Spectroscopic evaluation and characterization of different historical writing inks
Introduction
Important historical objects in libraries and archives (documents, manuscripts, maps) suffer very serious damage as a result of the destructive effects of different kind of inks. The reasons for this destruction are not fully understood yet. It is believed that main degradation mechanism of paper degradation is following: inks prepared with different ingredients causes both acidic hydrolysis and catalyzed oxidation of cellulose [1], [2], [3], [4], [5]. The desire to conserve the paper necessitates the development of effective treatments methods, which can only be possible after determination of the chemical composition of inks [6], [7]. Hundreds of recipes for ink have been published over centuries [8], [9]. The great variety of ink recipes and the variety of visual aspects of manuscripts suggest that many side effects could occur and contribute to the different aspects of paper degradation.
Several analytical techniques such as proton-induced X-ray emission spectroscopy [4], gas chromatography coupled with mass spectrometry [10], [11], UV–vis spectrometry [12], atomic absorption spectrometry [12], reflectance spectrometry [13], scanning electron microscopy and energy dispersive X-ray microanalysis [14], X-ray photoelectron spectroscopy [15] have been applied for determining the constituents of ink. Most of these techniques are complex and generally require several time consuming analytical steps. Besides, some proposed methods are based on very expensive instrumentation. It is well known, that definite substances can be identified by their IR spectra, interpreted like fingerprints. The spectra show certain bands, i.e., characteristic vibrations, which are typical of particular groups of atoms and which are defined by definite ranges of frequencies and intensities in the IR spectra [16], [17]. The recent results published [18], [19], [20], [21], [22] demonstrated clearly that IR spectroscopy is indispensable tool for the characterization of materials.
It was reported that this technique could be also employed for the examination of works of art. For instance, Calvini et al. [5], [23], [24] have used IR spectroscopy for the analysis of cellulose and its derivatives. Also, the composition and degradation of laboratory-made paper as well as of historic items has been investigated. The FTIR spectroscopy was used to characterize the blue pigments in different polychrome works of art [25] and to investigate the stability of offset inks on paper upon ageing [26]. In this paper we report the application of IR spectroscopic technique for the characterization of different historical writing ink samples, such as Pfalz ink from red wine, ink from the oak’s bark extract, different iron gall inks, black ink with iron(II) sulphate, black ink with copper sulphate and logwood tree ink. Our study is oriented on the investigations of changes in IR spectra, consequently on the determination of specific features of different inks depending on its’ chemical composition. To facilitate the interpretation of the results the pure ingredients of ink samples were also analysed by FTIR spectroscopy.
Section snippets
Experimental
Eight different writing ink samples were prepared using following recipes [9], [27], [28], [29], [30]. Analytical grade reagents and distilled water were used for the preparation of inks.
(I) Pfalz ink from red wine; 100 ml of red wine (Bulgaria) was carefully mixed with 5 g of powdered cherry gum (ZAO, Sankt-Peterburg) and 4 g of soot (Kremer Pigmente). The obtained mixture was stored for 2 weeks in closed vessel with intermediate (daily) shaking. The pH of the final ink solution was equal 3.51.
(II
Results and discussion
The IR spectra of all ink samples pressed into KBr pellets are presented in Fig. 1, Fig. 2. Broad absorptions in all spectra around 3700–3000 and 1670–1620 cm−1 indicate the presence of adsorbed water in the samples [31]. The bands at ca. 2360–2340 cm−1 presented in the spectra belong to the adsorbed carbon dioxide from the atmosphere. However, according to the origin of the bands, it is clearly seen that all inks are different regarding their chemical composition. For instance, the composition
Conclusions
In this investigation, the IR spectra of a wide series of historical writing inks have been recorded and analyzed. The infrared spectra of all samples were measured using three different techniques: KBr pellet, Si substrate and ZnSe cell. FTIR spectroscopic evaluation of evaporated to dryness different ink samples using the KBr pellet technique provides a possibility to identify historical inks regarding their chemical composition. According to the observed specific features in the FTIR
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2021, Vibrational SpectroscopyCitation Excerpt :Gas chromatography coupled with mass spectrometry [2,28] UV–vis spectrometry [2], atomic absorption spectrometry [2], reflectance spectrometry [29], scanning electron microscopy and energy dispersive X-ray microanalysis, X-ray photoelectron spectroscopy [30] have been applied for determining the constituents of ink. FTIR was employed by archaeological scientists to know organic and inorganic constituents of ink [31–37]. The degradation behavior of ink is due to the composition of original ink, pigment, mineral and vegetable oils used as binding agents and the aging process.