Direct evidence for processing Isatis tinctoria L., a non-nutritional plant, 32–34,000 years ago
Fig 5
Blue residues retrieved from the Dzudzuana pebbles.
Panels a-c: micrographs observed with OM in transmitted brightfield (a1, b1, c1) and cross-polarised light (a2, b2, c2) of the residues extracted from Dzu S1, Dzu S6 and Dzu S5 respectively. Panel d: µ-Raman spectra excited with a laser line at 785 nm, of the above-mentioned archaeological residues, compared with I. tinctoria blue residues obtained from the mechanical processing of modern leaves (Ref 2), and with the reference commercial indigotin (Ref1). The spectra have been normalised and the luminescence background has been removed. Characteristic bands of indigotin (Ind) and cellulose (C, CI) are indicated by their Raman shift.