Maya Blue Research Articles

Maya Blue: A Computational and Spectroscopic Study

Maya Blue pigment, used in pre-Colombian America by the ancient Mayas, is a complex between the clay palygorskite and the indigo dye. The pigment can be manufactured by mixing palygorskite and indigo and heating to T > 120 degrees C. The most quoted hypothesis states that the dye molecules enter the microchannels which permeate the clay structure, thus creating a stable complex. Maya Blue shows a remarkable chemical stability, presumably caused by interactions formed between indigo and clay surfaces. This work aims at studying the nature of these interactions by means of computational and spectroscopic techniques. The encapsulation of indigo inside the clay framework was tested by means of molecular modeling techniques. The calculation of the reaction energies confirmed that the formation of the clay-organic complex can occur only if palygorskite is heated at temperatures well above the water desorption step, when the release of water is entropically favored. H-bonds between the clay framework and the indigo were detected by means of spectroscopic methods. FTIR spectroscopy on outgassed palygorskite and freshly synthesized Maya Blue samples showed that the presence of indigo modifies the spectroscopic features of both structural and zeolitic water, although no clear bands of the dye groups could be observed, presumably due to its very low concentration. The positions and intensities of delta(H2O) and nu(H2O) modes showed that part of the structural water molecules interact via a hydrogen bond with the C=O or N-H groups of indigo. Micro-Raman spectra clearly evidenced the presence of indigo both in original and in freshly synthesized Maya Blue. The nu(C=O) symmetric mode of Maya Blue red-shifts with respect to pure indigo, as the result of the formation of H-bonds with the nearest clay structural water. Ab initio quantum methods were applied on the indigo molecule, both isolated and linked through H-bonds with water, to calculate the magnitude of the expected vibrational shifts. Calculated and experimental vibrational shifts appeared to be in good agreement. The presence of a peak at 17.8 ppm and the shift of the N-H signal in the 1H MAS NMR spectrum of Maya Blue provide evidence of hydrogen bond interactions between indigo and palygorskite in agreement with IR and ab initio methods.

Maya Blue: a long lasting mystery revealed

Maya Blue: a long lasting mystery revealed

Fe K-edge XANES of Maya blue pigment

The utilization of techniques used in Materials Science for the characterization of artefacts of interest for cultural heritage is getting more and more attention nowadays. One of the products of the ancient Maya chemistry is the “Maya blue” pigment, made with natural indigo and palygorskite. This pigment is different from any other pigment used in other parts of the world. It is durable and acid-resistant, and still keeps many secrets to scientists even though it has been studied for more than 50 years.Although the pigment is basically made of palygorskite Si8(Mg2Al2)O20(OH)2(OH2)4.4H2O and an organic colourant (indigo: C16H10N2O2), a number of other compounds have been found in previous studies on archaeological samples, like other clays and minerals, iron nanoparticles, iron oxides, impurities of transition metals (Cr, Mn, Ti, V), etc. We measured at the ESRF ID26 beamline the Fe K-edge XANES spectra of the blue pigment in ancient samples. They are compared to XANES spectra of Maya blue samples synthesized under controlled conditions, and iron oxides usually employed as pigments (hematite and goethite). Our results show that the iron found in ancient Maya blue pigment is related to the Fe exchanged in the palygorskite clay. We did not find iron in metallic form or goethite in archaeological Maya blue.

MAYA BLUE AND PALYGORSKITE: A second possible pre-Columbian source

Maya Blue is an unusual blue pigment used on pottery, sculpture, and murals from the Preclassic to the Colonial period. Until the late 1960s, its composition was unknown, but chemists working in Spain, Belgium, Mexico, and the United States identified Maya Blue as a combination of indigo and the unusual clay mineral palygorskite (also called attapulgite). A source of palygorskite in the Maya area was unknown for years; then ethnoarchaeological research in the mid-1960s demonstrated that the contemporary Maya recognized the unique physical properties of palygorskite and used it as an additive for pottery temper and for curing certain types of illnesses. Because of its importance in Maya Blue, pre-Hispanic sources of the mineral were then suggested based on ethnoarchaeological data. One of these sources was the cenote in the town of Sacalum, Yucatan. This paper briefly reviews the history of the Maya Blue research from an anthropological perspective and presents evidence of a second possible pre-Hispanic mining site for palygorskite at Yo' Sah Kab near Ticul, Yucatan. Archaeological and technological approaches have demonstrated the use, distribution, composition, and characteristics of Maya Blue, but ethnoarchaeology has related it to Maya language and culture and to possible pre-Hispanic sources of one of its constituents, palygorskite.

