Revealing the Organic Dye and Mordant Composition of Paracas Textiles by a Combined Analytical Approach

doi:10.21203/rs.3.rs-50791/v1

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Revealing the Organic Dye and Mordant Composition of Paracas Textiles by a Combined Analytical Approach

https://doi.org/10.21203/rs.3.rs-50791/v1

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published 27 Nov, 2020

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The object of this study is a wide selection of cotton and camelid samples from an important collection of 2000-year-old Paracas textiles, now at the Museo Nacional de Arqueología, Antropología e Historia del Perú (MNAAHP; Lima; Peru) and at the National Museum of World Culture (NMWC; Gothenburg; Sweden). The threads, chosen as representative of the whole palette, were selected from eighteen different textiles. A combined spectroscopic and spectrometric analytical approach was selected to characterize the composition of this wide set of samples. In particular, technical photography was used to gain a general overview of the samples, X-Ray Fluorescence (XRF) was employed for identifying the mordants and mapping the elemental distribution in the threads, while Liquid Chromatography coupled with Diode Array Detector and with High-Resolution Mass Spectrometry (HPLC-DAD, HPLC-HRMS) were used for characterizing organic dye composition.

This study provides fundamental pieces of information on the mordants used in the dyeing processes, rarely investigated up to now, and to the varieties of vegetal sources employed in Paracas textiles. The widening of Andean dyestuff database is highly important not only to acquire knowledge on Paracas culture, but also to ease the dye characterization of archaeological textiles from Peruvian region and South American area region in general.

Cultural Studies

Art History

Paracas textiles

organic dyes

mordants

HPLC-HRMS

XRF mapping

The Paracas civilization spread over six valleys along the Pacific coast in southern Peru, between 900 BC and 150 AD (1). This pre-Hispanic culture was renowned for the funerary bundles constituted by multi-layer textiles, garments and several other objects recovered from the necropolis. The fine Paracas textiles are embroidered with distinctive characters and imagery in elaborated patterns characterized by strong colours in numerous hues. Most often the fabric ground weaves are made of cotton while the embroidery yarns are of camelid fibres. The vegetal sources, recipes and techniques applied for dyeing the yarns are little known due to the lack of detailed historical written documents and the paucity of scientific studies.

The two-thousand-year-old Paracas textiles from where the fibres are sampled, were excavated and brought to Gothenburg in Sweden during the 1930s. The 89 large textiles constituted an important museum collection in Gothenburg for almost ninety years. After the exhibition “A Stolen World” (NMWC; 2008–2009), Peru asked for repatriation of the textiles. The textiles were repatriated to Peru in three clusters: 2014, 2017, and the last planned for 2021 (2).

This study builds on previous work in which mordants were investigated in situ by X-Ray Fluorescence (XRF) mapping of small areas on textile fragments and fibre strength was assessed by compression testing of thread samples (3). Measurements of pH and analyses by scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDX) were also carried out at the time but proved less informative than the other techniques. The aims of the previous study included an investigation of the condition of textiles that had undergone a deacidification treatment with ammonia in the 1990s. Notable differences in condition appeared to be related to the colours of the threads rather than their storage conditions or deacidification treatment. It was subsequently decided to further investigate this through identification of the organic colourant and inorganic components such as mordants or other dyeing auxiliaries. Additional threads were also subjected to compression testing in order to widen the dataset for condition assessment.

Relatively few studies deal with the characterisation of the molecular composition of south American reference dyeing materials and pre-Columbian archaeological textiles. The first papers on this topic were based on the identification of organic dyes by UV-Vis spectroscopy (4–8). Other spectroscopic techniques were also applied for dyes detection such as Fibre Optics Reflectance Spectroscopy (FORS) (9), microspectrofluorimetry (10, 11) and Surface Enhanced Raman Spectroscopy (SERS) (10, 12), while infrared spectroscopy (IR) (7) was rarely used due to the dominant absorption of the textile matrix in the spectra. Liquid chromatography coupled with spectroscopic detectors (9, 13–17) was frequently successful in identifying the different main components used in the dyeing processes, but only the coupling with High Resolution Mass Spectrometry (HRMS) lead to the unambiguous characterization of the single compounds and thus to fully characterise dyeing raw materials and archaeological samples extracts (14, 16). The new trends in rapid and efficient ambient ionization mass spectrometric techniques, such as Direct Analysis in Real Time (DART) (13, 18), paper spray (13) and flowprobe (19) (all coupled with HRMS), were also successfully applied for detecting dyes in Andean textiles.

Even fewer attempts were made to identify dyestuff mordants in pre-Columbian textiles; these studies were performed by XRF or SEM-EDX (3, 8, 10).

In this paper an analytical approach based on technical photography, XRF and Liquid Chromatography coupled with Diode Array Detector and High-Resolution Mass Spectrometry (HPLC-DAD, HPL-HRMS) was employed to characterize both the mordant and the organic dye sources used in a wide collection of Paracas textiles. An attempt to correlate the dyeing source and the mordant to the actual conservation state of the textile threads was performed, and all results are discussed in detail.

2.1 Historical samples

This study includes samples from a previous work, where 34 samples from 12 textiles were investigated (3). For the present study additional 14 samples were collected from 6 other textiles and from 2 of the previously sampled textiles. Figure 1 displays a selection of the textiles analysed. The thread samples were ca. 10 mm long and between 0.1-2 mg in weight. 1 mm sections of each of the threads were subjected to the same compression test as described previously (3). The same threads, including those left from the previous study, were documented by technical photography (38 threads), analysed by XRF mapping (34 threads) and HPLC-DAD, HPLC-HRMS (27 threads).

