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Introduction

This article introduces the background history to the detailed microbial analysis in the following paper by Sugiyama et al. in this book. Takamatsuzuka and Kitora tumuli located in Nara prefecture were both constructed between the 7th and 8th centuries during the so-called `big tomb' period. Both tumuli are famous for their beautiful mural paintings that were drawn directly on thin wall plaster in the stone chambers. Both the Takamatsuzuka and Kitora tumuli were designated as special historic sites, and Takamatsuzuka's mural paintings were designated as a national treasure. However, biological issues arose in the conservation of the mural paintings.

Through an exchange of information between France and Japan, commonalities between the situations of the paintings of the Takamatsuzuka and Lascaux cave have been identified. In both cases, the

paintings have existed in buried environments for a long time with a damp internal atmosphere. Since both mural paintings had historically been subjected to high humidity, it was feared that if the paintings were kept in a dry condition on site, they could peel off and this would be a catastrophe.

Beyond the difference in the ages of the Takamatsuzuka and Lascaux murals, an important difference between the Takamatsuzuka and the Lascaux paintings is their relative size. The Takamatsuzuka site is very small. The stone chamber is roughly 1.0 m wide, 2.7 m deep, and 1.1 m in height, which makes it a difficult place to work. A third difference is that the support layers of the paintings and pigments in Takamatsuzuka are also different from those in Lascaux. The chamber of Takamatsuzuka is constructed of rectangular stones of volcanic tuff. A very thin layer of plaster was applied over the inside surface, and the pictures were

Biological issues in the conservation of mural paintings of Takamatsuzuka and Kitora tumuli in Japan

Rika Kigawa 1, Chie Sano 1, Takeshi Ishizaki 1, Sadatoshi Miura 1 and Junta Sugiyama 2

1 National Research Institute for Cultural Properties, Tokyo2 TechnoSuruga Laboratory Co., Ltd., Tokyo Office, Professor Emeritus at the University of Tokyo

Fig.1 Left: Mound and facility of Takamatsuzuka tumulus (September 2001). Right: Painting of Asuka beauty (February 2006). (Photos: National Research Institute for Cultural Properties, Tokyo)

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painted directly on it using a variety of pigments. Some of the pigments are thought to be sensitive to some chemical disinfectants or fungicides. Consequently, different approaches from those used at Lascaux were adopted in Takamatsuzuka. These approaches were derived from the specific situation at Takamatsuzuka. Kitora was constructed in a similar manner to Takamatsuzuka. We would like to describe briefly the biological problems encountered in Takamatsuzuka and Kitora tumuli.

Takamatsuzuka tumulus

The Takamatsuzuka tumulus (Fig.1) was excavated in 1972. At that time, the policy of the conservation of its beautiful murals was discussed intensely. Specialists in the conservation of historic sites were invited from France and Italy. Although there was a suggestion to relocate the murals using a method like the strappo method used for frescos, there

was also great concern about the stability of the plaster paintings, which had existed in highly humid conditions of about 100% RH for more than a thousand years. The condition of its plaster by 1972 varied depending on its location in the tomb. Some places were very brittle and looked almost like sake lees, while other parts were firm and sound. With this combination of conditions, it was thought to be very difficult to detach the mural from the stone substrate for relocation. An additional concern was that the plaster layer had been kept under constant high humidity. There was concern that it would easily exfoliate with small changes in humidity. Drying and relocation could become very difficult challenges. Under these circumstances, it was concluded that the murals should be kept in this very highly humid environment without any relocation, and that the stone chamber should be totally closed to the public. To allow for periodic inspections of the interior conditions, a conservation facility was built to protect

Fig.2 Top: Schematic diagram of the facility at Takamatsuzuka (built in 1976). a. Stone chamber, b. Adjacent space, c. Front rooms, d. Mechanical room, e. Line of old mound, f. Line of recent mound. (Reprinted from Fig. 1 in Kiyuna et al. (2008)) Bottom left: Inside the stone chamber (a) (2001) (Photo: Agency for Cultural Affairs). Bottom right: Adjacent area (b) and a front room (c) (2001). (Photo: National Research Institute for Cultural Properties, Tokyo)

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the tomb environment from desiccation while allowing access to the chamber.

