Evaluation of carbonated fossil bone consolidation by induction of calcium hydroxide nanoparticles in a Miocene Cheirogaster richardi specimen

• Nanolime consolidation improves cohesion and hardness on carbonate fossil bones. • Nanolime consolidation improves penetration and cohesion on carbonate fossil bones. • Treatment generates almost negligible physicochemical and aesthetic changes. • Newly created calcium carbonate is compatible with carbonate fossil bone substrate. In this research, calcium hydroxide nanoparticles, as a carbonate consolidation method, have been evaluated on carbonated fossil bone samples from decontextualized Cheirogaster richardi specimens’ fragments. The main objective was to assess whether the treatment improved fossil bone surface cohesion and mechanical strength by creating a consolidated carbonate matrix in fossil substrate. Treatment penetration capacity and chemical compatibility without causing observable alterations in substrate porosity and external appearance were considered as significant questions to be assessed. Samples were analysed both before and after treatment using scanning electron microscopy, spectrophotometry, weight measurement control, water absorption assessment, conductivity and pH measurement, Vickers microindentation and tape testing. During analysis and evaluation, changes in fossil bone after treatment compared to its original condition have been taken into account. Results point out that hardness and cohesion increased significantly after treatment, bonding together disaggregated particles via a calcium carbonate micrometric layer, with almost negligible changes in surface topography and colour. In addition, calcium hydroxide nanoparticles penetration depth was remarkable. Conductivity, pH and weight hardly changed and porosity reduction was observed without complete pore blockage. To sum up, the treatment was effective and suitable for carbonate fossil bones having a highly compatibility with carbonate fossil bones substrates.