Monument Future

Results and Discussion

As a result of the deterioration assessment of all of the fossil sites, cracking, peeling, and chipping were observed in most areas, with cracking especially prominent. Additionally, the damage patterns varied by fossil sites. In particular, the Mumyeongsom, Nudebawee, Sanghanyeom, and the Gaemesom sites were identified as places where special treatments should be performed because the dinosaur egg fossils were highly likely to be lost in the future.

Figure 3: Test set up for monitoring reinforcement. (left) Experimental specimen, (right) Impregnation of specimens with reinforcing agent.

The rocks that constitute the fossil site are quartz wacke. Furtherore, the analysis of mineralogical 201properties showed that major rock-forming minerals were as follows: illite, plagioclase, mica, quartz, alkali feldspar, and calcite.

Figure 4: A test on the physical properties of specimen. (left) Ultrasonic measurement point, (right) Ultrasonic measurement method.

A P-XRF analysis was performed on the Nudebawee site by dividing contaminants into outcrops, soil deposits, and dinosaur eggs. The matrix layer had a slightly higher Fe level than other components, while the soil deposits showed little difference from the matrix layer. The dinosaur eggshells revealed a slightly high Ca level, while Cl was not detected except for one spot (Fig. 5).

Figure 5: Measurement results by P-XRF of the contaminants in the dinosaur egg fossil sites from Hwasung Gojeongri.

With an average ultrasonic measurement for all of the fossil sites of 1,987 m/s, all the fossil sites showed low ultrasonic wave velocities under 3,000 m/s. The relatively weathering indices of the sites were estimated between the moderately weathered (MW) stage and the completely weathered (CW) stage, while the majority of the sites belonged to the highly weathered (HW) stage, relatively. Meanwhile, the Hanyeom and Gaemesom sites had higher shares of CW than other regions, which is considered a result of their relatively longer exposure periods.

On the damaged parts of rock matrix that have cavities and cracks (such as blistering), the thermal conductivity and density decrease, resulting in changes in the heat transfer coefficient and thermal conductivity, compared to healthy parts. Additionally, the air layer created by such defects has a very small volumetric heat capacity, which causes it to respond to external temperatures with sensitivity. As a result, the damaged parts are heat up faster and cool down more slowly than healthy parts. In the thermal image, the healthy part is blue because its temperature does not increase more easily than its exfoliated part, which is red. 202Thus, the infrared thermography analysis of the scalingoff elements at the fossil sites revealed a distinct difference in thermal distribution between dinosaur egg fossils and the surrounding rocks (Fig. 6).

Figure 6: Thermographic images showing representative blistering zones of the dinosaur egg fossil sites in Hwasung Gojeongri.

The indoor reinforcing test performed to select a consolidation of reagents suitable for the study subjects revealed that Wacker OH 100 had the least difference in color from the original rock and the highest increase in ultrasonic wave velocity after the anti-swelling treatment, indicating the greatest effect in strengthening the specimens’ physical properties. Additionally, the SEM-EDS analysis of two dinosaur egg specimens from each group before and after reinforcing revealed that both specimens had substances similar to limestone; this implies that the consolidation reagents generally used for limestone, Remmers KSE-300 H/V, would be proper for consolidant treatment.

The conservation treatment for the fossil sites was conducted by selecting three sites around the fossil sites and classifying them into supplementing and reinforcing cracks. As a result of supplementing cracks using epoxy type L-30, L-50 and KSE-500, L-30, the treatement revealed a relatively better effect in strengthening the physical properties than the other two adhesives. OH 100 and KSE 300 showed a similar effect; after conducting a pre-treatment of anti-swelling and applying two types of consolidation reagents three times, it was found that OH 100 was relatively stable.

The measuement of ultrasonic wave velocity at each site was performed to monitor the effect of the trial preservation treatment and revealed that the average values before the treatment(2,091 m/s) was increased to 2,394 m/s after the treatment. In particular, the Sanghanyeom-21, Hanyeom-30, and Gaemesom-31, which had belonged to the CW stage, were upgraded to the HW stage due to the ultrasonic wave velocity increase after the preservation treatment. Although a short-term effect can be expected for outdoor fossil sites, it seems necessary to apply additional measures, coupled with a conservation treatment, in the long run (Fig. 7).

Figure 7: Trial conservation treatments and monitoring for effects of the dinosaur egg fossil sites in Hwasung Gojeongri. (left) Resin treatments within the cracks, (middle) Reinforcing the surface and (right) Effect monitoring by ultrasonic velocity.

