Even though processed rubber is widely believed to have originated in 19th-century Europe, an MIT research team that includes an undergraduate has demonstrated that by 1600 BC, an ancient civilization was processing latex to produce rubber.
The researchers -- Professor Dorothy Hosler, Assistant Professor Sandra Burkett and Michael Tarkanian, now a senior in materials science and engineering -- published their findings in a report, "Prehistoric Polymers: Rubber Processing in Ancient Mesoamerica," in the June 18 issue of Science.
The researchers' most significant finding is that the Mesoamerican civilization, which flourished from at least 2000 BC to the Spanish invasion in 1521 in what is now parts of Mexico and Central America, engineered the properties of latex from the native Castilla elastica tree. These ancient people enhanced the elasticity of this otherwise brittle material by mixing it with juice from the morning glory species Ipomoea alba.
The Mesoamerican peoples, known for their achievements in astronomy, civil engineering, urban planning and mathematics, used the resulting pliable, tough and workable material to make solid rubber balls, hollow human figurines and bindings.
The large, resilient balls, some of which are as large as beach balls and weigh up to 7 kilograms, were used in a ritual game in the context of elaborate religious ceremonies.
"This particular project is very exciting because the Mesoamerican rubber ball game was such a fundamental ritual and political event in these societies, and the ball game could not have developed without inventing the technology to process rubber," said Dr. Hosler, associate professor of archaeology and ancient technology in the Department of Materials Science and Engineering.
"These ancient people knew how to take materials from the environment and process them to achieve the qualities they wanted," said Michael Smith, professor of anthropology at the State University of New York at Albany. He said the MIT research, by providing more information about the specific properties of the balls used, also provides more insight into how the ball game was actually played.
A "materials archaeologist," Professor Hosler carries out much of her laboratory research on the relationships between ancient societies and the technologies they developed as a member of the MIT-based Center for Materials Research in Archaeology and Ethnology (CMRAE).
CMRAE is a consortium of eight Boston-area universities and museums that promotes the use of science and engineering in archaeology, anthropology and art history. The only multi-institutional academic facility of its kind in the world, CMRAE uses modern science and engineering methods to study ancient materials processing technologies.
MORE THAN A BALL GAME
The Popul Vuh, the Mayan equivalent of the Book of Genesis, describes a religious and sacred ball game that pits good against evil and revolves around human sacrifice, fertility and regeneration.
Sixteenth-century Spanish invaders reported that the ball game also involved gambling for land, slaves and other valuables.
These high-stakes games have no equivalent in modern society. The game -- which may have ended in ritual human sacrifice -- was "central to the culture's philosophical, ritual and political beliefs," Professor Hosler said. Originally, the game was played on earthen fields, and then on enclosed masonry courts that proliferated between 400 and 700 AD. Versions of the game in which players hit a small rubber ball with a bat or stick or slammed the balls with their hips were played from southern Arizona to northern South America.
A RESEARCH ADVENTURE
Mr. Tarkanian became interested in ancient Mexican rubber when, as a freshman, he wrote a paper on the ritual ball game for a class inMesoamerican archaeology taught by Professor Hosler.
The two were discussing the ball game one day when they realized that the properties required for the balls could not have resulted from the use of latex alone. Natural latex is a sticky, unworkable liquid that dries to a brittle solid.
So Mr. Tarkanian, with support from MIT's Undergraduate Research Opportunities Program (UROP), worked in the field and the laboratory with Drs. Hosler, Burkett and other members of the materials science and engineering and CMRAE faculties. They investigated how the people of Mesoamerica made large, resilient bouncy balls more than 3,000 years before vulcanized rubber was invented.
In the process, Mr. Tarkanian became one of a handful of undergraduates to have co-authored articles in the prestigious journal Science.
THE SCIENCE OF RUBBER
Charles Goodyear is credited with inventing rubber, which is gum treated with heat and sulfur. A process similar to his was patented in England in 1843. But Professor Hosler and Mr. Tarkanian's initial examination of 16th-century documents, archaeological reports and rubber artifacts at Harvard University's Peabody Museum made clear that rubber artifacts were used throughout ancient Mesoamerica.
At the museum, they identified a number of ancient hollow rubber figurines, a band made from rubber that secured a stone axe head toits wooden handle and numerous small rubber balls.
The 16th-century documents also mentioned that Mesoamerican people made rubber-soled sandals and rubber-tipped hammers and drumsticks. The documentary sources, ethnographic research and chemical data all indicated that ancient Mesoamerican people mixed natural latex with the juice of the morning glory vine, a plant prized for its curing and hallucinogenic properties that tends to grow near rubber trees.
"Our guess is that they mixed two sacred materials together," Mr. Tarkanian said.
In 1997, Professor Hosler and Mr. Tarkanian collected latex and Ipomoea alba during ethnographic research on the coastal plain of Chiapas, Mexico, where local communities still process rubber using the same methods recorded by 16th-century Spanish observers.
In 1998, Professor Hosler received permission from the Instituto de Arqueolgia e Historia, the institution that oversees all archaeological research in Mexico, to sample two ancient Mexican rubber balls dredged from Manati, an archaeological site in a swampin Veracruz. To prepare himself to slice off a section of an excavated rubber ball, Tarkanian cut pieces out of watermelons. "It was nerve-wracking," he said.
Dr. Burkett, the John Chipman Assistant Professor of Materials Chemistry, guided the analysis aimed at identifying the mechanisms responsible for coagulation of the latex/morning glory mixture. State-of-the-art testing techniques showed that mixing the two improves the material's elastic properties and creates a pliable, tough, workable substance suitable for a variety of uses. The morning glory plant contains sulfur compounds that are capable of cross-linking the latex polymers and introducing rigid segments into the polymer chains. When these chains interact with and entangle one another, they produce rubbery properties.
AN UNUSUAL OPPORTUNITY
Mr. Tarkanian, an accomplished saxophonist who has been playing since he was eight, thought he would major in chemical engineering at MIT. On his mother's advice and because it sounded "interesting," he chose Professor Hosler's first-year seminar on ancient and modern technologies. Then, closed out of a class on jazz, he signed up for her class on Mexican civilizations.
"I didn't plan on getting involved in archaeology, but I've really enjoyed it," he said. (He still plays the saxophone, although his workload has cut into his practice and performance time.)
Professor Hosler is pleased that a chance meeting through a freshman seminar has led to such a long-term, fruitful project.
"My Mesoamerican archaeologist colleagues are very excited about our work and I am delighted I was able to involve Mike from the beginning," she said. "Mike is a steady, straightforward and intellectually honest individual who knows how to follow his instincts and intuition. These are important qualities in any field of research."
Mr. Tarkanian has worked on this project every semester and summer of his time at MIT, sometimes for pay and sometimes for credit, through UROP, in which students can join a faculty member's research project and receive academic credit or pay for their work. More than 80 percent of graduating seniors have participated in at least one UROP project during their MIT careers.
"For almost four years, Mike has put an enormous effort into this project, both in the laboratory and on his several trips to Mexico," said Michael Bergren, program administrator for UROP. "He has made a big contribution to the field of archaeology, and UROP is thrilled to have supported his impressive work."
"As a materials science and engineering major, the lab experience I'm getting, along with the knowledge I have gained about rubber processing and polymers, have been invaluable," Mr. Tarkanian said. "This project has provided me with an excellent source of knowledge, not only for my major, but for a future career. UROP has been the best part of my experience at MIT."
A version of this article appeared in the July 14, 1999 issue of MIT Tech Talk (Volume 44, Number 1).
