Operation Night Watch is the largest research and conservation project that Rembrandt’s masterpiece The Night Watch (1642, oil on canvas, h 378.4 x w 453 cm) has ever undergone. In the summer of 2019, the Rijksmuseum embarked on this multi-year project with the goal of thoroughly studying the condition and painting technique to determine the best treatment plan for the large canvas painting. The Night Watch was researched in situ in the gallery inside an ultra-transparent glass chamber in full view of the public (Fig. 1). The multi-disciplinary team of Operation Night Watch includes scientists, conservators and art historians, and collaborates with museums and universities in the Netherlands and abroad. Together they work alongside each other on the acquisition and interpretation of the research data.

The latest and most advanced research techniques are being used, ranging from digital imaging and scientific and technical research to computer science and artificial intelligence. The non-invasive macroscale imaging technologies that have been employed include macro X-ray fluorescence, macro X-ray powder diffraction, reflectance imaging spectroscopy, optical coherence tomography, high resolution photography and 3D scanning. The combined approach was essential to gain insight into the complex (art)historical and material information to answer the (technical) art history, conservation, and scientific questions. Parallel to this, microscale imaging analyses were carried out on embedded and loose microsamples making use of light microscopy, imaging-ATR-FTIR, scanning electron microscopy combined with X-ray elemental analyses, micro-Raman and synchrotron-based X-ray fluorescence and diffraction techniques in 2D and 3D mode.

During the lecture, examples will be given of the lead and arsenic sulphide-containing pigments that Rembrandt used in The Night Watch. The use, distribution, condition, and degradation products of these pigments will be discussed on both a macro and micro scale and the implications for the ensuing conservation treatment will be outlined.

Figure 1. The Night Watch (1642) by Rembrandt van Rijn was investigated inside the glass chamber in the Gallery of Honour, Rijksmuseum, Amsterdam, The Netherlands

to be announced

Pigment-binder interactions occurring in paint layers of artworks can either contribute to the stability of paint films as well as they can cause their degradation, seriously affecting the appearance and stability of paintings. Depending on intrinsic (i.e., composition of pigments and/or binders, presence of additives etc.) or extrinsic factors (i.e., relative humidity, temperature, conservation treatment etc.), formation of metal carboxylates can fulfil both aspects. Metal carboxylates result from reactions between metal-based pigments with carboxylic acids originating from a fatty medium. In paint layers, the reactive metal pigments are represented especially by lead-based pigments (e.g., lead white, red lead, lead-tin yellows etc.) or zinc white while fatty binder usually means drying oils (e.g., linseed oil, poppy-seed oil, walnut oil etc.) or even egg yolk. [1, 2] On one hand, these pigments accelerate drying of paint layers but, on the other hand, the neo-formed crystalline phases tend to aggregate, resulting in formation of inclusions, protrusions, crusts, blisters or efflorescence. Moreover, reacting with atmospheric gases and pollutants, metal carboxylates can induce the cascade degradation, often accompanied by changes in the tonality of paint layers. Understanding the processes in paint layers is essential for the development of suitable conservation strategies which are necessary to prevent these types of degradation. Since the paintings comprise complicated multi-layered systems in which each particular layer consists of numerous inorganic and organic components, the experimental studies performed on simplified model paint systems are reasonable for identification and description of the pigment-binder interactions. Complementing vibrational spectroscopies, XRPD represents and effective tool for detection of crystalline phases, especially if unexpected product such as metal formates occur. [1] On the other hand, usually robust XRPD meets certain limits in case of metal carboxylates with undetermined crystal structure. [3] Finally, XRPD can be also beneficial for the description of metal carboxylates adopting ionomer structures. Within the contribution, the advantages and limits of XRPD for study of pigment-binder interactions in paint layers will be discussed.

Figure 1. Time-dependent XRD patterns of model paint consisting of minium and linseed oil (LO). The XRD patterns between 0 hours (0H) and 5 days (5D) were collected every 12 hours and, further on, every week. The detected phases: F – lead formate, Pb(HCOO)₂; M – minium – Pb₃O₄; S – Pb-soap/ionomer.

[1] Švarcová, S., Kočí, E., Bezdička, P., Garrappa, S., Kobera, L., Plocek, J., et al. (2020). Dalton Trans. 49, 5044.

