Nati Salvadó

The formation of lead apatites in heritage objects is increasingly recognized as a recurrent phenomenon, however their origins and formation mechanisms remain poorly understood. This study explores the process behind the darkening and surface clouding in Roman fresco paintings, providing novel insights into the formation of lead-calcium phosphates, Pb_xCa_(5−x)(PO₄)₃Cl_y(OH)_(1−y), and plattnerite, β-PbO₂, from the pigment minium, Pb₃O₄, linked to interactions with environmental factors and dust deposition. A combination of microanalytical techniques was used, including optical microscopy, scanning electron microscopy and elemental analysis, synchrotron-based X-ray diffraction and Raman and FTIR spectroscopy. The results show that slightly acidic rainwater or atmospheric moisture reacts with the minium and the calcium carbonate present in the wall painting’s binder, resulting in the formation of plattnerite and the release of Pb²⁺ and Ca²⁺ ions, while the environment supplies chloride and phosphate ions, present in the infiltrating water. This process culminates in the precipitation of the lead-calcium apatite, due to its high stability. This apatite acts as a cement that incorporates dust and organic residues, forming a layer several tens of micrometres thick that tends to expand outwards. These findings contribute to a better understanding of pigment degradation mechanisms and will help inform conservation strategies.

El procés de carbonatació en una pintura al fresc segueix els mateixos processos que en els sistemes biogènics. S’inicia amb la formació de carbonat de calci amorf hidratat, CaCO3·nH2O, que s’estabilitza a la superfície de les pintures, tant en morters calcítics com dolomítics, i a l’interior es transforma en calcita, o calcita i aragonita quan el morter és dolomític. En els morters dolomítics, l’hidròxid de magnesi no reacciona amb el CO2 mentre quedi hidròxid de calci per carbonatar, esdevenint, per tant, morters més reactius a llarg termini

The European Synchrotron Radiation Facility (ESRF) has recently commissioned the new Extremely Brilliant Source (EBS). The gain in brightness as well as the continuous development of beamline instruments boosts the beamline performances, in particular in terms of accelerated data acquisition. This has motivated the development of new access modes as an alternative to standard proposals for access to beamtime, in particular via the “block allocation group” (BAG) mode. Here, we present the recently implemented “historical materials BAG”: a community proposal giving to 10 European institutes the opportunity for guaranteed beamtime at two X-ray powder diffraction (XRPD) beamlines—ID13, for 2D high lateral resolution XRPD mapping, and ID22 for high angular resolution XRPD bulk analyses—with a particular focus on applications to cultural heritage. The capabilities offered by these instruments, the specific hardware and software developments to facilitate and speed-up data acquisition and data processing are detailed, and the first results from this new access are illustrated with recent applications to pigments, paintings, ceramics and wood.

A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro–X-ray fluorescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe₂O₃) by micro–X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, micro-XRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused “coffee rings” surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb₃O₄) and lead white (hydrocerussite [Pb₃(CO₃)₂(OH)₂] and/or cerussite [PbCO₃]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments. Significance Ink, invented in ancient Egypt circa 5,000 y ago, is the established and time-honored medium wherewith humankind commits words to writing. A comprehensive synchrotron-based microanalysis of a considerable corpus of ancient Egyptian papyri from the Roman period, inscribed with red and black inks, reveal a hitherto undetected complex composition of inks. Highlighted by the presence of iron, the red color can be attributed to the use of ocher. Unexpectedly, lead is regularly present in both the red and black inks and is associated to phosphate, sulfate, chloride, and carboxylate ions. The analysis shows that lead was probably used as a drier rather than as a pigment, similar to its usage in 15th century Europe during the development of oil paintings.

Lustering, a technique which involved the application of coloured translucent glazes over gilding and silvering was widely used to enrich and decorate altarpieces in the Baroque period. The decorations consist of a micrometric multilayered structure including several color glazes, metallic leaves and bole applied over a plaster ground. The collection of Baroque altarpieces, the oldest dating 1671 and the newest 1775 from the cathedral of Tortosa (Catalonia), is a perfect case of study of the materials used and the techniques employed throughout the period. Further information is obtained from the analysis of the reaction and aging compounds resulting from the interaction among the compounds present in the layers and between the different layers. A combination of sensitive analytical techniques, Synchrotron based μ-XRD and μ-IR and SEM-EDS which enabled the luster samples to undergo analysis without altering their original layered microstructure were selected. The nature of the compounds used to produce the yellow, green, red and blue glazes (pigments, pigment lakes and resins), metallic leaves and boles is presented. Relevant information from historical and conservation viewpoints about the origin and nature of the materials used, the making of the lusters and their reactivity and aging are also discussed.

The resin extracted from the species of the Pinus genus (Pinaceae family) is a widely used material. Primarily, resins are made up of two types of diterpenoids: abietanes and pimaranes. Their composition changes with aging, affecting their chemical and physical properties; however, the chemical changes that occur during aging are not yet fully known. Understanding the evolution of pimaranes and abietanes and the chemical composition of the aged resins is essential to make the most of this substance and of its derivatives. A systematic study of the aging of Pinus resin with Raman complemented with infrared (IR) spectroscopy was carried out. This study provided new information about the interactions among the constituting molecules in resins aged over many years. In particular the formation of intermolecular hydrogen bonds in aged samples was detected for the first time, and the formation of acid anhydrides from the reaction between pimaranes was demonstrated. Furthermore, Raman and IR spectra band assignments are proposed, and the specific markers of the main compounds of the resin are tagged. This will facilitate the qualitative analysis of resin compounds.

Resins obtained from Pinus genus species have been widely used in very different fields throughout history. As soon as the resins are secreted, molecular changes start altering their chemical, mechanical and optical properties. The ageing processes are complex, and the chemical and structural changes associated with resin degradation are not yet fully known. Many questions still remain open, for instance changes happening in pimaranes, one of the two diterpenoid constituents of the resin. A systematic study of the ageing process of Pinus resins is done through Fourier transform infrared spectroscopy (FTIR) using chemical standards and complementing the obtained results with gas chromatography coupled to mass spectrometry (GC/MS) analysis when necessary. Moreover, long-term degradation processes are also investigated through the analysis of a selection of dated historical resins. This study overcomes the limitations of GC/MS and brings new information about the reactions and interactions between molecules during Pinus resin ageing processes. It also provides information about which bonds are affected and unaffected, and these can be used as specific markers of the degradation and of the resins themselves. Changes in the IR spectral features due to the Pinus resin ageing processes

Micro-Infrared Spectroscopy (μSR-FTIR) and X-ray diffraction (μSR-XRD) with synchrotron light, Gas Chromatography/Mass Spectrometry (CG/MS), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM/EDS) were used to obtain the distribution of calcium salts of low molecular weight organic acids (LMWOA) in micro-layered micro-samples.