Abstract
Scientific analysis of panel paintings could provide key information to art historians and conservators about the composition and condition of the constituent layers. Knowledge of the structure, stratigraphy, and condition of the subsurface layers of these objects is highly relevant to conservation measures, when stability problems such as delamination or internal cracking are considered. Terahertz time-domain imaging (THz-TDI) in reflection geometry is capable of highlighting interfaces between layers in a stratigraphic buildup, and thus makes structural information available in the form of subsurface 3D images and stratigraphic images (B-scans). The technique is contactless and non-invasive, and has been successfully applied to investigation of panel paintings. Regarding gilded panel paintings, the extremely high reflectivity of metals at submillimeter wavelengths generally precludes the transmission of electromagnetic waves through metallic films. Therefore, imaging of subsurface features below gilded finishes may be regarded as Very challenging. A small but non-negligible direct transmission through metal films occurs if the film thickness is of the order of the skin depth of the metal in the terahertz range, due to the skin effect. The thickness of gold leaf, a fraction of a micrometer, matches the skin depth of gold in the terahertz frequency range covered by THz-TDI devices. We therefore investigated and imaged subsurface features of panel paintings through gilded finishes with THz-TDI. Subsurface layers of three gilded panel paintings (two contemporary tempera panel replicas and one fourteenth-century icon) have been successfully imaged behind gold finishes with THz-TDI.
Highlights
Panel paintings and gilded finishes in Europe: an overview Panels were used as supports in European painting from antiquity to the sixteenth century, when they were almost completely replaced by easel paintings on canvas
Terahertz time-domain imaging (THz-TDI) gives information about the painting technique used for the panel, proving that the paint layer was applied to the gold background, which covers almost the total area of the priming, except for the parts delimitated by the dashed red line in Fig. 3B, where the paint layer has been applied directly to the priming
We have shown that investigation of the subsurface features of gilded panel paintings and the characterization of their internal structure by means of THz-TDI in reflection geometry is possible, and, in particular, we have demonstrated that investigations behind gilding layers are possible
Summary
Panel paintings and gilded finishes in Europe: an overview Panels were used as supports in European painting from antiquity to the sixteenth century, when they were almost completely replaced by easel paintings on canvas. In the Byzantine world, panel paintings were largely in use before and after the iconoclastic periods (eighteenth and nineteenth centuries), while in Europe they were most prevalent in the thirteenth century. Given the widespread religious use of panel paintings, they. Gold foils were the first to be applied for decorative purposes, but rapidly the thickness of the foil was decreased, mostly to reduce costs.
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