Module:  Rubber Processing
                     in Ancient Mesoamerica

Theme:

Ancient Mexican peoples harvested latex from Castilla elastica, the indigenous rubber tree, and processed it using the juice of Ipomoea alba, a species of morning glory vine, to produce rubber. Their discovery of this rubber processing technology at 1600 BCE predated Charles Goodyear's discovery of vulcanization by approximately 3500 years. Ancient Mexican peoples used rubber principally as a ritual material, whereas the interests of modern western society lay in industrial applications. Ancient Mexicans made large, solid, heavy (7 kg) balls from rubber, which they used in a sacred ball game that became a key ritual event throughout Mesoamerica, from Olmec to Aztec times. They made solid and hollow rubber figurines to represent deities. Rubber was also engineered for practical ends to make sandals and to haft tools. This module explores the independent development of rubber in two distinct social and cultural milieux and illustrates the ways in which cultural variables can shape technologies.

Module program:

The module will be structured as lecture/discussion and laboratory sessions. Lectures will address the social context of rubber processing in ancient Mexico, in particular the Mesoamerican ritual ball game, and will contrast ancient Mexican and western uses of rubber. The materials engineering differences between the ancient and modern rubbers will be explored through consideration of their polymer chemistries, their performance as elastomers, and their response to property development. In laboratory, participants will reproduce ancient Mesoamerican rubber using the two indigenous materials (C. elastica and I. alba) and will test the mechanical properties of both the Mexican product and modern industrial rubbers.

Material culture component:

Participants will examine the cultural environment in which rubber processing developed in ancient Mexico through readings, lectures, and discussions and will compare this to the development of rubber production in western industrial society. We will consider and evaluate the historical evidence for the ancient processing of rubber, the botanical evidence for processing, and the ethnographic and archaeological data for processing. Discussions will focus on the ways in which social forces shape technical choices, principally in the products made from rubber (ritual rubber balls and figurines vs. automobile tires, for example) and in rubber processing technologies. In ancient Mexico the rubber ball game was a central event that recapitulated the Mesoamerican creation story in which forces of good challenged the forces of evil on a ball court. The victors, the forces of good, became the moon and the sun, thus setting the universe into motion. Thus rubber was a material intimately connected to the origins of society in Mesoamerican cosmology and in the ritual games that expressed that cosmology. Contemporary indigenous Mexican peoples continue to play versions of the ancient ball game, and in the coastal plain of Chiapas local villagers harvest latex and mix it with morning glory vine to form traditional products. The western experience is entirely different. Goodyear's discovery made the automobile possible and fueled industrialization. Multiple applications of latex and rubber allowed advances in medicine (urinary catheters, latex surgical gloves) and in other fields. Rubber in western society is relegated nearly exclusively to utilitarian applications as well as to sports and other non-sacred cultural activities.

Materials science/engineering and laboratory component:

Treatment of the mechanical behavior of polymeric materials will serve as the basis for a full discussion of ancient and industrial rubbers. Molecular weight, crystallinity, crosslinking, molecular orientation, and physical entanglements are the primary characteristics of polymeric structures that are important in determining the strength and overall mechanical behavior of polymers. We will pay particular attention to elastomers, which include natural and synthetic rubbers, as loosely chemically crosslinked, amorphous polymer networks typically with a low glass transition temperature below room temperature (Tg<RT). Elastomers exhibit non-linear deformation and full recovery and can extend elastically for strains up to several hundred percent. Comparison of Mesoamerican and industrial rubber processing will consider (1) the curing of natural latex by crosslinking of polyisoprene chains with sulfur (vulcanization), and (2) dissolution by I. alba of proteins that surround polyisoprene chains in the latex emulsion of C. elastica, enabling their entanglement, interaction, and stiffening of the material, as well as crosslinking or cyclizing of the chains by sulfonic acid and sulfonyl chloride moieties present in I. alba (ancient Mexican processing).

The laboratory: Laboratory sessions will include the processing of rubber and the mechanical testing of rubber made by different processing techniques.

If time allows, SI participants, faculty, and graduate students will assemble on the MIT playing field to play the Mexican ball game with the rubber balls made in the laboratory!