Within the GoGreen project, we will perform modelling of dynamic deformation of panel and canvas paintings or parchment covered with multi-layer decorative or pictorial layers using key properties of artistic and conservation materials: water vapour sorption isotherms, moisture-related expansion, coefficients of water vapour diffusion in the material and at the surface, stress-strain relationships and fracture toughness. The experimental programme will focus on determining the material properties at high temperatures and humidity levels typical of hot and humid climates. Using the Finite Element method, gradients of moisture content, as well as local deformation and stress in the object structure, will be modelled, and the risk of damage will be assessed for objects of varying shapes, sizes and material composition. The effect of crack networks (craquelures) making the decorative layers significantly less vulnerable to climate variations, will be investigated and taken into account by the inclusion of a sequence of periodic cracks – parallel or rectangular – in the decorative layer.
A key challenge is transferring information on physical damage risk obtained through the modelling to visual changes expected in cultural heritage objects. This is vital for their use for loss-of-value judgements necessary in professional decision-making and in public engagement with cultural heritage. This challenge will be met in two ways. First, we will link physical change in artworks to appearance change, like distances between cracks, areas of delamination, and degree of cupping or curling of substrates. Users will be able to view the appearance change on generic and real objects studied in the project. Secondly, the modelling of the risk of environmentally-induced damage will be validated by monitoring original objects using innovative approaches to trace climate-induced damage: Acoustic Emission monitoring, which records energy released as sound waves during fracture processes in materials; Digital Speckle Pattern Interferometry (DSPI), mapping cracking and delamination in decorated surfaces with micrometric resolution; 3D Digital Microscopy to scan surfaces with micrometric resolution and ‘stitch’ individual scans to recreate the full image of the cultural object. DSPI will also be used to evaluate consolidation treatments developed in WP5.
The existing web-based HERIe digital platform, developed by our group will be linked to the GoGreen Decision Support App so that the damage functions and models developed within the GoGreen are available to users. The material structure, shape and size of objects will be freely changed by users, including materials used for the stabilization of decorative layers in conservation treatments. Also, changes in material properties over wide ranges of temperature and relative humidity will be taken into account so institutions located in southern Europe or even in tropical climates will be able to use the tools. A new module will be developed, linking the physical damage risk to changes in the appearance of objects.