High performance liquid chromatography as a micro-destructive technique for the identification of anthraquinone red dyestuffs in cultural heritage objects

Abstract

This article describes two of the most common natural sources of red anthraquinones that have been used since antiquity for textile dyeing and as lake pigments, namely cochineal insect and the roots of Rubia and Relbunium plants. Carminic acid is the main component of carmine, the red colorant obtained from cochineal. Alizarin and purpurin are found in the extracts of Rubia roots, but Relbunium roots contain only purpurin. These red anthraquinones have been identified in a variety of cultural heritage objects. High performance liquid chromatography with diode array detection (HPLC-DAD) is described as the most suitable analytical technique for the identification of these dyestuffs, particularly in micro-samples from textiles or pigment layers in paintings and polychrome sculptures. Finally, application of HPLC-DAD analysis to the identification of lake pigments in micro-samples of mural paintings of two eighteenth century Andean churches in Peru is described.