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- Obsidian hydration dating
To measure the hydration band, a small slice of material is typically cut from an artifact. This sample is ground down to about 30 micrometers thick and mounted on a petrographic slide.
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The hydration rind is then measured under a high-power microscope outfitted with some method for measuring distance, typically in tenths of micrometers. The technician measures the microscopic amount of water absorbed on freshly broken surfaces. The principle behind obsidian hydration dating is simple—the longer the artifact surface has been exposed, the thicker the hydration band will be.
In case of measuring the hydration rim using the depth profiling ability of the secondary ion mass spectrometry technique, the sample is mounted on a holder without any preparation or cutting. This method of measurement is non-destructive. There are two general SIMS modes: Any mass-spectrometer can work in static mode very low ion current, a top mono-atomic layer analysis , and dynamic mode a high ion current density, in-depth analysis.
SIMS in general refers to four instrumental categories according to their operation; static, dynamic, quadrupole, and time-of-flight, TOF. In essence it is a technique with a large resolution on a plethora of chemical elements and molecular structures in an essentially non destructive manner. An approach to OHD with a completely new rationale suggests that refinement of the technique is possible in a manner which improves both its accuracy and precision and potentially expands the utility by generating reliable chronological data.
A test of the model followed using results from Mount 65, Chalco in Mexico by Riciputi et al. In Rhodes, Greece, under the direction and invention of Ioannis Liritzis, [11] the dating approach is based on modeling the S-like hydrogen profile by SIMS, following Fick's diffusion law, and an understanding of the surface saturation layer see Figure.
In fact, the saturation layer on the surface forms up to a certain depth depending on factors that include the kinetics of the diffusion mechanism for the water molecules, the specific chemical structure of obsidian, as well as the external conditions affecting diffusion temperature, relative humidity, and pressure.
This latest advance, the novel secondary ion mass spectrometry—surface saturation SIMS-SS , thus, involves modelling the hydrogen concentration profile of the surface versus depth, whereas the age determination is reached via equations describing the diffusion process, while topographical effects have been confirmed and monitored through atomic force microscopy. Several factors complicate simple correlation of obsidian hydration band thickness with absolute age.
When considered through temporal periods, the variables affecting the development of hydration rims are complex Anovitz et al. Michael Elam, Lee R. Riciputi, and David R.
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The Failure of Obsidian Hydration Dating: Sources, Implications, and New Directions. Journal of Archaeological Science Ancient Mesoamerica 4 2: Friedman, Irving and John Obradovich. Obsidian Hydration Dating of Volcanic Events. Friedman, Irving and Robert L. Part I, The Development of the Method. Friedman, Irving and F. Obsidian Hydration Dating Update.
Obsidian Hydration Studies | Willamette Analytics, LLC
American Antiquity 48 3: Trembour, and Richard E. In Chronometric Dating in Archaeology, edited by R.
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Quaternary Research 41 2: Reasserting the Utility of Obsidian Hydration Dating: Liritzis, Ioannis and Nikolaos Laskaris. Journal of Non-Crystalline Solids Jack Rink and Jeroen W.
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Encyclopedia of Earth Science Series. Springer Dordrecht, New York. What controls the process? There is a very strong relationship between the rate of hydration and the quantity of intrinsic water found within the glass. This is the water trapped in the obsidian at the time the lava hardens into a natural glass. The presence of intrinsic water opens up the glass structure and allows the atmospheric water to diffuse inward from the surface to form the hydration rim.
The more intrinsic water present within an obsidian artifact, the faster it will hydrate and the faster the hydration rim will form. Three steps are required to determine a calendar date from an obsidian artifact.
Obsidian hydration dating
These are the determination of: A hydration rate is determined for every artifact through a measurement of the amount of intrinsic water that is present. This is done by either a direct infrared spectroscopic measurement of the volcanic glass, or by a determination of the volcanic glass density made by submersion in a heavy liquid.
Once the quantity of water is known a hydration rate is estimated. A small sample is cut out perpendicular to the edge of the obsidian artifact using a diamond-impregnated saw. A lapidary machine is used to grind down the obsidian sample until it is very thin. It is glued to a clear microscope slide with Canada balsam.
The obsidian sample is ground a second time until it less than 50 microns in thickness. A microscope is then used to optically measure the hydration rind on the petrographic thin section. The hydration layer is measured at x using a Watson image-splitting instrument. This is the most precise optical instrument that can be used. It has an error factor of about 0.
In order to adjust the experimental hydration rate to the conditions at the archaeological site, the soil temperature and soil relative humidity need to be well estimated. On short term projects, ambient conditions can be estimated from weather records. For studies that take longer than a year, thermal cells can be buried at the archaeological site.