On Tar's Trail at the Recent SAA Conference in Vancouver
Tuesday, April 8, 2008
 
Keywords: bitumen, tar, asphalt, organic chemistry, Olmec, sourcing, economics
I've posted about bitumen before: here and here.  I did view this poster at SAA -- it was part of the "Archaeometry and Artifact Studies in Mesoamerica and Middle America" session on Thursday evening -- but only briefly, and I'll admit that I don't recall it well.  I have good excuses, though... really.  For one, I was eagerly awaiting posters in a session called "Innovations in Ceramic Analysis"... but, by the time I left the exhibit hall, there was only one of the three posters in the session up -- how disappointing!  Another reason is that, well, I was distracted from this good poster by a nearby bad one -- no, I'm not saying which one.  Lastly, an evening session on the first day is a horrid idea -- hear that SAA?  Everyone is meeting up with conference friends and hungry for dinner after a rushed (and expensive) lunch between morning and evening sessions, and I, too, was eager for dinner with colleagues.  But it looks like I walked too quickly past this interesting research on Olmec use of bitumen.
Above: Bitumen oozing out of carbonate boulders on a hot summer day.  Credit: Natural Resources Canada.
Excerpts from Science:
Following an Asphalt Trail to Ancient Olmec Trade Routes
By Heather Pringle
News Focus: Society for American Archaeology Meeting, 26-30 March 2008, Vancouver, Canada
When archaeologists teach about the Olmec culture, they flash images of massive stone heads, sculpted for a sophisticated elite who ruled the swampy lowlands of Mexico from 1200 to 400 B.C.E. But a poster by archaeologist Carl Wendt of California State University, Fullerton, throws the spotlight on Olmec commoners. Once dismissed as simple maize farmers, the ordinary Olmec apparently mastered a sophisticated technique for making asphalt, crucial to sealing wooden boats, and they traded the valuable substance to others. 
This research will shed new light on previously invisible trade routes, says Olmec expert David Grove of the University of Florida, Gainesville. Because Wendt can distinguish asphalt from various sources, Grove notes, the work "adds a significant new 'artifact' [asphalt] to the small list of artifacts that can be used in the study of trade in Mesoamerica at 1000 B.C.E." 
Earlier archaeologists paid little attention to asphalt, occasionally noting its presence on sacred figurines, tool handles, and potsherds. But during excavations at the Olmec site of Paso los Ortices, Wendt discovered a pit containing 250 kilograms of asphalt slabs. He wondered how the Olmec processed asphalt, what they used it for, and whether elites controlled its manufacture. 
To find out, his team studied thin sections of asphalt lumps from Olmec sites with a petrographic microscope. They noted even patterns of sand particles and impressions of decomposed plants, suggesting that these silica-rich materials were intentionally mixed in during heating to add structure to the asphalt. The team also identified and sampled more than 50 asphalt seepages in the Olmec region. 
Then they experimented, adding different plant additives and heating samples in clay pots over fires to produce an asphalt that was both flexible enough to apply to figurines and other objects and yet hard enough to resist melting in the sun. "We had a bear of a time trying to get it to that state," says Wendt. Some samples were simply too watery. But Wendt and his team processed other, stickier samples in just a few hours; they found that the leaves of a plant the local inhabitants use to wrap tamales produced the best asphalt. . .

To read the rest of the article, visit the Science website:
http://www.sciencemag.org/cgi/content/full/320/5873/174a





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