First, take the root of an orchid, slice it and dry the cross sections in the sun for about 72 hours. When they have hardened into chips, pound them into a powder, then add water, heat it and stir. The resulting goo will make a glue delicate enough to bind feathers to wood without damaging them and strong enough to last centuries.

This is how the Aztecs did it, according to anthropologist Frances Berdan of California State University at San Bernardino, who studies the economics of pre-colonial Mexico and the ways Aztec artisans made a living.

Berdan, who is analyzing adhesives from a dinner plate-size feather mosaic from Mexico City's National Museum of Anthropology, began researching Aztec glue about 10 years ago, working from texts written by 16th-century Spanish conquistadors.

"There are a number of documents that describe the glue, complete with drawings of the plants," Berdan said. "They appeared to be orchids, except there were so many kinds, I wasn't sure. But orchid dealers identified them immediately."

Berdan and colleagues collected some of the orchids, and using the recipes from the texts, managed to reverse-engineer the glue. What they got was a clear adhesive that artists used to attach colorful bird feathers to wooden or hide backings, creating fine mosaics used in ceremonies, worn as decorations or displayed in houses.

"It's a very ancient skill, but we only have eight samples from before the conquest," Berdan said. Many more mosaics survived from the first few decades after the Spanish arrived in 1519, she said, "but it was something that the upper-class Aztecs did, and by the end of the 16th century there were a lot fewer nobles."