The use of thin-layer chromatography in the identification of historic artificially colored varnishes and glazes

Judith J. Bischoff, Scott W. Nolley, and Jonathan Thornton

Abstract

Historically, natural dyes and resins have been used in the polychromed decoration of wood, as well as in clear colored coatings and glazes employed in the finishing of other types of artifacts. Largely impermanent as colorants, the presence of these materials in their aged and faded states can often go unrecognized when encountered in a darkened and yellowed varnish. Thus, it is important that the conservator be able to easily determine when an object has been intentionally colored. The goal of this study was to find a simple, low-cost method for the detection of colorants used in the historic production of such artifacts.

Thin-layer chromatography (TLC) was the principal method chosen for this investigation, based on its simplicity and low-cost. Some resinous materials used in the formulation of traditional varnishes, along with colored resins and natural and synthetic dye materials, were studied, alone and in combination. The method was assessed for its feasibility in the chromatographic separation of the various colored components and for its ability to aid in identification of these components.

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