*3.6. Paint Binder*

Obtaining a sample of the original paint layer from *Man-Eater* proved difficult considering the many layers of overpaint. In all samples, the presence of both pigments and fillers obscured most peaks in the fingerprint region of the μ-FTIR spectrum, generally in the mid-IR from 1800 to 500 cm−<sup>1</sup> [48]. Diagnostic C–O and C–C skeletal vibrations in the fingerprint region were obscured by the broad peaks of pigments such as ultramarine (1096 cm−1) and

chrome yellow (851 and 819 cm−1) and fillers such as calcium sulfate (1620, 1425 (sh), 1148 (sh), 1120, 670 cm<sup>−</sup>1), calcium carbonate (1803, 1447, 1411, 879 cm−1), and barium sulfate (1186, 1124, 1074, 982 cm−1). All pigments and fillers seen in Raman analysis of the cross sections were confirmed by μ-FTIR but assigning them to a respective stratigraphy is not possible. However, samples from different representative areas were analyzed by transmission μ-FTIR in hopes of identifying any binding media from the now brittle paint.

A carbonyl (C=O) stretching band at 1734 cm−<sup>1</sup> was detected in all μ-FTIR spectra from *Man-Eater*, with intensities varying from medium to very weak, exemplified here by a spectrum of a sample taken from the edge of the blue pennant (Figure 11). Detected across all spectra were C–H stretches at 2956 (sh), 2927, and 2855 cm−1. Blue was also identified in this sample by peaks at 2098 [ν(CN)] and 1415 cm−1, in addition to calcium sulfate (1620, 1425 (sh) 1148 (sh), 1120, 670 cm<sup>−</sup>1). An unidentified peak at 794 cm−<sup>1</sup> could belong to a silicate, perhaps quartz, considering the presence of silicon in the EDS mapping. This composition matches the Raman composition of the first paint layer in the blue cross sections, with only Prussian blue. While it is difficult to make a conclusive assessment without more chromatographic techniques, the identified bands in these spectra point towards an alkyd resin paint [49]. Alkyd paints were manufactured for commercial use, such as household or industrial paints, and only Winsor & Newton continues to have a line of artist-grade alkyd paints [49,50]. Calder's preference for these matte paints, especially those manufactured by Ronan, is well documented [8,9,14,39]. Most often, alkyd paints are polyester resin-based, made from combining polyhydric alcohol with a polybasic acid, to which monobasic drying oils are added, lending elasticity to an otherwise hard resin film. Here, the C=O band points to the polyester resin, as the fingerprint region is not particularly diagnostic for the drying oil; furthermore, oil C=O peaks are comparatively lower in absorption [49]. Conversely, the C–H bands probably belong to the drying oil component in alkyd paints, which can vary in concentration depending on the desired finish and drying time, among other factors [50]. Samples taken from the surface of the maquette are more representative of the binder in comparison with *Man-Eater* considering the absence of many layers of overpaint. The μ-FTIR spectra of the samples from the maquette showed the same C=O and C–H absorption bands as that of *Man-Eater*, indicating a possible alkyd binding medium as well.

**Figure 11.** A μ-FTIR spectrum acquired from a sample taken from the edge of the blue pennant in *Man-Eater*. The presence of Prussian blue as was detected in Raman spectroscopy in Layers 1A and 1B (†), and not ultramarine, possibly indicates this sample as original. A carbonyl (C=O) stretching band at 1734 cm−<sup>1</sup> and C–H stretches at 2956 (sh), 2927, and 2855 cm−<sup>1</sup> point towards an alkyd binder, but any remaining diagnostic peaks are obscured by the presence of CaSO4 (\*) and a silicate (‡).