[2] Švarcová, S., Kočí, E., Plocek, J., Zhankina, A., Hradilová, J., Bezdička, P. (2019). J. Cul. Herit. 38, 8.

[3] Kočí, E., Rohlíček, J., Kobera, L., Plocek, J., Švarcová, S., Bezdička, P. (2019). Dalton Trans. 48, 12531.

Keywords: metal carboxylates; pigment-binder interactions; paintings; XRPD

The study was supported by the Czech Academy of Sciences in the frame of the programme Strategy AV21 no. 23 - City as a Laboratory of Change; Historical Heritage and Place for Safe and Quality Life.

Upon the recovery of burnt remains in a forensic or archaeological context, bone is often fragmented and comingled, making differentiation between human and non-human samples extremely challenging and subjective. Due to thermal degradation of the organic component, biological techniques, such as DNA analysis, often render futile and so attention is drawn to the final surviving component of bone, the mineral hydroxyapatite.

Exploring the physicochemical modifications that occurs to hydroxyaptite upon heating has shown promise in differentiating between species based on characteristic changes within its crystal lattice structure, and the presence of extraneous mineral phases [1]. However, the effects soft tissue has on the heat induced changes are not fully understood, yet are of paramount importance as most bodies are intact, not skeletonised, during a burning event. This study aims to explore the effect heating has on fleshed bone, specifically investigating modifications to the nanocrystalline structure of bone mineral, and whether this has a significant impact on species differentiation.

Varying weights (5g, 7g and 10g) of muscle and fat, and one layer of skin were tested separately to understand their individual affect. A combination of the three tissue types was also considered. The samples were heated for two hours at various temperatures (200°C, 400°C, 600°C and 900°C) which are representative of those temperatures reached in historical forensic and archaeological cases. Powder X-ray diffraction (pXRD) analysis was utilised to calculate coherence length and lattice parameter values and the weight percentages of extraneous mineral phases to identify species differentiating characteristics. Coherence length, which gives an indication on crystallite size and strain, was calculated using the Scherrer equation and the full width half maximum (FWHM) peak values. Spectroscopic techniques including Fourier Transform Infrared (FTIR) and Raman spectroscopy were utilised to collaborate the XRD data and to further our understanding of the relationship between the degradation of the organic matrix and the crystallographic changes.

The purpose of this work was to uncover the real nature and composition of a dry black ink powder found in a bronze inkwell (Fig.1) of the 1st century A.D. It was discovered during the excavation of a cemetery in the locality of Morlungo, Palazzina-Capodaglio, in the municipality of Este in 1878 [1]. Since 2500 BC and up to the thirteenth century AD [2] the carbon-based inks were the most common used. They were mainly composed of amorphous carbon obtained from soot charcoal, or bone black [3,4] usually dissolved in a binder, mixed with a small amount of water. During the IV century AD, a new kind of ink, called iron-gall ink, emerged. It was obtained by mixing gall-nuts, iron or copper metal sulphates, water and Arabic gum. From the early Middle Ages onwards, it became the most common ink in the history of the western world [2]. However, some recent studies on the chemical composition of inks, already spread on their ancient writing supports (papyri, parchment or paper) [5–7], have changed this perspective. The importance and the novelty of this work resides principally in the opportunity of directly studying the ink powder, avoiding the interference from the writing support, as well as analysing its container that was fundamental for a correct interpretation of the experimental results. The investigation was conducted through a multi-technical approach, combining several and complementary synchrotron radiation (SR)-based techniques allowing us to confirm the ink nature of the sample and to distinguish its original formulation from the contaminants.

In particular, XRPD, XAS and FTIR measurements showed a substantial presence of silicates and common clay minerals in the ink along with cerussite and malachite, Pb and Cu bearing-carbonates, respectively. These evidences support the hypothesis of an important contamination of the ink by the burial environment (soil) and the presence of degradation products of the bronze inkpot. Moreover, the combined use of IR, Raman, and GC-MS evidenced that the black ink was mainly composed of amorphous carbon deriving from the combustion of organic material mixed with a natural binding agent, Arabic gum. This work also wants to underline how the intrinsic multidisciplinary approach based on SR experimental techniques represents the most efficient way to obtain a complete overview of complex materials such as archaeological artefacts.

