Classification of iron‐based inks by means of micro‐Raman spectroscopy and multivariate data analysis

Abstract

In this work, multivariate data analysis methods were applied to the analysis and interpretation of micro‐Raman spectra, collected from a broad set of historical iron‐based ink samples, previously characterised for the content of organic acids (gallic acid, ellagic acid and protocatechuic acid). The proposed method relies on principal component analysis of the noisy spectra typically obtained on original, degraded, organic samples, where fluorescence could affect the Raman signal. The signal components could be distinguished from the noise components and then used to build a linear discriminant analysis (LDA) model, achieving separation of the spectra into three classes. Selection of pure signal factors also improved effectiveness and performances of partial least square regression (PLS) algorithms, allowing quantification of condensed tannic acid residuals. Application of multivariate methods to discriminate signal from noise removes the need for spectral data manipulation (filtering, smoothing and differentiating). The obtained classification method for discrimination of historic inks and the regression method for determination of condensed tannic acid residuals supports the use of Raman analysis of fluorescing organic materials, and may provide information to scholars on ink composition and potentially on its provenance. Copyright © 2013 John Wiley & Sons, Ltd.

Characterisation of 19th and 20th century Chinese paper

“…Many non-destructive techniques have been used in historic paper research: of the Fourier-Transform Infrared (FTIR) sampling techniques, attenuated total reflectance is often used, however, the requirement to apply pressure during a measurement makes it unsuitable for fragile objects. Raman spectroscopy can be very useful for ink and pigment analysis [13] or characterisation of lignin and cellulose degradation products [14]. However, the often low signal-to-noise ratio and fluorescence make it less suitable as a general characterisation technique.…”

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

“…In recent years, there have also been significant advances in the identification of inks, including traditional inks such as sepia [66,264], bistre [265], and iron gall ink [26,27,178,238] and the ones used by modern artists such as the chrome logwood [34,62,65] and crystal violet inks used by Van Gogh [49,244].…”

Investigation of Vegetable Tannins and Their Iron Complex Dyes for Dye Sensitized Solar Cell Applications

“…The Turkish valonea and sweet chestnut are an abundant supply of gallotannin and ellagitannin and their derivatives, such as gallic acid, ellagic acid and hexahydroxydiphenic acid, while mimosa and quebracho tannins are rich in condensed tannins and their derivatives like catechin and epicatechin. The all-vegetable tanninFe complexes are used for making iron gall ink for centuries [25]. A tannin based-dye sensitizedsolar cell was reported by a group of researchers about ten years ago, and the efficiency found was too low [14].…”