Lac dye colours: A review of the origin, history and identification techniques in textiles

Lac dye, the dyestuff derived from Kerria scale insects, has been valued for millennia by various civilizations, which have appreciated its deep red shades in textiles, paintings, and other cultural artefacts. The colour derived from lac dye is complex both in structure and history, and has been the topic of numerous discussions addressing its origin, history and multiple uses as a dyestuff, medicine or cosmetic. However, there is still a significant lack of cohesion between sources, and no publication to date has offered a comprehensive overview of lac dye. This review aims to fill this knowledge gap by exploring the biological sources from which lac dye derives; the historical importance in Asia and the Mediterranean area; and the variety of processing techniques according to technical written sources. Particular attention is given to the use of lac dye on textiles by comparing the existing dyeing manuals and identification in historical textiles by analytical methods such as high-performance liquid chromatography (HPLC) coupled to diode array (DAD) and mass spectrometry (MS) detectors or surface-enhanced Raman spectroscopy (SERS). The review also offers an updated overview on the taxonomy of Kerria lac insects, highlighting their geographical diversity and suggesting future perspective of research. The discussion provides new insights into the complexity of lac dye and its use in the dyeing traditions worldwide, by intersecting sources from history, science and art.