable support (fagstone wall), the ground layer, a white prepa- data achievable with powers of 2–3 mW. ration layer, paint layer and a surface protective layer or 4. Small samples of the fragments and powder col- varnish. Te schematic diagram is shown in Fig. 2. It is lected on site and local soil samples were subjected noted that today traditional Tibetan wall paintings are to X-ray difraction (XRD).