The colour, the fabric, the relative object from which they were sampled, and the techniques used for analysing each sample are reported in Table S1 (Supplementary Materials).

2.2 Reference materials

Cosmos sulphureus petals were kindly provided by Dr. David Buti, who purchased the seeds from “La Semeria” (Aulla (MS), Italy).

2.3 Technical photography

For technical photography the samples were laid out on a filter paper and covered with silk netting to keep the fibres in place. A modified Nikon D5500 camera without its IR filter was used with a Nikon AF NIKKOR 50 mm 1:1.4 D Ø52 lens. The following light sources were used: UV < 400 nm (G. Engelbrecht UVA-366); vis 425–750 nm 3200 K and 5500 K (K. Aputure Amaran AL-528 C); vis 435–750 nm 3200 K; IR > 750 nm (Synergy 21 Allnet M30205) in conjunction with the following pass filters from Schneider / Kreuznach: UV Pass (− 400 nm ~ 85%, 450–685 nm 0%, 740 nm 50%, B + W 403); UV/IR Cut (- <375 nm 0%, 400–675 > 90%, > 700 nm 0%, B + W 486); NIR/IR Pass (- <650 nm 0%, ~ 700 nm 50%, > 730 nm > 90%, B + W 092); IR Pass (- <800 nm < 1%, ~ 830 nm 50%, > 900 nm > 88%, B + W 093).

2.4 HPLC-DAD and HPLC-HRMS

For the HPLC-DAD analyses the system consisted of a PU-2089 quaternary pump equipped with a degasser, an AS-950 autosampler, and an MD-2010 spectrophotometric diode array detector (all modules are Jasco International Co., Japan). The software used for the analysis was ChromNav (Jasco International). The diode array detector (DAD) acquisition was performed in the range of 200–650 nm every 0.8 s with 4 nm resolution.

For the LC-ESI-Q-ToF analysis the system consisted of a HPLC 1200 Infinity, coupled with a quadrupole-time of flight mass spectrometer Infinity Q-ToF 6530 detector by a Jet Stream ESI interface (Agilent Technologies). The ESI conditions were: drying and sheath gas N₂, purity > 98%, temperature 350 °C, flow 10 L/min and temperature 375 °C, flow 11 L/min, respectively; capillary voltage 4.5 KV; nebulizer gas pressure 35 psi. The fragmentor voltage was 175 V; nozzle, skimmer and octapole RF voltages were set at 1000 V, 65 V and 750 V, respectively. The high-resolution MS and MS/MS acquisition range was set from 100 to 1000 m/z in negative mode, with acquisition rate 1.04 spectra/sec. For the MS/MS experiments, 30 V were applied in the collision cell to obtain CID fragmentation (collision gas N₂, purity 99.999%). The FWHM (full width half maximum) of quadrupole mass bandpass used during MS/MS precursor isolation was 4 m/z. The Agilent tuning mix HP0321 was used daily to calibrate the mass axis.

The eluents used for the HPLC-DAD analyses were water and acetonitrile (ACN) both HPLC grade (Sigma Aldrich, USA), while the eluents for HPLC-ESI-Q-ToF analyses were water and acetonitrile, both LC-MS grade (Sigma-Aldrich, USA). All eluents were added with 0.1% v/v formic acid (FA; 98% purity, J.T. Baker, USA).

For both the systems, the chromatographic separation was performed on an analytical reversed-phase column Poroshell 120 EC-C18 (3.0 × 75 mm, particle size 2.7 µm) with a Zorbax pre-column (4.6 × 12.5 mm, particle size 5 µm), both Agilent Technologies. The flow rate was 0.4 mL/min and the program was: 15% B (0.1% FA in ACN) for 2.6 min, then to 50% B in 13.0 min, to 70% B in 5.2 min, to 100% B in 0.5 min and then held for 6.7 min. Re-equilibration took 11 min. During the separation, the column was kept at 30 °C.

All the samples were subjected to a mild pre-treatment consisting in: adding of 300 µL of 0.1% ethylenediaminetetraacetic acid disodium salt (Na₂EDTA; Fluka, USA) in water and dimethyl formamide DMF; 99.8% purity, J.T. Baker, USA) solution (Na₂EDTA in H₂O/DMF (1:1, v/v)) to the sample, extracting in ultrasonic bath at 60 °C for 1 h, filtering with PTFE filters (0.45 µm pore size), injecting 20 µL and 4–20 µL of the extract in the HPLC-DAD and HPLC-HRMS, respectively.

2.5 XRF mapping

For XRF mapping the thread samples were mounted on filter paper that was suspended over a hole in a plastic foam and covered with silk netting to keep the fibres in place. The entire area with 34 laid out threads was then mapped with a Bruker micro-XRF Artax 800 using a molybdenum x-ray tube at 50 kV and 600 µA and a poly capillary lens yielding a spot size of 60–70 µm. The map was collected in air as it was not possible to fix the samples in place to withstand the pressure from helium flushing. The scan live time per spot was 5 s, number of measurements 20155, spot distance 0.18 mm, scan area 26 mm x 25 mm and total scan time 61:35 h.

