IR Reflectography and Active Thermography on Artworks: The Added Value of the 1.5–3 µm Band

Abstract

Featured Application: The work described in this study can assist in the selection of an appropriate tool for art work inspection. In addition, the authors hope to provide an overview of potential application areas for the different measurement instruments discussed within the manuscript. Abstract: Infrared Radiation (IR) artwork inspection is typically performed through active thermography and reflectography with different setups and cameras. While Infrared Radiation Reflectography (IRR) is an established technique in the museum field, exploiting mainly the IR-A (0.7-1.4 µm) band to probe for hidden layers and modifications within the paint stratigraphy system, active thermography operating in the IR-C range (3-5 µm) is less frequently employed with the aim to visualize structural defects and features deeper inside the build-up. In this work, we assess to which extent the less investigated IR-B band (1.5-3 µm) can combine the information obtained from both setups. The application of IR-B systems is relatively rare as there are only a limited amount of commercial systems available due to the technical complexity of the lens coating. This is mainly added as a so-called broadband option on regular Mid-wave infrared radiation (MWIR) (IR-C'/3-5 µm) cameras to increase sensitivity for high temperature applications in industry. In particular, four objects were studied in both reflectographic and thermographic mode in the IR-B spectral range and their results benchmarked with IR-A and IR-C images. For multispectral application, a single benchmark is made with macroscopic reflection mode Fourier transform infrared (MA-rFTIR) results. IR-B proved valuable for visualisation of underdrawings, pencil marks, canvas fibres and wooden grain structures and potential pathways for additional applications such as pigment identification in multispectral mode or characterization of the support (panels, canvas) are indicated.

Latest Advances in Common Signal Processing of Pulsed Thermography for Enhanced Detectability: A Review

“…With the help of adapted image and signal processing algorithms, it is possible to detect small discontinuities inside structures or extract material characteristic information. By reducing the amount of acquired data, the process is accelerated, but a certain decrease in accuracy has to be kept in mind [27].…”

Remote and contactless infrared imaging techniques for stratigraphical investigations in paintings on canvas

“…In fact, thanks to the transparency of the paint layers in the NIR range, the incident radiation can reach the ground level where it can be either backreflected by the support or absorbed by the possibly present drawings, thus giving rise to contrasted features in the recorded reflectographic images. More recently, MIR has been also introduced for CH investigations [50] with the aim of detecting features complementary to those of the NIR reflectography. In fact, MWIR radiation is characterized by a larger penetration depth in comparison with the NIR one and, in addition, pigments typically show different optical absorption and scattering properties with respect to the ones in the NIR range.…”

Special Issue on ‘Novel Ideas for Infrared Thermography and Its Application to Integrated Approaches’

“…In [31], Peeters et al assessed to what extent the less investigated InfraRed-B band (1.5-3 µm) can combine the information obtained from InfraRed-A (0.7-1.4 µm) and InfraRed-C (3-5 µm) bands and the related experimental setups. In fact, the application of the IR-B systems is relatively rare as there are only a limited amount of commercial systems available due to the technical complexity of the lens coating.…”