Fig.2 shows a schematic diagram and photographs of the conservation facility. Staff could not stand up inside the stone chamber as it was very small. The environment of such a small space could be easily affected if it was opened directly to the outside. Therefore, this facility was constructed to limit such effects.

It was sometimes believed that the facility should have a heating, ventilation and air conditioning (HVAC) system to directly regulate the temperature and relative humidity inside the stone chamber at all times, but this is not true. As the surface of the paintings on the deteriorated plaster was very fragile, it was thought that such a plaster surface would not tolerate the effects of air flow caused by a direct HVAC system.

Thus, the policy was to leave the stone chamber just as it was in a natural buried environment, and the facility was designed to have three small front rooms in front of the stone chamber (Fig.2, top). When staff had to enter to check the conditions, the relative humidity and temperature of the front space were adjusted to match those measured in the soil close to the stone chamber. Thus the facility was constructed so that the conditions of the adjacent front rooms could be temporarily adjusted when someone had to enter.

More than 30 years have passed since the decision was made. Although great efforts have been made to maintain an internal environment close to the original one, on several occasions, changes in the conditions have caused fungal outbreaks on the paintings.

Conditions for microbial growthWhen we considered the climatic conditions

inside the caves and tumuli, we learned that the existing conditions at Lascaux also had to be maintained, especially for the paintings on the cave ceilings, where there was great risk of damage if the surface became dry. This same situation existed in Takamatsuzuka and Kitora, which both have detailed ceiling paintings.

When considering the favorable conditions for the growth of mold, there are many factors such as temperature, humidity, oxygen concentration,

nutrients and pH. But what we would like to focus on here is the chosen relative humidity (RH). Because of concerns about the plaster and the historical internal RH of 100%, maintaining the same RH was seen as the optimal condition in both tumuli. However, it was also quite obvious that this level of humidity is ideal for the growth of molds and bacteria.

Basic concepts for conservationIn the Lascaux case, achieving the natural

balance was attempted. The same idea was initially adopted for Takamatsuzuka, but due to the difficult conditions in the Takamatsuzuka case, how to conserve the Takamatsuzuka murals was a serious problem.

In the beginning, the burial site included ample nutrients for microorganisms, and we suspect that there was a lot of microbial activity. Afterward, the microorganism activity apparently declined to a state of equilibrium. However, any change in that balance, for example, if organic substances were introduced or the atmosphere altered, could act as a trigger for more microorganism activity.

Events at TakamatsuzukaIn Takamatsuzuka's known history, there were

several events that disrupted the tomb’s static balance of microbial activity. For example, in the twelfth or thirteenth century thieves opened the tomb and performed some excavation, and the balance must have changed considerably as a result. That event occurred a long time ago, and we are not able to verify any specific changes that may have taken place. However, in 1972, the archeological excavation took place. At this time, the environment was changed drastically, so again the balance was disrupted. After the excavation, it was decided that the murals were to be conserved in situ. However, if an exfoliating portion of one of the paintings fell, it would have been disastrous; therefore, necessary restoration work took place during that time to consolidate the murals.

The restoration required a long period of intensive work spanning from 1976-1981, and due to this necessary work the tomb's balance underwent further changes. During this time the first mold outbreak occurred. The synthetic resin Paraloid B-72 was applied to the areas of the mural which were exfoliated. But on some of those areas, fungi were

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able to colonize. In a period of signifi cant growth of molds and intensive efforts to stop the mold contamination, some of the lines of certain paintings were obscured or faded. Solutions of ethanol: formalin, 9:1, and Thiabendazole (TBZ) were used, but they were not very effective. Para-formaldehyde fumigation was adopted beginning in 1981, and entry into the stone chamber was restricted further. The mold outbreaks then declined, and balance seemed to have been restored until 2001.

In February 2001, a second crisis occurred. In the space adjacent to the stone chamber containing the murals, renovation work was done. Falling soil and leakage of rain water had occurred because the environmental preservation facility was getting old. The facility underwent renovation, and at that time consolidation of the soil around the tomb was performed. That process may have been another trigger for change. Some portions of consolidated soil and stones became covered with extensive colonies of fungi: Aspergillus sp., Cladosporium sp., Penicillium sp. and Fusarium sp., etc. (Fig.3). At the same time, changes in temperature and relative humidity and the likely introduction of nutrients and microorganisms occurred by the renovation work.