Figure 1. a. The bronze inkwell (front view); b. internal view of the inkwell with the black powder on the bottom and top view of the lid; c. the ink black powder residue collected from the bottom of the inkwell

[1] Presdocimi, A. Guida sommaria [2] Aceto, M., Agostino, A., Fenoglio, G., Gulminie, M., Bianco, V., Pellizzi, E. (2012). Spectrochim Acta Part A Mol. Biomol. Spectrosc.91, 352.

[3] Christiansen, T., Buti, D., Dalby, K. N., Lindelof, P. E., Ryholt, K., & Vila, A. (2017). J. Archaeol. Sci. Reports 14, 208.

[4] Lucas, A. & Harris, J. R. Ancient Egyptian Materials and Industries. (1962)

[5]. Ferrer, N. & Vila, (2006). Anal. Chim. Acta 555, 161.

[6] Tack, P., Cotte, M., Bauters, S., Brun, E., Banerjee, D., Bras, W., Ferrero, C., Delattre, D., Mocella, V. & Vincze, L., (2016). Sci. Rep.6, 1.

[7] Brun, E., Cotte, M., Wright, J., Ruat, M., Tack, P., Vincze, L., Ferrero, C., Delattre, D., and Mocella, V., (2016). Proc. Natl. Acad. Sci. U. S. A. 113, 375

The in-depth understanding of properties, manufacturing process and conservation of archaeological artefacts very often requires a reliable structural characterization. Non-destructive techniques, like X-ray diffraction and different kinds of spectroscopies (Raman, IR etc.), are usually employed to the study such materials. In recent years, the scientific community has also shown a renewed interest in characterization methods based on Transmission Electron Microscope (TEM); like High Resolution Transmission Electron Microscopy (HRTEM), Electron Diffraction (ED), Energy Dispersive X-ray Spectroscopy (EDX) and Electron Energy Loss Spectroscopy (EELS); which provide structural and chemical information at nm scale using very small quantities of material. In particular, we have shown how emerging diffraction techniques like Electron Diffraction Tomography (EDT) and Phase & Orientation mapping in TEM can be applied for the study of nanocrystalline phases present in Greek amphorisks, Roman glass tesserae and several Maya pigments [1, 2].

We are now working on the structural characterisation of corrosion products from different archaeological artefacts using TEM. In most cases, due to the very small quantity of existing corrosion products, conventional diffraction methods (single crystal X-ray diffraction or powder X-ray diffraction) are not suitable for a proper structural characterization. In particular, the pale blue corrosion products that form on ancient copper alloy artefacts have been subject of research for past several years, though the exact nature of such corrosion products have not yet been determined. Here, we present an innovative study based on EDT of a blue corrosion product forming on the surface of a Chinese Bronze artefact of the Shang dynasty (British Museum Collections).

For this study, a thin electron beam-transparent lamella (8 x 10 micron) was prepared from a larger poly-crystalline sample (100 x 200 micron) using Focused Ion Beam (FIB). Subsequently, EDX data was collected by a Scanning Electron Microscope (SEM). A very high quantity of Cu was observed, together with other elements like Ca, P and O. The thin lamella was then used for EDT study using TEM. EDT data was collected by stepwise rotation of the crystal around an arbitrary axis coupled with beam precession [Fig. 1]. From the EDT data, a monoclinic unit cell (a = 23.0 Å, b = 5.4 Å, c = 10.3 Å, b = 94.1°, space group P2/c) was determined. Interestingly the obtained unit cell does not match with any of the blue corrosion products reported in literature. Using the extracted intensity from EDT data, a preliminary structure was determined, which closely resembles one of the blue mineral, nissonite.

We believe that novel structural characterisations using EDT in future may not only help in the understanding of corrosion processes in ancient artefacts, but also can contribute to their optimum conservation and eventually provide information about their provenance.

[1] Zacharias, N., Karavassili, F., Das, P. P., Nicolopoulos, S., Oikonomou, A., Galanis, A., Rauch, E., Arenal, R., Portillo, J., Roque, J., Casablanca, J. & Margiolaki, I. (2018) Microchemical Journal, 138, 19.

[2] Nicolopoulos, S., Das, P. P., Pérez, A. G., Zacharias, N., Cuapa, S. T., Alatorre, J. A. A., Mugnaioli, E., Gemmi, M. & Rauch, E. F. (2019) Scanning.