*3.4. Red Paint*

The extant red paint on the pennants in Man-Eater was the most vibrant of the three primary colors on the surface. Nevertheless, the paint was brittle and chipped; in some areas, the aluminum coating was visible, in others, the rusted metal was exposed. Multiple cross sections were taken from the five red pennants and all revealed an identical stratigraphy (Figure 9). Some of the red hues veered darker even to the naked eye, especially those closer to the iron surface save for Layer 1 (Figure 9). Similar to the yellow and blue, SEM-EDS confirmed the presence of a steel rust layer followed by an aluminum paint coating. Raman analysis (Figure 10) proved crucial in analyzing the red pigments, where every layer contained one or more β-naphthol organic red pigments. This class of pigments first became available at the turn of the 20th century by coupling a substituted aniline ring with β-naphthol [40]. It is worth noting that assigning a particular shade to β-naphthol organic red pigments can be challenging because the presence of fillers, particle size, and method of manufacture all affect their final color [13]. These pigments also range in photosensitivity, and for some, white reduction from a deep shade using diluents, such as titanium white, can make them prone to fading, possibly due to catalytic effects also observed on other organic reds [28]. These pigments are sensitive to solvents, acids, bases, and some even to water.

**Figure 9.** Cross section imaging of a sample taken from one of the red pennants in *Man-Eater*. (**a**) Light microscope image at 20× magnification showing all 8 layers of paint and aluminum anticorrosive paint, and (**b**) BSE image of the cross section that shows the division between layers 5, 6, and 7 in particular. © 2021 MoMA, New York, NY, USA.

> In Layer 1, Parachlor Red (P.R. 6; C.I. 12090) was identified by Raman spectroscopy (163, 176, 219, 267, 331, 372, 394, 421, 465, 484, 533, 613, 635, 658, 710, 743, 763, 840, 861(sh), 985, 1091, 1103, 1132, 1140, 1158, 1180, 1218, 1243, 1265, 1291, 1326, 1392, 1447, 1474, 1485, 1555, 1565, 1584, 1605, 1623 (sh) cm−1). P.R. 6 was first synthesized in 1906 and was used until the late 1980s when it rapidly fell out of favor due to high solubility in organic

solvents and mineral spirits as well as poor lightfastness [13]. Nevertheless, this pigment was used in air-drying alkyd systems, because deep shades without much white reduction are relatively lightfast [40]. In the context of Calder's preference for matte paints, it is plausible that the original layer of paint was an alkyd one that contained P.R. 6. Chlorine Kα<sup>1</sup> and Kα<sup>2</sup> lines were obscured by Rh L-series lines and as such not discerned in XRF, and mapping with SEM-EDS only indicated that the paint was likely extended with silicates and/or magnesium silicates. Furthermore, the difficulty of detecting chlorine elementally is due to P.R. 6 having only one chlorine substituent. Layer 2 shows a mixture of P.R. 6 and Para Red (P.R. 1; C.I. 12070) in the Raman spectrum (185, 360, 410, 460, 1002, 1105, 1428, 1592 cm−1). The latter was the first synthetic organic red discovered in 1895 but has since lost its industrial significance. P.R. 1 has a dull brown hue, and is not fast against organic solvents, acids, bases, and even water; it is also prone to darken on exposure to light [40].

**Figure 10.** Raman spectra of all 8 Layers of a cross section from one of the red pennants in *Man-Eater*. All layers contain one or more β-naphthol red and all peak positions are listed in the text. In addition, Layers 4, 5, 6, 7, and 8 contain red lead (\*); and layers 5, 6, and 7 molybdate orange (†) at 825 cm−<sup>1</sup> and chrome yellow (‡) at 839 cm<sup>−</sup>1.