Crystal structure refinement of palygorskite from neutron powder diffraction

Palygorskite is a Mg-rich fibrous clay, present in nature as a mixture of two intricately intertwined polymorphs – monoclinic ( C2/m ) and orthorhombic ( Pbmn ) – characterized by the presence of channels along Z -axis, filled by weakly bound zeolitic water. A neutron powder diffraction study was carried out by full Rietveld refinement on a deuterated sample, measured at ISIS on the HRPD beam-line. The positions of oxygen and deuterium atoms of the zeolitic water were located ab initio through cyclically repeated Difference Fourier maps, and their atomic coordinates and occupancy factors were refined. The frameworks of both monoclinic and orthorhombic palygorskite do not differ significantly from the models reported in the literature, although they are more distorted. The arrangement of the zeolitic water molecules is highly disordered and different in the two polymorphs. Given the coexistence of several deuterium sets, two different H-bonding schemes are proposed for each polymorph. Further H-bonding alternatives could be derived by considering the location of oxygen atoms in partially occupied symmetry related sites. The links between the zeolitic water and the clay framework appear to be weaker in orthorhombic than in monoclinic palygorskite, as shown by the lower number and different strength of H-bonds. The detailed knowledge of the zeolitic water arrangement may help in better understanding the structural features and production techniques of palygorskite-based compounds of great interest, such as the Maya Blue pigment.

Identification of the Pre-Columbian Pigment Mayablue on Works of Art by Noninvasive UV-Vis and Raman Spectroscopic Techniques

UV-visible reflectance spectroscopy and Raman microspectroscopy provide a rapid way to unequivocally identify the pre-Columbian pigment Maya blue. Spectra of modern synthetic materials are compared with data from a contextualized archaeological sample and from an object in the collection of the Los Angeles County Museum of Art. UV-visible spectroscopy and Raman microspectroscopy, together with complementary techniques such as Fourier transform infrared microspectroscopy, reveal significant differences between spectra of indigo as pure crystalline solid or as complexed by palygorskite. These techniques are thus extremely specific, being able to identify Maya blue as a prepared pigment rather than detecting only its ingredients, indigo and palygorskite. Fiber optics UV-visible reflectance spectroscopy and Raman microspectroscopy present the additional advantage of being completely noninvasive and therefore suitable for the study of works of art. Lightweight portable fiber optics UV-visible reflectance spectroscopy devices make it possible to perform measurements in situ on wall paintings and other immovable objects. The spectral differences between pure indigo and the indigo-palygorskite complex can be interpreted in terms of different hydrogen bonding configurations for the indigo molecule.

Identification of the Pre-Columbian Pigment Maya Blue on Works of Art by Noninvasive UV-Vis and Raman Spectroscopic Techniques

Identification of the Pre-Columbian Pigment Maya Blue on Works of Art by Noninvasive UV-Vis and Raman Spectroscopic Techniques

The Nature of the Colour Centres in ‘Maya Blue’ — the Incorporation of Organic Pigment Molecules into the Palygorskite Lattice

AbstractIt is shown by optical spectroscopy that indigo molecules, most likely incorporated into the channels of the palygorskite host structure, are the solely colour centres in the ancient Maya Blue pigment — in use during the Maya cultural period in Yucatan and Guatemala. This study also shows that the blue colour of solid indigo shifts toward turquoise and greenish hues when fastened to the host; it is suggested that the corresponding spectral modifications originate from the energy when single indigo molecules undergo hydrogen bonding with the hydroxy‐groups in the channels (or in the open channels on the surface). Indeed artefacts from the Maya culture exhibit rather greenish than pure blue colours.Similarly a tetrachloro‐derivative of thioindigo forms hydrogen bonds with palygorskite, as evidenced by an again distinct colour change from red‐violet to blueish‐violet. Bulkier pigment molecules bearing hydroxy‐groups, such as anthrachinon derivatives, seem to directly react with the host surface, but without producing very significant colour shifts.

Is the indigo molecule perturbed in planarity by matrices?

Raman spectra of pure synthetic indigo and of Maya blue of a Mexican clay sculpture are compared. The Raman spectrum of Maya blue shows extra bands assigned to vibrational modes of B u symmetry as well as an increasing intensity of some other bands. The partial removal of the mutual exclusion rule for the centrosymmetric indigo molecule is supposed to indicate a loss of its planarity due to strong adsorption at the palygorscite matrix.

