Temple murals in Korea were painted on the mud wall of wooden buildings, and natural pigments and the vehicle were mixed to produce the painting layer after the wall was built with tree branches as its frames on top of wooden furniture and the soil as its major material (Lee, 2013). Murals, whose materials are mostly soft in nature, are reported to be vulnerable for conservation due to their material characteristics and the environmental factors in their locations (Lee et al., 2018a). Furthermore, due to some treatments conducted on temple murals in early days of the conservation of temple murals in Korea when there was a lack of studies on mural materials and manufacturing techniques, many murals have been damaged or made difficult for coneservation, which calls for a study on the manufacturing characteristics of murals. Hence, if materials and techniques used in the production of murals are identified accurately, it would make it possible to conduct a reliable study on the conservation of murals and suggest more systematic and effective conservation options (Lee, 2013).

Studies on the material characteristics and manufacturing techniques of temple murals in Korea include the first study in 2006 that scientifically demonstrated the traditional materials and manufacturing techniques of four-sided interior murals in Geungnakjeon Hall, Muwisa Temple, Gangjin (Chae et al., 2006; Fine Art Conservation Institute, 2006) and a 2008 study conducted on manufacturing techniques based on the material characteristics of Yeongsan Hoesang murals in Bongjeongsa Temple, Andong (Jeong and Han, 2008). Since then, there were studies comparing the characteristics of manufacturing techniques in temple murals, including murals at the back of the altar in Daeungjeon Hall, Heungguksa Temple, Yeosu, exterior murals in Mireukjeon Hall, Geumsansa Temple, Gimje, and murals at the back of the altar in Daeungjeon Hall, Seonunsa Temple, Gochang (Lee, 2016; Han, 2010). In particular, while studies in the past focused on scientific investigations about relatively important temple murals, studies are being conducted around 2020 by closely interpreting mural materials and production techniques and proposing conservation measures about bracket murals in Daeungjeon Hall, Jikjisa Temple (Lee et al., 2018a) and bracket murals in Daeungbojeon Hall, Naesosa Temple (Lee et al., 2018b).

Daeungjeon Hall, Gaeamsa Temple, Buan is currently designated as Treasure No. 292 and has 52 murals, including bracket murals painted on interior and exterior walls and murals at the top of Nemok-dori (Figure 1). While there are 32 interior bracket murals with 6 each on the east and west and 10 each on the south and north, 4 on the north have no painted image and 5 have been repainted relatively lately. The latest scientific investigation on bracket murals in Daeungjeon Hall, Gaeamsa Temple found that damage in the wall and damage due to the deteriorated painting layer had gotten worsen, which would require conservation treatment (Figure 2). Accordingly, a study identifying manufacturing conditions based on structures and materials, which constitute murals, would need to be conducted first to prepare stable Figure 1. Inside the Daeungjeon hall of Gaeamsa Temple, Buan. conservation options.

In this context, this study identified the manufacturing characteristics of bracket murals in Daeungjeon Hall, Gaeamsa Temple by closely analyzing the wall and painting layer consisting of the murals and wish to offer an effective reference for diagnosis the conservation conditions and prepareing conservative treatment of murals in the future.

By conducting a scientific analysis on the structure and material of the bracket mural paintings inside the Daeungjeon Hall in Gaeamsa Temple, Buan, the characteristics of the walls and painting layer and the method of manufacturing the murals could be grasped. The study results are summarized as follows.

First, an investigation into the wall structure revealed that branches were tied with straw rope and mud plaster was applied three times to produce the earthen wall.

According to studies on the wall structure of buddhist mural paintings in the Joseon Dynasty, showed that the structure of buddhist murals produced across the Joseon period includes distinguished wall into the support layer, middle layer, and finishing layer. Also, most of the support layer and middle layer generally have chopped straw mixed. Like some murals at Naesosa Temple in Buan, these types in which the absence of the middle layer and wooden materials mixed, but this does not belong to the general manufacturing style of buddhist mural paintings (Lee et al., 2018b).

