Use of Synchrotron Reflectance Infrared Spectromicroscopy as a Rapid, Direct, Non-Destructive Method for the Study of Inks on Paper

The analysis of inks and the paper to which they are applied is of great interest to a broad spectrum of science. From the historian and archaeologist to the forensic scientist, an understanding of ink-paper interactions is essential to the understanding of the ink and its subsequent changes upon application to paper. Determining chemical and other details of ink in a signature, for example, can be an exceedingly difficult task. Modern ballpoint writing inks are frequently mixtures of ink vehicles (used to dissolve the dyes or disperse pigments), dyes and/or pigments, various resins and polymers (to control the viscosity of the ink and to serve as “fillers”), acidic materials (frequently fatty acids that function as lubricants), and surface-active agents. Additionally, other organics may be used to control corrosion or improve solubility of the dyes and pigments. From the moment that a writing ink is applied to paper material, both the chemical composition of the ink and the ink/paper interface begin to undergo changes. Various physical and chemical processes occur, including the evaporation of solvents and other volatile compounds, polymerization, oxidation, cross-linking, and, in some cases, paper corrosion. These processes can also include those that are effected by external factors such as heat and light, with possible chemical reactions being photolytically induced. Other interactions with the paper are possible. In the present work, the use of synchrotron radiation-based infrared (SR-FTIR) spectromicroscopy offers a powerful, non-destructive method for the study and identification of inks on paper and the comparison of them to one another without the need for chemical separations and related laboratory work. Also, this method allows for a detailed analysis without the inherent destruction of the ink samples on the paper by more commonly used technique.