Evaluation of CO2 Snow Blasting on Paper for the Removal of Carbon-Based Graphic Marks and Multi-Analytical Surface Assessment

Previous studies have shown that CO2 snow blasting can remove loose particulate deposits from paper, but its performance on more strongly retained graphic marks remains unclear. This study evaluated charcoal and HB-grade graphite pencil marks (H and B denote hardness and blackness, respectively) on cotton paper and assessed treatment effects on cotton, kraft and coated papers. Specimens were treated at nominal pressures of 1 and 3 bar. Digital microscopy, CIELAB colourimetry, gloss, surface pH, wettability, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy and field-emission scanning electron microscopy (FE-SEM) were used to characterise cleaning response and substrate condition. At 1 bar, charcoal was substantially reduced, whereas HB graphite persisted despite partial attenuation. At 1 bar, the cotton-paper specimen showed a low colour difference and no appreciable morphological difference in the examined FE-SEM field relative to the untreated specimen. In contrast, kraft and coated papers showed morphological, optical or wetting changes at the same pressure. At 3 bar, FE-SEM observations indicated surface alterations in the examined fields of all three substrates, suggesting lower compatibility with the tested paper specimens. The observations indicate that CO2 snow blasting may reduce loosely retained carbon-based deposits on suitable paper surfaces, whereas more strongly entrapped graphite marks resist removal. Treatment parameters should therefore be selected according to both deposit retention and substrate structure.