Cleaning oil paintings: NMR relaxometry and SPME to evaluate the effects of green solvents and innovative green gels

Heavy metal carboxylate or soap formation is a widespread deterioration problem affecting oil paintings and other works of art bearing oil‐based media. Lead soaps are prevalent in traditional oil paintings because lead white was the white pigment most frequently chosen by old masters for the paints and in some cases for the ground preparations, until the development of other white pigments from approximately the middle of the 18th century on, and because of the wide use of lead‐tin yellow. In the latter part of the 19th century, lead white began to be replaced by zinc white. The factors that influence soap formation have been the focus of intense study starting in the late 1990s. Since 2014, nuclear magnetic resonance (NMR) studies have contributed a unique perspective on the issue by providing chemical, structural, and dynamic information about the species involved in the process, as well as the effects of environmental conditions such as relative humidity and temperature on the kinetics of the reaction(s). In this review, we explore recent insights into soap formation gained through solid‐state NMR and single‐sided NMR techniques.

Section: Unilateral Nmr Studies Of the Effects Of Water On Lead Whimentioning

confidence: 99%

Review of the use of NMR spectroscopy to investigate structure, reactivity, and dynamics of lead soap formation in paintings

Catalano

Tullio²,

Wagner

et al. 2020

“…[23][24][25][26] The ability of NMR relaxation times to detect material properties has already been shown in several studies dealing with the stratigraphy of oil paintings, [27] as well as the effect of cleaning solvent on the state of the binder layer. [28] Recently, the potential of unilateral NMR for real-time monitoring the change in binder-material properties [29] and the diffusion of cleaning agents into paint layers [30] were discussed.…”

Section: Introductionmentioning

confidence: 99%

“…[28] By monitoring the effects of solvents in a small region of the painting or in mock-up samples of a binder-varnish system, NMR can identify suitable solvents with minimal impact on the binder-material properties. [29] The noninvasive NMR technique can thus help to understand the impact of aging or cleaning procedures and to optimize conservation treatments, thus aiding the preservation of artworks.…”

Section: Introductionmentioning

confidence: 99%

NMR relaxometry of oil paint binders

Busse

Rehorn

Küppers

et al. 2020

Self Cite

Mobile nuclear magnetic resonance (NMR) is a flexible technique for nondestructive characterization of water in plants, the physical properties of polymers, moisture in porous walls, or the binder in paintings by relaxation measurements. NMR relaxation data report material properties and therefore can also help to characterize the state of tangible cultural heritage. In this work, we discuss the relaxation behavior in two series of naturally aged paint mock‐up samples. First, paints with different pigment concentrations were prepared and investigated in terms of the longitudinal and transverse relaxation‐time distributions. We document the evolution of both relaxation‐time distributions during the initial drying stage and demonstrate the heightened importance of transverse over longitudinal relaxation measurements. Second, we observe nonlinear dependences of the relaxation times on the pigment concentration in a typical oil binder. Third, in a study of naturally aged paint samples prepared in the years between 1914 and 1951 and subsequently aged under controlled conditions, we explore the possibility of determining the age of paintings using partial least square regression (PLS) by fitting T1–T2 data with the sample age. Our results suggest some correlation, albeit with significant scatter. Estimating the age of a painting stored under unknown conditions from NMR relaxation data is therefore not feasible, as the cumulative effects of light irradiation, humidity, and biological degradation further obfuscate the chemical and physical impact of aging on the relaxation times in addition to the impact of pigment concentration.

“…[24] A single-side sensor has been applied to evaluate cleaning methods. [25,26] Not only stones but also paper, [27] wood, [28] bones, [29,30] and parchments [31] can be analyzed.…”

Section: Introductionmentioning

confidence: 99%

Identification of complex structures of paintings on canvas by NMR: Correlation between NMR profile and stratigraphy

Brizi

Bortolotti

Marmotti³

et al. 2020

Paintings on canvas are complex structures created by superimposing layers of different composition. Investigations on the structure of these artworks can provide essential information on their state of conservation, pictorial technique, possible overpaintings, and in planning a proper conservation plan. Standard methods of investigation consist in sampling a limited number of fragments for stratigraphic analyses. Despite the recognized validity of these methods, they are affected by evident limitations. Nuclear magnetic resonance (NMR) profiling, often named NMR stratigraphy, is an NMR relaxometry technique applied by single‐sided portable devices developed to overcome the disadvantages of microinvasive stratigraphic analyses. The potential of this approach on artworks, including wall paintings and a few examples of painted canvas, is described in the literature. In this study, NMR profiles of painting on canvas were examined by analyzing transverse relaxation time data by T2 quasi‐continuous distributions and the results compared with standard stratigraphic cross‐sections analysis. Combining signal intensity and T2 quasi‐continuous distributions, the identification of textile, preparatory, and paint layers was enhanced. The diction “NMR stratigraphy” for these inhomogeneous layered artworks is also discussed. Indeed, unlike the stratigraphic cross‐sections, NMR profiles provide information on a volume (flat slice), rather than on a surface, and the collected signal can derive from nonuniform and partially overlapping layers. This study paves the way for extensive investigations on relaxation time quasi‐continuous distributions in various binder/pigment mixtures in order to improve the reliability of NMR profile as an innovative, non–invasive, and nondestructive method for analyzing paintings on canvas.