Sadatoshi Miura, Tadateru Nishiura, Zhang Yongjun, Wang Baoyi, and Li Shi
SINCE 1986, the Tokyo National Research Institute of Cultural Properties and the Dunhuang Academy have worked together for the conservation of the Mogao grottoes at Dunhuang. An agreement for this joint project was signed in December 1990 and includes three types of research on the grottoes: an environmental study, an analysis of deterioration, and a conservation study. The following is based on the environmental study of two grottoes from 1988 to 1992.
The Mogao grottoes consist of 492 cave temples excavated in a cliff above the Daquan River. The caves are situated at three levels—upper, middle, and lower—and vary considerably in dimension. While some can accommodate only one person at a time, others are large enough for many visitors.
The hypothesis was that different kinds of deterioration are caused by the different climatic conditions that may exist in certain caves. Caves 194 and 53 were chosen for measurement (Fig. 1). As Cave 194 is located on the upper level of the cliff and Cave 53 is on the lower level, the two caves were assumed to have different microenvironments, which would lead to different kinds of damage to their wall paintings (Miura et al. 1990).
Cave 194 is rather small. Its dimensions are approximately 3.6 x 3.6 m in depth and width, with a height of 3.3 m. The grotto has an antechamber and a lateral grotto, known as Cave 195. The paintings in Cave 194 are mainly from the Tang dynasty and are still intact today Many small areas of flaking are found by careful observation, however, as well as blistering of the paint surface.
Cave 53 is large, with dimensions of about 6.5 x 6.5 x 6.5 m. It also has a lateral grotto, Cave 469, the entrance of which was sealed during the measurement period. Sand to a depth of several meters had covered the floor of Cave 53 until the 1960s. In the past, river water had often entered through the front of the cave, giving rise to humid conditions that caused flaking of the paint and black spots on the lower part of the wall.
Measurements
The microclimates of the two grottoes have been measured since March 1988 to investigate the causes of deterioration. Figure 1 shows the location
Figure 1
Plan of Caves 53 and 194.
Of sensors. Temperature and humidity have been measured at three different heights at the center of each grotto. Since May 1991, temperature and humidity have also been measured inside a hole drilled in the ceiling of Cave 194 and in the floor of Cave 53.
Climatic data were recorded in data loggers every two hours (twelve times a day) from March 1988 to May 1991 (Li et al. 1990), and every hour (twenty-four times a day) from May 1991. The data are collected by a portable computer at the grotto or at the laboratory of the Dunhuang Academy by a radio system.
Average, maximum, and minimum climatic values are calculated from daily data. Monthly and annual values are derived from these daily calculations. Since Cave 194 is heated by sunlight during the day, the temperature measured at the entrance of this cave does not represent a typical outside value. Temperature and humidity measurements at the entrance of Cave 53 are used, therefore, as the external values for both grottoes.
World History
