When Europeans reached South America roughly 500 years ago, they were awed by all the rubber products in Aztec cities, including giant bouncy balls and rubber bands. Now scientists have figured out how the Aztecs manufactured different grades of rubber.
MIT materials scientist Dorothy Hosler worked with a team to recreate the manufacturing process the Aztecs would have used to make rubber, which comes down to different mixes of latex refined from tree sap and morning glory juice. Because so few rubber artifacts survive - only a couple of very brittle rubber balls - the researchers relied on reports from Spanish explorers to figure out all the rubber products the Aztecs had. Spanish accounts include descriptions of rubber-soled shoes, as well as rubber bands used for making spears. And it turns out that merely varying the ratio of latex to juice results in many different grades of rubber.
In the image above, you can see the Aztec god Ziuhtecuhtli using rubber balls in a ceremony.
According to MIT news:
Sure enough, varying the proportions produced different properties. A 50-50 blend of the latex and morning glory produced maximum elasticity, or bounciness, perfect for the rubber balls. Rubber used as an adhesive or for joining other materials (such as ceramic and wood) needs different properties - strength and damping ability - and for that, pure latex seems to work best. For sandals, where wear resistance is the most important quality, a three-to-one mix of latex to morning glory provides the most durable material.
The Mesoamericans had plenty of time to work out these properties through trial and error. By the time the Spanish arrived, Tarkanian says, "there was a large rubber industry" in the region, producing 16,000 rubber balls each year, and large numbers of rubber statues, sandals, bands and other products. Most of those were produced in villages in outlying areas, and were shipped to the capital city as a form of tax payment.
Long before European countries were using rubber in their manufacturing, the Aztecs had a thriving industry build around the substance.
via MIT News