The abbey’s church of Chaalis, in the North of Paris, was founded by Louis VI as a Cistercian monastery on 10th January 1137. In 2013, in the frame the European Commission's 7th Framework Program project CHARISMA [grant agreement no. 228330] the chapel was used as a practical case-study for application of the work done in a task devoted to best practices in historical buildings and monuments. In the chapel, three areas were identified as relevant. The first area was used to make an exercise on diagnosis of the different deterioration patterns. The second area was used to analyze a restored area. The third one was selected to test some hypotheses on the possibility of using the portable instruments to answer some questions related to the deterioration problems. To inspect this area, different tools were used: <ol>
-Visible fluorescence under UV,
- THz system,
- Stimulated Infra-Red Thermography, SIRT
- Digital Holographic Speckle Pattern Interferometry, DHSPI
- Condition report by conservator-restorer.
The complementarity and synergy offered by the profitable use of the different integrated tools is clearly shown in this practical exercise.
We systematically examined the mid-20th century Italian painting "After Fishing" (fig. 1) by Ausonio Tanda using multi-spectral (UV, RGB visible, tri-band IR), x-ray and terahertz time-domain spectroscopic imaging. THz-TDSI was performed in both transmission and reflection geometries and the results were compared.
Terahertz (THz) radiation is being developed as a tool for the analysis of cultural heritage, and due to recent advances in technology is now available commercially in systems which can be deployed for field analysis. The radiation is capable of penetrating up to one centimetre of wall plaster and is delivered in ultrafast pulses which are reflected from layers within this region. The technique is non-contact, non-invasive and non-destructive. While sub-surface radar is able to penetrate over a metre of wall plaster, producing details of internal structures, infrared and ultraviolet techniques produce information about the surface layers of wall plaster. THz radiation is able to provide information about the interim region of up to approximately one centimetre into the wall surface. Data from Chartres Cathedral, France, Riga Dome Cathedral, Latvia, and Chartreuse du Val de Bénédiction, France is presented each with different research questions. The presence of sub-surface paint layers was expected from documentary evidence, dating to the 13th Century, at Chartres Cathedral. In contrast, at the Riga Dome Cathedral surface painting had been obscured as recently as 1941 during the Russian occupation of Latvia using white lead-based paint. In the 13th Century, wall paintings at the Chapel of the Frescos, Chartreuse du Val de Benediction in Villeneuve les Avignon were constructed using sinopia under-painting on plaster covering uneven stonework.. This paper compares and contrasts the ability of THz radiation to provide information about sub-surface features in churches and Cathedrals across Europe by analysing depth based profiles gained from the reflected signal.
Terahertz pulse imaging (TPI) is a novel noncontact, nondestructive technique for the examination of cultural heritage
artifacts. It has the advantage of broadband spectral range, time-of-flight depth resolution, and penetration through
optically opaque materials. Fiber-coupled, portable, time-domain terahertz systems have enabled this technique to move
out of the laboratory and into the field. Much like the rings of a tree, stratified architectural materials give the
chronology of their environmental and aesthetic history. This work concentrates on laboratory models of stratified
mosaics and fresco paintings, specimens extracted from a neolithic excavation site in Catalhoyuk, Turkey, and
specimens measured at the medieval Eglise de Saint Jean-Baptiste in Vif, France. Preparatory spectroscopic studies of
various composite materials, including lime, gypsum and clay plasters are presented to enhance the interpretation of
results and with the intent to aid future computer simulations of the TPI of stratified architectural material. The breadth
of the sample range is a demonstration of the cultural demand and public interest in the life history of buildings. The
results are an illustration of the potential role of TPI in providing both a chronological history of buildings and in the
visualization of obscured wall paintings and mosaics.
Terahertz imaging will be presented as a novel method of nondestructively measuring otherwise inaccessible tree-rings
for the purpose of dendrochronologically cross-dating cultural heritage artifacts. Wood specimens were measured using
time-domain terahertz pulse reflectometry. Two-dimensional images of tree-rings were generated through analysis of
both time- and frequency-domain terahertz signals, which changed proportionally to the variations in wood density.
Terahertz pulse separation enabled wood specimens with at least two layers of coatings (primer and/or paint) to be
measured and the terahertz images were quantitatively compared to the optical photographs of related, uncoated
specimen. Tree-ring series and timelines were obtained for each terahertz image with respect to the source (reference)
ring series. Short ring width blocks were aligned to the reference series and combined to create an extended timeline for
each terahertz image. It was determined that while spatial resolution may be improved with analysis at high frequencies,
the lower signal to noise reduces the precision of the ring measurement. Constructing longer timelines from ring blocks,
significantly improves the overall quality of a match.