Micro-Raman Identification of Bloom Formed on a Historical Print Artifact

Abstract

An 1876 engraved bird's-eye view of Adelaide, the Calvert Panorama, was submitted to conservators after large quantities of loose white powder were noticed on the surface of the print and the overlying glazing. Previous conservation treatment had occurred in 1972, but no detail was given of the treatment processes. To establish what past treatments may have been applied and to prevent possible exposure to toxic materials, scientific analysis of these solids was performed. As described in this article, micro-Raman spectroscopy was employed to characterize the solid particles that composed the bloom. The unparalleled high spatial resolution (approximately 1 μm) of the technique ensured individual compound identification from a mixture of 4–60 μm-sized particles. No sample preparation was required. The analysis revealed that the bloom was predominantly paratoluenesulfonamide (the residue of chloramine-T, a chemical popular for bleaching paper in the 1960s and 1970s) and calcite, arising from the original deacidifier (calcium hydroxide). Traces of three other species—carbon black, yellow quartz, and cellulose—were also observed. None of the solids identified was a toxic pesticide residue as had been feared.