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[Display omitted] • Natural malachite and azurite contain many impurities. • Different solid phases are present in the pigments, and change when mixed with binders. • The binders form complexes with the pigments. Degradation processes of paintings, frescos, illuminations, and painted decorations represent a relevant challenge in the cultural heritage field for both conservators and scientists dealing with the causes of these processes. It is very important understanding the molecular origin of colour changes, like fading, yellowing, blackening, as well as the molecular origin of damages due to degradation, like cracking and fall of pictorial layers. Metal complexes, often indicated as "metal soaps", when referred to metal carboxylates, play a relevant role in degradation. However, their identification is not easy, and the involvement of the metal ions in the degradation mechanisms is often not clear. Continuous Wave Electron Paramagnetic Resonance (CW-EPR) spectroscopy is a very sensitive tool towards paramagnetic species (e.g., transition metal ions like Fe(III), Cu(II), Mn(II), radicals, etc.), providing relevant information on these species, not always well-characterized with other methods. In this paper, we use CW-EPR to study the formation of Cu(II)-binder complexes in natural malachite and azurite pigments mixed with several organic binders. We show that CW-EPR technique is able to detect easily Cu(II) complexes with organic ligands, and can additionally provide information on the pigments themselves. In particular, the first coordination sphere of the Cu(II) complexes is characterized by applying the Peisach-Blumberg method. Moreover, CW-EPR shows that binders can affect the structure of the raw pigments. [ABSTRACT FROM AUTHOR]

In this paper we present a new analytical GC/MS method for the analysis of mixtures of free fatty acids and metal soaps in paint samples. This approach is based on the use of two different silylating agents: N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). Our experimentation demonstrated that HMDS does not silylate fatty acid carboxylates, so it can be used for the selective derivatization and GC/MS quantitative analysis of free fatty acids. On the other hand BSTFA is able to silylate both free fatty acids and fatty acids carboxylates. The reaction conditions for the derivatization of carboxylates with BSTFA were thus optimized with a full factorial 3 2 experimental design using lead stearate and lead palmitate as model systems. The analytical method was validated following the ICH guidelines. The method allows the qualitative and quantitative analysis of fatty acid carboxylates of sodium, calcium, magnesium, aluminium, manganese, cobalt, copper, zinc, cadmium, and lead and of lead azelate. In order to exploit the performances of the new analytical method, samples collected from two reference paint layers, from a gilded 16th century marble sculpture, and from a paint tube belonging to the atelier of Edvard Munch, used in the last period of his life (1916–1944), were characterized. [ABSTRACT FROM AUTHOR]

Abstract: Zinc soaps of rubber seed oil (RSO) and epoxidised rubber seed oil (ERSO) were prepared and their use as PVC stabilizers investigated. Characterization of Zn soaps of RSO prepared by different techniques and ERSO gave information on the purity, structure and thermal behaviour of these materials. From the analysis, the production of these materials for use in thermal stabilization of PVC would be optimized as their use greatly enhanced the stability of PVC as obtained from the conductivity measurements using the 763 PVC Thermomat. The minimum amount of HCl release was obtained for the samples with Zn soaps and ERSO indicating a synergistic effect. Zn soaps having Zn(OH)2 stabilized PVC better than pure Zn soaps. [Copyright &y& Elsevier]

Thermal degradation studies of poly(vinyl chloride) in the presence of epoxidised Khaya seed oil and metal soaps (barium, cadmium, lead and zinc) of the oil under oxidative conditions were carried out at 190 °C. Changes in average molecular weight of the number polymer, chain scission per polymer molecule, obtained from intrinsic viscosity measurements in cyclohexanone solution and levels of unsaturation in degraded polymer samples were used to evaluate the effect of epoxidised Khaya seed oil and its metal soaps on the susceptibility of poly(vinyl chloride) to thermal degradation. It was found that the metal soaps of epoxidised Khaya seed oil reduced the level of unsaturation in the degraded polymer sample and the extent of the polymer chain scission, which accompanied dehydrochlorination. The stabilising effect of barium and cadmium soaps of the seed oil was also indicated from thermogravimetric and IR spectrophotometric studies. [Copyright &y& Elsevier]

● Green pigments and binding media in three late medieval painted wings from Norwegian churches were investigated. ● Paint presents lack of adhesion and delamination in many areas. ● GC-MS derivatization methodology applied for the detection of metal soaps in paint samples. Green pigments in micro-samples taken from three late-medieval painted objects from Norwegian churches have been investigated with the aim to characterize their constituents and understand how they relate to damages observed in passages containing green paints. The cross-sections were analyzed by optical microscopy under visible and UV light, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectrometry and vibrational spectroscopies (Raman, ATR-FTIR). In addition, Gas Chromatography coupled with Mass Spectrometry was employed for the characterization of binding media, using a derivatization methodology recently developed for the detection of metal soaps in paint samples. This extensive characterization aided the identification of the individual constituents and the stratigraphy of green paints. It also builds the foundation for future ageing studies that can provide better insights into the mechanisms of the processes at stake in selective delamination of paints containing copper complexes. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Metal soaps pose significant concerns in the preservation of paintings made with oil as a binding medium. In highly alkaline environments, metal soap aggregates may undergo mineralization processes with the formation of new phases, such as carbonates, chlorides, oxides and sulfates of the metal cations that are present in pigments or paint additives. In this work, we report new examples of the mineralization of lead soaps in paint-cross sections taken from a late-medieval panel painting owned by the Museum of Cultural History at the University of Oslo. Scientific analyses were carried out with optical microscopy under UV and visible light, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and Raman spectroscopy to investigate and characterize the nature of the compounds present in the samples. Lead (II,IV) oxide, which is presumed to be a secondary product in the mineralization of lead soaps, has been identified in lead-based paint. Unlabelled Image • Mineralized lead soaps were identified and investigated in paint samples from a late medieval panel painting. • Identification of secondary products in lead soaps. • Discrimination of new products and degradation products in the paint film. [ABSTRACT FROM AUTHOR]