An additional map of many of the same fibres had been collected previously but at lower resolution and on a different mounting material – polystyrene, which gave a lower Bremsstrahlung background in the XRF spectra compared to the filter paper background. But mounting the samples on polystyrene was problematic as it became static and fibres could easily lose their positions. The results of the two maps are comparable with the same elements present at predominantly the same relative intensities. This confirmed that the technique is valid for the relative or semi-quantitative assessment of inorganic components in textiles. The accumulated spectra from both maps show which elements were detected over the entire areas (Fig. 2). All spectra contain peaks for molybdenum (from the incident X-ray source) and argon (instrument specific). X-ray fluorescence response can be very different between different elements, meaning that peak heights or net peak area counts cannot be used to judge the quantities of elements within one spectrum, but semi-quantitative information can be gained from area maps, assuming that the sample matrix (i.e. thickness and density of the threads) is the same across all measuring points.

Results from the additional map are provided in Table S2 (Supplementary Materials) but are not discussed in the main text.

2.6 Compression tests

Samples were supported on glass microscope slides. One-mm sections were cut from each sample, ensuring that the yarn twist and ply were not altered. The sample was then covered with a 2 × 2 cm microscope slide cover glass and a 200-gram weight. Before and after compression images were taken with a stereomicroscope. The sample behaviour under compression was noted and used to subdivide the samples into three categories of stability: flexible/strong; fraying/weak and very fragile.

The results will be organised showing the results of the technical photography, then discussing the organic dyes first, followed by XRF mapping and compression testing in relation to the identified dyes. The organic dyes section will be subdivided in relation to the colour of the fibre. A complete summary of all the results is reported in Table 1.

Table 1

List of the Paracas fibres analysed with their relative description, identified inorganic elements, molecular markers, and hypothesis on dye sources. The colour of the cells for each element is related to its peak area intensity in XRF spectra, from the most intense (white) to the lowest (black) with one or two shades of grey in between (n.a. = not analysed).
Object	Sample	Colour	Fabric	Description	S	Cl	K	Ca	Mn	Fe	Cu	Zn	Molecular markers	Dye source
RT-02931 Mantel	MNAAHP 001	Red	Camelid	Embroidery									Pseudopurpurin, munjistin, lucidin, xantopurpurin, purpurin, rubiadin	Relbunium hypocarpium
	MNAAHP 002	Brown	Cotton	Ground weave									Luteolin-7-O-glucoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, luteolin, apigenin, chrysoeriol, indigotin, indirubin	Indigofera + Salix Humboldtiana Wild (?)
	MNAAHP 003	White	Camelid	Embroidery									-	-
RT-01683 Mantel	MNAAHP 004	Blu	Camelid	Embroidery	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	indigotin, indirubin, isatin	Indigofera
	MNAAHP 005	Brown	Cotton	Ground weave									-	-
	MNAAHP 006a	White	Camelid	Embroidery	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	-	-
	MNAAHP 006b	Gray	Camelid	Embroidery									Luteolin	Unknown luteolin-containing yellow
RT-39346 Border	MNAAHP 007	Red	Cotton	Ground weave									Pseudopurpurin, munjistin, lucidin, xantopurpurin, purpurin, rubiadin, nordamnacanthal (tr)	Relbunium hypocarpium
RT-02649 Fragment	MNAAHP 008	Yellow	Camelid	Embroidery									Luteolin-7-O-glucoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, luteolin, apigenin, chrysoeriol, indigotin, indirubin + unkn blue	Indigofera + Salix Humboldtiana Wild (?) + unk blue*
	MNAAHP 009	Red	Camelid	Embroidery									Pseudopurpurin, munjistin, lucidin, xantopurpurin, purpurin, rubiadin, nordamnacanthal (tr)	Relbunium hypocarpium
	MNAAHP 0010	Blue	Camelid	Embroidery									indigotin, indirubin	Indigofera
1935.32.0198 Border	PAR-001	Yellow	Camelid	Embroidery									Luteolin-7-O-glucoside, okanin glucoside, okanin, luteolin, butein	Cosmos sulphureus
1935.32.0211a Fragment	PAR-003	Yellow	Camelid	Embroidery									Luteolin-7-O-glucoside, okanin glucoside, okanin, luteolin, butein	Cosmos sulphureus
1935.32.0211c Fragment	PAR-005	Yellow	Camelid	Embroidery									Luteolin-7-O-glucoside, okanin glucoside, okanin, luteolin, butein	Cosmos sulphureus
1935.32.0205 Poncho	PAR-007	Red	Camelid	Embroidery									Pseudopurpurin, munjistin, xantopurpurin, purpurin, rubiadin	Relbunium hypocarpium
	PAR-008	Brown	Cotton	Ground weave									-	-
	PAR-028	White	Cotton	Ground weave									n.a.	-
	PAR-029	White	Cotton	Ground weave									n.a.	-
1935.32.0085 Tunic	PAR-009	Red	Camelid	Embroidery									Pseudopurpurin, munjistin, xantopurpurin, purpurin, rubiadin	Relbunium hypocarpium
	PAR-026	White	Cotton	Ground weave									n.a.	-
	PAR-027	White	Cotton	Ground weave									n.a.	-
1935.32.0179 Mantel	PAR-011	White	Camelid	Embroidery									-	-
1935.32.0190 Mantel	PAR-019	Red	Camelid	Embroidery									Pseudopurpurin, munjistin, xantopurpurin, purpurin	Relbunium hypocarpium
1935.32.0190 Mantel	PAR-020	Black	Cotton	Ground weave									Luteolin-7-O-glucoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, luteolin, apigenin, chrysoeriol, indigotin, indirubin	Indigofera + Salix Humboldtiana Wild (?)
1935.32.0188 Poncho	PAR-021	Red	Camelid	Embroidery	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	Pseudopurpurin, munjistin, lucidin, xantopurpurin, purpurin, rubiadin, nordamnacanthal (tr)	Relbunium hypocarpium
	PAR-022	Black	Cotton	Ground weave									Luteolin-7-O-glucoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, luteolin, apigenin, chrysoeriol, indigotin, indirubin	Indigofera + Salix Humboldtiana Wild (?)
	PAR-023	Brown	Cotton	Ground weave									-	-
1935.32.0213 Fragment	PAR-024	Blue	Camelid	Embroidery									Indigotin, indirubin	Indigofera
1935.32.0048	PAR-025	Red	Cotton	Ground weave									Pseudopurpurin, munjistin, lucidin, xantopurpurin, purpurin	Relbunium hypocarpium
1935.16.0165	PAR-030	White	Cotton	Ground weave									n.a.	-
1935.16.0165	PAR-031	White	Cotton	Ground weave									n.a.	-
1935.32.0122 a	PAR-032	White	Cotton	Ground weave									n.a.	-
1935.32.0122 a	PAR-033	White	Cotton	Ground weave									n.a.	-
1935.32.0122 b	PAR-034	White	Cotton	Ground weave									n.a.	-
1935.32.0122 b	PAR-035	White	Cotton	Ground weave									n.a.	-
1935.32.0173	PAR-036	Green	Camelid	Embroidery									Quercetin, methyl-quercetin, pseudopurpurin, munjistin, xantopurpurin, purpurin, indigotin, indirubin	Relbunium hypocarpium + Indigofera + quercetin based yellow dye
1935.32.0173	PAR-037	Green	Camelid	Embroidery									Indigotin, indirubin	Indigofera

