Abstract
Revealing precious hidden features by a completely non-invasive approach is one of the crucial issues in the Heritage Science field. In this regard, concealed fresco paintings still represent an analytical challenge. This paper addresses the specific issue in wall painting diagnostics by the photoacoustic (PA) imaging technique, already proven to be efficient in revealing underdrawings and internal stratigraphy in movable paintings on paper and canvas. A newly set-up reflection PA prototype was applied here for the first time to probe the charcoal, graphite and sinopia hidden sketch drawings in concealed (gypsum, limewash, overpainted) wall paintings. The results presented here push forward the frontiers of the PA imaging technique and point to its potential effectiveness of revealing hidden underdrawings in historical wall paintings with complex stratigraphy.
Highlights
Numerous historical wall paintings remain in part or completely covered by subsequent layers, including retouchings, overpaints, mortar coats, etc
There is a need for a robust methodology that is capable of addressing all the relevant art historical, material and conservation queries prior to any intervention on such multilayered wall paintings
Non-invasive PA imaging was tested for the first time tested as a tool for revealing hidden underdrawings in wall paintings with a complex stratigraphy
Summary
Numerous historical wall paintings remain in part or completely covered by subsequent layers, including retouchings, overpaints, mortar coats, etc. The novel epi-illumination PA imaging set up proved its efficiency in detecting underdrawings in simulated multilayered artworks [28], pointing to its applicability in a wide range of Cultural Heritage objects of arbitrary forms and shapes We tested it on designed wall painting mock-ups, prepared following the historical methodologies. The scope of this work was to evaluate the effectiveness of the new epi-illumination PA imaging set-up to detect the sketch drawings in simulated wall paintings These features are hidden under a secco paint layer or under both the fresco paint and the concealing limewash or gypsum coats of two different thicknesses. The same image processing function was applied to NIR images for comparison of the experimental results
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