高松塚古墳の微生物対策の経緯と現状

Takamatsuzuka Tumulus was excavated in 1972, and the policy of conservation of its beautiful plaster paintings was discussed intensely at that time. Specialists in the conservation of historical sites made of stone were invited from France and Italy. Though there was a suggestion to relocate the plaster paintings by a method like the storappo method used with fresco, there was also a great concern about the stability of the plaster paintings which had been kept in high humidity of about 100% RH for more than a thousand years. The plaster of the mural paintings had deteriorated significantly at the time of the excavation in 1972; exfoliation and flaking were seen at many places on the paintings. Considering such conditions, it was thought thatdesiccation would be catastrophic to the beauty and stability of the plaster paintings. It was also feared that storappo of such heterolytic plaster surfaces would be very difficult. Thus it was determined to maintain the plaster paintings on site, in very high humidity. The basic concept of this decision was to keep the plaster paintings in the original environment, hopefully in the environment of unexcavated, buried condition. High humidity was good for the physical condition of the plaster, but at the same time it imposed a very difficult situation on fighting biodeterioration of the paintings. None of the methods of control by chemicals, low oxygen atmosphere, very low temperature, etc. was realistic in this case. Keeping the plaster paintings in about 100% RH means relying mainly upon the natural balance of microorganisms in a closed environment. When a small system is shut out from the outside world, microorganisms such as fungi and bacteria would be active at the start, but gradually come to a balancing point of no drastic change. However every small perturbation of temperature, humidity, invasion of new kinds of microorganisms from outside, or change by restoration works would break the balance and cause a new outbreak of microorganisms. Thus the strategy for maintaining the paintings should be to keep any stimulations out from the stone chamber, to keep the original buried environment. A facility was constructed to maintain the temperature and humidity of the adjacent space the same with those in the soil when staff had to go into the stone chamber. Thorough disinfection has also been performed on mechanics and staff when restoration works or annual checking were necessary. More than thirty years have passed since the decision was made. Although great efforts have been made to keep the paintings free from outbreak of microorganisms, changes in the condition that occurred a few times have caused fungal outbreaks on the plaster paintings. Once such an outbreak occurred, fungi deteriorated the plaster paintings significantly both esthetically and physically. Such deterioration has accumulated to a very dangerous point for keeping the paintings in the present condition. Now it is considered time to make drastic decisions for the conservation and restoration of the paintings to protect them from further deterioration

〔報告〕キトラ古墳保護覆屋内の環境について（3）―カビ点検報告記録の解析―

Kitora Tumulus is located in Asuka-mura, Nara prefecture and is thought to have been founded in the late 7th century. It is famous for the wall paintings of Chinese god beasts and animal servants in its stone chamber. Excavation started in 2004 and the relocation of paintings is now being executed. In this article, the environmental conditions during conservation work of 2007 are reported. Environmental monitoring and disinfection work were conducted about twice a week in 2007. Sanitalization of the conservation facility was done quickly when the amount of bioaerosols in the facility was high. But the warm winter of 2006 induced a 1.5℃ rise in the lowest ground temperature recorded in June around Kitora Tumulus compared to the preceding year. This might have caused vigorous biological activity during 2007, resulting in biological damage of about 20% of the total area of the surface of the stone chamber, while during the preceding five months of 2006 only 0.3% damage to the total area was recorded