The First Direct Evidence for the Production of Maya Blue: Rediscovery of a Technology
Arnold, Dean E., Branden, Jason R., Williams, Patrick Ryan, Feinman, Gary M., Brown, J. P., Antiquity
An unusual blue pigment applied to pottery, sculpture and murals, Maya Blue is '... one of the great technological and artistic achievements of Mesoamerica' (Miller & Martin 2004: 252). Used predominantly during the Classic and Postclassic periods (AD 300-1519) from northern Yucat n to highland Guatemala and central Mexico, production also appears to have survived into colonial rimes (Cabrera Garrido 1969; Gettens 1955; 1962: 560; Haude 1998; Ortega et al. 2001a & b; Polette et al. 2000; Reyes-Valerio 1993; Sanchez de Rio et al. 2004; Tagle et al. 1990; Torres 1988). Maya Blue was not based on copper, ground lapis lazuli or azurite (Jose-Yacaman et al. 1996), but consists of a unique pigment in which indigo is chemically bound to the clay mineral palygorskite (Cabrera Garrido 1969; Chianelli et al. 2005: 133; Fois et al. 2003; Gettens 1955; 1962: 563; Giustetto et al. 2005; Hubbard et al. 2003; Kleber et al. 1967: 44-6; Ortega et al. 2001a: 755-6). It is resistant to diluted mineral acids, alkalis, solvents, oxidants, reducing agents, moderate heat and biocorrosion and shows little evidence of colour deterioration even after centuries of exposure to the harsh tropical climate of southern Mesoamerica (Fois et al. 2003; Gettens 1962; Sanchez del Rio et aL 2006).
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These characteristics and the widespread use of Maya Blue in ritual contexts have stimulated the interest of archaeologists, chemists and material scientists since the pigment was first identified by Merwin (1931) on the murals of the Temple of the Warriors at Chichen Itza (Figure 1). Its use in ritual contexts implies that it was highly valued, and this inference is borne out by its association with sacrifice, priests and Maya deities, especially the rain god Chaak (Arnold 2005; Reyes-Valerio 1993: 86; Tozzer 1957: 203). Indeed, the recent exhibition The Courtly Art of the Ancient Maya features pottery, murals and sculpture with headdresses, clothing and jewellery painted with Maya Blue (Miller & Martin 2004).
The production of Maya Blue
Two kinds of approaches have hitherto provided information about the production of Maya Blue: experimental approaches and contextual approaches. Experiments have produced a number of key results (Cabrera Garrido 1969; Littmann 1982; Reyes-Valerio 1993; Torres 1988). First, sustained low heat (<150[degrees]C) is critical in order to create the pigment, fix its colour and acquire its unique chemical and physical stability (Torres 1988; Van Olphen 1966). Second, very little indigo is necessary to make Maya Blue; the pigment can be synthesised using only 0.5-2 per cent indigo (Hubbard et al. 2003; Sanchez dei Rio et al. 2006; Van Olphen 1966). Experiments using sepiolite, a clay mineral similar to palygorskite, failed to produce a stable Maya Blue-like pigment with all of its unique characteristics (Sanchez dei Rio et al. 2006).
Contextual approaches to Maya Blue have also provided insight about its production. Data from the contemporary Maya have revealed probable sources of the palygorskite used in the pigment. Using a triangulation of ethnographic techniques and data from X-ray diffraction provided by clay mineralogist B.F. Bohor, Arnold demonstrated the link between the Yucatec Maya semantic category sak lu um and palygorskite (Arnold 1967; 1971). The contemporary Maya of Ticul and Sacalum recognise the unique properties of palygorskite, refer to it as sak lu'um (white earth'), and use it for pottery temper as well as for medicinal purposes (Arnold 1967; 1971; 2005; Arnold & Bohor 1975; 1976; Folan 1969). Evidence suggests that sources of sak lu'um in or near Sacalum and Ticul were likely pre-Columbian sources of palygorskite (Arnold 2005; Arnold & Bohor 1975; 1976; Folan 1969). The name of the town of Sacalum itself is a hispanicised form of the Yucatec Maya phrase, sak lu'um, and the town has been so named since before the conquest (Folan 1969). …