The heating process (30-200 QC) of a paly gorskite-indigo mixture has been monitored in situ and simultaneously by synchrotron powder diffraction and Raman spectroscopy. During this process, the dye and the clay interact to form Maya blue (MB), a pigment highly resistant to degradation . It is shown that the formation of a very stable pigment occurs in the 70-130 QC interval; i.e., when palygorskite starts to loose zeolitic water, and is accompanied by a reduction of the crystallographic a parameter, as well as by alterations in the C=C and C=O bonds of indigo. Mid-and near-infrared spectroscopic work and rnicroporosity measurements, employed to study the rehydration process after the complex formation, pro vide evidence for the inhibition of the rehydration of l\1B as compared with palygorskite. These results are consistent with the blocking of the palygorskite tunnel entrance by indigo molecules with a possible partial penetration inside the tunnels. The surface silanols of palygorskite are not perturbed by indigo, suggesting that MB is not a surface complex.