How it began
By 1600 BCE people in ancient Mesoamerica were processing latex into rubber. The oldest evidence comes from Manati, an Olmec site in a swamp in Veracruz, Mexico, where about a dozen rubber balls dated to roughly 1600 BCE were recovered. In 1999 Dorothy Hosler, Sandra Burkett and the undergraduate Michael Tarkanian of MIT published an analysis of the material in the journal Science under the title Prehistoric Polymers.
Before it existed
Natural latex on its own is a sticky, unworkable liquid that dries to a brittle solid. It could not have produced the large bouncing balls known from ancient Mexico. Processed rubber was widely believed to have originated in 19th-century Europe and the United States, where a comparable curing process was patented in England in 1843.
How it works
Ancient Mesoamericans mixed latex from rubber trees with juice from the morning glory vine Ipomoea alba, which tends to grow near rubber trees. The vine contains sulfur compounds able to cross-link the latex polymers and add rigid segments to the polymer chains. When the chains entangle they give the material its rubbery behavior. A later MIT study found that a 50-50 blend of latex and morning glory juice gave maximum elasticity, suited to balls.
What changed first
The pliable, tough and workable material was made into solid rubber balls, hollow human figurines and bindings, including a rubber band that fixed a stone axe head to its wooden handle. The balls, some as large as beach balls and weighing up to 7 kilograms, were used in a ritual ball game played in the setting of elaborate ceremonies.
What lasted
The MIT work showed that Mesoamerican peoples made large, resilient rubber objects more than 3,000 years before vulcanized rubber was invented. The researchers reproduced the process in the field in Mexico with fresh latex and morning glory vines, and their findings gave archaeologists new information on how the ball game was played.
