Vittoria Guglielmi

Field and Laboratory Spectroscopic Methods for the Identification of Pigments in a Northern Italian Eleventh Century Fresco Cycle

The pigments of an XI-century fresco cycle in a small pre-alpine church of northern Italy were characterized by means of field techniques, in particular imaging spectroscopy, and laboratory spectroscopic techniques, namely total reflection X-ray fluorescence, micro-Raman, micro-Fourier transform-Raman, and micro-Fourier transform infrared spectroscopies, thus achieving a complete identification of the ancient painters palette. Advantages and limitations of each technique in its application to the study of fresco pigments are discussed. The artistic value of the fresco cycle and the religious role in the year 1000 of the church where it is located (S. Michele Arcangelo in Gornate Superiore, Varese, Italy) were demonstrated by the precious and elaborate materials used by the painter. Different pigments were used for different hues of the same color, e.g., azurite, carbon, and the most precious lapis-lazuli for blue, while mixtures of pigments were recognized in details having a particular tint, e.g., lapis-lazuli and minium for violet.

Micro-Raman identification of the palette of a precious XVI century illuminated Persian codex

Abstract A remarkable, richly decorated Persian manuscript dating from 1537 was investigated by Raman microscopy in order to assess the nature of the pigments used. Although the decorated area measures just a few tens of cm 2 and doesn’t include any anthropomorphic motif, but consists in a very geometric, lacework-like decoration, it contains very elaborate and precious details. A very rich palette was revealed, showing extensive use of the extremely valuable and costly pigment lapis-lazuli, gold and orpiment, besides malachite, vermilion and red lead. With the exception of the choice for an expensive pigment such as lapis-lazuli even for the background, the experimental data confirm that the art of miniature making, as well as the painting materials used in the Middle East, didn’t actually differ much from what is considered to be the acknowledged practice for western art in the same period.

Multi-technique characterization of dyes in ancient Kaitag textiles from Caucasus

Kaitag textiles, named after the Kaitag district of Southwest Daghestan, Russia, where it is being manufactured, are a unique embroidered textile art form. They were used by families on special occasions such as the birth, marriage or death of one of their members and were thus passed down from generation to generation as family heirlooms. Today, only a few hundred of these precious antique specimens can still be found, and surviving examples are mostly from the seventeenth and eighteenth centuries. In this article, an extensive work for the scientific analysis of Kaitag textiles is presented as the logical continuance and updating of the investigations performed by thin layer chromatography almost two decades ago. A multi-technique approach involving the combined use of micro-invasive and nondestructive techniques suitable for in situ analyses was used, aiming to identify the colourants of Kaitag textiles and the inks employed for the underlying drawing. Analyses were performed by high-performance liquid chromatography, surface-enhanced Raman spectroscopy, scanning electron microscopy combined with energy dispersive X-ray analysis, as well as visible reflectance spectroscopy and X-ray fluorescence. In addition, infrared reflectography and ultraviolet fluorescence were employed to visualise underlying drawings and possible restorations. Corrosion phenomena observed in brown- and black-dyed areas were also investigated.

Exploiting external reflection FTIR spectroscopy for the in-situ identification of pigments and binders in illuminated manuscripts. Brochantite and posnjakite as a case study

In the present work, the use of portable instrumentation allowing in-situ reflection FTIR analyses is exploited to identify the coloring matters of northern-Italian illuminations dating to the XVI century. In order to build a database of spectra, reference paint samples were prepared spreading the pigments on parchment with two different binders, i.e. gum arabic and egg white, used in antiquity. Pigments for the database were chosen considering their use in the Middle Ages and in the Renaissance and their response in the mid- and near-IR region. The reflection FTIR spectra obtained resulted to be dominated by the specular reflection component, allowing the use of the Kramers-Kronig transform to convert them to the more conventional absorbance FTIR spectra. Several pigments could thus be identified in ancient illuminations, even if some green details showed a spectral pattern different with respect to the most common commercial green pigments of the database. Therefore, in addition, basic copper sulfates brochantite and posnjakite were synthesized and characterized. In three green details, posnjakite was identified, both as a pure compound and together with malachite.

Identification of Natural Dyes on Laboratory-Dyed Wool and Ancient Wool, Silk, and Cotton Fibers Using Attenuated Total Reflection (ATR) Fourier Transform Infrared (FT-IR) Spectroscopy and Fourier Transform Raman Spectroscopy

Attenuated total reflection (ATR) infrared and Fourier transform (FT) Raman spectra were obtained from wool threads dyed in the laboratory with natural dyes used in antiquity, following a procedure similar to ancient methods for dyeing wool. The ATR spectra were primarily dominated by the signals of the wool, making it difficult to identify the dye on the fibers only by visual inspection of the infrared spectrum. However, the Raman spectra showed more significant characteristics attributable to the dyes as previously studied in the literature on modern synthetic dyes. A library-search method was thus applied to the second derivatives of both the ATR and Raman spectra to verify the possibility of identifying the dye. Two libraries were constructed, one consisting of the ATR spectra of undyed wool (raw, washed, and mordanted) and the transmission spectra of pure dyes and the other consisting of the Raman spectra of undyed wool and of pure dyes. Correlation and first-derivative correlation search algorithms were used. The results presented here suggest that the two types of spectroscopy are complementary in this kind of work, allowing the almost complete identification of historic dyes on wool. In fact, through the combined use of the two searches, most dyes were identified with a good index of similarity and within the first five hits. Only for annatto was identification totally impossible using either technique. Subsequently the same method was applied to wool, silk, and cotton threads taken from ancient Caucasian and Chinese textiles.

Identification of archaeological triterpenic resins by the non-separative techniques FTIR and 13C NMR: the case of Pistacia resin (mastic) in comparison with frankincense.

The use of spectroscopic techniques such as Fourier-transform infrared (FTIR) spectroscopy and carbon 13 nuclear magnetic resonance ((13)C NMR) using the J-mod experiment is proposed as an effective alternative to gas chromatography-mass spectrometry (GC-MS) for the analysis and identification of natural resin samples found in archaeological environments. The spectral features of the most common diterpenic and triterpenic resins and also two gum-resins are reported and discussed for both techniques. The analytical procedure based on the combined use of FTIR and (13)C NMR is then applied to two archaeological samples from the Milano of the Roman age allowing their identification as Pistacia resin, or mastic, as confirmed by the traditional GC-MS method, and also elucidating some effects of aging on such material.

In situ nondestructive identification of natural dyes in ancient textiles by reflection fourier transform mid-infrared (FT-MIR) spectroscopy.

Silk embroideries and cotton grounds of ancient Caucasian (Kaitag) textiles were analyzed in situ by a portable Fourier transform infrared (FT-IR) spectrometer equipped with a reflection module. Differently colored areas were analyzed for the purpose of identifying the dyes fixed on the fibers. The spectra so obtained were elaborated by calculating the corresponding second derivative, and a library search was then performed using a database including the second derivative spectra of a large range of historical dyes and the corresponding undyed fibers. The results presented here suggest that this technique, combined with the library search method, has a good capability of recognizing natural dyes on both types of ancient textile fibers, in an entirely nondestructive way.