12 July 1996
Vol 273, Issue 5272

About The Cover

Section of a mural (dated 700 A.D.) found in an archeological site at Cacaxtla, Mexico [under protection of the Instituto Nacional de Antropología e Historia (INAH)]. The quetzal (70 centimeters, head to tail) is painted with Maya blue dye, a dye first discovered at Mayan sites. It is a mixture of clay, indigo, and metal particles in a silicate substrate. The clay and indigo form a superlattice, and scattered metal particles disperse light, producing this long-lasting blue color. See 223. [Photo: Authorized reproduction of the INAH, under its responsibility.]