Rheological Modelling of Plaster Deposition for Painting Restoration

Abstract

This paper reports on the result of rheological modelling of plaster deposition for paintings restoration. A typical plaster recipe was changed in order to check the effect of water level on rheological properties, both performing oscillatory tests and measuring plaster viscosity at two different temperatures. A model based on momentum balance on a vessel-nozzle geometry for a shear thinning fluid was set-up to simulate the deposition process and numerical results were compared to experimental data. A good agreement was found for moderate deposition times. At high process time, due to phase-separation in plaster, a loss in matching between the simulation and experimental point was found, because the modelling assumption of “pseudo-homogeneous” behaviour does not apply anymore. Simulations allowed operating charts to be prepared reporting the deposited plaster volume as a function of the main process variables (temperature and pressure) and rheological properties of the plaster. This model could effectively support the development of an automatic deposition system able to recognise the filling volume over the painting surface and to control autonomously feeding of the plaster from a vessel through the deposition nozzle.

Keywords

• plaster
• suspension
• flow modeling
• viscosity
• collagen
• painting restoration