The Organic Materials in Wall Paintings (OMWP) project seeks to develop an analytical protocol for the study of organic materials used in wall paintings. Effective techniques for identifying different types of organic materials—and for gaining a better understanding of the behavior and role of these materials—are fundamental for conservators in their efforts to develop appropriate conservation and maintenance procedures for wall paintings.
The OMWP project brings together an international group of conservation science laboratories—including the GCI's—with expertise in the study of wall paintings and in the use and evaluation of analytical techniques. A feasibility study of the project was completed in spring 2003 (see Conservation, vol. 18, no. 3), and work has begun on the project's first phase—an evaluation of techniques used to determine the presence and nature of organic materials in wall paintings.
Since November 2003, the research laboratories participating in the project have been evaluating a series of 18 lime-based wall painting replica samples made between 1993 and 1997 by the late Leonetto Tintori and archived at the Tintori Center in Prato, Italy. Following the work plan developed by the group, each research laboratory has systematically applied one or more investigation techniques on selected replicas.
The Tintori replicas are painted in sectors, using different types of binders, pigments, and/or phases of application. The binders contained in the first group of replicas analyzed include whole egg, linseed oil, walnut oil, rabbit skin glue, calcium caseinate, ammonium caseinate, and Arabic gum. These materials have been applied with different types of pigments, including several types of earth pigments (ochers), copper-based pigments, lead white, and madder lake. The binder-pigment mixtures can be applied in different phases: on fresh, semidried, and completely dried plaster. On some sectors, the pigments are applied only with water—no binder is used. When this is done on fresh plaster, it corresponds to the traditional a buon fresco technique.
Each Tintori sample includes a document describing the materials and methods used to paint each sector and, in some instances, the relative amounts of the binders and pigments used. When the amounts are provided, it is possible to make a theoretical calculation of the binder-to-pigment ratio of the dry paint layer. This calculation is useful in the evaluation of techniques that provide information on the type and amount of organic materials used. As part of the project, the descriptions have been organized in a database to allow searching of the sectors by binder and/or by pigment.
Noninvasive imaging techniques have been applied to each of the replica samples. Point analysis and analytical invasive technologies, which required the removal of a small amount of material, have been applied on selected sectors.
The research team is completing testing on this first group of samples and has been meeting in specialized groups to discuss the results and evaluation of the various techniques and to discuss developing a protocol for examining a wall painting. In addition, the group is selecting a new set of replica samples to continue the evaluation of techniques in the coming year.
Results from the two years of investigation will be compiled beginning in summer 2005, and a case study on a wall painting undergoing conservation will follow. The case study will help demonstrate the analytical protocol and the level of information required to ensure the appropriate conservation of a painting.