Inspection of panel paintings beneath gilded finishes using terahertz time-domain imaging,

http://chsopensource.org/2015/09/12/inspection-of-panel-paintings-beneath-gilded-finishes-using-terahertz-time-domain-imaging/
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.

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We developed Pigments Checker for photographers, conservators and scientists interested in technical documentation of paintings. It has 54 swatches of historical pigments designed for infrared photography, ultraviolet photography and other technical photographic methods for art examination. Check it out!

Pigments Checker is a collection of 54 swatches of his­tor­i­cal pig­ments that have been applied using gum ara­bic as a binder on a cel­lu­lose and cot­ton water­color paper, acids and lignin free. This paper is not treated with opti­cal bright­en­ers, it’s slightly UV flu­o­res­cent, and it reflects IR. Two cross-hair lines, 0,2 mm (ver­ti­cal) and 0.4 mm (hor­i­zon­tal) are printed on each swatch of paper before the appli­ca­tion of paint, in order to have a means to eval­u­ate the pig­ments’ trans­parency in the IR andIRR imag­ing. Among all the pig­ments and their vari­eties ever used in art these pig­ments col­lec­tion select the most used ones from antiquity to early 1950’.

CHSOS has been collaborating with Corinna Koch Dandolo, PhD student at the prestigious DTU (Technical University of Denmark) Fotonik, whose research focuses on developing art examination applications for the THz (Terahertz) imaging technique. This is a video about THz technique “Terahertz and Art Examination.” We did THz examination of the newly discovered frescoes in Aci Sant’Antonio and the study of two wooden statues. International Researchers are welcomed to propose scientific art examination research for field projects in Sicily.

Corinna, PhD Student at the Technical University of Denmark, Fotonik – Department of Photonics Engineering, is analyzing with the Terahertz scanner the 1300s panel painting “Madonna and Child”.

Corinna, PhD Student at the Technical University of Denmark, Fotonik – Department of Photonics Engineering, is analyzing with the Terahertz scanner the 1300s panel painting “Madonna and Child”.