Structural Study of Maya Blue: Textural, Thermal and Solid-State Multinuclear Magnetic Resonance Characterization of the Palygorskite-Indigo and Sepiolite-Indigo Adducts

AbstractPalygorskite-indigo and sepiolite-indigo adducts (2 wt.% indigo) were prepared by crushing the two compounds together in a mortar and heating the resulting mixtures at 150 and 120°C, respectively, for 20 h. The samples were tested chemically to ensure that they displayed the characteristic properties of Maya Blue. Textural analysis revealed that no apparent changes in microporosity occurred in sepiolite or palygorskite after thermal treatment at 120°C (sepiolite) and 150°C (palygorskite) for 20 h. Micropore measurements showed a loss of microporosity in both sepiolite and palygorskite after reaction with indigo. The TGA-DTG curves of the sepiolite-indigo and palygorskite-indigo adducts were similar to their pure clay mineral counterparts except for an additional weight loss at ∼360°C due to indigo.The 29Si CP/MAS-NMR spectrum of the heated sepiolite-indigo adduct is very reminiscent of the spectrum of dehydrated sepiolite. Crushing indigo and sepiolite together initiates a complexation, clearly seen in the 13C CP/MAS-NMR spectrum, which can be driven to completion by heat application. In contrast to the broad peaks of the pure indigo 13C CP/MAS-NMR spectrum, the sepiolite-indigo adduct spectrum consists of a well-defined series of six narrow peaks in the 120.0–125.0 ppm range. In addition, the sepiolite-indigo spectrum has two narrow, shifted peaks corresponding to the carbonyl group and the C-7 (C-16) of indigo. A model is proposed in which indigo molecules are rigidly fixed to the clay mineral surface through hydrogen bonds with edge silanol groups, and these molecules act to block the nano-tunnel entrances.

Crystal structure refinements of palygorskite and Maya Blue from molecular modelling and powder synchrotron diffraction

Maya Blue, a synthetic pigment produced by the ancient Mayas, is a combination of a specific clay, palygorskite (or sepiolite), containing large channels in the crystal structure and the organic dye indigo. Little is known about the interaction of the two components to give the most stable pigment ever produced. The aim of this work is to obtain a refined model for the Mexican palygorskite used to prepare the pigment and to elucidate the structure of the clay-indigo complex, using both molecular modelling and Rietveld refinement on data collected with synchrotron radiation. Molecular modelling proved that indigo can fit into the channels without steric impediment (forming strong hydrogen bonds between the C=O group of the dye and the structural water of the clay) and produced a model, showing reasonable distances and angles, used as the starting set for the Rietveld refinement. Difference Fourier maps, calculated without indigo, showed a residual of electron density coherent with the expected disordered position of the indigo molecule. A refinement carried out using the model of palygorskite obtained in this work and a 6-fold disordered arrangement of indigo confirmed these findings. The ratio between the two polymorphs of palygorskite (monoclinic and orthorhombic) present in the natural clay was obtained for our sample and for several palygorskite specimens coming from different sites. Samples within the same outcrop show similar ratios, while samples from different locations do not. This may be used to characterize the provenance of ancient specimens, with the goal of determining whether Maya Blue was invented and produced in one place only or if the production technology was widespread in all the Mayan region.

On the unusual stability of Maya blue paint: molecular dynamics simulations

Classical molecular dynamics simulations of the indigo-containing clay palygorskite (Maya blue) have been carried out at different temperatures in order to get insight into the high stability of this paint. After several tens of picoseconds the molecules set into stable sites along the channels of the clay, where they remain for relatively long times even at high temperature (573 K). The hydrogen bonds between indigo carbonyl and structural water are seemingly the most important guest–host interactions, however, there is some evidence that they are not essential in keeping the organic dye trapped in the stable sites. Therefore, van der Waals interactions are expected to be crucial in stabilizing Maya blue, allowing to fit the bulky indigo molecules into the palygorskite channels. Furthermore, we successfully tested the possibility that a direct interaction between indigo and clay octahedral cations (not mediated by structural water) could also play an important role in trapping the indigo molecules.

