1 INTRODUCTION

Identification of binding media in the painted layers on ethnographic objects is an important step prior to any conservation treatment. The first attempts to paint with colored materials were made without using any binding media or using only a temporary binding medium (water). Eventually craftsmen and artists realized that such procedures did not give satisfying or long-lasting results. They recognized the need for binding media that would hold pigment particles together and adhere the pigmented layer to the substrate.

The problem of identifying binding media in ethnographic objects is complex. Each culture and each time period had a set of favorite media. The range of binding media used on ethnographic objects is broad and covers a variety of materials from tree gums, salmon eggs and orchid juices to modern synthetic polymers. Binding media found on ethnographic objects are raw natural products (egg, honey, or blood), processed natural products (animal glue, casein, starch, or oil), or synthetic organic materials. This paper focuses on natural binding media that chemically belong to groups of lipids (vegetable oils, or lard), carbohydrates (honey, tree gums, or starches), and proteinaceous materials (animal glue) and on complex binding media (egg, blood, or fruit juices). For example, egg is a complex binding medium that contains proteins, oils, and carbohydrates. Blood contains proteins, oils, carbohydrates, and hemoglobin.

Several simple chemical tests have been modified for identification of binding media in paint layers of art objects. These tests are based on qualitative spot tests (Feigl 1966), microchemical analytical procedures (Schramm and Hering 1988), or chemical microscopy methods (Masschelein-Kleiner 1986). The literature mentioned serves as a good introduction to these methods and contains references needed for more detailed study.

The aim of this study was to develop a simple binding media identification system that would not require extensive training to master and would not use sophisticated chemical and physical instrumentation, which is beyond the means of many conservation laboratories. Because of their simplicity and widespread availability, commercial test kits developed for modern medical diagnostics are the basis for much of our work. Some additional tests were added using methods of qualitative analytical chemistry and forensic science. We have made every effort to include test reagents that are readily available worldwide. Some tests included in the binding media identification procedure give straightforward and reliable answers. In some cases, there is a need for a combination of tests to identify the binding medium class.

Each test was checked for possible interference from the other binders considered in this study. The possible effect of some pigments important in ethnographic art objects was studied; they include yellow and red ochre, kaolin, limestone, gypsum, ultramarine, charcoal, manganese dioxide, and “battery black” (an impure form of manganese dioxide extracted from old batteries by Australian and African ethnographic artists and used after World War II). Where interference was observed, it is noted under the comments for the individual tests.