Obsidian Hydration Dating
Obsidian hydration dating (OHD) originally promised to be a rapid, inexpensive, simple .. R. RidingsWhere in the world does obsidian hydration dating work?. Results ofa field study at Pot Creek Pueblo indicate that when effctive hydration temperatur-e varies significantlv wit errors in obsidian hydration age estimates. They introduced the obsidian hydration dating method to the archaeological community With this background work done, the environmental conditions can be.
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,  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-SSthus, 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.
Temperature is known to speed up the hydration process.Archaeology Dating Lecture Part 1
Thus, artifacts exposed to higher temperatures, for example by being at lower elevationseem to hydrate faster. As well, obsidian chemistry, including the intrinsic water content, seems to affect the rate of hydration. Once an archeologist can control for the geochemical signature of the obsidian e. Water vapor pressure may also affect the rate of obsidian hydration. The first step concerns the calculation of a 3rd order fitting polynomial of the SIMS profile eq. The second stage regards the determination of the saturation layer, i.
Hydration rind thickness is a non-linear function of time. The hydration rate is primarily a function of temperature, though chemical composition of the sample is also an important factor.
For this reason, it is necessary to calibrate the samples within a limited geographical area against a sample of known age and similar chemical composition. Hydration forms at different rates on different obsidians. Under the same conditions of temperature and humidity some glasses will hydrate rapidly while others are very slow. 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.
Obsidian hydration dating - Wikipedia
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 How is an Obsidian Sample Processed?
Three steps are required to determine a calendar date from an obsidian artifact. 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.
- Obsidian hydration dating
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.
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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. The small capsules are placed at multiple depths that typically span a depth range of 5 cm to cm below ground surface.
About 8 cells are required to establish a temperature and relative humidity curve for the site. With this background work done, the environmental conditions can be determined for any context at a site.
The Limitations of Obsidian Hydration Dating Using this technique, any sample of obsidian can be dated. There are several limitations, however. The rate of hydration is not uniform throughout the world. Variations exist in temperature over time from site to site.