- Publikační typ
- tisková chyba MeSH
Many issues in the conservation of paintings from the early modern period are still unresolved due to lack of information on paints from the late 19th and early 20th centuries, in particular their production, formulations, and later degradation processes. The inconsistency of the names that paint manufacturers chose for their products furthermore compounds the challenges faced by conservators and chemists wishing to study them. This paper addresses a number of these issues through investigations of commercial tube oil paints from a paint box owned by the Norwegian painter Harriet Backer (1845-1932). Samples were analyzed using a multi-instrumental approach. Micro-attenuated total reflection Fourier transform infrared spectroscopy and micro-Raman spectroscopy - supported by micro-X-ray powder diffraction - allowed the identification of binders, pigments, and extenders. The data highlight the use of materials that were new at the time and not reported in the manufacturer's catalog. Furthermore, zinc stearate has been detected for the first time. Its detection and the absence of any zinc-based pigments confirms that zinc stearate was already used as dispersing agent in paint formulations at that time.
- Klíčová slova
- Metal carboxylates, Micro-ATR-FTIR, Micro-Raman, Micro-XRPD, Pigments, Zinc stearate,
- MeSH
- difrakce rentgenového záření MeSH
- malířství * dějiny MeSH
- nátěrové hmoty * dějiny MeSH
- Ramanova spektroskopie metody MeSH
- spektroskopie infračervená s Fourierovou transformací MeSH
- Publikační typ
- časopisecké články MeSH
The lack of an appropriate methodology makes numerous important issues related to miniature paintings unresolved-despite the fact that the portrait miniatures of the seventeenth to the nineteenth century represent a highly specific and significant field of European fine art. One of these issues is represented by chemical degradation of miniatures and its analytical evidence. Fragility, variability of the employed materials, and detailed execution make their analysis highly challenging-since no sampling is usually allowed and any change on their surface is immediately noticeable. Therefore, this study focused on finding a fully non-invasive multi-analytical approach to describe degradation processes resulting from the interaction of lead pigments and oils. For this purpose, a representative set of miniature portraits on various supports (ivory, metal, glass) has been selected. For the first time, Pb carboxylates (lead soaps) have been evidenced in miniatures painted in oil and also in a combined technique (gum + oil). Their distribution and crystallinity was described by a combination of X-ray-based (X-ray fluorescence and X-ray diffraction) and micro-spectroscopic methods. At the same time, a number of new findings about the employed painting technique and involvement of various pigments in the degradation processes were obtained. For example, a possible saponification of a mixed Pb-Sn-Sb yellow was indicated for the first time. Although the degradation is clearly at an advanced stage, it has not shown yet any visible symptoms that might warn restorers and curators. Therefore, without targeted analysis, it would remain overlooked.
- Klíčová slova
- Metal soaps, Miniature paintings, Non-invasive analysis, Spectroscopy, X-ray diffraction, X-ray fluorescence,
- Publikační typ
- časopisecké články MeSH
Lead carboxylates are an extensive group of compounds studied for their promising industrial applications and for their risky behavior when they are formed in oil paintings as corrosion products of lead-based pigments, leading to serious deterioration of paintings. Although the processes leading to the formation of aggregates, protrusions or inclusions, affecting undesirably the appearance of paintings, are assumed to be long term, neo-formed lead carboxylates are detectable in the early stage of paint drying. To uncover the chemical changes in lead pigments during the drying of oil paint films, model systems consisting of minium (Pb3O4) and four common drying oils were studied by X-ray powder diffraction (XRPD), 13C and 207Pb solid state NMR (ssNMR) spectroscopy and Fourier-transformed infrared spectroscopy (FTIR). For the first time, a degradation mechanism of Pb3O4via the crystallization of lead formate (Pb(HCOO)2), at the end of oxidative polymerization of oil paint films, was uncovered. The formation of formic acid in oils was proved by gas chromatography-mass spectrometry (GC-MS). Vapor experiments evidenced the susceptibility of Pb3O4 to react with volatile formic acid released during the autoxidation of oils comparably to the direct pigment-binder interactions in paint films. The investigation of the local environment of lead atoms in the paint film by 207Pb WURST-CPMG NMR spectroscopy showed that Pb(ii) atoms reacted with linseed oil preferentially to form highly crystalline Pb(HCOO)2, while the local chemical environment of Pb(iv) atoms did not change. The results proved the co-existence of (i) highly crystalline Pb(HCOO)2, (ii) a highly mobile amorphous phase corresponding to free carboxylic acids or a nascent lead soap phase and (iii) the remaining Pb3O4 in the polymeric/ionomeric network. Pb(HCOO)2 is assumed to be an intermediate for the conversion of Pb3O4 to lead soaps and/or lead carbonates.
- Publikační typ
- časopisecké články MeSH
