Salts and synthetic coatings on wall paintings: characterising their transformation, interaction and contribution to deterioration

Salts and degraded coatings-typically inherited from failed conservation interventions-are ubiquitous problems in cultural heritage conservation. In wall paintings, salt deterioration leads to powdering and flaking of the support and paint layer, causing serious loss. Synthetic coatings often discolour or become opaque, and may contract and pull off the painting; they may also become insoluble, making their removal impossible. When salts and coatings occur in combination, the problems are compounded, but there is a dearth of understanding on the mechanisms of deterioration and how these complex and heterogeneous phenomena may be addressed. To date, investigation of these issues has largely been limited to empirical treatment-oriented trials and to experimental research in controlled laboratory conditions. For a more informed approach to actual conservation problems in the field, research is urgently needed that combines experimental study with rigorous in situ analysis.

The proposed research will examine the problem of salts and degraded coatings through in situ characterisation of the deterioration phenomena (singly and in combination), and of the impact of the prevailing environmental conditions. Two wall painting sites have been selected for study where salts and coatings are causing widespread damage: Hardham Church, with one of the finest and earliest schemes of medieval painting in the UK, and Nagaur Fort (India) with exceptionally important 18th-century Rajput-Mughal paintings. The sites are radically different in their geographical location, macroclimate, physical history and the paintings' original technology, yet there are similar deterioration phenomena. At both sites, the paintings suffer from severe salt-related damage and deteriorated coatings applied during previous conservation interventions. The synthetic surface coatings act as impervious layers and in conjunction with moisture movement and phase changes of salt, they contribute to catastrophic decay and loss. 'Protective' coatings are still widely applied to salt-laden wall paintings and stone monuments, and the field of practical conservation is in critical need of a better understanding of their ageing and deterioration characteristics under real environmental parameters. Conservation projects are underway at both sites, involving passive conservation measures at Hardham, and treatment at Nagaur. Both projects are managed by the host organisation, the Courtauld Institute of Art.

The research is designed to study the current physico-chemical characteristics of degraded surface coatings at both sites, the impact of environmental parameters on salt phase changes, the interaction between surface coatings and soluble salts and their contribution to the deterioration of the wall paintings. The aim will be to apply, evaluate and further develop non-invasive, non-contact, cost-effective characterisation and analytical techniques for in-situ analysis, and to evaluate and calibrate these methods against more sophisticated laboratory-based techniques. By integrating complementary in-situ investigations with cutting-edge scientific research this study aims to widen the impact of scientific analysis on the conservation of wall paintings. Although the research will focus on two sites, its methodological approach and findings will be applicable to many other sites and works of art. The Project Partners supporting the proposed research are English Heritage (already involved in the Hardham conservation project) and the Mehrangarh Museum Trust (responsible for the site of Nagaur). Through a broad dissemination plan, this research will have a considerable impact across the various disciplines in the academic field and wider conservation community, and will help to raise public awareness of conservation and of the integral role of science in the conservation of cultural heritage.

One of many ways in which the proposed research will have an impact beyond academia is through the Fellow's close collaboration with English Heritage, the Government's statutory adviser on the historic environment. Through his work with the Building Conservation and Research Team of this Project Partner, the Fellow's research will be disseminated to English Heritage's professional staff, and to a wider public through the organisation's published output.

Through both the sites on which the Fellow will be focusing - Hardham Church (UK) and Nagaur Fort (India) - proposed research will impact on a wide range of non-academic organisations, conservators, and stakeholders. At Hardham, these include Church of England organisations responsible for the preservation as well as continued use of this and many similar buildings; and at Nagaur, will include the Mehrangarh Museum Trust (Project Partner) and its own Conservation Centre, as well as a wider body of conservators and conservation scientists in India.

Since salts and coatings are ubiquitous problems in conservation worldwide - of both the movable and immovable heritage - the proposed research will have a significant effect well beyond the wall paintings field. For instance, it will be of benefit to the conservation staff of the British Museum, where soluble nylon - the most problematic coating at Hardham - has been widely used on objects in the past. While the Courtauld Institute has close links with English Heritage and the British Museum, the methodology and results of the research will be disseminated to a much wider non-university audience through publications, workshops and lectures.

The proposed research will also be disseminated to governmental and other participants in the Courtauld's multiple conservation and training projects throughout the world. In at least some cases, it will have a direct impact on these projects, currently in Bhutan, China, Cyprus, Jordan and Malta, as well as the UK and India. All these projects involve salts problems, and all but one harmful coatings, thus demonstrating again the ubiquity of these two problems. Dissemination will be further achieved in some of these cases by the Courtauld's training of local conservators as an essential element of the projects. The research at both Hardham and Nagaur will be made available in various ways to a wider public, thus raising public awareness of the contribution of scientific research to cultural heritage conservation. Finally, the research will of course have a direct impact on the conservation of the internationally significant wall paintings at both sites.