The annual check of the mural paintings inside the stone chamber had been postponed until the adjacent space was totally cleaned up. After six months, in September 2001, the stone chamber was opened, and we found fungi near the mural paintings (Fig.4). At that time, the fungus observed was Penicillium sp., and three months later, by December 2001, the area where we had found fungal colonies had expanded (Fig.5, left). Additionally, the temperature at that time was at the highest part of the curve of natural annual change in the underground stone chamber, since the temperature change underground lagged three to four months behind that of the outside climate. For the fi rst time black fungi began to be observed; Acremonium (sect. Gliomastix) sp., which had also been found in Lascaux in 2002 (Orial and Mertz 2006, Dupont et al. 2007), and

Fig.3 Fungal colonies developed after the renovation of the adjacent space, Takamatsuzuka (March, 2001). (Photo: Agency for Cultural Affairs)

Fig.4 Fungal colonies near mural paintings, Takamatsuzuka (September, 2001).

(Photo: Agency for Cultural Affairs)

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Fig.5 Left: Fungal colonies near mural paintings, Takamatsuzuka (December, 2001). Right: Black stains in almost same location (October, 2002). (Photos: Agency for Cultural Affairs)

Fig.6 Left:Moldsonmuralpaintings,Takamatsuzuka.Right:themagnifiedpart(X50)wherepigmentsarecoveredbymycelia(September, 2004). (Photos: National Research Institute for Cultural Properties, Tokyo)

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Cylindrocarpon sp. were isolated. In the following year, 2002, more severe black stains were found (Fig.5, right).

In 2004, even though the periodical inspections and cleaning and disinfection work took place, not only fungi but also biofilms including bacteria and yeast became obvious. In September 2004, when the temperature went above 20 degrees Celsius, extensive white mycelia of fungi covered part of the paintings, and along with them mites were discovered. The tomb's interior surface was clearly becoming a food chain. Because it seemed to be a nutrient-rich situation, we could not leave it as it was. Fig.6 is a photo of a mural paintings with pigments covered with mycelia of fungi. As an immediate response we sprayed disinfectant, using mainly ethanol as it was thought to be one of the mildest with respect to the pigments used. However, we could not clean the mycelium off from the painting because physical cleaning might have damaged the pigments of the mural. After 2005, isopropanol was used as a disinfectant after further consideration of the problem of the biofilm. Such disinfectants were not very effective, however. Various possibilities were discussed, but none of the methods of control using chemicals, a low oxygen atmosphere, very low temperature, etc., were considered realistic at that time in that given situation.

When such outbreaks occurred, fungi caused significant deterioration of the murals, both esthetically and physically. Such deterioration had reached such a high level that it became dangerous to continue to keep the paintings in the original environment. Drastic moves to protect the paintings from further deterioration were considered, and finally relocation of the stones of the entire chamber was performed in 2007.

Kitora tumulus

Kitora was excavated in 2004, more recently than Takamatsuzuka. As a result of the preliminary investigation, some differences from Takamatsuzuka were discovered. At the Kitora tumulus, the paintings are also on a very thin layer of plaster. However, cracks were very obvious, and the plaster was loosely held to the rock, so with a slight impact it could be easily made to fall (Fig.7). Therefore, it was decided

that the paintings should be detached and relocated immediately. The Takamatsuzuka and Kitora tumuli are very similar, having been built around the same time period, but the initial methods adopted for their conservation were quite different.

Conservation process for KitoraIn January 2004, excavation of the Kitora

tumulus took place, and the relocation of the paintings started in 2004. However, after people began to go into the tumulus, we started to see fungal growth. In the beginning, fungi such as Trichoderma sp., Penicillium sp. and Fusarium sp. were seen inside the tumulus. Ethanol was mainly used to kill and remove such colonies, as it was thought to one of the mildest of fungicides with respect to the pigments used in the murals. Phialocephala sp. was also found on stones in the front room, the antechamber. In early 2005, small colonies of viscous gel appeared on some parts of the walls. In the summer of 2005, the viscous gel suddenly developed to form a biofilm on the wall plaster (Fig.8). The gel was a mixture of bacteria and fungi. The biofilm was removed where possible with a low concentration of hydrogen peroxide solution, then the area was treated with about 70% isopropyl alcohol. This method was effective in some areas where the plaster was relatively intact and robust, but it could not be applied to places where the plaster was very fragile. In the fall of 2005, small holes with black substances inside became obvious on the plaster walls; the holes seemed to have developed behind the plaster. An investigation performed by a specialist on microbes in concrete suggested that such holes might have also been caused by the activity of microbes.