Maya blue: application of XAS and HRTEM to materials science in art and archaeology

Maya blue is a famous blue pigment composed of palygorskite clay and indigo. It was used by the ancient Maya and provides a dramatic background for some of the most impressive murals throughout Mesoamerica. Despite exposure to acids, alkalis, and chemical solvents, the color of the Maya blue pigment remains unaltered. Herein, we present studies on the role of iron in authentic and synthetic samples of Maya blue using X-ray absorption spectroscopy (XAS) and high-resolution transmission electron microscopy (HRTEM). Iron nanoparticles were found outside the lattice of the crystallites of palygorskite as well as inside the channels. Iron oxide and an amorphous phase of FeO(OH) were also found in authentic samples of Maya blue, and may contribute to the optical properties of the pigment or in the characteristic brilliant color.

Experimental and theoretical studies of palygorskite clays

We have studied the structure and properties of palygorskite clays. A structure analysis was performed using two different models to reproduce the monoclinic and orthorhombic lattices, using the atomic positions and cell parameters of palygorskite structure suggested by several authors, we simulated structures using Molecular Dynamics and Quantum Mechanics. Modifications on the structure and elemental atom changes were made to obtain more stable configurations. X-ray diffraction patterns and high resolution electron microscopy images from simulated structures were compared with experimental results. It could be observed that orthorhombic model shows a better fitting than monoclinic models. These results might help to understand many of the properties of archaeological pigments, such as, Maya Blue, in which palygorskite clay was the main component.

High Resolution Electron Microscopy of Maya Blue Paint

Reports on systematic studies of Maya blue paint using high resolution electron microscopy, electron energy loss, scanning electron microscopy, and related techniques. A model to explain the well-known properties of the paint, such as acid resistance, is presented. -- AATA

Maya blue: its presence in cuban colonial wall paintings

AbstractA blue pigment frequently found in Cuban colonial decorative wall paintings from about 1750 to 1860 has been identified with the aid of thin-layer chromatography, IR spectrometry, X-ray diffraction, thermal analysis, scanning electron microscopy and X-ray microanalysis as ‘Maya blue’. This is the first reported occurrence of Maya blue from a period after the conquest and in a non-Mayan cultural area.

Maya Blue: Its Presence in Cuban Colonial Wall Paintings

Maya Blue: Its Presence in Cuban Colonial Wall Paintings

Maya Blue: How the Mayas Could Have Made the Pigment

AbstractFor over 50 years Maya Blue has been an unsolved problem in the manufacture of ancient pigments. It can be reproduced with several procedures using palygorskite, indigo and heat; however we do not know how the Mayans made this pigment. Interpretation of ethnohistoric data allows us to deduce that Prehispanic, and even Spanish Colonial, procedures for manufacturing indigo may produce Maya blue if clay is added during the process.We present ethnohistoric and archaeological evidence to support this hypothesis and following the proposed procedures, Maya Blue is reproduced in the laboratory. Microscopic examination and chemical microscopy are applied to the synthetic Maya Blue to characterize and compare it with original Mayan samples.

Maya Blue—A New Perspective

A detailed and critical review of the literature pertaining to Maya Blue led to the conclusion that the presence of indigo as an integral component of the pigment has not, as yet, been established by acceptable scientific criteria. A Maya Blue was prepared from indigo and attapulgite which had all the observed properties of the authentic pigment. Although the experiments performed in the present study can hardly be called scientific proof of the composition of the prehistoric material, they strongly suggest that the colorant was indigo, at least in one type of Maya Blue.The strong emphasis usually placed upon the identification of attapulgite as the base mineral of Maya Blue seems to be an exercise in the use of identification equipment. The question of whether attapulgite, a clay of variable composition and available from widely separated sources, is the base of Maya Blue is immaterial. It appears that any clay containing palygorskite, sepiolite, montmorillonite, or possibly other minerals free of plate-like crystal structures can be converted to a Maya Blue pigment with all the observed chemical and physical properties of the authentic material.The present experimental work and some reported observations regarding variations in shade and color of Maya Blue specimens suggest there may be more than one pigment so designated and that a blue mont-morillonite is one of the alternatives to an indigo-colored clay for post-firing decoration of pottery and mural painting.The technical studies which form the basis for some of the conclusions reached will be found in the appendix to this report.

Sacalum, Yucatán: A Pre-Hispanic and Contemporary Source of Attapulgite

AbstractA survey of a cenote in Sacalum and the Chilam Balam of Chumayel suggests strongly that Sacalum, Ticul, and probably Tixtohilcheen have been a source of the mineral attapulgite used variously in the manufacture of Maya Blue, for medicinal purposes, and as a pottery temper.