3.1 Technical Photography

The technical photography revealed some UV fluorescence effects. Figure 3 shows the visible light photograph and the UV induced visible fluorescence image of all the samples analysed. The white camelid samples (PAR-011, MNAAHP-006a and MNAAHP-003) are the only ones showing UV induced visible fluorescence. All three were shown to be undyed by chromatographic analysis (see paragraph 3.2.1 and Table 1). The natural fluorescence of wool is a known phenomenon (20). None of the other images collected during technical photography showed recognisable photochemical effects.

3.2 Analysis of the organic dyes

3.2.1 White threads

The white threads (samples MNAAHP-003, MNAAHP-006a, PAR-011 and PAR-026) were analysed by HPLC-DAD and the chromatograms extracted at all the channels in which red, yellow, green, blue and dark fibres may absorb (450 nm, max abs 300–400 nm and max abs 550–650 nm) are shown in Figure S1a-c. (Supplementary Materials). All chromatograms (Figure S1a-c) are flat allowing us to conclude that the white cotton yarn (sample PAR-026) and the camelid threads (samples MNAAHP-003, MNAAHP-006a and PAR-011) are undyed. LC-HRMS confirmed the lack of dyes above detection limit in all the white samples.

3.2.2 Red threads

The HPLC-DAD chromatograms of all the red fibres of the set (samples MNAAHP-001, MNAAHP-007, MNAAHP-009, PAR-007, PAR-009, PAR-019, PAR-021 and PAR-025), extracted at 450 nm to enhance the S/N ratio for the peaks due to the anthraquinone red compounds, are reported in Fig. 4a.

All the HPLC-DAD chromatograms (Fig. 4a) show the same qualitative profile despite the different peak intensities given by the different absolute concentration of the extracts. Pseudopurpurin (14.9 min), munjistin (15.3 min) and purpurin (20.5 min) were identified thanks to the comparison with reference materials, analytical standards, and based on UV-Vis spectra reported in literature (21), while the UV-Vis spectrum of the unidentified peak at 11.5 min featured a maximum of absorbance at 490 nm and the typical shape of anthraquinones. The high sensitivity and selectivity of HRMS allowed us to unequivocally identify and confirm the presence of several anthraquinones thanks both to the exact mass values acquisition and the comparison with the tandem mass spectra of known compounds (13, 21): pseudopurpurin (m/z = 299.019), munjistin (m/z = 283.002), lucidin (m/z = 269.043), xantopurpurin (m/z = 239.031), purpurin (m/z = 255.029), rubiadin (m/z = 253.051) and nordamnacanhtal (m/z = 267.035; in traces). The HPLC-ESI-Q-ToF Extract Ion Chromatogram (EIC) of sample MNAAHP-009 is shown as representative (Fig. 4b). Unfortunately, no peaks ascribable to the unidentified anthraquinone detected by HPLC-DAD were found in the Total Ion Chromatogram collected by HPLC-ESI-Q-ToF, possibly to its low-ionization.

The reported composition suggests that the dye source employed belonged to Relbunium vegetal species. The comparison of the obtained profiles with those of some Relbunium species employed for dyeing alpaca and sheep fibres from the Saltzman collection (Relbunium hypocarpium, Relbunium ciliatum, Relbunium-unknown species), already characterized in the literature (13, 18) allowed us to conclude that the most plausible vegetal source for the three samples is Relbunium hypocarpium. The small differences in composition could be due to the use of a mixture of different Relbunium species, different dyeing processes or degradation of the textiles.

3.2.3 Blue threads

The HPLC-DAD profiles of the three blue fibres of the collection (sample MNAAHP-004, MNAAHP-010 and PAR-024) feature two peaks ascribable to indigoid compounds: indigotin (20.4 min) and indirubin (21.6 min) (Fig. 5). The analysis performed with HPLC-HRMS confirmed these attributions and revealed the presence of isatin (m/z = 146.023), indigotin precursor, in MNAAHP-004. These indigoids are the molecular markers for the identification of Indigofera o Isatis vegetal species (22).

