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Archaeometry ••, •• (2014) ••–••
doi: 10.1111/arcm.12144
S PE C TROCHE M ICAL CHARAC TER I ZATI O N O F R ED P I G ME N TS USE D IN CL ASSIC P ER I O D MAYA FU N ER A RY P RACT ICES * P. QUINTANA,1† V. TIESLER,2 M. CONDE,1 R. TREJO-TZAB,3 C. BOLIO,2 J. J. ALVARADO-GIL1 and D. AGUILAR1 1
CINVESTAV Unidad Mérida, Departamento de Física Aplicada, A.P. 73, C.P. 97310, Mérida, México 2 Facultad de Ciencias Antropológicas, Universidad Autónoma de Yucatán, Mérida, Yucatán, México 3 Facultad de Ingeniería Química, Universidad Autónoma de Yucatán, Mérida, Yucatán, México
We studied the composition, colour chromaticity and form of application of red pigments in human bone samples from seven Classic period Lowland Maya sites. The samples were analysed by X-ray diffraction, scanning electron microscopy (SEM) and X-ray energydispersive spectroscopy (EDS). Colour was measured using conventional colour identification standards (Munsell) and reflectance spectroscopy. Cinnabar and hematite were identified as the pigments used. We conclude that the reflectance method has advantages over conventional visual results, as it provides precise, objective and quantifiable optical data to distinguish the chromaticity, colour saturation and brightness of the pigments. KEYWORDS: MAYA, PIGMENTS, BONE REMAINS, HEMATITE, CINNABAR, COLORIMETRY, XRD, REFLECTANCE SPECTROSCOPY, SEM
INTRODUCTION
Pigments were widely used by the ancient Maya in Mesoamerica; they have been found as decorations in pottery, murals, codices, sculptures, burials and other archaeological materials. Red colours were generally produced from earth-based red pigments containing iron oxide. The mineral hematite (α-Fe2O3) was very common, while cinnabar, a mercury sulphide (HgS), had to be imported from the highland territories. Red pigments could be applied on wood, stone or used in ritual contexts in wall paintings or on selected human bones buried in graves, below building floors or even in skin-paintings (Morley 1982; Ruz-Lhuillier 1991; González 1998; Tiesler et al. 2004; Vandenabeele et al. 2005; Vázquez de Agredos 2009). The colorimetric range among red pigments embraces pale and dark reds, brick red and violet tones; the latter two colours are reached by using iron oxide or cinnabar as chromophores, respectively. When hematite is the main iron oxide, a red colour is observed (Munsell chart, various saturation levels between HUE 7.5R and HUE 5R). Cinnabar, HgS, usually shows a brighter reddish colour (Munsell chart, saturated HUE 7.5R), also known as vermillion. Among the ancient Maya, red pigments were especially prominent in elite funerary practices. Their uses span at least two millennia of the pre-Hispanic Maya past, as indicated in the archaeological record (Ruz-Lhuillier 1991). Not only were red hematite or cinnabar the pigments of choice to fill funerary vessels and to paint the floors and walls of the tombs of paramount chiefs, but they were also used to cover the corpses of their occupants. Our notion regarding the *Received 19 March 2014; accepted 28 May 2014 †Corresponding author: email
[email protected] © 2014 University of Oxford
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technical processes implied in pigment preparation and its forms of application in ancient Maya mortuary treatment is still relatively vague, although recent scholarship has unveiled a great diversity in these colourful corpse coatings. These appear to range from powder sprinkling to blends of cinnabar and organic adhesives, and from interceded layers of cinnabar and bitumen coats to glazed blends of smooth reddish pastes (García-Moreno and Granados 2000; Tiesler and Cucina 2006; Vázquez de Agredos 2006, 2007). Regarding its mineral properties and provenience, hematite constitutes an anhydrous iron oxide, which forms in the interior of caves and in termite mounds in the territories that encompass the Maya area (Morley 1982). Cinnabar is a mercury sulphuric compound, which was procured in mines operating in the volcanic ridges of the Highlands of Chiapas, Guatemala, Honduras and El Salvador. In the Maya Lowlands, which saw a peak in cultural achievement and social complexity towards the Late Classic period (ad 600–800), cinnabar was imported after processing and consumed abundantly in elite workshops. Its uses were predominantly for funerary rituals and were restricted mainly to the higher social sectors. Well known is its application as body and shroud paint in Calakmul’s dynastic tomb occupied by Yuknom Yich’ak K’ak (García-Moreno and Granados 2000; Vázquez de Agredos 2006, 2007), or the last precinct of Palenque’s Janaab’ Pakal and his female consort from adjacent Structure XIII sub, who has popularly been named the ‘Red Queen’ due to her massive cinnabar cover (Tiesler and Cucina 2006). Both bodies had been covered with thick layers of this vermillion pigment prior to the sealing