Frequently Asked Questions

The energy dispersive x-ray fluorescence (edxrf) technique employed at GRL is COMPLETELY non-destructive; no portion of a sample is altered in any way during analysis. Unlike some instrumental techniques, which require sacrificing (powdering, breaking into small chips, or otherwise modifying) some portion of the specimen, after edxrf analysis all specimens will be returned in the same condition as they were received at the lab.

The time it takes to complete a project varies, depending on: 1) the number of samples you submit, 2) the number of samples and projects that are in front of yours. Projects with smaller numbers of specimens can be completed much more quickly than projects involving hundreds of samples. In general, project submissions of 50 or fewer specimens can be completed within 2-4 weeks of receipt, depending on 2) above. If your project can't wait that long for results, please contact Dr. Hughes to discuss the situation. See Expedited (Priority) Processing

Reliable quantitative composition estimates (in parts-per-million and weight percent) can be obtained on specimens as small as ca. 9-10 mm in diameter and ca. 1.5- 2mm thick, with at least one relatively flat (lenticular or biconvex) cortex-free surface onto which the x-ray beam can be directed. Specimens > 9-10 mm diameter and > 2 mm thick can be readily analyzed. Some samples can be analyzed if they are somewhat < 9-10 mm in diameter IF they are > 2mm or so thick, thanks to a sample mass correction algorithm developed at GRL which compensates for reduced diameter. However, if a sample is > 10 mm in diameter, it may not yield reliable quantitative composition estimates for certain elements IF it is extremely thin (e.g. < 1 mm thick) because of current difficulties in compensating mathematically for the effects of varying x-ray penetration properties.

In some parts of the United States (e.g. southern and central California, the Great Plains and Rocky Mountains, Midwestern states) it is possible to make secure artifact-to-source (chemical type) attributions non-destructively for very small flakes and artifacts (< 9-10 mm diameter and <1.5-2 mm thick) using integrated net peak intensities (i.e. using elemental peak counts and ratios thereof). This approach has proven highly reliable in many archaeological situations (most recently in the Great Plains, Rocky Mountains, and Midwestern U.S.), though integrated net peak intensities usually will not yield satisfactory results in areas where archaeologically significant obsidians have generally similar, though subtly distinct, trace element compositions. Contact Dr. Hughes in advance to discuss whether or not net peak intensity analysis is appropriate for your study area.

After edxrf analysis is complete, you will be sent a letter reporting the results. Each letter report specifies technical parameters (laboratory equipment, analysis protocol, literature references), provides all measurements generated for each specimen analyzed, and includes a brief summary of the results. Each letter report has its own GRL letter report designation, which can be formally cited in reports, manuscripts and publications.

In addition to hard copy, the letter report and all accompanying data tables can be sent to you as email attachments at no additional cost.

Following completion of edxrf analysis, a letter report summarizing the results is prepared, and an invoice is issued for the work. The invoice typically contains billing information specified in your cover letter (see What to Send With the Samples), which may include a governmental or institutional purchase order or requisition number. GRL is a member of the U.S. government’s System for Award Management (SAM) and is able to receive electronic payment for U.S. Department of Defense, U.S. Department of the Interior (Bureau of Land Management and National Park Service) and U.S. Department of Agriculture (Forest Service) projects via PayPal, in addition to conventional two-party checks.

No, GRL specializes exclusively in "sourcing" (geochemical characterization) studies. However, the lab maintains an up-to-date list of qualified obsidian hydration analysts, and would be happy to make a recommendation if you would like to have hydration analysis undertaken. After source analysis is completed at GRL, samples can be forwarded to the hydration analyst of your choice at no additional cost.