Information Gathering and Assessment
Research, compilation, and review of material on Cave 85 and the Mogao Grottoes was undertaken in order to carry out the assessments of significance, management, and condition as well as the diagnostic investigation to understand the causes and mechanisms of deterioration.
A bibliography has been compiled and periodically updated since the start of the project.
- physical description of Cave 85 and its wall paintings and sculpture, including information on the geology and hydrology of Mogao, construction, and painting techniques and iconography
- historical information on the physical history and historical context of the site and Cave 85 through archival records, historical photographs, and oral sources
- conservation history including previous interventions and information on the type and extent of past interventions at the site and in Cave 85—and general knowledge about conservation practices at Mogao
Central to this component was the assessment of cultural significance and the resulting Statement of Cultural Values and Significance. The significance assessment was an essential component of the project as it took into consideration the artistic, historic, social, and scientific values of the site thereby guiding the overall decision-making process in order to preserve values.
The management assessment considered all the factors other than condition that affect the present and future conservation and sustainable management of the site. The management assessment for Cave 85—done as a component of the separate master plan for the site as a whole—requires understanding and analysis of the management structure responsible for the conservation and maintenance of the site. The management assessment for the Mogao Grottoes included understanding:
- who is responsible for conservation and management decisions and for the day-to-day management of the site;
- the processes by which decisions are made and recorded;
- the security and regular maintenance of the site;
- the expertise, resources, skills, budget, and time available for the completion of the project, from both the Dunhuang Academy and the GCI perspective.
The aim of the condition assessment was to gain a comprehensive understanding of the state of the cave's preservation through identification and recording of the types and distribution of deterioration phenomena. The assessment included:
- detailed examination of the paintings and sculpture;
- comprehensive color and black-and-white photographic surveys of wall paintings;
- graphic documentation to map the types of deterioration and their distribution; and
- creation of an illustrated glossary in Chinese and English of condition terms.
The main deterioration phenomena observed in Cave 85 included surface deterioration of wall paintings (exfoliation and flaking), and subsurface deterioration (plaster detachment and disruption, powdering of the plaster, and areas of loss of plaster and painting). All are conditions commonly found in other caves at Mogao, in varying degrees. The graphic condition recording showed that the distribution of deterioration—both surface and subsurface—increased in severity and extent toward the rear (west) end of the cave.
The diagnostic investigation in Cave 85 aimed to identify and understand the causes and mechanisms of deterioration of the wall paintings in order to formulate appropriate conservation treatments. Research and investigations were carried out by the conservation, analytical, and environmental teams. Focused research into the main types and location of active deterioration, original materials, painting techniques, soluble salts, and environmental conditions provided the basis for formulating and testing hypotheses of deterioration. See also scientific investigation.
Identification and determination of active deterioration
Building upon the condition assessment, the main types of deterioration were categorized as active or historical in nature. Active deterioration refers to phenomena that are continuing; historical deterioration refers to ones no longer active.
Both types can be determined through review of historical records, such as past conservation reports and photographs showing change over time that may indicate recurring deterioration after repeated treatment, as well as by in situ examination of the paintings.
Two principal types of active deterioration were identified in the wall paintings:1) Exfoliation: the lifting and resulting loss of paint, ground, and upper plaster layers. The severity of this phenomenon was often associated with previous treatments for flaking of the paint layer with extensive use of synthetic, impermeable fixatives. As the causes of deterioration remained, the flaking recurred in a more serious form as exfoliation.
2) Plaster detachment: loss of adhesion between the earthen plaster and the conglomerate rock. Detachment and subsequent collapse of the painted plaster has been a long-term problem in Cave 85 and in many of the caves at Mogao. Previous attempts at solving this problem—including the use of cross braces and anchors to secure detaching plaster to the conglomerate—have failed.
The large-scale extent of exfoliation and, in particular detachment, were considered the most urgent and severe problem affecting the wall paintings.
Page updated: January 2014