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The Organic Materials in Wall Paintings project was developed to improve the practice of wall paintings conservation through a methodology for the identification of organic materials used in wall paintings. The project evaluated methods to study organic materials, which are vulnerable to time and to conservation treatments and difficult to identify, and applied them to wall painting conservation case studies to illustrate practical advantages and benefits. This was achieved through the following components:

Background
Historically, wall paintings are made with a variety of supports, types of plaster, and painting materials (pigments and binders). The knowledge of the nature and of the behavior of the materials used is fundamental to ensuring appropriate conservation and maintenance procedures. While identifying inorganic components in wall paintings today is a relatively straightforward process, doing the same for organic materials remains a challenge.

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When dealing with wall paintings, organic materials are typically added in smaller quantities than inorganic materials (pigments and mortar). Advanced methods of investigation available today have demonstrated that organic materials were used in wall paintings far more frequently than was thought in the past. Their identification is therefore an essential part of preliminary research in any conservation projects to minimize the risk of damage, to improve methods of intervention, and to plan long-term maintenance programs.

Organic materials are also less stable and deteriorate faster than the inorganic components, and because of this, often only traces remain in centuries-old murals, making these organic components difficult to identify. In addition, the contamination by materials used in previous restoration interventions, such as the application of egg-based fixatives or synthetic resins, hinders further the identification of the original organic components. Finally, wall paintings are typically heterogeneous, painted with mixed technique, and cover large surfaces (often several hundred square meters). Therefore an appropriate sampling, informed by non-invasive examination strategy is crucial.

For all these reasons, it is challenging to identify organic materials in wall paintings, thus making it necessary to use and combine information from several types of investigations. First, noninvasive investigations (that do not require sampling) provide topographical information on the possible presence and distribution of organic materials on the surface; and second, invasive investigations (carried out on samples removed from the mural) provide stratigrafic and much more specific information on the nature and distribution within the paint layer of the carefully selected area sampled.

The identification of organic materials in wall paintings is an important step in any conservation program for three main reasons (1) diagnostic: contribute to the knowledge required for the understanding of deterioration processes (2) preservation: provide the basic knowledge to develop an appropriate conservation intervention (particularly cleaning and consolidation) and long-term maintenance programs and (3) art historical: support and advance the study of mural painting techniques and the understanding of artistic intent.

Overview
Over the past twenty years, the GCI has developed an expertise using invasive techniques such as infrared spectroscopy and gas chromatography and mass spectroscopy for the identification of organic materials in easel paintings. Based on this expertise and on the expertise of the project partners, the GCI developed the Organic Materials in Wall Paintings project joining the interest of several conservation and scientific institutions with expertise in noninvasive and invasive technologies to identify organic materials in wall paintings. The project was conducted in two phases: (1) assessment of a group of investigation techniques on wall painting replica samples and (2) application of the results of the assessments to ongoing conservation projects.

First Phase: Background Research and Evaluation

To aid future study and to improve conservation treatments, historical and analytical information on organic materials in wall paintings was collected and tabulated. The historical literature was reviewed, looking at types of materials and their preparation methods as described in manuscripts, treatises, and manuals. A review of the analytical literature was carried out to determine which types of organic materials have been identified, while recording the analytical techniques used for this purpose. This bibliographic research was published in Reviews in Conservation, 2004, pp. 6380.

To evaluate investigation techniques, the OMWP project used a set of wall paintings replicas made by Leonetto Tintori that had been prepared with different types of binders and pigments applied on lime-based plasters. The OWMP investigation methodology was grouped by technique type—invasive or noninvasive. For wall paintings, noninvasive technologies must be portable, available for use often high up on scaffolding. To that end, the OMWP project evaluated a variety of available portable techniques for organic materials identification. The evaluation was carried out to both assess the accuracy of the results and the level of information provided by each technique.

Second Phase: Application of the Methodology

The application of the methodology in case studies helped to illustrate the methodological approach and can be used to highlight the implications the presence of organic materials has in wall paintings conservation and the ways this information can be used by conservators to develop their intervention and to plan the monitoring of conditions.

Once of the most significant outcomes of the OWMP project is related to the noninvasive investigations and the assessment of the capacity and limitation of each investigation technique tested, particularly for new portable methods. Another valuable contribution was bringing scientists onsite to work side by side with conservators to address conservation issues.

A publication on the Organic Materials in Wall Paintings project is forthcoming from Getty Publications.

Last updated: March 2011