Combining a novel technique, the voltammetry of microparticles, with spectrometric, nuclear magnetic resonance, electron microscopy, and atomic force microscopy data, Maya Blue is detected in wall paintings of the Substructures A-3, A-5, and A-6, dated in the Early Classical period (440-450 a.c.), and the Substructure II-C, dated in the Late Preclassical period (150 b.C.), in the archaeological site of Calakmul (Campeche, Mexico), thus providing evidence on the use of the pigment 750 years prior to the date currently accepted. Electrochemical measurements, supported by spectrometric data, indicate that the presence of palygorskite-attached dehydroindigo, the oxidized form of indigo, contributes to the greenish color of Maya Blue. Enthalpy and entropy of attachment of such compounds to palygorskite are calculated from the temperature dependence of electrochemical data. Both attachment processes are endothermic, becoming thermodynamically spontaneous at moderate temperatures. Accordingly, ancient Mayas may modulate the hue of Maya Blue from turquoise to greenish blue by controlling the temperature during the crushing process.

Maya Blue, an ancient nanostructured organic-inorganic hybrid material resulting from the attachment of indigo, a natural dye, to a phyllosilicate clay, palygorskite, has received considerable attention of late. Despite intensive research, several aspects remain unsolved, in particular the nature of the indigo-palygorskite association. Recent results suggest that the Maya Blue pigment is a complex system in which different topological isomers of various indigoid molecules attached to the palygorskite matrix coexist.

The voltammetry of microparticles methodology is applied to describe the electrochemistry of indigo and Maya Blue, a nanostructured organic-inorganic material, in contact with different MeCN electrolytes. The voltammetric response of synthetic specimens and genuine Maya Blue samples differ significantly from that of indigo microparticles, all being conditioned by the size-dependent insertion of electrolyte ions into the solid. Electrochemical data indicate that formation of Maya Blue involves a significant reorganization of zeolitic and/or structural water of the clay and confirms the presence of dehydroindigo accompanying indigo in the palygorskite matrix.