The indigotin/indirubin ratio (in this case, the ratio between the DAD peak area of indigotin and indirubin (A_Ing/A_Inr) cannot provide a criterium to unambiguously identify the specific indigo plants used, given that the quantity of indigoid dyes depends on extraction procedures and dyeing recipes (23), but can highlight differences or similarities amongst sample sets. First, all the samples analysed show a proportion of indirubin to indigotin higher than that of any European Indigofera species (22). This is in accordance with previous evidences collected from the analysis of some pre-Hispanic Andean cotton blue fabrics (24). A plausible explanation for this difference may consist in a South American vat dyeing technology which favoured the formation and uptake of indirubin by the yarn.

Moreover, while in sample PAR-024 and MNAAHP-010 the concentration of indigotin is three times higher than that indirubin (A_Ing/A_Inr 3.2 and 3.1, respectively), in sample MNAAHP-004 it is nearly the same (1.2). This might suggest the use of a different recipe or a different dye source.

3.2.4 Green and yellow threads

The yellow fibres (sample MNAAHP-008, PAR-001, PAR-003 and PAR-005) and the green ones (PAR-036 and PAR-037) will be discussed together, since green hues were usually obtained by consecutively applying yellow and blue dyes. The HPLC-DAD chromatograms of the samples are shown at max absorbance of 300–400 nm (yellow) and 500–600 nm (blue) and reported in Figure S2a-b (Supplementary Materials). The two green samples (PAR-037 and PAR-036) both contain indigotin and indirubin. Indigotin was also detected in MNAAHP-008, along with three unknown blue compounds (b_1 − 3) in the 19.7–22.6 min time range, whose UV-Vis spectra do not allow a straightforward interpretation (Figure S2d, Supplementary Materials). The presence of indigotin and other blue components in this sample might be due to a contamination of the fibre from adjacent threads. Nevertheless, a different source of blue in addition to Indigofera or Isatis species was used in this case.

With regard to the yellow components, all the HPLC-DAD chromatograms show very small peaks, with the exception of those in the 18.6–21.8 min time range (g_1 − 5) in the green sample PAR-036, whose UV-Vis spectra are typical of yellow flavonoid compounds (Figure S2c, Supplementary Materials). High Resolution MS allowed us to identify these yellow flavonoids as quercetin (m/z = 447.070), and methyl-quercetin (m/z = 315.049). The comparison between the profiles of reference alpaca and sheep yellow dyed fibres from the Saltzman collection materials (Baccharis floribunda, Kageneckia lanceolata, Hypericum larcifolium) and that of sample PAR-036 allowed us to exclude that any of these three quercetin containing species was used for the Paracas fibres under study (13, 14).

Besides blue indigoids (indigotin and indirubin, both m/z = 261.064) and yellow flavonoids, red anthraquinones were also detected (pseudopurpurin, m/z = 299.019, xantopurpurin, m/z = 239.03, purpurin, m/z = 255.029), as shown in the EIC chromatograms (Fig. 6a), whose profile suggests that the source of red is Relbunium. Evidences of textiles from Paracas Necrópolis dyed with a mixture of yellow and blue vegetal source to yield green nuances or with red (Relbunium species) and blue for the violet hues have already been mentioned in the literature (17), but no previous report is available on any yellow-blue-red recipes for obtaining green.

With regards to the other green sample PAR-037, the yellow component was neither detected by HPLC-DAD nor by High Resolution Mass spectrometry.

The application of HPLC-HRMS allowed us to characterize in detail the source used in the yellow fibres. Several flavonoids were unequivocally identified in samples PAR-001, PAR-003 and PAR-005 (the EIC chromatograms of yellow sample PAR-001 are presented in Fig. 6b): luteolin 7-O-glucoside (m/z = 447.070), okanin glucoside (m/z = 449.105), okanin (m/z = 287.030), luteolin (m/z = 285.030) and butein (m/z = 271.057) (25, 26). The positive matching with the profile of the extracts of Cosmos sulphureus petals, allowed us to suggest that this is the raw source used for dyeing (25). The use of Cosmos sulphureus for dying in yellowish-orangish hues is reported in the literature (27, 28) but, to be the best of our knowledge, it is the first time that it has been identified in ancient textiles.

Finally, the extract of the yellow sample MNAAHP-008 contains luteolin-7-O-glucoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, luteolin, apigenin, and chrysoeriol. This profile is typical of Reseda luteola, one of the most used yellow dyes in the Old World, and matches with the so-called “[LUTE-APIG] group” described by Wouters and Rosario-Chirinos (17). More specifically, the profile is extremely similar to that provided in (29) for the extract of the leaves of the South American Salix Humboldtiana Wild. At present, only a tentative attribution can be made, since Antúnez de Mayolo identified fifteen Andean plant species as sources of yellow dyes (30), and among them Zumbhul (31) described three plants as luteolin-containing species: Alnus jorulensis, Baccharis genistelloides, and Bidens andicola, whose chromatographic profiles are not available in the literature yet.

