Non-invasive study of natural dyes on historical textiles from the collection of Michelangelo Guggenheim

Multi-Analytical Techniques for the Study of Burial Clothes of Polish King Sigismund III Vasa (1566-1633) and His Wife Constance Habsburg (1588-1631)

The subjects of this research are the burial clothes of Polish King Sigismund III Vasa and his wife Constance, which were woven and embroidered with silk and metal threads. Fragments of the textiles underwent spectroscopic, spectrometric, and thermogravimetric analyses. The hydrofluoric acid extraction method was improved to isolate various classes of dyes from the textile samples that had direct contact with human remains. High-performance liquid chromatography, coupled with diode array and tandem mass spectrometry detectors with electrospray ionization (HPLC-DAD-ESI-MS/MS) facilitated the detection and identification of colorants present in the textiles. Cochineal, indigo-, madder-, orchil-, and tannin-producing plants were identified as the sources of dyes used. Scanning electron microscopy with an energy-dispersive X-ray detector (SEM-EDS) was employed to identify and characterize the silk fibers and mordants and the metal threads. The presence of iron, aluminum, sodium, and calcium in the silk threads suggests their potential use as mordants. The analysis of the metal threads revealed that most of them were made from flattened gilded silver wire, with only a few being cut from a sheet of metal. Typical degradation mechanisms of metal threads were shown, resulting from both burial environment and earlier manufacturing process, and the use of the textiles in clothing, i.e., a significant loss of the gold layer was observed in most of silver gilt threads, caused by abrasion and delamination. The results of the thermal analysis confirmed the presence of silk and silver threads in the examined textiles.

A precise self-built secondary mass database for identifying red dyes and dyeing techniques with UPLC-MS/MS

Dyes on ancient silks have been a worth studying field through human's history, although current reports ignore the connection between natural dyes origin and relevant colour reduction methods, which poses an insurmountable obstacle for restoration of historical silks. In this paper, a series of 12 red hue silks from six natural dyes (sappanwood, Chinese madder, safflower, lac, cochineal, dragon's blood) via three different dyeing techniques were used to establish a self-built precise tandem mass spectrometry (MS/MS) database. With organic solvent extracting on those manual-dyed silks, ultraperformance liquid chromatography - electrospray ionization - quadrupole time of flight mass spectrometry (UPLC-ESI-QTOF-MS) was utilized to form preliminary MS database for screening and identifying of the potential dyes compounds without standard references. Furthermore, combining the targeted MS/MS mode and the matching threshold of 70.00, a self-built secondary MS/MS database was successfully established, which contains 33 compounds, 32 chromatograms and 32 MS/MS fragments. As for real sample application, the self-built precise MS/MS database had revealed that the dyes on two historical silks (Shanghai Museum, China) belong to Chinese madder just with different mordant dyeing ordinal. Additionally, by experimental restoration, visually indistinguishable silks (ΔEab * < 1.5 NBS) were successfully restored. This explorative methodology can further inspire the traceability of biological dyestuffs, which lays instructive foundation on protection and restoration of artefacts, connecting the archaeological science and human art.

Microextraction of Reseda luteola-Dyed Wool and Qualitative Analysis of Its Flavones by UHPLC-UV, NMR and MS

Detailed knowledge on natural dyes is important for agronomy and quality control as well as the fastness, stability, and analysis of dyed textiles. Weld (Reseda luteola L.), which is a source of flavone-based yellow dye, is the focus of this study. One aim was to reduce the required amount of dyed textile to ≤50 μg for a successful chromatographic analysis. The second aim was to unambiguously confirm the identity of all weld flavones. By carrying out the extraction of 50 μg dyed wool with 25 μL of solvent and analysis by reversed-phase UHPLC at 345 nm, reproducible chromatographic fingerprints could be obtained with good signal to noise ratios. Ten baseline separated peaks with relative areas ≥1% were separated in 6 min. Through repeated polyamide column chromatography and prepHPLC, the compounds corresponding with the fingerprint peaks were purified from dried weld. Each was unequivocally identified, including the position and configuration of attached sugars, by means of 1D and 2D NMR and high-resolution MS. Apigenin-4′-O-glucoside and luteolin-4′-O-glucoside were additionally identified as two trace flavones co-eluting with other flavone glucosides, the former for the first time in weld. The microextraction might be extended to other used dye plants, thus reducing the required amount of precious historical textiles.