Layers 3 and 4 are similar in composition and could have been applied in two coats succession. They both also contain P.R. 1 according to their Raman spectra (185, 326, 360, 410, 461, 614, 632, 729, 986, 1002, 1105, 1167, 1201, 1228, 1257, 1324, 1396, 1428, 1496, 1592 cm−1), with SEM-EDS indicating the presence of a calcium-based filler in addition to silicates and/or magnesium silicates. However, Layer 4 also contains some red lead (Pb3O4) as evident by lattice bands at 121 (A1g), 151(E2g), and 547 (A1g) cm−<sup>1</sup> [41] in addition to lead Mα and Mβ lines in SEM-EDS. Red lead (P.R. 105; C.I. 77518), one of the earliest pigments to be artificially made, has been used as a red pigment since as early as the 5th B.C. century in China [42]. Today, it is manufactured by heating lead oxides and is mostly used as a protective pigment to passivate iron and steel and inhibit corrosion [13]. The choice of a paint containing red lead might have seemed appropriate at the time of repainting because of evidence of rusting on the red pennants.

Layers 5, 6, and 7 are rather complex paint layers, with at least 4 pigments present, one organic and three inorganics, and could be three coats applied in one campaign. Layer 5 seems to be painted over a physically degraded Layer 4 since it fills several voids to form a jagged layer. The organic pigment, chlorinated para red (P.R. 4; C.I. 12085) is a positional isomer of P.R. 6 and has a yellowish red hue (313, 340, 358, 594, 624, 708, 719. 736, 769, 890, 986, 1096, 1117, 1125, 1188, 1296, 1337, 1396, 1451, 1487, 1555, 1587, 1617 cm−1). P.R. 4 has lost much of its commercial impact, as it is tinctorially weak and loses much of its light fastness in white reductions, while, in contrast, even full shades darken upon exposure to light [40]. The inorganics include red lead, chrome yellow—possibly the monoclinic form with few or no sulfates considering the position of the ν1(CrO4 <sup>2</sup>−) stretch at 839 cm<sup>−</sup>1—and molybdate orange (P.R. 104; C.I. 77605).

Molybdate orange is a solid solution of PbCrO4·PbMoO4·PbSO4, used mainly in paints, coatings, and colored plastics. It was first industrialized in 1934-35, and commercial pigments contain ~10% lead molybdate (PbMoO4) [38]. This pigment is often found in mixtures with chrome yellow to match the color of the orange basic lead chromate (PbCrO4·PbO), which

is no longer of commercial importance. Molybdate orange is also found in mixtures with organic reds to give an extended color range and impart lightfastness and weather resistance onto a paint film [13]. Molybdenum was first identified in the paint stratigraphy through non-invasive XRF and confirmed by Raman spectroscopy with a ν1(CrO4 <sup>2</sup>−) symmetric stretch at 825 cm−<sup>1</sup> presenting as a doublet with chrome yellow [43].

Layer 8 is a mixture of both red lead and toluidine red (P.R. 3; C.I. 12120). P.R. 3 is the most lightfast of the β-naphthol reds in deep shades and is manufactured and used on a large industrial scale. Primarily employed in air drying paints, it is the most important of the β-naphthol reds and was also used in printing inks, pastels, and watercolors [40]. Nevertheless, much as with the remaining β-naphthol reds, it suffered from a sensitivity to light and solvents and declined in popularity after the 1970s. SEM-EDS indicated Layer 8 to be extended with a calcium-based filler, silicates, and magnesium silicates. In comparison with *Man-Eater*, the red on the maquette appears to have been painted in two layers, a very thin preliminary one with a thicker coat of red on top. Unlike the blue and yellow pennants, the red paint was applied directly to the aluminum with no white layer. While Raman and SEM-EDS analysis indicated that they are similar in composition, the lower layer is visually more saturated in color. The pigments consisted of P.R. 4 and molybdate orange, the latter identified in the Raman spectrum by a ν1(CrO4 <sup>2</sup>−) stretch at 827 cm−<sup>1</sup> and a ν1/ν2(CrO4 <sup>2</sup>−) bending multiplet at 341/359 cm−1. Mo was observed in the XRF spectrum using the Tracer 5i and confirms the presence of molybdate orange. The paint also included TiO2 in rutile form (449, 612 cm<sup>−</sup>1) and CaSO4 (1020 cm<sup>−</sup>1). The B1g mode at 144 is obscured due to a broad band at 155 ascribed to Pb–O lattice modes in lead chromate [44]. Similar to the rest of the primary colors on the maquette, the red pennant is different in shade and composition than in *Man-Eater*.
