Scientific assessment of using gellan gum modified with calcium carbonate for surface cleaning a tarnished vintage daguerreotype

Purpose This study aims at evaluating the efficacy of gellan gum system saturated with calcium carbonate solution in removing tarnish from a selected vintage daguerreotype. Design/methodology/approach Preliminary tests were applied on a tarnished silver coupon so as to prevent any potential risk to the original photograph which is a valuable 19th century daguerreotype of an anonymous seated old lady. A multi-analytical approach was conducted during this study using visual inspection, UV fluorescence imaging, digital microscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) and atomic force microscopy (AFM). EDS was used to study the composition of the tarnish. Findings Examination under UV light showed that the gellan gum pad saturated with a 5% suspension of calcium carbonate did not leave any residues after treatment. ATR-FTIR confirmed the absence of gel residues on the surface post treatment. SEM/EDS revealed the presence of gold indicated that the daguerreotype is gilded. Silver and mercury were detected as the final image material. The tarnish was found to be silver sulfide. Although the selected treatment was found to be successful in reducing the sulfur level, the two- and three-dimensional AFM images and roughness parameters Ra and Rq revealed a very modest increase in the roughness of the treated surface. Originality/value This paper evaluates a novel treatment for surface cleaning tarnished vintage daguerreotype that is safe, cost-friendly and eco-friendly.