Fig 1.
Left: Location of Dzudzuana cave (modified after Google Earth) and cave entrance (Image by LL). Right: map of the cave with the excavated area inside the red circles (redrawn and modified from Bar-Yosef et al. 2011, p. 334, Fig 2 [50]), red squares show where the six pebbles were retrieved from. Excavations in squares G-7, G-8 and I-8 reached the full depth of the archaeological sequence. These are also the squares where the stone pebbles were retrieved.
Fig 2.
Out of the six stone pebbles retrieved in Unit D, here are imaged five archaeological pebbles showing the position of the analysed moulds indicated by blue dashed lines, and from which micro-residues have been extracted and use-wear traces have been identified.
Table 2.
The sequential sampling procedure.
Fig 3.
Microstructure and surface alterations of the pebble stones.
Two upper rows: modern reference pebbles collected from the Nikrisi River. Panels a-c: SR-μCT of a fragment sampled from a reference pebble; a and b: slices of the inner structure showing the pits and cracks (indicated by the red arrows); c: 3D reconstruction of the sample volume with overall microporosity shown in green. Panels d-f: surface roughness of the reference pebbles used in the replicative experiments as observed with the SEM (WD 2-3 mm, 4-5 kV), highlighting the presence of micro residues including a fibre entrapped in pits or cracks (f). Two lower rows: moulds of the archaeological pebbles Dzu S1, Dzu S2 and Dzu S5. Panels g-i: examples of use-wear traces including flattened areas, polish and striations as observed under the metallographic microscope. Panels j-l: microtopography of sampled areas as imaged by confocal profilometry. The false-colour maps show the pebbles’ surface texture, highlighting the presence of pits (j) as well as flattened areas and striations (k and l).
Table 1.
Summary of the analytical techniques utilised and samples investigated.
Fig 4.
Archaeological elongated blue micro-fragments extracted from the innermost 2nd mould.
Micrographs observed with OM in transmitted brightfield and cross-polarised light show nodes and kink-bands/dislocations (a: Dzu S1, mould m2; b-c: Dzu S1, mould m7; d-e: Dzu S5, mould m1), e-f: archaeological trichome showing the characteristics bumps (OM and SEM).
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.
Fig 6.
Micro-residues retrieved from the Dzudzuana pebbles.
OM, LSCM and SEM images (a, b, c), and µ-Raman spectra (d). Panel a: blue micro-fragments, retrieved from Dzu S5, exhibiting non-coloured regions (OM). Panels b-c: vascular elements retrieved from Dzu S6; b: vascular tissue with aligned pits (OM) and a zoomed region as observed by SEM, retrieved from Dzu S5; c: fusiform (spindle-shape) structure tapering at each end (LSCM) and the nodes displayed in the insert (OM) retrieved from Dzu S5. Panel d: µ-Raman spectra of the micro-residues shown in the micrographs (a: spectrum of a non-coloured region of the blue fragments; b and c: spectra of non-coloured micro-residues), compared with non-coloured I. tinctoria fragments obtained from the processing of modern leaves (Ref3). The spectra have been normalised and the luminescence background has been removed. Characteristic bands of constituting molecules such as cellulose (C), and characteristic signals of its polymorphs (CI, CII), pectin (P), lignin (L) and indigotin (Ind) are indicated by their µ-Raman shift. Details of the spectra are reported in S14 Fig.
Fig 7.
Comparison of blue archaeological micro-residues (a1-a2) with modern non-coloured (b1-b2) and blue (c1-c2) jeans fibres.
BF-OM view (a1, b1, c1), P-OM view (a2, b2, c2). Panel d: µ-Raman spectra of a representative archaeological blue micro-residues (Fig 7 d, red line a1-2, reprised from Fig 6 d, line a) compared with blue and non-coloured jeans fibres (Fig 7 d, black c1-2 and grey b1-2 lines, respectively). µ-Raman spectra are presented after normalisation and luminescence background removal. Panel e: reflectance µ-FTIR spectra of the above-mentioned samples. Vibrational bands characteristic of cellulose polymorph II (CII), pectin (P) and lignin (L) are reported. Details of the spectra are reported in S16 Fig.