We discuss applications of pump-probe microscopy to the investigation of pigments in artworks. In pump-probe, a series of ultrafast laser pulses probe molecular state dynamics, which is governed by several physical mechanisms that evolve on timescales ranging from sub-picoseconds to many microseconds. The interplay of these mechanisms can lead to complex dynamics and is sensitive to a pigment’s structure, composition, and environment. We describe strategies to interpret pump-probe dynamics and to disentangle the underlying contributions from different physical mechanisms. We also report on applications to the studies of Cadmium pigments, carbon-based black pigments, and their degradation mechanism.

Varnishes made of natural terpenoid resins are vulnerable components of paintings since they can undergo complex and differentiated chemical and structural changes over time depending on the type of varnish and the conservation conditions. The present work aims at studying the in-depth effects of natural and artificial aging on terpenoid varnish layers using nonlinear optical microscopy (NLOM) in its modality of multiphoton excitation fluorescence (MPEF) complemented with laser-induced fluorescence (LIF) and optical microscopy measurements. To this end, solvent-based terpenoid varnishes with different thicknesses and degrees of aging were considered. A homemade nonlinear optical microscope, based on a tightly focused pulsed femtosecond laser emitting at 800 nm, was used for the MPEF investigation. Single-photon LIF measurements served to determine the degree of surface aging and the optimum NLOM-MPEF operating conditions and helped to interpret the results obtained by applying the latter. The LIF results showed an increase of fluorescence intensity and a red shift of the maximum of emission for varnishes subjected to longer aging periods and of thinner layers. The purely non-invasive NLOM-MPEF approach serves well to assess the in-depth-dependent degradation gradients across the thickness of the layers and its dependence on the aging time and the thickness of the varnish layer. Acknowledgments This research has been funded by the Spanish State Research Agency (AEI) through project PID2019-104124RB-I00/AEI/1013039/501100011033, by the H2020 European project IPERION HS (Integrated Platform for the European Research Infrastructure ON Heritage Science, GA 871034), and by the Community of Madrid project Top Heritage-CM (Tecnologías en Ciencias del Patrimonio, S2018/NMT_4372). Support by CSIC Interdisciplinary Platform “Open Heritage: Research and Society” (PTI-PAIS) is acknowledged.

X-ray Fluorescence images often contain many spectral layers, which can result in long computation times when performing analysis. In this talk, discrete wavelet transformation is used in order to reduce the spectral layers, whilst maintaining the image information so that analysis may be performed at a reduced runtime. Furthermore, once the analysis of the transformed image has been complete, the inverse discrete wavelet transformation is then used to return the image cube back to its original dimensions. The proposed method is effective for cultural heritage as the elemental analysis gathered from XRF images is now obtained in a timely manner.

In this work we present a novel hyperspectral camera based on a compact birefringent interferometer to perform reflectance measurements on works of art. The innovative aspect emphasized in our system lies the capability to acquire hyperspectral images of the sample at different magnification, allowing to image a field of view ranging from few millimetres to tens of centimetres. With our work, we want to demonstrate the effectiveness of this system when performing hyperspectral imaging of painted surfaces at the macro scale, i.e., with few millimetres of field of view, and discuss its potential to resolve the details of a painting as pigments’ grains.

Active pulsed thermography was applied for paintworks characterization and under surface defects analysis. Following rapid flash lamp excitation of the samples, a time-resolved thermal response in an extended infrared spectral range was recorded by two high-speed, high-sensitive mid- and long-wavelength infrared cameras. 2D phase shifts images were provided by the FFT software. The method is appropriate for rapid, remote, non-destructive characterization of various defects on painting layers and canvas, and detection of under-drawings, pentimenti, etc. Dynamic multispectral imaging in a wide infrared range may provide complementary information on cultural heritage specimens under inspection for their documentation, preservation and conservation.

Within the framework of IPERION-CH, a program that supports the creation of new mobile instrumentation, Laser-induced breakdown spectroscopy (LIBS), laser-Induced Fluorescence (LIF), Raman Spectroscopy and diffuse reflectance spectroscopy were combined to provide simultaneously elemental and molecular complementary information from the same analysis point. The prototype has been implemented for cultural heritage applications on Müstair Monastery mural paintings in the context of Molab European transnational access of IPERION-HS . We demonstrated through previous work the analytical possibilities of this instrumentation on mock-up and several cultural heritage materials and we also described the design and the implementation of the set-up that has been developed taking into account the heritage science constrains. At Müstair Monastery, the first implementation of this new analytical instrumentation on real site has been achieved. This paper will focus on the discussion on the advantages and limitations of this instrumentation in this specific context and the improvement in the development.

Being one of the most frequently used colour, green colourants not only discolourate but also corrode the paper substrate. However, the degradation phenomena and mechanisms have not been sufficiently studied. In this research, eight valuable objects from 15th – 17th century are selected from the collections in the Maurits Sabbe Library KU Leuven as case studies. Coupled with machine learning methods, narrowband UV-VIS-NIR multispectral imaging (NBMI) and fibre optics reflectance spectroscopy (FORS) are demonstrated as the state-of-the-art techniques to gain an in-depth understanding of the degradation of the green colourants, its effect on the paper substrates, and the preservation needs for the collections.

About three centuries ago Newton discovered that white light is a “mix of rainbow’s colors”. Since then scientists and artists tried to bound the concept of colours into some definition and into collections and catalogues of colours. The results was to have many theories and many ways of classifying colours. The study of human vision and the way our retina works suggested a tristimulus model that began a mathematical model in the ’30 of last century thanks to the work of the CIE (cie.co.au). Although the model evolved in its almost one century of life, the basis are the same of the original one. The model has a couple of huge advantages: it allows to assign to each colour some numeric colorimetric coordinates that can be propagated across any media to “communicate the colour”, and, being based on human physiology, it is able of predicting our perception of colours and colour differences. In the era of digital communication, practically speaking the 100% of images and colours are represented following this model and, if all the colour management chain is correct, we can hardly distinguish the original colour of a flower from its representation on a colour monitor. So one could think that the problem of representing colours is solved. Unfortunately not at all. Reducing a colour to three numbers (the colour coordinates, XYZ or Lab) is an irreversible process, so given XYZ coordinates these could correspond to infinite number of spectra (each of which would give to our eyes the same colour stimulus). This ambiguity generates the metamerism. The spectrum of colour of a flower will be not the same spectrum of the representation of that flower on a monitor, even if they seems to be the same colour. Digital colour imaging fidelity is totally based on the metamerism. We most that we can say of two colours is that they are colorimetrically equal. Colorimetry allows to communicate a stimulus that induces a specific colour in our eyes, it doesn’t communicate the real physical nature of that colour. Every time we need to associate colour to matter, colorimetry become useless. Only a complete spectrum can do that, and this brings us to the need of a spectral imaging approach in all the fields where matter matters. In the first part of this work the authors propose a flexible approach based on custom multibandpass filters and AI calibration that allows to achieve the needed spectral resolution with a tuning of the amount of spectral images used, that will be always less that the classical “one band – one filter” approach. In the second part the spectra obtained from images are compared to spectra measured with laboratory spectrophotometers to establish the reliability of the approach. The third part is a collection of spectral imaging case studies in the field of Cultural Heritage, Architecture and Archeology, where identification of matter was a key factor more than having digital images with colorimetric high fidelity.