Aged Natural and Synthetic Maya Blue-Like Pigments: What Difference Does It Make?

Maya Blue-like pigments were prepared by two routes using a palygorskite from the Maya region. Synthetic indigo was used as a dye in one case, while the other used the anil plant (Indigofera suffructicosa). Both synthetic and natural Maya Blue pigments were aged and characterized in order to clarify the interaction of the dye-palygorskite. Natural and synthetic fresh Maya Blue pigments were very different; the synthetic ones obviously stabilized the indigo molecule probably at the clay surface and may be in the grooves, but the natural ones stabilized indoxyl molecules in the tunnels and over time oxidized to indigo. The presence of indigo, originating from the anil plant, into palygorskite tunnels was evidenced in aged natural pigments by Si-29, Al-27, C-13, and Xe-129 NMR. The persistence of color was evaluated as a function of leaching dye under acidic conditions.