3.2.5 Brown, black and grey threads

The HPLC-DAD profiles of all the brown (sample MNAAHP-002, MNAAHP-005, PAR-008 e PAR-023), black (sample PAR-020 and PAR-022) and grey (MNAAHP-006b) samples (Figure S3, Supplementary Materials) are rather flat. In MNAAHP-002 extract several peaks were detected and assigned to flavonoid compounds: luteolin-7-O-glucoside (10.7 min), apigenin-7-O-glucoside (12.2 min), chrysoeriol-7-O-glucoside (12.6 min), luteolin (14.8 min), apigenin (16.3 min) and chrysoeriol (16.7 min). The analysis by HR-LC-MS confirmed the attribution of these peaks for sample MNAAHP-002, detected the further presence of indigotin and indirubin in the extract, and highlighted the same composition for the black fibres of PAR-022 and PAR-020 and grey MNAAHP-006b. In particular, the EIC profiles (the EICs of PAR-022 are provided in Fig. 7) featured: luteolin-7-O-glucoside (m/z = 447.070), apigenin-7-O-glucoside (m/z = 431.072), chrysoeriol-7-O-glucoside (m/z = 461.103), luteolin (m/z = 285.030), apigenin (m/z = 209.038) and chrysoeriol (m/z = 299.045) (32–34), in addition to indigotin and indirubin (m/z = 261.064).

The presence of indigoids accounted for the dark coloration of the threads. Due to the lack of reference materials with comparable profiles, the raw material used can only be assigned to the “[LUTE-APIG] group” mentioned above for sample MNAAHP-008. Interestingly, all the textiles which contained “[LUTE-APIG] group” molecular markers, also contained indigotin and indirubin, thus suggesting that this dye source was preferably used in combination with an indigoid dye.

In the grey sample MNAAHP-006b only luteolin was detected, thus no clear attribution can be inferred.

Finally, the brown samples (PAR-008, PAR-023 and MNAAHP-005) do not contain any dyes above detection limit; thus, their coloration is likely provided by the natural colour of the raw cotton fibres.

3.3 Analysis of the inorganic components

In µXRF mapping every pixel corresponds to a spectrum; from the data cube is thus possible to visualize a separate grayscale map for each element detected, where the brightest areas correspond to the highest peak areas, while the black represents the lowest values or absence of the peak, Fig. 8.

In order to be able to tabulate and compare data from the generated maps, the peak intensities were visually sorted into three or four categories from brightest (white) to darkest (black) with one or two shades of grey in between, see Table 1. The data were interpreted crosschecking the results with the detected dyestuffs, in order to assess whether additives, auxiliaries or mordants could be identified, bearing in mind that the most common mordant, alum (an Al salt), could not be detected. Moreover, we aimed at comparing the results obtained on single threads with those achieved by micro-XRF elemental maps of textile fragments in a previous study (3).

The following observations can be drawn from the comparison amongst the samples set:

as expected, sulphur was only detected in the camelid fibres (white or grey categories), as it is due to the sulphur containing proteins in keratin;
chlorine also appeared to be generally higher in proteinaceous fibres, although the highest chlorine levels in the entire map are associated to one cellulosic black thread (PAR-020). It is important to note that the chlorine peak appears as a shoulder on the sulphur peak, so its presence in the proteinaceous fibres (rich in sulphur) may be an artefact;
potassium was also relatively high on most colours apart from undyed white cotton; the two highest potassium levels were recorded on yellow threads and could indicate the use of a dyeing auxiliary, even if the organic yellow dyes are different (MNAAHP-008 was dyed with Indigofera, a flavonoid dye of the [lut-apig] group and an unknown blue, while PAR-005 with Cosmos sulphureus);
calcium amount was highest in two black cotton threads that were shown to be dyed with Indigofera plus a yellow dye, but was present in every thread with the lowest levels recorded for most red threads and the undyed cotton (marked as dark grey in Table 1);
iron was present in every sample but generally was the lowest in undyed and blue threads; it was highest in the red cotton thread PAR-025 dyed with Relbunium and in a grey camelid thread (MNAAHP-006b) that contained an unknown luteolin-based yellow dye. This may imply that iron was a mordant for the red and yellow dyes, also when used with indigo for green, brown and black threads;
copper was barely detectable above the background but nevertheless yielded a clear map with relevant signals in several red, yellow and one green camelid threads. In particular, three samples of yellow camelid embroidery, dyed with Cosmos sulphureous, all contained relatively high amounts of copper: this may suggest that copper was used as a mordant. This distribution is very consistent with the data obtained for the mapping of the whole textile fragment 1935.32.0211a, as presented in (3);
zinc was barely detectable, but the highest amounts can be clearly pinpointed on the two undyed white camelid threads, the two blue camelid threads and the grey camelid thread with an unknown luteolin-based yellow dye.

3.4. Compression tests

Compression test results are presented in Fig. 9. Compression tests for the cotton showed that the white fibres are mostly in reasonable condition while the brown and black fibres tend to have a wider distribution of conditions, with a higher number of weak or very fragile brown samples compared to the white samples. Of the eleven brown cotton threads tested, four were also analysed by XRF and HPLC-DAD-HRMS. Three of those, one from each category: flexible, weak, fragile, were most likely undyed, while the fourth one (weak) was dyed with a combination of Indigofera and a yellow dye.

Similarly, the undyed white or grey camelid yarns tend to still be flexible/strong whilst the red and possibly the black fibres tend to be in the worst conditions.

Samples from ammonia treated cotton and camelid textiles occur in every category suggesting that the treatment did not have a lasting, or any, effect, except perhaps for red camelid samples. Interestingly, the only red camelid samples that are not classified as very fragile are those that underwent the ammonia treatment. These samples come from different textiles, and do not vary in terms of organic dye or inorganic content. In detail, the dyes in seven of the nine red threads were analysed and all were identified as Relbunium species, and the inorganic components in the red dyed camelid samples were consistent. One sample was relatively high in copper (very fragile), a second one relatively high in iron (weak), while almost all were relatively low in calcium compared to the other colours. Notwithstanding this, the number of observed specimens is too low and the condition assessment method too subjective to conclusively state that the ammonia treatment had any preservative effect.