Fiber Optic Reflection Spectroscopy-Near-Infrared Characterization Study of Dry Pigments for Pictorial Retouching

A deep comprehension of composition of pigments, employed nowadays in the field of pictorial retouch is considered essential for a deeper knowledge of their behavior with time once applied on artifacts. A commercially available set consisting of 27 pigments employed for the conservation of both historical and contemporary artworks has been characterized through Reflectance Spectroscopy in the VIS and NIR spectral range. The pigments included in the investigated set are classified into four categories: (i) dyes and colors from plants, (ii) modern pigments, (iii) pigments of own production and historical pigments, and (iv) natural earths. Recorded spectra were interpreted with the aim to detect existing coloring and filling phases and obtained results were compared with available data sheets: some inconsistencies were found, as well as lack of some compounds among the reported ones. Attributions were found for many features, even if in some cases detailed information for a comparison was not found in the literature, especially regarding NIR spectra. The proposed paper aims to provide a useful tool for the study of real artworks with a detailed overview of material characteristics in the visible and near infrared spectral range.

Integrating liquid chromatography mass spectrometry into an analytical protocol for the identification of organic colorants in Japanese woodblock prints

Three Japanese woodblock prints from the Edo period (1603–1868) underwent a scientific investigation with the aim of understanding the changes in the colorants used in Japanese printing techniques. A multi-analytical approach was adopted, combining non-invasive techniques, such as fiber optic reflectance spectroscopy (FORS), Raman spectroscopy, multispectral imaging (MSI), and macro X-ray fluorescence (MA-XRF) with minimally invasive surface-enhanced Raman spectroscopy (SERS). The results enabled many of the pigments to be identified and their distribution to be studied, apart from two shades of purple of organic composition. Consequently, the potential of high-pressure liquid chromatography tandem mass spectrometry (HPLC–MS/MS) was explored for the first time with application to Japanese woodblock prints. The intrinsic sensitivity of the instrument and an effective extraction protocol allowed us to identify a mixture of dayflower (Commelina communis) blue and safflower (Carthamus tinctorius) red in purple samples constituted of 2–3 single fibers. In addition to the innovative integration of MA-XRF and HPLC–MS/MS to investigate these delicate artworks, the study concluded on the use of traditional sources of colors alongside newly introduced pigments in late Edo-period Japan. This information is extremely important for understanding the printing practices, as well as for making decisions about display, conservation, and preservation of such artworks.

Investigation of the new possibility of mathematical processing of Raman spectra for dating documents

The use of spectral analysis methods to determine the age of writing inks is an important forensic task. However, the use of spectral data for this purpose has a number of limitations and difficulties. This paper considers the application of the Raman spectroscopy method to an urgent forensic task. The known mechanisms of dye degradation are analyzed; Raman bands are identified that are related to the age of the sample. In a sample of 5 randomly selected writing inks, temporary markers were identified. Narrow sections of Raman spectra containing characteristic lines were used for analysis. It was shown that processing narrow sections of the Raman spectra using the PCA chemometric method allowed the separation of writing inks into groups (clusters) corresponding to different creation intervals.

UV-Vis spectroscopy

UV-Vis reflectance spectroscopy has been widely used as a non-invasive method for the study of cultural heritage materials for several decades. In particular, FORS, introduced in the 1980s, allows to acquire hundreds of reflectance spectra in situ in a short time, contributing to the identification of artist’s materials. More recently, microspectrofluorimetry has also been proposed as a powerful non-invasive method for the identification of dyes and lake pigments that provides high sensitivity and selectivity. In this chapter, the concepts behind these spectroscopic methodologies will be discussed, as well as the instrumentation and measurement modes used. Case studies related with different cultural heritage materials (paintings and manuscripts, textiles, carpets and tapestries, glass, metals, and minerals), which show the usefulness of UV-Vis reflectance spectroscopy and microspectrofluorimetry applied to the study of artworks, will also be presented.