References

Lee, C. H. and Jo, Y.H, 2017, Correlation and correction factor between direct and indirect methods for the ultrasonic measurement of stone samples, Environmental Earth Science, 76:477.

Lee, Y. N., Jeong, K. S., Chang, S. K., Choi, M. Y., Choi, J. I., 2000, The preliminary research on the dinosaur eggs and nests found in the reclaimed area south to the Siwha Lake, Gyeonggi Province, Korea, Journal of the Paleontological Society of Korea, 16(1), 27–36. (in Korean with English abstract)

Lee, Y. N., 2003, Dinosaur bones and eggs in South Korea. Memoir of the Fukui Prefectural Dinosaur Museum, 2, 113–121.

Lee. S. J., 2009, Study on the consolidating mechanism of stone monuments containing clay minerals with swelling properties. Ph.D. Thesis, Kyeongju National University, 1-110 (in Korean with English abstract).

Zhao, Z. K., and S. R. Ding. 1976. Discovery of the dinosaur eggs from Alashanzuoqi and its stratigraphical meaning, Vertebrata PalAsiatica, 14, 42–44.

203

MATERIAL CHARACTERISTICS AND NON-DESTRUCTIVE DIAGNOSIS OF STONE STANDING BUDDHA AND STONE CHAMBER OF MIREUKRI TEMPLE SITE IN CHUNGJU, KOREA

Hee Young Park¹, Sun Young Park², Chan Hee Lee^2*, Jun Hyoung Park²

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

1 Chungbuk Research Institute of Cultural Heritage, Cheongju, 28443, Republic of Korea

2 Dept. of Cultural Heritage Conservation Sciences, Kongju National University, Gongju, 32588, Republic of Korea

* chanlee@kongju.ac.kr

Abstract

The Stone Standing Buddha and the Stone Chamber of Mireukri temple site in Chungju is a semi-built artificial stone grotto temple that inherited the Gyeongju Seokguram Grotto (AD 751) in South Korea. It was designated as Korean Treasure No. 96 in recognition of its value as a cultural heritage site like the huge Stone Standing Buddha (10.6 m in height), a unique architectural structure.

However, the Stone Chamber had problems with its structural stability as its masonry was constructed after being built on top of weathered granite, where the original ground sloped to the west. Due to continuous creep, the structural deformation was clearly visible in the western wall of the Stone Chamber in 2014, which was decided to be dismantled in 2016. Currently, the dismantling and repair work is in progress on all sections of the western wall and some sections of the southern wall.

With the repair work, an overall conservation scientific investigation including non-destructive diagnosis for the Stone Standing Buddha and Stone Chamber was carried out. As a result, the main rocks that make up this study subject are pinkish medium-grained biotite granites, which as Wolaksan granite. The deterioration assessment on the Stone Standing Buddha indicated moderate conditions for all types of damage. However, in the analysis of surface contaminants, there was a singularity that the content of lead on the statue’s face was measured to be relatively higher than other parts.

The physical evaluation by ultrasonic velocity showed third grade deterioration (moderately weathered – MW) in the Stone Standing Buddha, while the Stone Chamber before dismantling was shown to be fourth grade (highly weathered – HW). Finally, by examining petrographic homogeneity with granitic rocks in the surrounding area, it was found that the rocks around Mireukri in Chungju and the quarry in Mungyeong are highly similar with those of the study subject.

Keywords: Mireukri temple site, Deterioration, Creep, Nondestructive diagnosis, Petrographic homogeneity

Introduction

The Stone Standing Buddha and the Stone Chamber, that is the main Buddha and Geumdang (the main temple) of the Mireukdaewonji, are located in 204Mireukri, Chungju City, Korea. The Mireukdaewonji is one of the important Buddhist temples in the Goryeo Dynasty (AD 918 to AD 1392) of ancient Korea. Within this cultural heritage zone, various stone cultural heritages such as the Five-story Stone Pagoda in Mireukri (Treasure No. 95) are widely distributed.

The Stone Standing Buddha is composed of six stones and is surrounded by masonry on three sides: east, south, and west. It is presumed that there was a wooden structure on the upper part of the Stone Chamber, but is no longer present (Ryoo, 2018). There is no exact historical record of when it was destroyed.

