The Fluoride Dating Service Center provides fluoride measurements on bone and other materials on a fee-per-service basis.

The fluoride measurements are usually used for relative dating.

 What is Fluoride Dating?

 Fluoride (or fluorine) dating is a relative dating method that can be used to date archaeological bone.  As a relative dating method, it can determine the relative age of specimens, but cannot provide a calendrical date unless the fluoride chronology is calibrated with an absolute dating method.

 Bones are primarily composed of the mineral calcium hydroxy apatite.  When exposed to water that contains fluoride, a fluoride ion (F-) can replace a hydroxyl ion (OH-) in the bone mineral.  The resulting fluor-apatite is more stable than the original form, thus the fluoride content of a bone will increase over time if it is exposed to a solution containing fluoride ions.  Fluoride ions are present in trace amounts in most soils and groundwaters.  Over time, buried bones pick up fluoride ions from soil moisture or exposure to groundwater.  Older specimens have higher fluoride contents than younger ones when burial conditions are identical.  The requirement of identical burial conditions means that fluoride dating works best when it is applied within a single site with little variation in soil chemistry.

 How is Bone Fluoride Content Measured?

  Many different techniques can be used to measure bone fluoride content, but measurement by ion selective electrode is the easiest and simplest method available today.  The fluoride selective electrode uses the same principle as the familiar pH electrode.  When the electrode is placed in a solution that contains fluoride, it produces a voltage that is proportional to the amount of fluoride in the solution.  A calibration curve can be produced by measuring standard solutions of known fluoride concentration.  The calibration curve is then used to determine the fluoride content of unknowns.  A desciption of the method is given in:

  Schurr, Mark R.1989.  Fluoride dating of prehistoric bones by ion selective electrode. Journal of Archaeological Science 16: 265-270.

 What Does Fluoride Dating Offer?

   It can be used to determine the relative dates of faunal materials.  The relative dates can be used to date contexts that did not contain diagnostic artifacts or that did not provide carbon suitable for radiocarbon dating.

•    It can be used to evaluate the integrity of an archaeological context.  Relative dates can be used to identify the degree of mixing in contexts that were not obviously mixed or stratified.
•    It can be used to study changing patterns of faunal utilization over time within a single site.
•    It is economical, costing less than $20 per sample (with three replicate measurements).  The charge mainly covers undergraduate student assistant labor.
•    Fluoride dating uses very small samples.  This example used 5 mg samples, but we have successfully analyzed samples as small as 0.5 mg.  Compare this with a conventional radiocarbon date, which requires about 10 grams of bone and costs around $400.
•    Fluoride dating can measure very small chronological differences.  Samples with fluoride contents that differ by as little as 0.024 % can be statistically distinguished from each other.  Under favorable conditions, this can represent a time resolution of 10 to 20 years!

What does it cost?

  The Service Center charges $16.50 per sample (please contact the Center for the most current rates).  This covers cleaning the sample, preparing it for analysis, making three replicate measurements on each specimen, calculation of the fluoride content, and entry of data into a spreadsheet.  Statistical evaluation of the data and consulting reports are available on request.

Will fluoride dating work at my site?

 Fluoride dating has been successfully used in a wide variety of settings, ranging from extremely arid Sudanese Nubia, to the humid eastern USA.  It has been applied to sites ranging from very old to very recent (for example, the famous Piltdown specimens contained both), and with bones that range from partially fossilized to less than a thousand years old.  A bibliography of fluoride dating applications is available.

Fluoride dating of control samples and burial treatment clusters was used to establish the contemporaneity of the burial treatments at the Middle Mississippian Angel site in southwestern Indiana. Each of the clusters represents a different type of burial treatment.  The error bars on the fluoride measurements are one standard deviation limits, so all of the treatments represent contempory burial modes, with one cluster (Cluster 6, flexed burials with artifacts, lowest fluoride content) possibly being among the latest.

At the Los Pozos site in Arizona, fluoride dates from intersecting features (such as those shown here) excavated by Desert Archaeology, Inc. were used to establish a relative chronology for house basins at the site.

  Where more older features were cut into by more recent ones, the more recent features tend to produce bones with lower fluoride contents.  The results from these control features show that fluoride dating can be used to date house basins at Los Pozos that have not been cross-cut by other features (the majority of house basins at the site). The complete text of the poster presented at the 2000 Society for American Archeology Annual Meeting is now on-line at http://www.nd.edu/~alfac/schurr/ .

  Fluoride is transmitted through ground water, so optimum performance is obtained on sites where the soil chemistry is consistent, the are not dramatic differences in soil moisture, and where the sediments are relatively fine grained.

  In most cases, we recommend a pilot project using samples of known chronology to evaluate the effectiveness of fluoride dating on your samples before starting a large-scale project.  We will be happy to consult with you to develop a project custom tailored to your needs.

What type of samples are required?

  Fluoride dating works best when bones of similar density are compared.  Therefore, it is rarely possible to mix results from skeletal elements with widely differing densities (i.e., femur cortical bone versus vertebral fragments), or to compare juveniles with adults, or to compare bones from very large or very small mammals.  For faunal specimens, we recommend long bone fragments, which are usually very abundant.  For humans, either ribs or cortical bone fragments both give good results, as long as one type of bone is consistently used.

  We require at least 0.1 gram of bone simply for handling convenience.  The actual measurements will only consume about 15 mg.  The remainder will be returned to you in a labelled vial.

For more information, contact:

  Dr. Mark R. Schurr
  Director, Fluoride Dating Service Center
  Department of Anthropology
  University of Notre Dame
  Notre Dame, IN 46556   USA

  Phone:  (219) 631-7638
  FAX: (219) 631-8209

Email: Mark.R.Schurr.1@nd.edu

This page's WebCounter count says you are visitor number