Diffusion Laboratory
Obsidian Hydration Dating and X-ray Fluorescence Analysis
Archaeometry for Applied Archaeology
Diffusion Laboratory is a facility dedicated to the dating of obsidian artifacts and establishing the provenance of archaeological materials.
Obsidian hydration dating is conducted by infrared photoacoustic spectroscopy-- a method that provides a superior level of measurement precision.
X-ray fluorescence analysis of material trace elements is used to establish the geological origin of cultural artifacts.
Exploring the possiblities
of science
Obsidian Hydration Dating
Diffusion Lab offers a new and highly precise method to convert the amount of diffused water within the obsidian hydration layer to a relative or absolute age. Hydration rim measurement is conducted by infrared photoacoustic spectroscopy (PAS) (Stevenson et al. 2001). Thermal expansion of water molecules induced by the infrared light creates a pressure wave at the surface of the artifact that is converted into a spectrum with characteristic water peaks. The more intense the photoacoustic response, the higher the peak, and the thicker the hydration layer. Peak intensities are converted to hydration layer thicknesses using a set of SIMS calibrated samples.
Chronometric hydration age estimates may be made when the structural water content of the obsidian and the ground temperature of the archaeological site are known. Infrared PAS measurements determine the obsidian structural water content and from these values the experimental hydration rate constants are estimated. The constants are then adjusted to reflect ambient temperatures at the archaeological site. Archaeological age estimates using this method have a precision of approximately +/- 40 years.
Optical image of a hydration layer
Infrared photoacoustic instrument
Ceramic Rehydroxylation Dating
New Application
Coming Soon
Ceramic rehydroxylation dating is a new, non-destructive method recently deveoped by British material scientists. It is best suited for unglazed ceramics that come from buried contexts. This includes earthenware, brick and tile.
Rehydroxylation dating is based on the principle that a ceramic matrix will absorb and bond with water molecules at a constant rate over time. The total amount of water within the ceramic is a measure of the age and can be converted to a date once the rate of accumulation is determined.
The rate of water accumulation is determined by first heating a sherd to 550 degrees centigrade. The sample is removed from the furnace and placed on an analytical balance. The enclosed chamber of the balance is maintained at a constant temperature and relative humidity. Measurements are taken every one minute to track the mass uptake of water.
As in the figure on the right , water uptake is initially rapid but then declines significantly at the top of the curve and takes on a linear form. Linear regression analysis of the tail of the curve is used to establish the rate of uptake which usually conforms to Time^0.25.
Wilson et al. (2009) Proceedings
of the Royal Society
X-ray Fluorescence Analysis
X-ray fluorescence analysis (XRF) is a well established method in archaeological studies that examine human interaction. Procurement and exchange behaviors can be established by linking artifacts to their points of geological origin, or distribution, by comparing artifact trace element concentrations with natural sources in the region. Non-destructive XRF is very well suited for the analysis of obsidian and fine grained volcanic rocks such as rhyolites and basalts.
A typical analysis applied to an obsidian assemblage consists of the non-destructive determination of ten trace elements (Fe, Ga, Mn, Nb, Rb, Sr, Ti, Y, Zr). Distinctions between obsidian sources are made through a statistical comparison of concentration values.
QuanX XRF Instrument
1) Hydration rim measurement by infrared spectroscopy: $22 per sample
2) Hydration rim measurement, structural water analysis, and age calculation: $45 per sample
3) Empirical induced hydration experiment for hydration rate estimation: $2000 per source
4) SIMS (secondary ion mass spectrometry) of hydrated obsidian surfaces: $435 per sample
1) Ceramic rehydroxylation to determine relative age: $250
2) Ceramic rehydroxylation dating with temperature determination and age estimation: $350
1) XRF analysis of 10 trace elements and source attribution:
a) 1-10 samples: $35
b) 11-50 samples: $32
c) 51-100 samples: $31
d) 100+ samples: $30
2) XRF analysis of geological source material in conjunction with a project:
a) 1-50 samples: $28
b) 51+ samples: $25
Contact Us
Christopher M. Stevenson, Ph.D.
e-mail: DiffusionLaboratory_gmail.com
Address:
1755 S. Sycamore Street Petersburg, VA 23805 USA
About Us
Diffusion Laboratory is an independent small business owned by Christopher M. Stevenson, Ph.D. A graduate of Pennsylvania State University, Dr. Stevenson has over 20 years of experience in the field of obsidian hydration and cultural material characterization studies. Diffusion Laboratory serves its clients with the objective of providing high quality analytical services in a timely manner.
Listed below are a selected number of publications that reflect the content and quality of our laboratory research:
Stevenson, C., Glascock, M., Speakman, R. J., McCartney, M. 2008. Expanding the geochemical database for Virginia jasper sources. Journal of Middle Atlantic Archaeology 24: 57-78
Stevenson, C., Wheeler, D., Novak, S.W., Speakman, R. J., Glascock, M. 2007. A new dating method for high calcium archaeological glasses based upon surface water diffusion. Archaeometry 49: 153-177
Stevenson, C., Abdelrehim, I., Novak, S.W. 2004. High precision dating of the Hopewell Site and Mound City group earthworks using secondary ion mass spectrometry. American Antiquity 69: 555-568
Infrared photoacoustic
analysis
