1. INTRODUCTION
Buddhist murals in Korea are constantly damaged due to environmental factors, limitations of the materials, and structural factors of the wooden structures (
Lee, 2012). Especially the murals painted on earthen walls suffer from various types of damage compared to damage on other relics, therefore it is necessary to continuously record and observe the damage.
Research related to the conservation of the Buddhist murals in Korea has been widely conducted since the 2000s and in addition to theoretical studies such as damage factors and conservation methodology, research applicable to conservation treatment, preliminary investigation and diagnosis, and restoration materials treated in the past, research results were published. As an example of mural diagnosis research conducted in Korea, there is a study on the status of damage to the murals on the inner wall of Geungnakjeon Hall of Muwisa Temple in Gangjin (
Institute of Conservation of Paintings, Konkuk University et al., 2006) and overseas, there is a diagnostic study on the mural in Phaya-Thone-Zu Temple in Bagan, Myanmar (
Korea Cultural Heritage Foundation et al., 2018).
The Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural in Geungnakjeon Hall of Daewonsa Temple in Boseong are on the east and west walls inside of Geungnakjeon Hall. The two murals, said to have been made in the mid-18
th century, were designated as treasures in 2015 and conserved for their cultural value (
Figure 1). It is estimated that the murals were repaired at the time of repair of Geungnakjeon Hall and Dancheong in 1983 and reported that conservation treatment was made in 2012 by universities in Korea and Japan (
Kim, 2018).
The wooden structure of the Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural of Geungnakjeon Hall of Daewonsa Temple in Boseong is formed between the Jongryang (floorboard) at the top and the Changbang (lintel) in the center, with the central Goju (high column) of the two rows of left and right side walls of the Geungnakjeon Hall building. In the center of the mural, a two-row vertical Jungbangjae (windowsill) prevention is located. The Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural are painted on the earthen wall and Jungbangjae (windowsill), and represent the style for making Buddhist murals in the Joseon Dynasty.
For the wall, wooden lath was weaved with twine to prepare a frame, and then the first layer, middle layer, and finishing layer were made with pugging mixed with sand, red clay, and fibers. For the painting layer, green earth was used to form a ground layer, and then pigments such as lead white, white clay, atacamite, copper green, smalt, cinnabar, hematite, and minium were used(
Bosung-gun et al., 2021).
As part of the mural conservation treatment project in 2021, a investigation on the conservation status of the murals was conducted, and damage such as cracks and exfoliation of the wall, deterioration of the painting layer, contamination, and damage due to restoration materials, and it was confirmed that conservation treatment was necessary (
Bosung-gun et al., 2021).
Scientific diagnosis and investigation of the murals can record the degree of damage and reveal the cause and suggest a more reliable and effective conservation methodology (
Lee et al., 2018). Therefore, in this study, various scientific diagnostic methods were applied to the Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural in Daewonsa Temple, and the physical properties of the murals were identified, and the overall conservation status was evaluated by comparing and analyzing the results of the conservation status investigation.
2. RESEARCH METHOD
2.1. Investigation of Conservation Status
To understand the type and degree of damage to the murals, the status of conservation was investigated based on the visual investigation. A digital camera (G-15, Canon, Japan; TG-3, Olympus, Japan) was used to record the damage. The damage was divided into the wall and painting layer and subdivided by the main type (
Table 1). To create damage mappings for murals, we used digital image analysis program PicMan (WaferMasters, Inc., USA) and the image editing program Photoshop (Adobe, USA). The conservation status was evaluated by creating a damage mapping based on the color information of the mural’s digital image and comparing it with the damage status investigation result.
2.2. Optical Survey
Infrared and ultraviolet photography was carried out to identify matters such as the presence of drawings, which are difficult to visually confirm, and traces of past conservation treatments such as repainting. Infrared photography was used by installing a 912 filter on an IR lamp and infrared camera (EF-X8, Fujifilm, Japan). The ultraviolet photograph was performed u sing a UV lamp and DSLR camera (EOS 800D, Canon, Japan).
2.3. Infrared Thermography
A high-resolution thermal imaging camera (Testo 882, Testo, Germany) and interlocking software were used to diagnose the surface cracks and delamination of the murals. Since the investigation environment is indoors, an active method of applying heat using a halogen lamp was used.
2.4. Ultrasonic Examination
To identify the distribution of the surface properties of the murals, ultrasonic measurement (Ultracon-170, MKC Korea, Korea) using a needle rod type probe was performed. Measurement was carried out by an indirect method, and the measurement conditions were set as P wave, voltage of 1200 V, and a frequency of 5 Hz. The distance between the probes was 150 mm, and the ultrasonic speed was measured at 276 points for the Avalokitesvara Bodhisattva mural and 262 points for the Buddhist Monk Bodhidharma mural, and then an image distribution map was created based on the average value.
2.5. 3D Scanning
3D-scanning (Faro X330 3D Laser Scanner, Faro Technologies Inc., USA) was performed to evaluate the wall spacing and wall surface smoothness. Since the murals are placed high on the left and right walls of the building, a wideband scan was performed to obtain 3-dimensional shape coordinates.
4. DISCUSSION
As a result of the investigation of conservation status of the Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural in Geungnakjeon Hall of Daewonsa Temple, the types of damage are largely divided into the wall and finishing layer damage, painting layer damage, damage due to restoration materials, stains and contamination, and biological damage and the damage types are similar in both murals.
The cracks in the walls of the Avalokitesvara Bodhisattva mural and the Buddhist Monk Bodhidharma mural are mainly found in the location adjacent to the north side of the building. Damage to the finishing layer was mainly found in the area where the Junggit and the wall meet, and it was confirmed by the 3D scanning result that part of the finishing layer was separated around the Junggit. In a wooden architecture heritage, the load on the roof is large and the structural members tend to be deformed due to the anisotropy and corroding nature of the wood itself, and such changes worsen the damage such as cracks and exfoliation of the wall (
Lee et al., 2015).