of their mortuary monoliths. In this work, we combine different analytical tools in a series of selected pigmented bone samples from available pre-Hispanic burial contexts, which include different social sectors, as inferred from the burial accessories, and geographical locations within the Maya area. To identify the mineral composition, we examine, using X-ray diffraction (XRD), small areas with a heterogeneous sample surface that contains pigmented grains. The pigment morphology is observed by scanning electron microscopy (SEM), whereas energy-dispersive spectroscopy (EDS) provides information on the make-up of the chemical elements: diffuse reflection UV-Vis spectroscopy determines the absorption properties, together with spectro-photo-colorimetry, which measures the trichromatic coordinates in the CIE (1976) L*a*b* space. MATERIALS AND METHODS
The archaeological context and sampling procedures We studied 88 pigmented bones from seven archaeological sites in Mexico and Guatemala, all dated to the Classic period (ad 250–900). From these, 76 samples sufficed in amount to be included for this study on pigment use, as part of ongoing collaborative bioarchaeological work in these collections since 2000 (see the Acknowledgements). The majority of the samples (N = 49) come from the small settlement of Xcambó, located on the north coast of Yucatán. The site was once an important salt production centre and trading port, which flourished during the first half of the Late Classic (ad 550–700). Xcambo’s dead, who were allotted simple but rich burial outfits, reflect the general wealth of the living population and emulate the exclusive funerary attires of Maya dynasts from the urban inland centres further south. Inland elite contexts make up most of the remainder of the available sample for this study (N = 27). These include a sample from the remains of king Okit Kan L’ek Tok from Ek Balam, who reigned during the Terminal Classic (N = 1). From the Puuc area, two specimens (N = 2) were sampled from elite contexts at Oxkintok. Another series, which pertains to mostly privileged © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–••
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burials (N = 17), comes from the ancient capital of the ‘Snake Empire’ of Calakmul (Folan et al. 2001) and neighbouring Dzibanché (N = 2). Further south, we included two pigment samples (N = 2) from tomb burials, interred in the ancient city of Sacul from the south-eastern Petén, Guatemala. On the western fringes of the Maya area lies Palenque (N = 3), where cinnabar was popular and abundantly used in the last rites of the site’s dynastic paramount chiefs (Tiesler 2006). From here, we sampled pigmented, embedded bone fragments from the body of ruler Janaab’ Pakal (PAL01). This paramount chief lived during most of the seventh century ad and was buried inside a monumental funerary chamber in the core of the Temple of the Inscriptions. A second sample (PAL02) was processed from a thin section of a female dignitary from the adjacent Temple XIIIsub (Tiesler and Cucina 2010) This mature woman has been popularly called the ‘Red Queen’ due to the lack of positive personal identification and because of the bright vermillion coating of her body. The pigmented samples from the above-described contexts range from 1 to 5 cm2 (and vary from 0.07 g up to 2.8 g) for the histomorphological and molecular procedures. For the latter analyses, a tiny portion of the pigmented covers (around 15 mg) was abraded off the surface and powdered. In the case of more deteriorated, smaller specimens, the sample was left intact to avoid further disintegration. Each sample was labelled according to its place of origin, followed by the sample number. For example, sample number yy = 18 from Calakmul appears as CAL18. Chemical analysis Morphological characterization was carried out in a scanning electron microscope (SEM, Philips XL30ESEM). To identify the chemical element composition of the pigments, an energydispersive X-ray spectrometer system (EDS), equipped with a Si (Li) X-ray detector at 30 kV, was used. The samples were deposited on a standard carbon tape for observation and the images were taken under low-vacuum conditions (secondary electrons). Some samples were analysed by X-ray diffraction (XRD) by scratching the painted surface, or the whole bone was used when the pigment covered a flat surface (approximately 0.5 cm2). The samples were registered with a diffractometer (Siemens D-5000), operated at 35 kV and 25 mA with monochromatic Cu–Kα radiation (λ = 1.5418Å), using a step time of 3 s and a step size of 0.02°. Optical microscopy Thin sections were obtained in five samples. The sections were processed following a standardized protocol for undecalcified bone sections in the Laboratory of Bioarchaeology (Universidad Autónoma de Yucatán) in Mérida, Mexico (Tiesler et al. 2006). Biodur™ resin was used as an embedding medium