Terahertz time-domain imaging (THz-TDI) and Spectral domain optical coherence tomography (SD-OCT) are two investigation methods capable of providing 3D datasets from which depth profiles, cross-sectional images, plan-type images and volume rendering of an object can be derived. These novel photonic technologies are extremely relevant to the field of heritage science, for which the comprehension of the stratigraphic structure of a cultural heritage object may help in the understanding of its manufacturing technology and state of preservation. Different imaging depths, fields of view and axial/lateral resolutions characterize the two imaging technologies, which thus provide different but complementary information of the same scanned object. In this study we show how the THz-TDI and SD-OCT scans performed on a fragment from the underside of an Egyptian coffin (Theban area, 21st/22nd Dynasties, Egyptian Antiquities department of the Louvre museum, Paris, France) gave precious insights on its full structure and stratigraphy.
The demand for non destructive and non invasive structural diagnostic techniques able to perform on field remote structural evaluation of historical structures and works of art it faces an increased demand. The techniques must have some basic important characteristics The non destructivity, accuracy, repeatability, non physical contact, portability, resolution, broad range of applicability depending on the type of artwork and the question at hand, are all among the important requirements underlying the requirement for on-field structural diagnostics. In this respect there are two known techniques that have been developed at full to provide a suited structural diagnostic application in artwork conservation. The systems presented here but discussed in detail elsewhere are stimulated infrared thermography (SIRT) and digital holographic speckle pattern interferometry (DHSPI) the prior can be found n market at commercial devise level while the latter is at laboratory prototype level. The two systems are being exploited for their complimentary advantages and in this paper are used in combined testing on art related targets according to the above criteria to confirm the enhanced diagnostic information that their complimentary use provides. Results confirm the effectiveness of each technique alone and the combination of data of both techniques in the conservation field. Each system is first briefly described and examples are given with the aim to present the suitability and appropriateness for use in structural documentation analysis and reports. The experimental work is in laboratory work-in-progress focusing on the hybriding of data synthesis.
In the field of Cultural Heritage and conservation science the development of non-invasive tools to retrieve information on artworks and historical artifacts remains one of the most important and increasing demands. In this work a focus was made on the capability of THz imaging to investigate the internal structure of objects made of superposed plaster layers. In particular, a first attempt of investigation was made for gypsum based plaster used for a stucco reliefs. After a feasibility phase on plaster moke up samples, a 15th century painted stucco relief was investigated by means of THz-TDI in the framework of the ESPRIT project, promoted by the Louvre Museum. The objectives were to assess the presence of internal layers made of different plaster mixtures, to locate them and give useful information about the supposed manufacturing techniques. The refractive indexes of different plasters were measured. Due to multiple scattering inside the samples and the impact of the heterogeneity of the material on this refractive index, the interface between plaster/plaster seems difficult to detect.
Such developments come from conservation experts in the community of cultural heritage - encompassing artworks, museum artifacts or historical monuments - for less intrusive and non-destructive tools to gain information about the subject. Increasingly the demand is for information regarding internal structures and indications of life histories and behaviors of an object. As it is well known, the deterioration due to the capillary rise of water through the walls is a very widespread problem. In this paper, a study of Stimulated Infrared thermography and Evanescent-Field Dielectrometry was applied to a non-destructive mapping, in situ, and in a semi-quantitative way the distribution of water, salt and the structural deterioration induced in a wall of the 13th century of the abbey’s church of Chaalis. Complementarity of the both techniques will be underlined. The Stimulated Infra-Red Thermography (SIRT) is a contact free technique and allows the detection of plaster layers delamination of masonry. Evanescent-Field Dielectrometry (EFD) is a recent diagnostic method based on dielectric spectroscopy at microwave frequency. The measuring instrument is a portable resonant microwave device for mapping the water content and salinity on flat surface up to a depth of 2–3 cm in real time, in a non-destructive way. The method detects the water content and salt concentration in frescoes and walls by estimating the dielectric properties of tested porous materials that is viewed as a “binary” dielectric mixture consisting of bulk material and water, by the contrast between the dielectric constant of a dry material and water. According to the resolution of the optics, the SIRT has a less lateral resolution and more limited in depth, but it is easy to implement and can be used on-site, like in scaffolding conditions. Moreover, this technique gives an overview at a larger scale (metric) than EFD (centimetric).
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:
-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) spectroscopy and imaging is a non-destructive, non-contact, non-invasive technology emerging as a tool
for the analysis of cultural heritage. THz Time Domain Spectroscopy (TDS) techniques have the ability to retrieve
information from different layers within a stratified sample, that enable the identification of hidden sub-layers in the case
of paints and mural paintings.
In this paper, we present the THz TDS2 system developed in the European Commission's 7th Framework
Program project CHARISMA [grant agreement no. 228330]. Bespoke single processing algorithms; including a
deconvolution algorithm can be deployed to increase the resolution and the global performance of the system. The
potential and impact of this work is demonstrated through two case studies of mural paintings, where the capability to
reveal the stratigraphy of the artworks is demonstrated.
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.
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