One of the things which is striking about Mayan archaeological sites in Latin America is the blue colour used on pottery. Till recently, the origin of this unique colour and its resistance to biocorrosion were mysteries. Now, scientists from Mexico have carried out high resolution electron microscopy alongwith X-ray microanalysis to decode the pigment. The colour contains clays, mainly palygorskite mixed with other types. The palygorskite crystals form a superlattice as a result of mixing with indigo molecules. There is also a silicon substrate which contains metal and oxide particles on the surface. It is now believed that the colour is obtained only when both the superlattice and the particles are present ( Science , Vol 273, No 5272).