Behavior of Historical Printing Inks on Paper in High-Frequency Cold Plasma Discharges

This paper reports on the behavior of red and black ink from a historical printed book, subjected to a plasma discharge treatment, applied for the decontamination and cleaning of naturally aged paper. As some preliminary experiments using high-frequency (HF) plasma showed a slight fading of red ink, the study was focused on the comparison of HF cold plasma and afterglow plasma treatments in order to get conclusive information on the effect of plasma active species on the red ink. Energy Dispersive X-ray Scanning Electron Microscopy SEM-EDX and Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy FTIR-ATR analyses were used for the identification of inks and binder, while the impact of plasma on inks was assessed by SEM analysis and color determinations. The experiments have been performed on an especially designed modular equipment, allowing the samples to be subjected alternately to HF cold plasma or afterglow plasma treatment. The study proved that direct HF plasma could result in a more important deterioration at treatment duration exceeding 5 min, while in afterglow plasma, this discoloration is not observable. The color fading is imputable to the corrosion of pigment crystallites produced by direct plasma discharge.