The combined analytical approach allowed us to thoroughly formulate hypotheses on the mordants and the wide plethora of vegetal sources employed by Paracas civilization for dyeing cotton and camelid fibres.

The mild sample pre-treatment adopted was effective in extracting the dyes from the cotton and camelid fibres, and the consecutive application of HPLC-DAD and LC-HRMS techniques allowed us to assess the composition of the dyestuff for most of the samples.

All the red fibres were probably dyed with Relbunium species, most likely Relbunium hypocarpium or a mixture containing this specie. Animal dye sources, such as cochineal, were not detected in any sample. Besides alum, which cannot be detected by XRF mapping in air, both iron and copper have been detected in few red threads. The available data do not allow us to assess whether their use was made on purpose to yield specific colour hues.

The blue, green and black samples were dyed with Indigofera or Isatis tinctoria species, alone or in combination with yellow dyes. Indigoid plants are the most commonly used sources of natural blue dyes, and the samples dyed with them contained a relevant amount of calcium, possibly used as an auxiliary in the vat dyeing process.

While the source of yellow employed for dyeing the yellow fibres are probably the petals of Cosmos sulphureus, possibly used with a copper mordant, the identification of the yellow raw material used in mixture with indigotin and indirubin in green, brown and black fibres is not straightforward. The LC-HRMS profiles of these fibres are rich in flavonoids and their relative glucosides, resembling those of Reseda luteola, a typical European dye plant. Among the hundreds of yellows available in the Andean area, all extracted from plants (30, 31), the composition of Salix Humboldtiana Wild is the one which matches with that of Reseda luteola and of green fibres despite is not possible excluding that other Andenian dying sources, not described and characterized in detailed, may present an analogues composition.

Some brown fibres and all the grey and white ones are undyed; thus, their colour is given by the natural colour of camelid or cotton.

The results reported in this paper will contribute to fill the knowledge gap on the dyeing materials of Andean culture, providing important hints on the mordanting processes and recipes adopted in textiles manufacturing.

Availability of data and materials

The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests

Funding

No funding was received.

Authors' contributions

AJ and MH selected the samples and designed the experiment. FS, MB, AJ, and MH performed the analyses and ID contributed in interpreting the chromatographic and mass spectrometric data. All authors equally contributed in drafting the manuscript. All authors read and approved the final manuscript.

Acknowledgements

Kaj Thuresson and Magnus Mårtensson are acknowledged for assistance with XRF and technical photography at the Heritage Laboratory, Swedish National Heritage Board.

Carmen Thays Delgado and María Ysabel Medina Castro are acknowledged for assistance with sampling at the National Museum of Archaeology, Anthropology, and History in Lima, Peru. Dr. David Buti (Institute of Heritage Science – CNR, Italy) is acknowledged for providing us with the Cosmos sulphureus petals used as reference material in this study.

University of Pisa and Prof. Francesca Modugno are acknowledged for funding FS’s scholarship under the BIHO2019 programme.

