Hexi painting on Xitian Fanjing, a Qing imperial Buddhist temple in Beijing, China: technology revealed by analytical approaches (an initial report)
© The Author(s) 2016
Received: 23 September 2016
Accepted: 22 November 2016
Published: 14 December 2016
Hexi painting (和玺彩画) refers to a specific kind of polychromed paintings (known as caihua 彩画 in Chinese) decorated on the exterior or interior surface of Chinese Qing (1644–1911 AD) imperial wooden architecture (such as palace and temples for residence and religious use by the royal families). Textual analysis points out that Hexi, a historically recorded term, refers to a highly organized and specialized painting and decorative technique that incorporates all the best-known technical skills (carving, coloring, embossing, etc.) into one single decorative form and results in highly precious painting and decoration . If this interpretation is sound through time and across regions, it instantly makes Hexi painting the most representative architectural decorative art throughout the 270-year-long Qing history. A series of content and textual analyses on Hexi painting has been carried out since the 1980s, regarding its history and development in different stages of the Qing Dynasty [1–3], technical features and possible application procedures , patterns/decorations and their stylistic and aesthetic implications [2, 3, 5, 6], and so forth, which greatly advances our understanding of Hexi painting as a combination of the highest levels of technical knowledge and skills and the most popular religio-aesthetic needs of the Qing royal families. Two other useful sources of information contribute to the understanding of Hexi painting as well: observations on painting and decoration practiced by present-day Chinese craftsmen in imitation of ancient architectural decorative art (Hexi painting in particular) on modern pseudo-classical architecture or in architecture conservation projects; and analytical studies on materials used in the preparation of and on Hexi painting. Of the above three, textual analysis has often encountered doubts and uncertainties regarding interpretation of historical terms and records, while crafting skills/techniques are always modifying and changing over time and place and often result in unpredictable changes in technological details. In this respect, analytical studies become a more reliable source of information in that they can confirm and complement the other two approaches by revealing the actual use of materials and the way they were used.
Unfortunately, published analytical studies on Hexi painting have been very rare. Unlike many other painting forms in the Qing and previous periods, Hexi painting demonstrates a greater technological complexity as it combines carving, coloring, embossing, and other techniques and involves the use of a wide range of materials. More importantly, its technological features were developed to serve the religio-aesthetic needs of a particular group of people with power, authority, and wealth, and therefore must be very carefully selected and developed. Given these observations and thoughts, comprehensive technical investigations into representative Hexi painting samples are required to help us understand: how exactly, from a technological and analytical perspective, did the Qing craftsmen apply Hexi painting to imperial architectural decoration, using what materials and following which application procedure? Results from such studies would not only bring new insights into the techniques that produced Hexi painting, but also have broader impact by allowing comparison between Hexi painting and other contemporaneous painting and decorative techniques, which advances our understanding of how technological choices were made to meet motivations of politics, religion, and aesthetic psychology in the Qing period. Technical studies on Hexi painting have more practical impact as well: it has direct influence on decision-making and conservation strategies for preserving and restoring the Qing wooden buildings upon which Hexi painting is decorated.
In this paper, we present a technical case study on Hexi painting fragments sampled from Xitian Fanjing (Western Paradise, 西天梵境), a Buddhist temple in Beijing, China. It aims to reveal, from a crafting perspective, how Hexi painting was prepared and applied to imperial temples. Cross-sectional examination of recognizable fiber, pigment/dye, and paint layers between the innermost and the outmost suggests the complexity of painting/decoration process and the elaborateness of preparation for Hexi painting. The subsequent layer-by-layer fiber/phase identification and compositional analysis add additional technological details. Finally, technical studies lead us to understand the technological features that make Hexi painting special.
Hexi painting fragments
A Nikon SMZ1500 stereoscopic microscopy was used to assist the observation and examination of layers on cross sections of golden-dragon Hexi painting fragments. Selected fragments were polished by hand on water-proof sandpapers until a smooth surface was produced for better layer-structure examination. The cross-sectional observations offered insights about the decoration and painting procedure. The identifiable layers lay the basis for subsequent analytical studies carried out to explore technological details.
Scanning electron microscope with energy dispersive X-ray spectrometer (SEM-EDX)
A FEI Quanta 400 environmental scanning electron microscope (ESEM, Philips, The Netherlands) was used to help identify fibers noticed underneath the ground coat layer by offering super high-resolution images of fine features on fibers’ longitude and cross-section views. Equipped with an Inca 300 energy dispersive x-ray spectrometer (EDX, Oxford, UK), the ESEM was operated at 30.0 kV and 60 μA, with a vacuum chamber pressure of 0.4–0.5 mb. In addition to the SEM identification of fibers, EDX was utilized to determine the kinds of pigment(s) and chemical composition of the golden color.
An MXP18AHF x-ray diffractometer (MAC Science, Tokyo, Japan), equipped with a Cu x-ray tube, was utilized to characterize inorganic substance(s) in the ground coat layer and pigment that produces the dark emerald green background on Hexi painting by determining their crystalline phase(s). The x-ray diffraction (XRD) unit was operated at 40 kV and 100 mA, with diffraction angle ranging from 10° to 70°. XRD patterns for reference materials (quartz, anorthite, atacamite) were cited from the International Center for Diffraction Data (ICDD) PDF cards (PDFs: 79–1906, 76–0948, and 71–2027).
