During the earlier water screening process, one four liter sample (picture 1) was set aside from each of the 34 soil sample collected from the midden material recovered at Ft Meigs (http://ohio-archaeology.blogspot.com/2007/04/never-ending-field-work.html)The reason for doing this was to use another collection strategy called flotation (pronounced flow-tay-shun). This method is fairly simple and is used to collect charred wood, seeds, nut shells and other material that could otherwise be lost during the dry screening and wet screening process. From this we can learn what plants people were eating and using for firewood. Even the time of year could be determined based on the types of seeds and nut shells were present.
The flotation method we used involved the use of water, notched 5 gallon bucket and fine screening material. The soil sample was put into the bucket along with water. The bucket is tipped and water agitates the soil just enough to allow water to escape through the notch (picture 2). When the water hits the cloth, small particles of charred material are collected (picture 3). This is called the “light fraction”. This process continues until no charred material is seen floating on the top of the water in the bucket. The fabric holding the light fraction is gathered together, tied at the top and hung up to dry.
Then the bucket is emptied into a screen and the denser items like pottery, bone, flint and rock are washed and set out to dry (picture 4). This dense material is called the “heavy fraction”.