Primary Sources for Organic Materials Study

The historical literature was reviewed, looking at the types of organic materials used in wall paintings as described in manuscripts, treatises, and manuals. The objective of the historical review was to identify and collect references on the typology and use of organic materials. The review focused on literature addressing western European lime-based wall paintings from the late medieval period to the 18th century. Historical sources such as manuscripts, treatises, and manuals that describe the methods and materials for painting on walls provided interesting insights into the variety of organic materials, including pigments, used by artisans over the course of centuries.

A total of 231 recipes were reviewed and 16 general classes of organic constituent were identified, including beer, wine, vinegar, egg (white and yolk), gall, glues, flour and starch, oils, gums, resins, varnishes, waxes, milk, sugar, vegetable products, and human metabolic products. Around 60 recipes addressed gilding methods, describing the preparation of glue for metal foil, its use as a varnish to imitate the color gold or as a protective coating for gold, silver, and tin foils. The classifications are not meant to represent a scientific nomenclature but rather a simple way to group recipes through their ingredients as cited in the manuscripts. All these recipes are organized in a ProCite® database at the Conservation Institute. Whenever possible, the reference is given to a text that includes the recipe in English. When available, the recipe in the original language is also included in the database.

The review of the analytical literature was carried out to determine which types of organic materials have been identified in wall paintings and which analytical techniques used for this purpose. To achieve this goal, analytical literature on wall painting studies from 1960 to 2002 was reviewed. References to organic materials identification in historic wall paintings were organized according to the analytical technique used to determine the presence of organic materials. Approximately 60 references have been identified and the information is stored in a database, organized by author, date, type and period of the wall painting studied, techniques used, and type/class of organic materials found.

Throughout his professional life, the late Leonetto Tintori at the Laboratorio per l'Affresco di Elena e Leonetto Tintori was interested in and studied the role of organic materials in wall paintings. In his extensive career as a wall painting conservator, Tintori had constant reminders of the need for understanding the presence and the role of these materials for the appropriate preservation of wall paintings. He concentrated his work on this subject beginning in 1983, when he created a center at his house in Vainella near Prato, Italy, to study these problems and to teach wall painting techniques.

In pursuit of this interest, Tintori made hundreds of wall painting replicas simulating different techniques and material combinations. The replicas are painted in sectors—i.e., an area completely covered with the same painting technique and phase of application. Used in these sectors were organic materials such as egg, oil, casein, and milk, in combination with different types of pigments and mortars. Tintori documented each replica in terms of the materials and methods used and, in some instances, the relative amounts of the binders and pigments used. These replicas were cataloged in a database that will allow for identifying sectors by binder, pigment, and phase of application.