The multilaser confocal Renishaw InVia Reflex Raman spectrometer (Gloucestershire, UK) was used to identify pigments and dyes that produce different colors on golden-dragon Hexi painting. Two excitations (514.5 and 785 nm) were tried to obtain the best Raman signals for each color (white, dark emerald-green, sky blue, dark red, and black). Raman spectra were recorded in wavenumber between 100 and 3000 cm−1, with spectral accuracy of about 1 cm−1. An optical microscope was used to focus the laser on samples, at ×50, throughout the analysis. Calibration is carried out on the Raman spectrometer on a daily basis using the Raman signal of silicon at 520 cm−1. Background spectra of water and carbon dioxide are obtained in ambient air. Raman spectra presented here were smoothed without baseline correction.
Results and discussion
The ground layer
The ancient Chinese architectural paintings in North China almost always have a ground layer as the very bottom layer. (By contrast, those in South China sometimes do not have a ground layer ). The preparation of a ground layer in architectural paintings clearly originates from ancient Chinese wall painting manufacturing techniques. It was done for several purposes, including (but not necessarily limited to): to produce a smooth surface upon which paint layers can be easily applied; to serve as a support for paint layers and prevent them from cracking; and to allow absorption of liquids (such as oil and water) from the paint layers and therefore produce better visual effects in paintings . The preparation of a ground layer for architectural paintings, just as done for wall paintings, usually cannot be accomplished all at once. It involves several rounds of repeating steps (using the same or different materials) and results in tightly overlapped layers. Due to the difference (or similarity) in materials (such as fibers and coating pigments) used in each round of coating, the ground layer can (or cannot) be further divided into sublayers. Sometimes, even different parts of the same ground layer differ in the number of subdivisible layers. Our observations on cross sections of golden dragon Hexi painting fragments suggest that Hexi painting has a ground layer that makes a distinction between two layers with completely different base materials: a fiber (organic) layer and a coat (inorganic) layer upon it, the latter of which often is further divisible.
(1) The ground fiber layer
(2) The ground coat layer
The blue paint layer
The white paint layer
A white paint layer, 0.1–0.2 mm thick, is noticed right on the top of the thin blue layer. It is composed of whitish materials that created the embossed dragon and cloud patterns on golden-dragon Hexi painting. Therefore, the shape and embossed height of patterns determines the white paint layer’s thickness. Raman spectrum of the white color, as shown in Fig. 5b, demonstrates three instantly noticeable Raman peaks at 284, 717, and 1091 cm−1, all of which have been confirmed as characteristic of calcium carbonate (CaCO3) . The source of calcium carbonate can be attributable to chalk, a very finely grained limestone deposit. Chalk has been used to paint white for quite a good long time (from Neolithic to modern China), and its application on Neolithic dwellings as well as on modern architecture have been widely reported within and beyond China. In traditional Chinese architecture painting and decoration, chalk is often referred to as baitu (literally translated as white clay, 白土) and used for the preparation of the ground coat layer or for decoration purpose . Textual researches and analytical studies that aim to reconstruct architectural painting and decoration techniques in the Qing period have confirmed that chalk was usually not used alone, but mixed with China wood oil (桐油, a drying oil extracted from seeds of tung tree, Vernicia fordii) or sometimes with plant or animal glue instead. Such a practice is the core of lifen tiejin (沥粉贴金, embossed patterning and gilding), a technique during which chalk and drying oils are mixed in a certain ratio and filled into a container (such as pig’s bladder), and then squeezed out for embossing through a small opening [27, 28]. When wet and mixed with China wood oil, chalk is turned into soft paste that can be easily (re)shaped and (re)coated, which is very important for creating embossed patterns (such as the dragon and cloud patterns on golden-dragon Hexi painting). Therefore, while organic materials such as China wood oil awaits confirmation in future studies, the identification of chalk in the white paint layer suggests that lifen tiejin might have been used for embossing the dragon and cloud patterns on Hexi painting.
The gold-colored layer
The partially applied white color and other issues
Some initial thoughts on the preparation of Hexi painting
Summary of the main findings revealing the use of materials in Hexi painting
Ground coat layer
Blue paint layer
White paint layer
Gold-silver (quite possibly 76Au:24Ag, wt%)
Other colors on Hexi painting
Lead white (2PbCO3·Pb(OH)2)
Dark emerald green
Carbon black (C)
- Step 1:
Preparation of the ground layer (including a fiber layer and coat layers). Surfaces of the wooden materials are fully leveled and polished to produce a smooth surface. A layer of ramie fibers, probably mixed or covered with wet paste prepared from brick powder, is then applied. The ground coat layer uses brick powder as the main (if not the only) coating pigment, and it is prepared by several rounds of coating. Chinese wood oil or other organic materials might be used to mix with fibers and/or brick powder.
