The investigation of dye aging dynamics in writing inks using Raman spectroscopy

Abstract

a b s t r a c tThe durability against light and aging dynamics of heteroatomic aromatic dyes and pigments containing nitrogen atoms used in writing inks was studied using Raman spectroscopy. The mechanisms of their thermal and photo-decomposition were proposed and the rates of these processes were determined. According to Raman spectroscopy, it was found that depending on the presence of one or another colorant, there are three main types (Type A, Type B and Type C) of blue dye inks used in ballpoint, gel and capillary pens which were studied in this work. Each type is characterized by a certain set of signals in Raman spectra. Time dependencies of Raman signal intensities for each type revealed the dynamics of the processes occurred with colorants included in the studied inks from the moment when they were printed on paper. Thus, the results obtained in this study can be used for the age estimation of the paper documents up to 15 years.

Analysis of the Aging Processes of Writing Ink: Raman Spectroscopy versus Gas Chromatography Aspects

“…For that reason, a detailed investigation into the mutual influence of the volatile and dye components of writing inks was performed. In turn, for convenience and better understanding, in the proposed methodology, we have to appeal to some previously reported results [16]. The methodological distinction of this from similar studies [1,2,13,17,18] was in considering the fact that the peak intensity in Raman spectrum also depends on the concentration of the studied compound within the focal spot of the laser beam, which was impossible to control in our case.…”

“…[16]) was studied. All writing inks were printed on paper as 2 to 3 cm strokes and were subsequently investigated using the methods of spectroscopy and chromatography.…”

“…Thus, in order to eliminate the influence of the concentration factor, we used the ratio of intensities instead of absolute intensity values. Furthermore, in [16] we found that the time dependency of Raman peak ratios has a complicated nature: it consists of three fragments of monotonous change in spectral properties and two extrema, making it impossible to use this dependency for the estimation of the age of writing ink without further analysis of its nature [16].…”

“…Finally, it is also should be pointed out that the main goal of the previously published work [16] was to evaluate the capability of Raman spectroscopy to study the processes of the temporal degradation of dyes, and it did not contain any methodological developments. In particular, it was pointed out that the overlapping of the Raman peaks of solvent and dye may have an interfering influence on such studies.…”

“…Based on direct measurements, these results provide the approximate estimation of the date of handwritten inscriptions placed on paper without using comparative databases. The dependencies of Raman peak intensities ratios plotted for the B-type writing ink at the time when the ink was drawn on paper [16].…”