and the enclosed specimens were left to dry in this polymeric medium for at least a week. The processed blocks were removed from the casts and sectioned using an Isomet™ diamond blade to obtain 1 mm thick cross-sections. The slices were mounted on a glass slide, and were manually abraded and polished until reduced to a thickness of 50–70 μm. The microscopic analysis of the pigmented surfaces was carried out with a Leica® loup microscope, using reflected and transmitted light. Chromatic characterization The chromatic characterization of a pictorial layer is commonly measured by applying subjective methods based on visual comparison between the sample and a pre-established colour table such © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–••
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as the Munsell code. However, the information generated is prone to be influenced by extrinsic factors, such as the illumination used during the comparison, the colorimetric recognition abilities of each observer and the chromatic stability of the patterns used for comparison. For this study, we compared our conventional visual colour chart identifications with the results obtained from optical reflectance spectra measurements of the samples, which were performed in the spectral range from 400 nm to 800 nm, using an AvaSpec-2048 fibre optic spectrometer coupled with a bifurcated fibre probe (FCR-7UV100-2-1X25) and an AFH-Ocular from Avantes at 45°. The latter minimized the specular/diffuse reflectance ratio of the captured radiation (Edreira et al. 2001; Tücks and Beck 2005). In this configuration, the sample is illuminated with a deuterium– halogen light source (model AvaLight DH-S-BAL) and the sample reflectance is sent to the spectrometer. For the reflectance measurements, an Ocean Optics WS-1-SL, made using Spectralon as the reflective material, was used as a reference, with 99% of the reflectivity in the range from 200 nm to 2.5 μm. The reflectance spectra of the pictorial surfaces of all the samples have been registered in the visible range over several areas (an illumination spot 1 mm in diameter). Five measurements were performed for each sample in order to obtain a representative value. A ceramic WS-1-SL (Ocean Optics) standard tablet was used as a white pattern. The colorimetric information was obtained from the reflectance data in the visible region using a D65 deuterium–halogen lamp, which simulates daylight, as an illuminant. The colour was described in terms of the L*a*b* colour space, defined by the CIE (1976), where L* is the achromatic lightness and there are two chromatic components, a* (green–red axis) and b* (blue–yellow axis). These variables define the hue and colour saturation and are represented in the colour space diagram. RESULTS
Mineral phase identification by X-ray diffraction Mineralogical X-ray diffraction analysis was conducted on 53 bone remains, to confirm the presence of cinnabar, HgS (Figs 1 (a) and 1 (b)), and hematite, Fe2O3 (Fig. 1 (c)). The powder patterns were easily distinguishable from the hydroxylapatite bone matrix, Ca5(PO4)3(OH), and also from other minerals that are often associated with bone pigments, such as carbonates and silicates (Fig. 1 (d)). Calcium carbonate, CaCO3, was the main component in all analysed samples. The origin of the calcite is most probably related to the ancient colouring practices, destined to dim brighter colours and to improve pigment properties, and possibly their adherence to various support materials. Other minerals present, as quartz, dolomite CaMg(CO3)2, gypsum CaSO4·2H2O and anhydrite CaSO4, are associated with the mineralogical soil composition of the burial location. In other cases, their presence could be due to the pigment contamination with the soft lime plaster or calcareous sediments of the tomb environment, which contains high levels of calcite and clay minerals. Cinnabar was present in all of the sampled pigments from the inland sites (N = 14) and in two samples from Xcambó (XCA-21 and XCA-33); and was identified by the characteristic diffraction peaks at 26.4 and 31.1° (2θ) (Fig. 1 (a)). The cinnabar, obtained from the skeleton of the Red Queen (XIII-3) in Palenque, was the purest when compared to the remainder of the analysed samples, showing the sharpest intensity peaks, and no additional crystalline phases were detected. At other sites, such as Calakmul, cinnabar was found mixed with other minerals, such as calcite, CaCO3, and feldspar—for example, anorthite—along with traces of other clays, such as talc, phyllite and paligorskite (Fig. 1 (b)). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–••
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Figure 1 X-ray diffraction patterns of the pigments and the detected minerals: (a) a cinnabar sample from Palenque; (b) cinnabar and calcite from Calakmul; (c, d) hematite and other carbonate minerals from different samples from Xcambó.