The temple’s history and name were revealed by conducting five excavation surveys from 1977 to 1991 (Kim, 2008). Since then, various art historical and archaeological studies have been carried out on the stone chamber structure, the only Stone Standing Buddha facing north in Korea, the form of the Bogae (a kind of stone hat), and the hand gestures holding a flower bud-shaped object (Jeong, 2008). On the other hand, conservation-related scientific investigation was not sufficient, and only visual observation of the physical, chemical and biological factors and surroundings was conducted.

With obvious structural deformation occurring in the western wall of the Stone Chamber, dismantling and repair work is currently underway (Fig. 1). In addition to this, to prepare the basic data for conservation and maintenance of the Stone Standing Buddha and Stone Chamber, a need for the scientific investigation has emerged. It is also required to examine the substitute stone for damaged parts of the Stone Chamber. Therefore, we expect that the results of this study will provide the basic data for the establishment of the long-term conservation management plan and the provenance interpretation for stone heritages.

Figure 1: Photographs showing the dismantling and repair work of the Stone Standing Buddha and Stone Chamber in the Mireukri temple site. (A) Before 2015, (B) March 2018, (C) March 2019.

205Research Methods

This study conducted not only prior research including historical and archeological studies but also an overall conservation scientific survey of the Stone Standing Buddha and Stone Chamber.

We analyzed the petrological characteristics of the constituent rocks by observing the microscope and measuring the magnetic susceptibility and so on. Samples collected from the dismantled stone walls and the surrounding sites were examined using stereoscopic and polarizing microscopes, and X-ray diffraction analysis, and the geochemical properties were also examined using ICP-AES, ICP-MS, and INAA. The chromaticity was also measured to check the quantitative color of the samples.

A deterioration map was prepared to evaluate the conservation status of the Stone Standing Buddha, and infrared thermography analysis was performed to detect the damaged zones that are not easily detectable with the naked eyes (Jo and Lee, 2014), and the P-XRF was performed to analyze surface contaminants. Besides, to evaluate the material properties, the degree of weathering and internal defects of the Stone Standing Buddha and Stone Chamber, ultrasonic velocity was conducted (Lee et al., 2017). By comparing P-wave pulse velocities measured by the indirect method in the masonry before dismantling and those of the Stone Standing Buddha, the degree of weathering in physical properties both were considered. Quantitative stages of weathering were calculated based on the coefficient of weathering (K) proposed by Iliev (1966). K value is defined as the rate of change in the ultrasonic velocity of fresh and weathered rock.

Results and Discussion

According to the results of the analysis of the material characteristics, the rocks that make up the Stone Standing Buddha and Stone Chamber are pinkish medium-grained biotite granite, milky medium-grained biotite granite, porphyritic granite, and aplite. The host rock is pinkish medium-grained biotite granite that accounts for more than 90 percent of the total, while other types of rocks are used as stones to fill the inside or between the walls (Fig. 2). Particularly, the Urna on the forehead of the Stone Standing Buddha and one Stone Seated Buddha enshrined inside the chamber consist of limestone.

Figure 2: Diagram showing the proportion for constituent rocks of the Stone Chamber in the Mireukri temple site.

The pinkish medium-grained biotite granite, a representative rock, is about 1 to 5 mm in grain size and composed mainly of quartz, alkali feldspar, plagioclase, and biotite. The magnetic susceptibility is measured in the range of 0.08 to 2.04 (× 10^–3 SI unit) in the Stone Standing Buddha and 0.01 to 2065.24 (× 10^–3 SI unit) in Stone Chamber. Generally, it is distributed below 2.00 × 10^–3 SI unit and the mean values are similar.

As a result of on-site investigation, damage types in the Stone Standing Buddha are mainly observed for physical damage such as crack, scaling, scale-off, and break-out, while chemical deterioration is found to be black, brown, white discoloration and believed to be red pigment in the lips. No biological damage is identified as the cleaning treatment was completed. As each damage type of the Stone Standing Buddha occupies below 6 % of the whole, by and large, the Stone Standing Buddha was found to be of good condition in deterioration assessment. In the case of the Stone Chamber, complex cracks in each material are mostly observed and discoloration caused by oxidation of minerals like iron and manganese is partially confirmed.

Infrared thermography analysis showed local exfoliations in the entire of the Stone Standing Buddha, which covered with surface contaminants before cleaning. Exfoliation occupied less than 3 % overall but the frequency of occurrence was high. Relatively large exfoliations were identified in the left arm and the pedestal.

