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

Abstract

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.