Assessment of Pentelic Marble Surfaces After Ammonium Oxalate Protective Treatments

The artificial oxalate method has been thoroughly studied over the last decades as a compatible and performing protective treatment for marbles and other calcite stones. In this study, the most widely used synthesis (5% w/v ammonium oxalate aqueous solution) was applied by brushing on pentelic marble surfaces and assessed in terms of surface texture alterations. Three differently textured marble surfaces were produced in terms of roughness levels, and were measured by a mechanical roughness meter. Scanning Electron Microscopy (SEM) proved to be an indispensable tool in order to investigate the morphological alterations of the process through the comparison of the original surface texture with the one induced by the conversion of calcite into calcium oxalate. The calcium oxalate formation was verified by Raman spectroscopy, where whewellite was clearly detected. Finally, the digital imaging processing of the SEM images served as an indicative tool for the quantification of the process, regarding the surface percentage that is covered by the newly formed calcium oxalate.