Title: HOW AZTECS PLAYED THEIR RUBBER MATCHES , By: Stokstad, Erik, Science, 00368075, 06/18/99, Vol. 284, Issue 5422

HOW AZTECS PLAYED THEIR RUBBER MATCHES

When 16th century Spanish clerics came to the New World, they were enthralled by a fast-paced and sometimes bloody sport. Teams of up to six athletes would whack heavy, solid balls through hoops several meters above the stone courts using anything but their hands or feet. Apart from the occasional postgame human sacrifice, what most astonished the Spanish were the ricocheting balls. "I do not understand," wrote Pedro Martyr, the official historian of the Spanish court in 1530, "how when they hit the ground they are sent into the air with incredible bounce." For Europeans used to playing with pigskins, the rubber balls were practically miraculous.

The native Americans made their seemingly magical material, Martyr wrote, by collecting sap from lowland trees and mixing in juice from a vine. Four centuries later, this crude recipe has finally given up some of its secrets. On page 1988, researchers describe how the Olmec, Maya, and other ancient Mexican and Central American cultures turned raw latex into rubber. This feat of chemistry, which converts the slippery polymers in raw latex to a resilient structure, was not duplicated until the mid-19th century. "It's a marvelous example of technology demonstrated at an incredibly early stage," says Frank Bates, a polymer chemist at the University of Minnesota, Minneapolis.

The ball game, invented at least 3400 years ago, was an important ritual for many Mesoamerican societies. To the Maya, for instance, the game--called chaah--reenacted portions of their creation story. By the 5th century A.D., many towns had central stone courts, some of which could hold thousands of spectators. Leaders tested prophecies through tournaments, rival cities took out their aggressions on the court, and the rich placed huge wagers. According to a 16th century codex, the Aztec capital Tenochtitlan demanded 16,000 rubber balls each year as tribute from one province. The ballmakers "were the ancient equivalent of Rawlings," the sporting goods manufacturer, says Warren Hill, an archaeologist at the New World Archaeological Foundation of Brigham Young University in Provo, Utah. These societies also used rubber for a host of other products, including religious figurines, incense, and even lip balm.

Last summer, Massachusetts Institute of Technology (MIT) archaeologist Dorothy Hosler and undergrad Michael Tarkanian traveled to Chiapas, Mexico, to gather the raw materials for rubbermaking mentioned in ancient documents. To their surprise, they saw farmers collecting latex by slashing the bark of Castilla elastica trees, then mixing in juice from pulverized morning glory vines that wrap around the trees--just as the 400-year-old texts described. "It was amazing," recalls Tarkanian. "After about 10 minutes, a mass of rubber rose to the surface. We formed it into a ball that would easily bounce over your head."

The pair brought the ball, as well as raw latex and vine juice, back to their lab. A battery of tests showed that the homemade rubber was about twice as elastic as dried latex, which cracks when handled. With MIT materials scientist Sandra Burkett, the researchers probed the material with nuclear magnetic resonance spectroscopy, finding unidentified organic compounds in the latex that were absent from the rubber.

The team speculates that some of these mysterious compounds might be plasticizers, which would keep the latex runny by preventing its polymer molecules from linking to each other. (Modern rubber is made by cross-linking polymers.) If the vine juice dissolves the plasticizers, the researchers thought, polymer molecules would be more likely to entangle and form a rubbery mass. Although they failed to find direct evidence for cross-linking, they did discover vine juice components--traces of sulfonyl chlorides and sulfonic acids--that can react with polymers, stiffening segments and making them more likely to interact. The team says that only a few such entanglements would be enough to give the rubber its spring.

Understanding ancient rubbermaking "teaches us how conscious these people were of their environment and how they were able to manipulate it," Hosler says. She and her colleagues next plan to test rubber made with varying amounts of vine juice to see whether the Olmec, Maya, and Aztec could have engineered rubber with specific elasticities. No matter what they find, the Mesoamericans have earned the respect of modern chemists. "To discover [the process] and refine it to make those products is impressive," says Bates. "They probably had a pretty good R&D team."