The Hunt for Maya Purple: Revisiting Ancient Pigments Syntheses and Properties

Syntheses of analogues of historical indigo and Maya blue pigments using an inquiry-based approach are presented. Derivatives of indigo were synthesized (in particular Tyrian purple) and used as vat dyes for dyeing cotton or wool fabrics or mixed with a sepiolite clay to create new hues or colors of Maya blues using a green chemistry hydrothermal microwave synthesis. The hydrothermal approach allows a very quick preparation of Maya analogue pigments (typically 1 h) while illustrating a green chemistry approach. The obtained Maya pigments can have very different colors (or not) from their initial indigo derivative and furthermore undergo color change under annealing (thermochromism) or mechanical grinding (tribochromism). In particular, the Tyrian purple/sepiolite chromism allows a direct visual illustration for students of the structural changes in sepiolite host-matrix associated with its pores closure and water loss.