Canales EL. La Cultura Paracas. In: Paracas Exhibition catalogue. Museo Nacional de Arqueologia, Antropologia e Historia del Peru; 2013. p. 11–26.
Javér A. Analysis of Paracas fibre material from the Gothenburg Collection. In: Bjerregaard L, Peters A, editors. PreColumbian Textile Conference VII / Jornadas de Textiles PreColombinos VII. Lincoln, NE: Zea Books; 2017. p. 398–404.
Javér A, Hacke M, Delegado CT, Thuresson K. Paracas textiles – Colour and condition. Investigation of the mordants and state of degradation of the Paracas textile collections in Peru and Sweden. In: ICOM-CC 18th Triennial Conference Preprints. 2017.
Saltzam M. The Identification of Dyes in Archaeological and Ethnographic Textiles. In: Archaeological Chemistry—II. p. 172–85.
Saltzman M. Analysis of dyes in museum textiles or, you can’t tell a dye by its color. In: Textile Conservation Symposium in Honor of Pat Reeves. 1986.
Martoglio PA, Bouffard SP, Sommer AJ, Katon JE, Jakes KA. Unlocking the secrets of the past: the analysis of archaeological textiles and dyes. Anal Chem. 1990;62(21):1123A–1128A.
Jakes K., Katon J., Martoglio P. Identification of dyes and characterization of fibers by infrared and visible microspectroscopy: Application to Paracas textiles. Archaeometry. 1990;90:305–15.
Wallert A, Boytner R. Dyes from the Tumilaca and Chiribaya cultures, south coast of Peru. J Archaeol Sci. 1996;23(6):853–61.
Degano I, Colombini MP. Multi-analytical techniques for the study of pre-Columbian mummies and related funerary materials. J Archaeol Sci. 2009;
Bernardino ND, Faria DLA [de, Negrón AC V. Applications of Raman spectroscopy in archaeometry: An investigation of pre-Columbian Peruvian textiles. J Archaeol Sci Reports. 2015;4:23–31.
Claro A, Melo MJ, de Melo JSS, van den Berg KJ, Burnstock A, Montague M, et al. Identification of red colorants in van Gogh paintings and ancient Andean textiles by microspectrofluorimetry. J Cult Herit. 2010;11(1):27–34.
Burr E. Dye analysis of archaeological Peruvian textiles using surface enhanced Raman spectroscopy (SERS). 2016. PhD Thesis. UCLA. UCLA; 2016.
Armitage RA, Fraser D, Degano I, Colombini MP. The analysis of the Saltzman Collection of Peruvian dyes by high performance liquid chromatography and ambient ionisation mass spectrometry. Herit Sci. 2019;7(1):81.
Degano I, Magrini D, Zanaboni M, Colombini MP. The Saltzman Collection: A reference database for South American dyed textiles. In: ICOM-CC 18th Triennial Conference Preprints, Copenhagen,. 2017.
Saito M, Hayashi A, Kojima M. Identification of six natural red dyes by high-performance liquid chromatography. Dye Hist Archaeol. 2003;19:79–87.
Zhang X, Boytner R, Cabrera JL, Laursen R. Identification of Yellow Dye Types in Pre-Columbian Andean Textiles. Anal Chem. 2007;79(4):1575–82.
Wouters J, Rosario-Chirinos N. Dye Analysis of Pre-Columbian Peruvian Textiles With High-Performance Liquid Chromatography and Diode-Array Detection. J Am Inst Conserv. 1992;31(2):237–55.
Armitage RA, Jakes K, Day C. Direct analysis in real time-mass spectroscopy for identification of red dye colourants in Paracas Necropolis Textiles. Sci Technol Archaeol Res. 2015;1(2):60–9.
Kramell AE, Brachmann AO, Kluge R, Piel J, Csuk R. Fast direct detection of natural dyes in historic and prehistoric textiles by flowprobe^TM-ESI-HRMS. RSC Adv. 2017;7:12990–12997.
Collins S, Davidson RS, Hilchenbach MEC, Lewis DM. The natural fluorescence of wool. Dye Pigment [Internet]. 1994;24(2):151–69. Available from: http://www.sciencedirect.com/science/article/pii/0143720894800073
Rafaëlly L, Héron S, Nowik W, Tchapla A. Optimisation of ESI-MS detection for the HPLC of anthraquinone dyes. Dye Pigment. 2008;77(1):191–203.
Mantzouris D, Karapanagiotis I, Panayiotou C. Comparison of extraction methods for the analysis of Indigofera tinctoria and Carthamus tinctorius in textiles by high performance liquid chromatography. Microchem J. 2014;115:78–86.
Sanz E, Arteaga A, García MA, Cámara C, Dietz C. Chromatographic analysis of indigo from Maya Blue by LC–DAD–QTOF. J Archaeol Sci. 2012;39(12):3516–23.
Splitstoser JC, Dillehay TD, Wouters J, Claro A. Early pre-Hispanic use of indigo blue in Peru. Sci Adv. 2016;2(9).
Deng Y, Lam S-C, Zhao J, Li S-P. Quantitative analysis of flavonoids and phenolic acid in Coreopsis tinctoria Nutt. by capillary zone electrophoresis. Electrophoresis. 2017;38(20):2654–61.
Yang W-Z, Ye M, Qiao X, Wang Q, Bo T, Guo D-A. Collision-Induced Dissociation of 40 Flavonoid Aglycones and Differentiation of the Common Flavonoid Subtypes Using Electrospray Ionization Ion-Trap Tandem Mass Spectrometry and Quadrupole Time-of-Flight Mass Spectrometry. Eur J Mass Spectrom. 2012;18(6):493–503.
Wallert A. The Unbroken Thread: Conserving the Textile Traditions of Oaxaca. Klein K, editor. 1997.
Safford WE. Cosmos Sulphureus, the Xochipalli or Flower Paint of the Aztecs. J Washingt Acad Sci. 1918;8(19):613–20.
Boucherie N, Nowik W, Cardon D. La producción tintórea Nasca : nuevos datos analíticos obtenidos sobre textiles recientemente descubiertos en excavaciones. Mundo Nuevo – Nuevos Mundos, Colloq. 2016;
Antúnez De Mayolo KK. Peruvian natural dye plants. Econ Bot. 1989;
Rosario-Chirinos N. Tintes en el Perú prehispánico, virreynal y republicano - Dyes in Pre-Hispanic, Viceregal and Republican Peru. In: Tejidos Milenarios del Perú - Ancient Peruvian Textiles. Lima: Integra AFP; 1999.
Hughes RJ, Croley TR, Metcalfe CD, March RE. A tandem mass spectrometric study of selected characteristic flavonoids22Dedicated to Professor N.M.M. Nibbering for his many contributions to mass spectrometry. Int J Mass Spectrom. 2001;210–211:371–85.
Ma YL, Li QM, Heuvel H Van den, Claeys M. Characterization of flavone and flavonol aglycones by collision‐induced dissociation tandem mass spectrometry. Rapid Commun Mass Spectrom. 1998;11(12).
Mouri C, Mozaffarian V, Zhang X, Laursen R. Characterization of flavonols in plants used for textile dyeing and the significance of flavonol conjugates. Dye Pigment. 2014;100:135–41.

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Revealing the Organic Dye and Mordant Composition of Paracas Textiles by a Combined Analytical Approach

Status:

Journal Publication

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Abstract

Figures

1 Introduction

2 Methods

2.1 Historical samples

2.2 Reference materials

2.3 Technical photography

2.4 HPLC-DAD and HPLC-HRMS

2.5 XRF mapping

2.6 Compression tests

3 Results And Discussion

3.1 Technical Photography

3.2 Analysis of the organic dyes

3.2.1 White threads

3.2.2 Red threads

3.2.3 Blue threads

3.2.4 Green and yellow threads

3.2.5 Brown, black and grey threads

3.3 Analysis of the inorganic components

3.4. Compression tests

4. Conclusions

Declarations

Availability of data and materials

Competing interests

Funding

Authors' contributions

Acknowledgements

References

Supplementary Files

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