- Step 2:
Preparation of the background layer. The indigo-blue and atacamite-green serve as two major background colors on Hexi painting. A usual practice is to apply indigo to paint the blue layer, and then atacamite to paint a green layer upon the blue one wherever necessary. Based on our visual inspection of Hexi painting on Xitian Fanjing, we believe that an inverse order, although not noticed in our samples, could also be true (i.e., painting the atacamite-green layer as the main background first and then overlapping it by indigo-blue layer).
- Step 3:
Preparation of the embossed dragon and cloud patterns. These patterns are embossed by squeezing and shaping soft, wet chalk-white paste out of a container’s opening, following the lifen tiejin technique. The fine particles of chalk must have been mixed and diluted with water and/or oily materials.
- Step 4:
Preparation of the gold-colored layer. The application of hand-hammered gold-silver (quite possibly 76 Au:24Ag, wt%) foils makes sure that the dragon and cloud patterns look prestigious with a yellow gold color, a color highly valued and reserved only for the Qing emperor and his association. Plant or animal glues should be used to glue the foils onto the patterns.
- Step 5:
Application of lead white and other pigments on Hexi painting, the last few steps for painting and decoration. Lead white is applied on the corner of curved surfaces of the dragon and cloud patterns to make sure that a bright white color can always be noticed. Carbon black is used to draw black boarder lines, and hematite to paint the red color.
Clearly, the preparation of Hexi painting follows a few standardized steps (surface leveling, the preparation of ground layer, coloring, embossing, etc.), which have been especially widely noticed on architecture from the Ming and Qing periods onward in many parts of China [e.g., 11, 13, 34, 35], therefore revealing no uniquely special treatment in the painting and decorating procedure. Regarding the use of materials in Hexi painting, a few findings attract our attention, which include: (1) using ramie fibers, rather than wheat/rice straw or cotton fibers [34, 35], for preparing the ground fiber layer; (2) using brick powder, in contrast to chalk or unfired loess [34, 35], for coating the ground layer; (3) using chalk, rather than talcum powder and others , for creating embossed patterns; (4) using indigo, rather than inorganic blue pigments [20, 34, 36], to dye blue; and (5) using substantial gold-silver (chijin) foils to decorate the outermost surface of dragon and cloud patterns. However, it is soon realized, upon further consideration, that none of these ‘features’ was exclusively restricted to Hexi painting. That is to say, ramie fibers and pigments used on Hexi painting (such as brick powder, chalk, lead white, atacamite, hematite, and carbon black) can also be noticed on other forms (folk art, for example) of Qing architectural decoration [e.g., 13, 34–36], although they rarely are incorporated into one single package as the case with Hexi painting. Indigo, indeed, is barely reported as blue color on the Qing imperial architecture, but case studies do exist [19, 20]. The extensive use of chijin on golden-dragon Hexi painting is remarkable and undoubtedly a distinctive feature of Hexi painting, considering the substantial amount of gold-silver foils needed. But we do not know whether or not this assumption still holds true when more samples (from other Qing imperial and non-imperial architectural paintings) are included and analyzed for comparison. Given all findings made so far, we propose that neither the kinds of (inorganic) materials nor the painting and decorating process makes Hexi painting uniquely distinguishable from many (if not all) other Qing imperial or folk architectural paintings and decorations. Instead, it is the combination of material use and the painting/decorating process that seems to make Hexi painting special. Considering this possibility, the interpretation that Hexi is a decorative art that “incorporates all the best-known technical skills” seems to make some sense, even though more analytical studies are needed to test whether each feature really is technologically “the best” compared to other contemporaneous techniques and methods of the same kind.
Analytical studies on golden-dragon Hexi painting fragments, which were sampled from Xitian Fanjing in Beihai Park in Beijing, China, made a few things clear(er) to us about Hexi painting: (1) there is a ground layer which consists of a ramie fiber layer at the very bottom and probably multiple coat layers (using fired brick powder as coating pigment) upon it; (2) both inorganic pigments (atacamite; lead white; hematite; carbon black) and organic dye (indigo) were used for coloring; (3) chalk was the material that created embossed dragon and cloud patterns; and (4) gold-silver foils was used to paint the outer surfaces of dragon and cloud patterns in a golden color. Considering that our study focused almost entirely on inorganic materials, further studies are needed to confirm the use of organic materials (oily materials, plant or animal glues, etc.) in the preparation of Hexi painting.
NL provided the samples to be investigated in this study; JC, TZ, and HH carried out SEM-EDX, XRF, and Raman analyses, respectively; QF and SZ conducted a microscopic examination of the samples; TL and TZ interpreted the analytical results and drafted the manuscript. All authors read and approved the final manuscript.
This research was financially supported by the National Natural Science Foundation of China (Grant No.: 41103013). The authors would like to express gratitude to Mr. Yi Xu (University of Electronic Science and Technology of China, Chengdu, China) for his assistance with literature search. Ms. Jiali Wan (Sun Yat-sen University, Guangzhou, China) and Mr. Biao Cui (Zhejiang Provincial Institute of Cultural Relics and Archaeology, Hangzhou, China) also provided useful references.
The authors declare that they have no competing interests.
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