Last summer, I had the good fortune to spend a couple of days (including a day at the Clunie Site) with Heather Walder, PhD candidate from the University of Wisconsin, Madison. As part of her dissertation work, Heather is using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) to do some really cool research into the chemical makeup and chronology of certain early blue glass beads and she agreed to incorporate a bead from the Clunie site into her sample. And because one project is never enough, she, along with Laure Dussubieux from the Field Museum, Chicago, was also involved in a study using LA-ICP-MS and portable x-ray fluorescence (pXRF) to differentiate between native copper and European smelted copper. Having long-wondered about the origin of the copper beads and scraps from our Clunie site excavations, I was eager to contribute a sample to their research.
I am happy to announce that, in a poster titled Identifying American native and European smelted coppers with pXRF: a case study of artifacts from the Upper Great Lakes region, the results of their study will be presented this week at the Society for American Archaeology 79th Annual Meeting in Austin, TX. To quote from their poster, this study “assesses the reliability of portable x-ray fluorescence (pXRF) as a fast and effective method of identifying cold-worked native versus European smelted coppers without any sample preparation.” Their sample includes a series of 11 copper beads and scraps from the (protohistoric) Clunie site and 32 similar artifacts from the (protohistoric and later historic) Rock Island site in Wisconsin. Prior to using pXRF, an attempt was made to categorize each artifact as native or European copper based on archaeological context and visual inspection. As a test of the accuracy of the pXRF assessments, eighteen of the artifacts were further analyzed using LA-ICP-MS.
Briefly, they found the completely non-destructive pXRF technique reliably, and relatively inexpensively, differentiated between native and European smelted copper. There was no disagreement between the pXRF and LA-ICP-MS results. Further, they found that visual assessment alone, especially from the earlier protohistoric contexts, was quite unreliable. The big news for the Clunie site is that while most of the beads and scraps are cold-hammered native copper, one of the scraps is, indeed, smelted European copper!
If you’re attending the SAAs this year you should definitely stop by, say hello to Heather, and check out the poster! It will be given in Austin on Thursday, April 24th in the session titled: Compositional Analyses and Sourcing Studies in Archaeology.