Nano- to microscale three-dimensional morphology relevant to transport properties in reactive porous composite paint films

Abstract

The quantitative evaluation of the three-dimensional (3D) morphology of porous composite materials is important for understanding mass transport phenomena, which further impact their functionalities and durability. Reactive porous paint materials are composites in nature and widely used in arts and technological applications. In artistic oil paintings, ambient moisture and water and organic solvents used in conservation treatments are known to trigger multiple physical and chemical degradation processes; however, there is no complete physical model that can quantitatively describe their transport in the paint films. In the present study, model oil paints with lead white (2PbCO3·Pb(OH)2) and zinc white (ZnO) pigments, which are frequently found in artistic oil paintings and are associated with the widespread heavy metal soap deterioration, were studied using synchrotron X-ray nano-tomography and unilateral nuclear magnetic resonance. This study aims to establish a relationship among the paints’ compositions, the 3D morphological properties and degradation. This connection is crucial for establishing reliable models that can predict transport properties of solvents used in conservation treatments and of species involved in deterioration reactions, such as soap formation.

A Critical Review on the Analysis of Metal Soaps in Oil Paintings

“…In fact, the characterization of model paint samples prepared under controlled conditions with varying paint compositions (including different pigments, pigment‐to‐oil ratios and additives) allows the controlled study of the effect of paint ingredients on metal soap formation. [ 35 , 49 , 51 , 55 , 58 , 63 , 64 , 65 ]…”

“…Other FTIR applications for the study of metal soaps involve the use of synchrotron light in combination with micro‐FTIR spectroscopy (μSR‐FTIR)[ 33 , 105 ] and micro‐FTIR spectroscopy combined with X‐ray micro‐tomography and photothermal induced resonance. [ 65 , 106 ] Romano and co‐workers performed multivariate analysis on micro‐FTIR data from cross‐sections characterised by zinc soaps formation. They were able to detect a zinc carboxylate gradient in the cross‐sectional view of the gel material, where the edges were rich in zinc carboxylates, and the centre contained quantities of unreacted linseed oil.…”

“…Results obtained from model samples are fundamental for interpreting complex issues related to the mechanisms of soap formation and migration. In fact, the characterization of model paint samples prepared under controlled conditions with varying paint compositions (including different pigments, pigment‐to‐oil ratios and additives) allows the controlled study of the effect of paint ingredients on metal soap formation [35,49,51,55,58,63–65] …”

After the paint has dried: a review of testing techniques for studying the mechanical properties of artists’ paint

“…The use of these spectroscopic techniques becomes difficult on dried historic paints where the pigment, binder, or both are not stable over long periods of time, since the particular chemical peaks tracked in this study can change quite a bit over longer periods of time. Some more recent work has used X-ray micro-or nano-tomography to determine the pigment to binder ratio for the full volume of a paint sample [14].…”

“…Single-sided NMR has been employed to look at both PVC and the effects of solvent on painting materials. Model systems of traditional oil paints, water-miscible oil paints, and acrylic paints with varying PVC values were studied to determine if the comparative results could be quantified as a function of increasing PVC [14,[129][130][131][132]. One of these studies looked to extend their findings with young model systems to see if they could develop a protocol for determining the age of paint materials based on the response of the relaxations times, which was unfortunately inconclusive [131].…”