By Esther White / Director of Archaeology
When we’re excavating, one of the popular questions is always, “What do you do with all that dirt?” The quick answer, “We screen it to recover artifacts” isn’t quite the whole story. The dirt from the midden went through one of four screenings depending on where it was from:
In the early 1990s when the midden was excavated, we used two sizes of wire mesh, 3/8” and ¼”, to dry screen most soils. Other soils were processed using water, either through a water screen which captures materials as small as 1/16” or through flotation designed to recover in a mesh cheese cloth microscopic seeds, charcoal and items that can float on water. Just keeping track of which method should be used for which soils was a pretty big job. Our research design, a document that posed questions to be answered from the excavation of the midden, provided a blueprint for making those decisions during the four year excavation.
Because our primary research interests with the midden revolve around George and Martha Washington’s life and Mount Vernon in the 18th century, we wanted to be able to devote the most time, energy and money to artifacts that inform those questions. The table shows how we decided on a processing method for each depositional phase.
As you can imagine, each processing method has advantages and disadvantages – which our research design helped us to think through. Dry screening is fastest to process and analyze but doesn’t capture all the details. Flotation, on the other hand, captures almost everything (but not pollen, phytoliths or chemicals in the soil which are a whole other story). However, this “light fraction,” the small seeds and charcoal which are lighter than water, require specialized training in archaeobotany to identify and analyze – our contracted archaeobotanist is Justine McKnight.
Anna Dempsey spent her summer sorting the smallest of the “heavy fraction,” — artifacts between 1/16” and ¼”. It’s not a particularly difficult job, but does require more time and patience to process and analyze these smallest artifacts. We think waterscreening and flotation are incredibly important for understanding the whole picture of an archaeological site. Without these methods seeds from fruits and vegetables, fish bones, straight pins, metallic threads, beads and gunshot, are grossly underrepresented in the archaeological record. It’s hard to make a case for what life was like if you only have part of the story!