The results of P-XRF measurement on surface contaminants indicated that manganese, iron, calcium 207and lead acted as the main determinants of black, brown, white discoloration and red pigment, respectively. Remarkably, the content of lead on the face of the statue was measured to be 18 times higher than other parts. This allows us to estimate the possibility of using the white pigment, hydrocerussite (2PbCO₃·Pb(OH)₂). It is necessary, however, to carry out further research to investigate a definite cause for this phenomenon (Fig. 3).

Figure 3: Current state of the face on the Stone Standing Buddha and result by P-XRF analysis. (A) Front view of Buddha’s face, (B) Urna and heart-shaped small hole on the face, (C) Measurement points of P-XRF and 2D modeling of Pb contents.

Physical evaluation by ultrasonic velocity was performed at 571 spots on the surface of the Stone Standing Buddha. As a result of ultrasonic measurements, the mean ultrasonic velocities of 2,710 m/s in the Bogae and over 3,000 m/s in the rest of the statue were shown. By applying the absolute coefficient of weathering (K), the weathering indices of the whole were estimated to be in the moderately weathered (MW) stage except for the Bogae which was in the highly weathered stage.

The ultrasonic velocity of the western wall in the Stone Chamber before dismantling was shown to be in the highly weathered (HW) stage with an average ultrasonic wave velocity of 2,291 m/s and coefficient of weathering (K) of 0.55. Therefore, we identified that the degree of weathering on the Stone Chamber is worse than that of the Stone Standing Buddha, which is assumed to be due to the exposure of continuous creep and complex physical damage over long periods (Lee, 1998). Creep that occurs to the west of the lower ground of the western wall causes structural imbalance, resulting in partial load difference that adds to the crack. Consequently, if this phenomenon lasts, the weathering of the masonry becomes more severe and the physical properties become weaker.

To select the substitute stone for damaged parts of the Stone Chamber, the petrographic homogeneity with granite in the surrounding area was examined. Samples used in the analysis were collected in Mungyeong, Danyang, Sangju, and Mireukri in Chungju. Considering the petrographic characteristics, the magnetic susceptibility and geochemical characteristics, the granites around Mireukri in Chungju are the most similar, and the second–most-similar is the quarry in the Mungyeong area (Kim and Shin, 1990). Therefore, it is reasonable to utilize the rocks from these areas as alternative stone in terms of authenticity of the cultural heritage.

Also, the availability of rocks used for the stone cultural heritage around the Mireukdaewonji was investigated. The results of investigating the old cutting traces, petrographic characteristics and the distribution of magnetic susceptibility, showed that there is a similarity between the stone cultural heritage and nearby rocks. It is supposed that there is a possibility to obtain stone from neighboring rocks when constructing stone cultural heritage because a river transportation system has not been developed on a large scale. However, it is necessary to reveal more direct and clear grounds through further quantitative analysis with regards to this.

This study will provide the basic data for making a stable conservation management plan of the Stone Standing Buddha and Stone Chamber, and choosing a substitute stone for masonry repair. It will also be used as an important source of regular monitoring after repair works, helping to determine the progress of damage.

References

Jeong, S. K., 2008, A study on the opening period of ‘Jungwon Mirekri temple site’. Dongak Art History of Korea, 9, 145–172 (in Korean with English abstract).

Jo, Y. H., Lee, C. H., 2014, Quantitative modeling of blistering zones by active thermography for deterioration evaluation of stone monuments. Journal of Cultural Heritage, 15, 621–627.

Kim, H. R., 2008, A study on the Construction method of the Stone chamber for protection at mireukri temple site in Jungwon. Journal of Chungbuk Research Institute of Cultural Heritage, 1, 51–70 (in Korean with English abstract).

Kim, K. H., Shin, Y. S., 1990, Petrochemistry of the granitic rocks in the Chungju, Wolaksan and Jecheon granite batholiths. Economic and Environmental Geology, 23, 245–259 (in Korean with English abstract).

208Lee, C. H. and Jo, Y. H., 2017, Correlation and correction factor between direct and indirect methods for the ultrasonic measurement of stone samples. Environmental Earth Science, 76, 477–489.

Lee, S. H., 1998, Weathering and crack development in the rocks of protecting-chamber for Standing-Buddha of Mireuk-ri temple site at Jungwon. Journal of the Korea Society of Conservation Science for Cultural Properties, 7, 68–79 (in Korean with English abstract).

Ryoo, S. L., 2018, A study on the original shape of the stone structure of Maitreya temple in Chungju City. The Journal of Cultural Heritage, 22, 263–293 (in Korean with English abstract).