Chemometric Tools to Point Out Benchmarks and Chromophores in Pigments through Spectroscopic Data Analyses

Abstract

Spectral preprocessing data and chemometric tools are analytical methods widely applied in several scientific contexts i.e., in archaeometric applications. A systematic classification of natural powdered pigments of organic and inorganic nature through Principal Component Analysis with a multi-instruments spectroscopic study is presented here. The methodology allows the access to elementary and molecular unique benchmarks to guide and speed up the identification of an unknown pigment and its recipe. This study is conducted on a set of 48 powdered pigments and tested on a real-case sample from the wall painting in S. Maria Delle Palate di Tusa (Messina, Italy). Four spectroscopic techniques (X-ray Fluorescence, Raman, Attenuated Total Reflectance and Total Reflectance Infrared Spectroscopies) and six different spectrometers are tested to evaluate the impact of different setups. The novelty of the work is to use a systematic approach on this initial dataset using the entire spectroscopic energy range without any windows selection to solve problems linked with the manipulation of large analytes/materials to find an indistinct property of one or more spectral bands opening new frontiers in the dataset spectroscopic analyses.

An overview of Principal Components Analysis approaches in Raman studies of cultural heritage materials

“…In addition to a portable Raman with sequentially shifted excitation (785 and 853 nm), an innovative commercial instrument combining XRF and Raman (785 nm) spectroscopies has been used to characterize a wall painting in northern Sicily, as well as on a set of 48 reference pigments. 31 FTIR was also applied to the samples; 220 spectra were retained of the 316 acquired, excluding spectra with too much noise and/or no signals (such as mainly green, blue, black and organic pigments and lakes). Linear interpolation, normalization and weight standardization of the Raman spectra have been carried out prior to PCA.…”

Assessment of Easily Accessible Spectroscopic Techniques Coupled with Multivariate Analysis for the Qualitative Characterization and Differentiation of Earth Pigments of Various Provenance

“…Along with handheld XRF analysis [50], these techniques are probably the most commonly used analytical tools in conservation science, as they offer a series of advantages such as: relatively low-cost, non-or minimalinvasiveness and an immediate response in terms of results [51]. Chemometrics, such as PCA, applied to different spectroscopic data, is a powerful analytical tool, widely used in recent years for discrimination analysis, including the classification of pigments [52,53].…”

The colours of Segesta. Searching for the traces of the lost pigments

“…On the other hand, since the integrity of the traces is a key role and, quite often, the heritage objects are non-movable, the analysis of trace pigments necessarily requires in situ measurements with portable equipment. Thus, it is very important selecting the physico-chemical analytical techniques for a non-destructive char-acterization [21] to determine the real pigments present in any studied object [22] . Bracci et al, discussed about the methodology to investigate the traces highlighting the rules of the use of several non-invasive methods [23] and about a different methodological approach to identify the traces of color on statues excavated from the archeological site of Hierapolis of Phrygia (Turkey) [24] .…”