Testing and Development
Development, through research and testing, of intervention strategies to preserve the cave through preventive measures and remedial treatment.
Preventive measures aimed to mitigate and reduce the causes and mechanisms of deterioration of the wall paintings in Cave 85 included:
- closing of the outside door during periods of high humidity and heavy rainfall to lessen the intrusion of exterior humid air into the cave; and
- use of an ultrasonic humidifier (i.e., a Preservation Pencil®) to reduce surface and subsurface salts in areas of high salt content.
Soluble salts have been established as the main cause of deterioration of the wall paintings in Cave 85. Therefore environmental control measures are the most effective means of slowing salt-related deterioration. A simple but effective strategy of keeping the outside door to the cave closed significantly reduces the air exchange rate of the interior microclimate with the exterior climate, particularly during periods of rain, thus maintaining stable environmental conditions.
Reduction of soluble salts was also undertaken, although difficult given the fragile condition of the painted earthen plaster and the water sensitive nature of the materials. Surface salt reduction in limited areas was carried out with an ultrasonic humidifier in areas of high salt content to address salt accumulation at the surface and/or slightly below the paint layer. The ultrasonic humidifier projects a fine mist of warm water, which is used in conjunction with highly absorbent tissue to deliquesce and absorb surface and subsurface salts.
Development of conservation interventions to stabilize the paintings follows principles of minimal intervention, compatibility, and retreatability and was based on understanding of the causes and mechanisms of deterioration. Particularly important was the realization that the soluble salts could not be completely removed and that mitigation of deterioration is only possible through control measures. Therefore all treatment materials were selected to exist in areas of high salt content and to withstand possible fluctuations in relative humidity. Remedial treatments included:
- emergency stabilization: treating areas of exfoliation at the onset of the project through microgrouting using an earth-based slurry to provide both bulking and adhesion to the area behind the exfoliated layers;
- grouting: reattaching detached plaster to the conglomerate by injection of a fluid earth-based mixture with adhesive and bulking properties;
- fixing and consolidation: reattaching flaking paint layers and consolidation of powdering plaster areas with a 1 percent gelatin solution;
- plaster edging repairs: securing the edge of original plaster with an earth-based plaster similar in composition to the original in areas where loss of plaster had occurred.
A methodological approach to treatment development was designed and was applicable to all interventions. It included the following steps:
- establish existing treatment conditions based on results of the diagnostic investigation and how they will impact the design of the treatment;
- assess treatment options and determine the most appropriate choices;
- undertake a literature search on current research on treatment interventions selected;
- specify desired performance characteristics of treatment materials indicating the long-term behavior of the material in its final state (which measures how a material will function over time);
- specify desired working properties of treatment materials indicating the short-term behavior of the material in the state it is applied (which measures its practical ease of use);
- select and formulate treatment materials based on desired performance characteristics and working properties;
- design testing protocol and procedures for laboratory and in situ testing to evaluate performance characteristics and working properties;
- undertake testing; and
- evaluate results.