PhD POMMIER : Perception and multimodal objectivation of an intervention in restoration-conservation

Visual perception is an essential notion when it comes to the evaluation of the conservation-restoration process: the eye is the expert's tool of diagnostic and validation, as well as the observer's path to appreciate the work. Several studies have already focussed on the evaluation of the visual modification occurring due to restoration. For instance, the choice of replacement stones for monuments, the visual impact of biocides on paintings, the impact of removing a yellow varnish from a painting or the comparison of the different digital retouching methods. Nevertheless, only a few studies have focussed on sensitive perception thresholds and have taken the restoration process into account. Thus, questions are raised about the relevance of an objective measurement in the evaluation process of paintings undergoing restoration. How can new non-invasive methods of characterisation provide an additional tool for traceability to experts? For example, different parts of a series of paintings can be in different museums. If so, the sole eye of the restorers cannot be sufficient to match restorations between paintings. Indeed, even under the exact same lighting conditions, the eye cannot remember colours at a high precision, and this is why optical instruments are needed. Some colorimetric studies already exist about colours before and after cleaning but they never raise perceptual matters. The aim of this PhD is to link perceptive measurements from sensorial analysis and classical optical methods during a specific restoration intervention: cleaning. There are a lot of studies concerning cleaning but rather in the fields of conservation sciences or chemistry [5]. This study main aim is the perceptive aspect of colour and gloss and its modification during the process of cleaning. Thanks to objective physical measurements of colours and gloss, which is linked to surface state and rugosity, we will try to answer several questions: How one evaluates the cleaning homogeneity? What is the relation between appearance and cleaning level ? During this PhD I will analyse the advantages of instrumental measurements as a complementary tool for the conserver-restorer in his decision making and work tracking. A first questionnaire will be sent to restorers to understand what is important for them during cleaning, such as the type of light source and its direction, in order to define parameters and descriptors for psycho-perceptive experiments which will be submitted to experts and inexperienced people. At the same time, objective optical measurements will be carried out on samples in order to corelate them with the perceptive data. The first results will be presented on the poster.