The geographical condition of Geungnakjeon Hall, around which there are mountains and a lake (Juam Lake), can accelerate physical changes in the structure of the building and the walls. Also, considering that the two murals are large, the micro-movement and deformation of structural members due to the self-load and the surrounding environment are factors that can cause cracks in the walls and damage to the finishing layers.
Damages such as wall cracks and exfoliation of the finishing layers found in various parts of the murals can also be related to the influence of the wooden lath, which is the wall structure, and as a result of infrared thermography, the temperature distribution image in the form of a grid was confirmed for both murals.
This is considered to be due to the result that the murals of Geungnakjeon Hall in Daewonsa Temple were made with the wooden lath adjacent to the finishing layer compared to other Buddhist murals. The ultrasonic measurement results of both murals were found to be somewhat higher than those of the existing Buddhist murals of the Joseon Dynasty (
Chun et al., 2009;
Kim et al., 2014;
Lee et al., 2018).
This is due to the influence of the wooden lath, which has a higher ultrasonic speed than the wall and it is assumed that the wooden lath is close to the wall surface therefore the average speed is measured high. Ultrasonic speed values were also high in some wall cracks or delamination sites, and it was confirmed by the infrared thermal imaging results that the wooden lath inside the wall was located in those parts (
Figure 13D,
13E,
13F).
If structural deformation of the murals occurs under the condition that the wooden lath is adjacent to the surface of the mural, cracks in the wall or exfoliation of the finishing layer may be developed faster, and additional damage may occur in the current conservation status. Therefore, it is necessary to observe the physical change in the murals through periodic monitoring and to respond promptly when a change occurs.
Another factor that affects wall damage is the wall restoration material used in the past repair. Through various diagnostic techniques, damage to the wall caused by the restoration material or damage caused to itself was confirmed. The difference in physical properties between the wall and the restoration material was identified through infrared thermography and ultrasonic examination (
Figure 13A,
13B), and as a result of the 3D scanning, deviation or separation from the original wall was confirmed (
Figure 13C). Since the difference in the physical properties of the wall and the restoration material and the physical change of the wall can indicate continuous damage, reinforcement using materials with similar properties to the wall as a supplement for a weak element or a wall reinforcement should be considered.
In addition to the examination of the diagnosis results, it was possible to understand that the structure inside the walls affects the ultrasonic speed during the ultrasonic examination (
Figure 13E). Since the ultrasonic examination result is not an absolute value indicating the physical properties of the murals, this study suggests that it is necessary to use it along with a technique such as infrared thermography in order to increase the reliability of the physical property diagnosis result.
In the case of painting layer damage, exfoliation and delamination were observed mainly in the painted area of the Junggit. It seems that the coefficient of contraction and expansion of wood is larger than that of the wall, and the decay status of wood also affects it. The main factor in the exfoliation of the painting layer is a decrease in adhesion due to the decomposition of the medium, but it may also occur due to the different physical properties of the painting layer and the support layer. Therefore, it can be said that a fixing treatment is necessary for the deteriorated painting layer to increase the bonding force between the pigments and the adhesion with the support layer.
As a result of the optical survey, the conservation status of various types of painting layers was identified through ultraviolet fluorescence reaction. There are two aspects of staining, the first aspect seems to be the effect of the presumed fixative used in the past conservation treatment, and the second aspect is the influence caused by a specific action taken at the time the mural was painted or after the mural was painted.
In some cases, the conservation status is good where a stain caused by a presumed fixative is found, but there are parts where the painting layer has deteriorated (
Figure 14B). It seems that measures such as fixation treatment are necessary for areas where the painting layer is cracked or exfoliation or delamination off due to the change in the presumed fixative. Also, areas showing luster and stains while the presumed fixative forms a film of paint on the surface of the painting layer may show damage due to deformation or discoloration in the future, therefore a methodology for periodic inspection and stabilization should be prepared (
Figure 14A,
14C).
Another type of stain is the irregular stains seen in many painting layers. It is found mainly in the orange robes of the Buddhist Monk Bodhidharma mural, and this is also confirmed in some cases in the UV fluorescence response to other Buddhist murals. It can be said that a detailed investigation of the cause is needed through additional research.
And UV fluorescence reaction different from the surrounding color was confirmed in the parts that were repainted on restoration material in the past repair. It is necessary to periodically observe the change in color or restoration material area while maintaining the current condition for regions that do not show great heterogeneity in the visible light area.
As a result of comparing the area values of the two murals by type of damage, the Buddhist Monk Bodhidharma mural showed 1.84% higher damage to the wall and finishing layer than the Avalokitesvara Bodhisattva mural, and in particular, the damage to the delamination of finishing layer showed a greater difference. The damage to the painting layer is 3.29%, indicating that the Avalokitesvara Bodhisattva mural is more damaged than the Buddhist Monk Bodhidharma mural (
Figure 15).
In addition to structural factors, damage to murals is caused by various factors such as the materials used, painting techniques, and the surrounding environment. Although the types of damage caused to the two murals are similar, the Avalokitesvara Bodhisattva mural was evaluated to have a relatively greater degree of damage compared to the Buddhist Monk Bodhidharma mural. Although the two murals were created inside the same building, as mentioned above, the degree of damage varies depending on the structural relationship where the murals are located in the building, the environmental conditions, the materials and painting techniques used to make the murals, and the restoration materials, methods and range. Therefore, management through periodic inspection of the relevant elements is necessary, and a countermeasure for damage that may occur in the future should be prepared along with intensive monitoring of the major damage identified in this diagnosis result.