Laurence de Viguerie

Understanding radical processes in drying oils is essential for both heritage science and materials chemistry, as these reactions govern film formation and long-term stability in historical paintings. In this study, we investigate radical mechanisms in linseed oil, a traditional paint binder. Gold salts are used as probes to elucidate film-drying reactions. The introduction of gold salts into both raw and lead-treated linseed oils leads to the formation of gold nanoparticles, whose size, morphology, and distribution are monitored by spectroscopic methods and transmission electron microscopy (TEM). Under ambient conditions, spherical gold nanoparticles form during the drying of both oil types. Electron paramagnetic resonance (EPR) reveals oxygen-centered radicals (peroxyl (ROO^●) or alkoxyl (RO^●) radicals) involved in the oil-curing process. The addition of lead, following historical oil preparation recipes, increases radical activity and promotes the formation of additional species, suggesting more complex reaction pathways. In lead-treated oils, 3–4 nm lead-based nanoparticles are observed both in the oil bulk and in dried films, formed during the oil preparation.

The drying of egg yolk tempera paint in the dark has been investigated from 24 h up to 2 years by nuclear magnetic resonance (NMR) relaxometry and spectroscopy. Variations around a reference recipe have been carried out to investigate several aspects: the amount of added water to the binder, the nature of the minerals or the pigments and the drying time. The ¹ H signal measured here corresponds to the ¹ H contained in the fatty acids of the egg yolk (EY). The NMR dispersion (NMRD) profile increases when the added water in the preparation of the tempera is above 50 wt% linked to a destructuration of egg yolk high‐ and low‐density lipoproteins (HDL and LDL). In addition to the chemical nature of the minerals, the shape and the surface area also play an important role in the destructuration of egg yolk HDL and LDL. The most striking result is the discontinuous evolution of the NMRD with time with the appearance of a step around 1 or 2 months. Depending on the water content in the initial tempera, a steep change in is observed while before and after only a weak evolution occurs.

Renaissance Masters often prepared siccative oils by heating linseed oil with siccatives, particularly lead oxide, inducing partial saponification and altering its properties. Our reconstructions show that lead-saponified oils naturally separate into two phases. In this study, we investigate the differences between these two phases through a comprehensive set of analytical methods, from macrolevel assessments (rheology) to microlevel characterizations (small and wide-angle x-ray scattering, optical microscopy, and scanning electron microscopy) and chemical analyses. The lower phase is enriched in free fatty acids and lead carboxylates, especially saturated species—both as free acids and metal soaps—prone to self-organization. As a result, the lower phase displays a pronounced lamellar organization with partial crystallization and exhibits viscoelastic and shear-thinning properties. In contrast, the unstructured upper phase behaves as a Newtonian fluid. The observed phenomena share similarities with the formation of soap-related defects such as protrusions, linked to saturated lead soaps.

Tiebas Castle, located near Pamplona (Northern Spain), was constructed in the thirteenth century under the reign of Theobald II of Navarre. Among its most distinctive decorative elements were slip-decorated carreaux de pavement—dichromatic paving tiles that adorned multiple rooms within the Castle. These tiles bear strong stylistic and technological similarities to those found at various archaeological sites in the former county of Champagne (Northeastern France), indicating a connection between the two regions in terms of production techniques and artistic influences. To better understand their provenance and the artistic practices involved in their manufacture, we conducted a comprehensive analysis of the three primary raw materials: the red clay used for the ceramic body, the kaolin for the slip decoration, and the lead employed in the glaze. Comparative reference samples from both Champagne and Navarre were examined using a multi-analytical approach, including X-ray fluorescence (XRF), X-ray diffraction (XRD), and high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Our results revealed that the ceramic bodies from both regions were composed of decalcified clay, rich in quartz and haematite but low in calcite. However, significant geochemical differences emerged: the ceramic body of the Tiebas tiles closely matched local Navarre clay, with a notably lower zirconium content compared to Champagne samples, where zirconium levels were consistently higher. This strongly suggested that, while the production took place in Navarre, it was likely carried out by artisans from Champagne. Additionally, the kaolin used for the slip did not correspond to any known local Navarre sources, indicating it was imported. Its composition closely matched kaolin deposits from Champagne, further supporting the idea of material exchange between the two regions. Finally, this study also sheds new light on the provenance of the lead used in the glazes, offering fresh insights into medieval ceramic production networks.

By tuning emulsion structure, artists could control paint texture and flow without altering pigment load. Rheology and microscopy reveal how dispersed phase composition impacts impasto and spreadability.

Diluting egg yolk with water modifies the interaction between the lipoproteins and affects the water accessibility to iron.

Since antiquity, artists have been using egg yolk as an additive in the preparation of \textit{tempera} paints. Mixture of egg yolk and water is the dispersing medium for pigments to start with, but once on the canvas, it acts as a binder and plasticiser, procuring adhesive properties to the applied paint. A series of water/egg yolk mixtures is investigated here using a combination of rheology, Fourier Transform Infrared (FTIR) spectroscopy, Nuclear Magnetic Resonance spectroscopy (NMR) and small angle X-ray scattering (SAXS). The effects of water dilution on the organisation of the main egg yolk components, plasma and granules, is explored. The results show that added water affects the tertiary/quaternary protein structure leading to a destabilization of the lipoprotein dispersion.

Drying oils such as linseed oil form a polymer network through a complex free-radical polymerization process. We have studied polymerization in this challenging class of polymers using a quartz crystal microbalance (QCM). The QCM is able to measure the evolution of polymer mass and mechanical properties as the oil transitions from a liquid-like to a solid-like state. Measurements using bulk materials and thin films provide information about the initial polymerization phase as well as the evolution of the mass and mechanical properties over the first two years of cure. The temperature-dependent response of the cured linseed oil films was also measured. These results were combined with previously published results obtained from traditional dynamic mechanical analysis to give a unified picture of the properties of these materials across a very broad temperature range.

The supramolecular and mesoscopic architectures of lead-saponified linseed oil, used by painters since the Renaissance, have been characterised and linked to their rheological properties. The multi-scale organization of saponified oils has been demonstrated by SAXS (Small Angle X-ray Scattering), FF-TEM (Freeze-Fracture Transmission Electron Microscopy) and DIC (Differential Interference Contrast): some of the lead soaps (formed when the oil is heated in the presence of PbO) are organized into microscopic lamellar domains, distributed in a continuous matrix made up of unorganized species (partially saponified triglycerides, glycerol, remaining soaps, etc.). The concentration of lead soaps in the oil controls the average size and interaction between the lamellar domains. Linseed oil + PbO 17 mol% is viscous and consists of aggregates of lamellar domains isolated within the continuous unorganized matrix. In contrast, in linseed oil + PbO 50 mol%, the domains are homogeneously dispersed and form what can be described as a three-dimensional network, giving the system viscoelastic properties.

Varnish layers are optical coatings that act as physico‐chemical barrier between the historical paint layers and the environment. Understanding how varnish materials protect historical paintings over time and in the presence of humidity or organic vapors is of central importance for art preservation. However, probing the behavior of varnish after aging in real conditions remains a challenge. Here the question is addressed by “reshaping” the varnish material from the masterpiece of G. Bellini, the “Transfiguration”, into an optical layer; coupling in situ Ultraviolet‐Visible (UV–vis) and Infrared (IR) ellipsometries, the chemical state is correlated, optical properties and swelling of the varnish in presence of water and organic vapors. It shows that the varnish material aged since the 1950s still exhibits effective water repellence. The methodology may be applied to other relevant historical systems beyond paintings and may help in establishing more efficient preservation strategies for historical artworks.