Characterization of aging and solvent treatments of painted surfaces using single‐sided NMR

Abstract

Typical experiments conducted with single-sided NMR are incapable of unique chemical identification and, thus, often rely on comparative measurements in scientific study. However, cultural heritage objects have unique natures and histories, making a genuine 'control' sample a rarity and complicating many scientific investigations. In this paper, we present some comparative results enabled by such a rare, control sample. Two paintings, The Dinner and The Dance from the 1616 set Pipenpoyse Wedding, were made by the same artist with indistinguishable materials and techniques. However, despite their shared history, The Dinner has undergone varnishing and subsequent varnish removal multiple times, whereas The Dance has not. NMR measurements on these two paintings show the effect of organic-solvent-based treatments on the stiffness of the paintings as measured by T(2,eff), supporting visual and tactile observations that The Dinner is stiffer throughout its thickness than The Dance, probably due to ingress of natural resins and organic solvents into the paint and ground layers. In addition to a comparative analysis of these two paintings, initial experiments to compare solvent penetration with different varnish removal methods are described. Model canvas painting samples were treated with solvent in two ways--with free solvent on a swab and with cellulose gel thickened solvent in a tissue. Both treatment methods cause a measurable change in T(2,eff) ; however, the thickened-solvent method affects a narrower region of the model than does the free solvent.

Mobile NMR: An essential tool for protecting our cultural heritage

“…The NMR‐MOUSE proved to be a useful tool for the comparative analysis of materials and techniques used in paintings. Thus, when studying two paintings, The Dinner and The Dance , from the Pipenpoyse Wedding series made by the same artist with the same materials and methods, Fife et al observed differences in the transverse relaxation times between the painted treated by a conservator ( The Dinner ) and the untreated painting ( The Dance ) . This exemplifies the feasibility of this method to be applied for comparative analysis of paintings, opening the possibility of using this method to examine differences between authentic and forged paintings, where a comparative analysis could reveal differences in the techniques and materials used by the painter and by the forger.…”

Cultural Heritage Studies with Mobile NMR

“…[60] This effect was reliably observed in two paintings from 1616 by the same artist, one in its original state,the other one having been cleaned with solvents at least twice (Figure 6). [35] Theo pposite effect is observed when repairing an object with an elastic consolidant, or when employing stone strengthener to repair weathered stone. [24,62] Moreover,h ydrophobic substances are employed to reduce capillary water uptake while keeping the pore network intact so that the stone can still transport water vapor.…”

Aging of polymeric materials by stray‐field NMR relaxometry with the NMR‐MOUSE

“…B, Accelerated light aging (top) and natural aging over hundreds of years of tempera paint . C, “The Dinner” and “The Dance” painted in 1616 (top) and T 2 depth profiles through the paint layers suggesting differences between natural aging and aging by solvent cleaning…”

“…The NMR‐MOUSE, in fact, is a highly suitable tool to follow the solvent ingress and drying in paint and polymer layers (S Prati, G Sciutto, F Volpi, C Rehorn, R Vurro, B Blümich, L Mazzocchetti, L Giorgini, C Samorì, P Galletti, E Tagliavini, R Mazzeo, under review). With each solvent exposure, not only varnish is removed, but low molecular weight compounds are also washed out from the paint layer as suggested by a comparative study of two paintings from 1616, one in its original state and the other having been restored by solvent cleaning (Figure C) . While the paint layer in its original state shows a T 2 gradient across its width with low values near the surface and higher ones deeper down, the paint layer from the restored painting shows the low T 2 value across its entire width.…”

“…With each solvent exposure, not only varnish is removed, but low molecular weight compounds are also washed out from the paint layer as suggested by a comparative study of two paintings from 1616, one in its original state and the other having been restored by solvent cleaning (Figure 2C). 30 While the paint layer in its original state shows a T 2 gradient across its width with low values near the surface and higher ones deeper down, the paint layer from the restored painting shows the low T 2 value across its entire width. This observation is in accordance with the explanation that low molecular weight compounds have evaporated from the unrestored painting surface over the painting's lifetime of four centuries similar to the loss of plasticizer in PVC, and that solvent exposure during cleaning of the other painting has enabled that loss also at higher depths reminiscent of wax leaching from polyethylene during solvent exposure.…”