Lasers, Ceramics, and Numbers
posted March 07th, 2011
February 14 through February 17 I used the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) at the Elemental Analysis Lab to source decorated earthenware from the prehispanic site of Tanjay on Negros Island, Philippines. This research will address the debate on the importance of craft specialization to the development of pre-modern complex societies and elucidate exchange networks for prestige goods in prehispanic Southeast Asia.
Here is a little bit on how LA-ICP-MS works…
LA-ICP-MS is a widely used analytical technique in a variety of scientific fields including geology, biology, and archaeology. A sample is placed in a vacuum-sealed chamber and a microscopic amount of matter is extracted from the sample by focusing a laser beam on its surface. The energy provided by the laser is absorbed by the sample resulting in vaporization and generation of aerosol which is subsequently transported by a carrier gas through tubes to the ICP-MS instrument. Here the sample is ionized by the ICP-torch and then analyzed by the Mass Spectrometry instrumentation.
The really "cool" part of the LA-ICP-MS device is the fact that the torch reaches temperatures of 10,000 Kelvin! Therefore, while you are running the machine, a miniature SUN is flickering nearly 2 feet from your face. Needless to say, the protective shielding is a bit more elaborate on the LA-ICP-MS then the mesh on your household microwave. The laser itself is controlled through a user-interface that is connected to a miniature video monitor that allows for pinpoint precision. In fact, aiming the laser is quite like a video game where instead of blasting zombies you're avoiding temper (which can mess with your results if you're examining ceramic pastes) and making sure you don't blast the same spot twice. Fortunately for me, the LA-ICP-MS is virtually dummy-proof and training only a half hour. Mark Golitko, Post-Doctoral Researcher here at the Field Museum, was a more than capable teacher (he was so good, in fact, he's the one featured in the thumbnail for this post).
Unfortunately, the initial wonder and awe wears off after the first hour of loading the ceramic sample, vacuum-sealing the chamber, shooting the sample, and repeating. The process is incredibly motononous and requires white, elastic booties (contamination issues in the lab). Over my week I was able to analyze a total of 33 samples, make several thousand ablations, and now all that is left is to crunch the numbers. The work is far from complete, however, since for every hour of lab time, THREE hours are spent on the statistics. If only Isaac Newton were here to help me!
If you're interested in how LA-ICP-MS works check out this link which features the University of Missouri Archaeometry Lab where a lot of this sort of research is undertaken. My colleague Lisa Niziolek and I hope to present this work with decorated earthenware at upcoming professional conferences and possibly co-author a journal article or book chapter. We are also collaborating with Laura Junker, Associate Professor at UIC (Dept. of Anthropology), who has conducted extensive excavations at Tanjay.