As of February 2008, almost all the paintings on the side walls have been relocated by applying a protective facing and cutting away, except for those which might have been hidden by a thin layer of mud on the walls. The relocation of the star charts on the ceiling had been left to the end of the process, but it is now taking place.

Understanding and elucidating the causes and processes

Detailed analysis of what kind of microorganisms were involved in the deterioration in the tombs is provided in the following paper by Sugiyama et al. in this book. After the identification of the organisms,

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Fig.7 Left: Situation of cracks on the plaster of Kitora (early 2004). Right: Inside the stone chamber of Kitora (2004). (Photos: National Research Institute for Cultural Properties, Tokyo)

Fig.8 Biofilmonpaintings,Kitora(September,2005).(Photos:NationalResearchInstituteforCulturalProperties,Tokyo)

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we must consider their bioprofiles, i.e. the characteristics of the microorganisms, such as whether they produce organic acids that affect plaster, whether they can tolerate or assimilate some kinds of disinfectants, whether they can assimilate some kinds of resin used at the sites, etc. We have to understand those characteristics in relation to the deterioration and treatments to determine in full the causes of the observed deterioration patterns, and how best to approach any future in-situ treatments.

Acknowledgments

We thank the Agency for Cultural Affairs, Japan, and Wataru Kawanobe of the National Research Institute for Cultural Properties, Tokyo, for providing many important photographs for this article. We also express our special gratitude to Tom Strang of the Canadian Conservation Institute for his critical reading of the manuscript.

References

Dupont, J., C. Jacquet, B. Dennetière, S. Lacoste, F. Bousta, G. Orial, C. Cruaud, A. Couloux and M.-F. Roquebert : Invasion of the French Paleolithic painted cave of Lascaux by members of the Fusarium solani species complex, Mycologia, 99, 526-533 (2007)

Kigawa, R, C. Sano and S. Miura : Past and present situation of microorganisms in Takamatsuzuka Tumulus (in Japanese), Science for Conservation, 43, 79-85 (2004)

Kigawa, R., C. Sano, H. Mabuchi and S. Miura: Investigation of moulds in Kitora tumulus during its excavation and restoration works (in Japanese), Science for Conservation, 44, 165-171 (2005)

Kigawa, R., H. Mabuchi, C. Sano and S. Miura : Investigation of biological issues in Kitora Tumulus during its restoration work (2) (in Japanese), Science for Conservation, 45, 93-105 (2006)

Kigawa, R., C. Sano, T. Ishizaki and S. Miura : Concept and measures of the conservation of Takamatsuzuka Tumulus for thirty years and the present situation (in Japanese), Science for Conservation, 45, 33-58 (2006)

Kigawa, R., C. Sano, H. Mabuchi and S. Miura : Investigation of issues in Kitora Tumulus during its restoration work (3) (in Japanese), Science for Conservation, 46, 227-233 (2007)

Kiyuna, T., K.-D. An, R. Kigawa, C. Sano, S. Miura and J.

Sugiyama : Mycobiota of the Takamatsuzuka and Kitora Tumuli in Japan, focusing on the molecular phylogenetic diversity of Fusarium and Trichoderma, Mycoscience, 49 (5), 298-311 (2008)

Orial, G. and Mertz, J-D. : Lascaux: ne grotte vivante. Étude et suivi des phénomenes microbiologiques, Dossier Les grottes ornées, semestriel 2, Monumental, 76-87 (2006)

Pallot-Frossard, I. : Similitudes japonaises: le tumulus de Takamatsu-zuka attaque par les moisissures, Dossier Les grottes ornées, semestriel 2, Monumental, 82 (2006)