Step 1: Physical pretreatment

The first step for all samples submitted to the laboratory is physical examination and cleaning. It may seem obvious, but identification labels and descriptions are examined carefully to insure that what we are about to analyse is what the submitter thinks they have submitted.

rafter scientist physical pretreatment

This is not a trivial step since:

  • A textile may be made of more than one type of material.
  • Charcoal may prove to be degraded and oxidized plant fragments.
  • Shells may have a powdery/chalky appearance, indicating recrystallization.
  • Sediments may be submitted which, when examined under the microscope, turn out to be a mixture of soil, flecks of charcoal, fragments of wood and plant debris. Each of these components was deposited in the sediment from a different origin and possibly could have different ages.

In each of these cases, we would report our observations and discuss with the submitter which fraction is the most optimal for dating based on their research objectives. Because the sample size requirement for AMS is so small, it is possible that different fractions within the sample can be separated, dated independently and the ages compared.

During physical pretreatment, samples are examined under a microscope. Obvious extraneous materials such as rootlets or thread are picked out with forceps. Surface dirt and contamination such as glue or ink is removed. Exterior parts of the sample are washed or otherwise cleaned as appropriate for the type of sample. Some samples are sieved to select an appropriate size fraction. Finally, the sample is crushed or ground to reduce it in size and increase the surface area.