Hematite, Fe2O3, was detected in 35 burials from Xcambó, showing high intensity peaks at 24.2° and 33.2° (2θ), indicating that the pigment has a high crystallinity. Calcite, calcite magnesian (Ca,Mg)CO3 and quartz, SiO2, were also found (Fig. 1 (c)). In many samples from Xcambó, the main reflection of calcite at 29.5° (2θ) exhibits a dissymmetric peak, which confirms the presence of other types of calcium carbonates; that is, a stoichiometric calcite and other carbonates enriched with magnesium and/or iron that replace some of calcium atoms (Fig. 1 (d)), such as ankerite, Ca(Fe,Mg)(CO3)2 (Cailleau et al. 2005). The formation of ankerite identifies a diagenetic process due to dissolution of the hematite and subsequent substitution of calcium in the carbonates of the soil (Xu et al. 2005). We also identified traces of clay minerals, such as smectite interstratified with kaolinite or illite and palygorskite. Optical microscopy Surface images and thin sections of different bone samples were obtained in an optical microscope using transmitted and reflected light. The magnifications ranged from 2.5× to 40×. The histological results suggest that cinnabar pigmentation was usually applied in the form of a paste, © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–••
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as evidenced by the homogeneously compact texture of the coloured layer, with the visible admixture of amorphous particles. This is the case, for example, in specimen CAL01 from Calakmul’s Tomb II-5a (Fig. 2), showing that the bone surface is covered by a homogeneous, compacted layer of vermillion cinnabar without inclusions (0.09 mm thick). Its distribution suggests that it had been applied together with the addition of an amorphous material of organic origin, possibly to form the red paste to be applied. Additional substances, such as amorphous blackish agglutinants, which we have also documented in this study for Calakmul and Palenque, could have been added as paint vehicles, perhaps to improve durability and facilitate application of the colourants as paint or paste. However, there were also exceptions such as the specimen from Calakmul’s Tomb II-4 (CAL16); in this case, a thin, dispersed coat of cinnabar powder can be observed on top of a vertebra. The grain distribution forms a heterogeneous pigmentation layer with a thickness between 0.09 mm and 0.3 mm (Fig. 2). Differently from cinnabar, it appears that red hematite was more commonly applied on corpses in the form of powder among the Classic period Maya (Fig. 2). For example, XCA25 (Burial 76) from Xcambó, Yucatán, displays inclusions of other substances in the hematite layer (maximum thickness of 0.20 mm). Probably, the powder presentation facilitated contamination with exogenous matter, given that the pigmented layer (with a thickness between 0.18 mm and 0.30 mm) clearly contains particles that originally did not form part of the pigment application, as shown in sample XCA23 (Fig. 2). However, there are exceptions. In some few cases, such as in sample XCA39, it looks as though the reddish hematite was applied as a paste, resulting in a homogeneously pigmented layer on top of the body, then bone. Its homogeneous distribution suggests the presence of an organic medium within the coloured layer, to vanish in the course of the decomposition process. Morphology and chemical analysis by SEM–EDS When the amount of pigment was small, or if the surface was too irregular to be analysed by XRD (e.g., in a rib or a pelvic bone), scanning electron microscopy (SEM) coupled to an energydispersive X-ray spectrometer (EDS) was applied to identify the presence of iron, sulphur or mercury, and also to visualize the grain morphology and the pigment distribution over the bone surface. In order to identify hematite and cinnabar by SEM, the images were analysed applying the backscattered electron mode, where brighter particles were associated with the presence of heavy metals, such as Fe and Hg, which have a higher atomic number. The samples from Xcambó (Fig. 3 (a)) were mainly pigmented with hematite, which displayed several small brighter particles (
