Abstract
A multi-tool analytical practice was used for the characterisation of a 16th century carpet manufactured in Cairo. A mild extraction method with hydrofluoric acid has been evaluated in order to isolate intact flavonoids and their glycosides, anthraquinones, tannins, and indigoids from fibre samples. High-performance liquid chromatography coupled to spectroscopic and mass spectrometric detectors was used for the identification of possible marker compounds with special attention paid to natural dyes present in the historical samples. Weld, young fustic, and soluble redwood dye were identified as the dye sources in yellow thread samples. Based on the developed method, it was possible to establish that red fibres were coloured with lac dye, whereas green fibre shades were obtained with indigo and weld. Tannin-containing plant material in combination with indigo and weld were used to obtain the brown hue of the thread. Hyphenation of high-performance liquid chromatography (HPLC) with quadrupole time-of-flight mass spectrometry (QTOF MS) and triple-quadrupole mass spectrometry (QqQ MS) enabled us to recognise four uncommon and thus-far unknown dye components that were also found in the historical samples. These compounds probably represent a unique fingerprint of dyed threads manufactured in a Turkish workshop. Scanning electron microscopy with energy-dispersive X-ray detector (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR) were used for the identification and characterisation of substrates and mordants present in the historical carpet. Carbon and oxygen were detected in large quantities as a part of the wool protein. The presence of aluminium, iron, and calcium indicated their usage as mordants. Trace amounts of copper, silica, and magnesium might originate from the contaminants. FT-IR analysis showed bands characteristic for woollen fibres and SEM micrographs defined the structure of the wool.
Highlights
Scientific analysis of objects of artistic and historic significance is the key to reconstructing their story and elucidating the circumstances under which they have been created
The structures of the identified dyes were confirmed by high-performance liquid chromatography (HPLC)-ESI(-)-quadrupole time-of-flight (QTOF) analysis using an Agilent 1290 LC system coupled to the Agilent QTOF mass spectrometer G6540 (Santa Clara, CA, USA) operated in negative ionisation scan mode under the same chromatographic conditions
Identification of colouring compounds was performed by comparing their retention times and UV and mass spectra in the negative ionisation mode (ESI(−)-MS and MS/MS) to those obtained for the compounds found in weld (Reseda luteola L.), lac dye (Kerria lacca Kerr), and indigo (Isatis tinctoria) extracts and standards of flavonoids under the same chromatographic conditions
Summary
Scientific analysis of objects of artistic and historic significance is the key to reconstructing their story and elucidating the circumstances under which they have been created. The first objective of historical textile reconstruction is the identification of fibres’ constitution They are generally made of organic materials, such as plant and/or animal fibres or silk. An exact identification of the colouring substances in biological sources gives us the information necessary to determine the origin of dyestuffs used to create the object This data, with additional information about metal ions (mordant-type dyes) and the type of textile raw material used to produce an artefact, can help in determining how, when, and where these works of art were made. Milder extraction methods based on the use of ethylenediaminetetraacetic acid (EDTA) or citric, tartaric, formic, or hydrofluoric acid are currently being tested [14,15,16,17,18] Identification of these components in complex mixtures requires sensitive and selective analytical techniques. The results reported in the present paper enabled full dye fingerprints in the fibre samples
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