Manufacturing technique
There are no records of the manufacturing techniques used to create the painted clay sculptures in the Buddha Pavilion of Jingyin Temple. This investigation is intended to record details of the basic structure and the painted layers, and other information about the sculptures, by onsite observation and sample analysis of the damaged surfaces and sections of the sculptures.
(1) Tutang Buddha
The Tutang Buddha is a sculpture representing Amitabha. According to the inscription (Records of the Tutang Pavilion Reconstruction in the twentieth year of the reign of the Jiajing Emperor in the Ming dynasty, 1541, and inscriptional record of re-gilding the statues of Buddha in the forth year of the reign of the Qianlong Emperor in the Qing dynasty,1739 )[20], the Tutang Buddha was carved out of the hill. Observation of the damaged part of the sculpture ( the finger ,the clothes and the lotus ) indicates that there were coarse and fine layers of clay mixed with wheat straw. Obviously, the construction of the Tutang Buddha is different with the traditional technique of the painted sculpture.
The Tutang Buddha’s whole body is gilded, with the hair painted in blue. The inner clothing is red, and the exterior is golden, which emphasizes the three-dimensionality of the figure. The lotus seat is red, which is one of the five superior colors traditionally used in ancient sculpture and painting. It is found that the gilded surface is painted with exquisite blue pattern (Fig.2(a)), at the belt of the sculpture. The traditional LiFen technique is applied in drawing intricate patterns at the edge of the dress(Fig.2(b)). Unfortunately, it is impossible to know the full view of the Tutang Buddha, because of the flaking of the surface paint layer and the contaminants covered on the sculpture.
There are at least two layers of heavily applied paint. The outermost layer (Fig.2(c)) of paper on the Buddha’s face, which covers the original red pigment, was gilded after being glued. The surface layer of the lotus seat (Fig.2(d)) is red, and the underlying layer is green.
(2) The two bodhisattvas
The style of the painted sculptures of the bodhisattvas on either side of the Tutang Buddha dates them from the Ming dynasty. Thus they are later than the Tutang Buddha. Observation of the damaged part of the sculpture (the internal timber framing was not exposed to the air, and so could not be sampled) indicates that construction also used the traditional technique of creating a wooden frame covered by layers of coarse clay, fine clay, lime, paper, and paint. The two bodhisattva sculptures had been repainted but not reshaped(Fig.3(a),(b),(c)).
Analysis of construction materials
(1) Pigment analysis
The gold, red, black, blue, green, and white paint samples from the three sculptures were analyzed using Raman spectroscopy and SEM/EDS(Fig 4-1, 4-2,5-1,5-2).
The results (Table 2) show that the gold foil on the surface of the Tutang Buddha is Au, the lime layer is calcium carbonate, and the red pigment is a mix of cinnabar and minium. On the Mahasthamaprapta bodhisattva, gold foil on the surface of the statue is Au, the red pigment is a mixture of cinnabar and minium, and the blue pigment is azurite. On the Avalokitesvara bodhisattva, gold foil on the surface of the statue is Au, and the green pigment is atacamite. Analysis of some pigments was inconclusive because of environmental damage, and further analysis is needed.
(2) Ground layer analysis
It is clear to the naked eye that the outermost layers of paint on the Buddha and the two attendants are painted on paper. The paper fibers were viewed through a biological microscope (Fig.6 (a),(b),(c)). The fibers in the outermost paper of all three statues were found to be ramie[28,29]. We infer that the three statues were likely to have been refinished at the same time, with the same materials being used.
(3) Clay layer analysis
Component analysis
Only samples of painted clay layers were taken for testing because of technical restrictions on sampling historical artifacts. XRD analysis showed that the composition of the painted clay layers was very similar in all three statues. The fine clay layers of the two attendants are identical; they contain calcite, gypsum and soda feldspar. The fine clay layer of the Tutang Buddha contains silica, calcite and soda feldspar.
We collected some deep-buried soil from the hillside close to Jingyin Temple to compare its composition with the clay layers of the statues. The analysis showed that the local soil, which contained silicon dioxide[30], calcite[31], and calcareous feldspar, is similar in composition to the fine clay layers of the sculptures in the Buddha Pavilion. This result suggests that there is an authentic local source of repair material for filling and grouting the sculptures.
(4) Particle size analysis
A laser particle size analyzer was used to create particle size distributions of the local soil samples and the fine clay layers of the three sculptures. The distributions were calculated using the Chinese particle size grouping (Table 3).
The particle size of the fine clay layers of the three sculptures is mainly distributed in the range 0.0002–0.20 mm, covering the clay, powder, and sand particle groups. Coarse powder accounts for >50%, followed by clay particles and fine powder particle. The smallest proportion is fine sands. When these results are considered together with the XRD analysis, we see that the fine clay layers of the three sculptures are similar in composition and are little different from the local soil. We conclude that the materials used to create the painted clay sculptures were obtained locally.