Identification of indigoid compounds present in archaeological Maya blue by pyrolysis-silylation-gas chromatography–mass spectrometry

A study based on the use of pyrolysis-silylation-gas chromatograpy–mass spectrometry (Py-GC–MS), which aimed to identify indigoid compounds and to clarify the multicomponent composition of Maya blue (MB) pigment, has been carried out. A series of reference compounds and synthetic MB specimens prepared in the laboratory have been analysed by this technique. An analysis of archaeological MB samples from 14 Maya archaeological sites from Mexico and Guatemala has also been performed. The obtained results demonstrate that, in addition to indigo, oxidised species such as dehydroindigo, which is formed as a result of redox processes taking place while preparing the pigment, are present in archaeological MB samples. Remarkably, the results of the chemometric analysis carried out with the set of obtained Py-GC–MS data agree with the notion that the pigment preparation procedure varied locally and evolved in time during the Maya civilization.