Organic Materials Replica Studies

Twenty-four wall painting replicas from the Laboratorio per Affresco Elena e Leonetto Tintori were selected for this project. From these, 164 sectors were studied, 45 of which were sampled for study with invasive methods. The organic binders included in these are limited to rabbit-skin glue, casein, whole egg, linseed oil, walnut oil, and gum arabic. In addition, two organic pigments are included: indigo and madder lake.

The majority of investigations carried out provide information on organic materials. Occasionally, when the instrument was the same, methods providing information on inorganic compounds were also included. The investigations have been grouped according to the sample requirements.

Noninvasive investigations (no sampling required)

Imaging and surface mapping—provides topographic information on areas of the paintings

Point analysis—explores a tiny area of the painted surface

Invasive investigations (sampling required)

Nondestructive—carried out directly on an unmounted sample without altering it

Paradestructive—carried out on a prepared sample (e.g., mounted as a cross section or thin section showing the painting stratigraphy). Preparation procedures may induce physical and chemical alterations and prohibit the recovery of the sample in its original form; however, the same sample may be used for other analytical procedures, such as:

• imaging and surface mapping—providing topographic information on an area of the prepared sample (cross section)
• noninvasive point analysis that explores a point-like surface of the sample as is or prepared in a cross section

Destructive—completely consumes the sample analyzed

Following the application of all the techniques to the study of the replicas, these techniques are to be evaluated according to the type of information required. There are four levels of information that are considered criteria for identification of:

• presence or absence of binder
• class of binder (protein, lipid, gum)
• binder identification (egg, glue, casein, linseed oil, walnut oil, gum Arabic)
• binder identification in mixtures (egg and oil, glue and oil)

The methodology or approach to be developed is not a fixed protocol but rather a range of techniques that can be used to obtain the information required for each type of conservation problem that needs to be addressed.

The results of the evaluation of the techniques were presented at a symposium on May 12, 2006, at the Conservation Center of La Venaria Reale.