Thursday, September 13, 2018

What in Flotation do we have here!?!


August 15, 2018

WOW-WOW-WE-WOW everybody!

Unit N11 W4 southeast corner full of oxidized soil, ash, and charcoal.
Andrea here, and today I am going to get down and dirty on float sampling. But first, let me give you a little background on how our sample came to be. It was the 3rd of August 2018, and the day before the annual Fort St. Joseph Open House (and for the record our unit floor was extremely level at this point). Our south east corner was looking rather oxidized, ashy and full of charcoal. It was decided that our unit would be sampled. To begin, we measured and marked out a 45cm x 75cm square. We needed to fill a 10 liter bucket. We literally chunked up large pieces of sediment to prevent compromising any of the organic material that may be in the soil sample. Our purpose for taking the float sample was to hopefully gather remains of any organic material consumed or utilized by the inhabitants of Fort St. Joseph. So, we filled our bucket, but we may have forgotten to keep in mind we weren't going to go past 45cm below our datum point. As we cleaned up our South East corner it was clear we had gone too deep approximately 47cm below datum. And that's how we came to have our undulating (uneven/really bumpy) floor...
Undulating floor.


Austin teaches students how to use the flote-tech flotation machine.
Flash forward 2 weeks later, our hideous floor has been buried and we are out of the swamp and back in the lab at WMU. Today, a past field school student came in to show us how to use the flote-tech flotation system machine (there was no manual and the video was on VHS). This machine looks like a hotdog vender cart turned into a fancy wet screen operation.  It consists of a water reservoir, flotation tank and a water pump. The machine is split in half and the pump is used to move the 100-gallon water supply in a closed loop from the water reservoir into the floatation tank. One half of the machine houses the coarse-fraction screen and the other the fine-fraction screen. The machine gyrates and separates the organic material (fine-fraction) from the soil, it then floats to the surface while the heavier particles (coarse-fraction) sinks to the bottom. The floating material floats over the lip of the flotation tank and into the fine-fraction screen. As we began to process our sample the water movement was non-existent. We drained the tanks and began to disassemble the loop of PVC pipes for the pump system. The system was clogged! We blasted the slimy clay like silt from the pipes and every nook and cranny with the hose.  After reassembling the system, we started to process the sample again and boy did it make a difference!  We were cooking with gas and organics were floating to the surface with a purpose. After all of the fine-fraction organics have floated over and all of the soil has completely filtered out of the coarse-fraction screen we removed both screens. The fine-fraction screen is tied up to dry to await analysis (most likely under a microscope) and the coarse-fraction screen is set aside for further screening. When you pull out the course-fraction screen many artifacts are immediately visible for example lead shot, seed beads, and bone; these artifacts will be bagged and sorted like usual. After we finished processing all the samples we tore the machine down and flushed it out for the next guy! All in all, it was a great day and another archaeology skill in the playbook.

Austin and Gary cleaning the flotation machine. 
Fine-fraction and coarse-fraction samples after screening.



Diagram of the Flote-tech flotation system machine. 

Fine-fraction organics floating into the fine-fraction screen. 
Andrea and Gary fluffing the coarse-fraction ( I like to imagine he is a proud papa!).


Austin and Gary clean out the pipes.















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