X-RAY FLUORESCENSE ANALYSIS
What is X-ray Fluorescence?
X-ray fluorescence (XRF) is a non-destructive analytical technique that uses low-level radiation to excite elements. When excited, elements fluoresce (emit light) at known energy frequencies, revealing an object’s elemental fingerprint as unique as your own but on a much smaller scale! Think of an XRF spectrometer as a high-powered flashlight, it allows scientists to detect what human eyes cannot see--the different elements that make-up material (Figure 1). There is a lot to discover using this investigative tool. Researchers can use XRF in many contexts, because it works on almost anything— from determining the geological source of rocks or clays, to the composition (characterization) of copper.
What can XRF tell us about the Tse’K’wa collection?
By investigating the Tse’K’wa collection using XRF we learned more about the geology, chemistry, and geography involved in ancient resource use by Indigenous people in the Peace River region. The XRF analyses show the types of rocks people chose to make their tools long ago. The twenty-two lithics in the teaching kit are made from six raw material types: quartzite, black chert (cryptocrystalline silicate), nephrite, ironstone, amphibolite and obsidian (Figure 2, spectrum example). This is surprising, considering how different looking many of the rocks are. The elemental concentrations (raw photon counts) of each rock determine their type. In other words, it’s what’s on the inside that counts. Colour is not very important.
Some of these carefully chosen raw materials (e.g. quartzite and black chert), were available locally in the Peace River area. Others, such as obsidian, may have been acquired through trade and/or exchange. The source of the obsidian is Mt. Edziza, in northwestern BC, far from the Peace River. We know this because the elemental fingerprints of the obsidian tools match reference library fingerprints of known sources identified on the mountain. If source fingerprints did not match (Figure 3) we would eliminate Mt. Edziza as a potential place of origin. Knowing where raw material comes from does not explain where the tool was made, nor by whom. But, it does show the long-distance networks established by ancient peoples to transport goods. It also provides a possible indication of obsidian’s value.
At this time, the other Tse’K’wa tools could not be matched to known sources. Further mapping and analyses of sources in British Columbia will need to be undertaken by present and future researchers—maybe you? This type of exciting work often involves traversing mountainous terrain to remote locations (Figure 4). The cumulative shared results of these research expeditions help people to understand the past in different ways by blending Indigenous knowledge with current scientific methods.
Interested in seeing the XRF results table and spectra? Click here to download the results.
Web page written by Robyn Ewing. Web page design by Melissa Rollit, 2017.
Special thanks to Dr. Rudy Reimer, XRF analyst.