Comparing the characteristics of the previously reported buddhist murals with the bracket murals of Daeungjeon Hall in Gaeamsa Temple, it can be that the murals at Daeungjeon at Gaeamsa belong to the category of general buddhist mural paintings. However, it is not a general tendency that the middle layer is applied more than once, that wood is mixed in the wall, and that materials presumed to be chopped straw were rarely identified. The thickness of the bracket murals of Daeungjeon Hall in Gaeamsa Temple was investigated to be about 60 mm, and the thickness of the support layer was about 50 mm. This result is similar to the thickness of the general buddhist murals, but compared to the murals in which the middle and finishing layers are created one at a time with a thickness of about 10 mm, the bracket murals of Daeungjeon Hall in Gaeamsa Temple have two or more layers. It seems that the middle layer and finishing layers of Gaeamsa Temple’s mural paintings have a thin thickness. Multiple applications of thin walls have the advantage of preventing cracks and allowing the walls to dry well (Hwang, 2008). While if it is manufactured without considering the particle size, the adhesive force between the layers may be lowered, thereby aggravating the damage caused by the separation between the layers. And since fiber reinforcements used in the wall, such as chopped straw, prevent cracks and dispersions due to the contraction of the wall (Han, 2003), the absence of such materials would serve as a vulnerability if physical damage to the wall occurs.

An analysis of the microstructure and chemical composition of particles consisting of each layer of bracket murals detected soil particles of various sizes or crystal aggregates in plates and chemical components usually found from soil materials such as silicon (Si) and aluminum oxide (Al). Furthermore, the mineral crystal habit such as quartz and feldspars was identified, demonstrating that the main materials of the wall layer and the finish layer were weathered soil and sand originating from rocks, which is consistent with the results of a previous study on the wall material characteristics of temple murals (Lee, 2016).

A particle size analysis found that the support layer had a high content of loess, while the middle layer and the finishing layer had a fairly high content of sand. In the support layer, above medium sand accounted for 7% and below fine sand 93%. And since the proportion of soil less than silt is 53.6% even in the soil of fine sand or less, it is estimated that the support layer is made by mixing soil of relatively even and fine soil materials to produce the murals. In the middle layer, above medium sand accounted for 40% and below fine sand 60%, showing that it had a higher fine sand content than the support layer. In the finishing layer, above medium sand accounted for 60% and below fine sand 40%, compared to other layers, the proportion of very coarse sand and coarse sand size soil is high, indicating that the content of large sand is high. The difference in the particle size distribution of the soil at each layer indicates the difference in the voids according to the arrangement of the soil particles, and the attractive force according to the particle gap affects the cracks or strength of the wall, which is directly related to the conservation of the mural. In particular if moisture were absorbed and released repeatedly in the wall, this condition would lead to changes in the volume fraction between wall layers, create a difference in stress over the long term, and cause physical damage such as cracks and separations between the layers (Lee et al., 2018b). As it can be seen that the pattern of damage confirmed in the current murals of Gaeamsa Temple reflects some of these structural and material characteristics, attention is required for the conservation of the murals.

An analysis of samples by the digital microscope found five colors: white, dark green, pale green, red as well as ochre in the ground layer. From the ochre ground layer, silicon (Si), aluminum oxide (Al), calcium (Ca), and iron (Fe) were detected as the main components, which suggest soil pigments such as loess or kaolinite may have been used. In the white color layer, lead (Pb) and sulfur (S) were the main components, and lead (II) sulfate seems to be have been used. For green, copper (Cu) and chlorine (Cl) were observed as the main components, and atacamite may have been used. For red, mercury (Hg) and sulfur (S) were detected, showing that mercury sulfide pigments may have been used. The existence of the ground layer and the pigments used in the painting layers identified in the bracket mural paintings of Gaeamsa Temple belong to the category of the types of pigments applied to the buddhist murals of the Joseon Dynasty investigated so far, and their production methods are similar. It has been reported that the conservation condition of the painting layer is relatively good compared to the wall, and, judging from the pigment used or the composition of the painting layer, no factors directly affecting the damage have been identified so far. The structure and materials of the bracket mural paintings of Daeungjeon Hall in Gaeamsa Temple, Buan have a similar manufacturing style in terms of the earthen wall layer, pigments, and techniques, compared to the Buddhist mural paintings in the Joseon Dynasty studied so far. Such information can provide useful data for diagnosing the conservation status of the bracket mural painting in Gaeamsa Temple and is expected to provide effective information on materials and technologies for conservation treatment planning.