Compatibility between traditional ground layers and 3D printing materials

Starting point of this work was the restoration of a Panel Painting depicting the Adoration of the Shepherds with a Saint Bishop, by an unknown author, stored in the Galleria Regionale della Sicilia di Palazzo Abatellis, in Palermo. It was decided to integrate a missing angular decorative element of the painting’s frame in order to restore the integrity of the frame by reverse engineering and 3D printing. Reintegration was feasible as the frame has a modular decorative pattern and the remaining three corners were available. Reverse engineering and 3D printing techniques have been used in order to find a solution according to the principles of recognition, reversibility and compatibility. Moreover, this method allowed to produce two substitutive corners with the very same shape but with different surface: the first one simulating wooden support and the second designed to illustrate the original stratigraphic technique of the frame. In order to choose the proper material for 3D printing process a research has been performed to individuate a suitable 3D printing material compatible with the finishing materials used in the restoration field. Three different 3D printing materials have been chosen: two with a cellulosic filler and one characterized by a good resistance to various deterioration causes. Samples were prepared by applying two traditional ground layers, i.e. gypsum or calcium carbonate with rabbit glue, and a ground layer based on plextol adhesive. The samples underwent accelerated artificial ageing procedures, i.e. thermal, humidity and UV cycle, in order to evaluate the compatibility between 3d printing polymers and ground layers by microscopic observation of the samples, leading to the choose of coupled materials to be used to produce the substitutive frame corner reproducing the finishing technique.