Flotation

When excavating each level in a unit or a feature, we need to set aside a bucket of dirt to bag up for flotation.  The importance of this is to be able to essentially investigate the soil and separate the organic materials it contains.  Once the soil is bagged and tagged in the field, we take it to the lab and put it through the flotation machine.  This is a device where you place the dry dirt on the top of the screen to be sifted.  Water then bubbles up from the machine and pushes the dirt through the screen.  This action separates the lighter organic materials like charcoal and seeds from the heavier materials like bone fragments and small rocks that sink to the bottom.

Here's a corny video that properly explains and depicts the process better than I can explain with just words:

Flotation Cartoon

When doing my research on the flotation method, I learned that the device was first created by an archaeologist at a Hopewell site in the 1960's, making the site and the flotation methods performed there more relevant.  The importance of flotation is that we are better able to take the organic materials from a feature or unit more in context, since it is separated in a collection of soil rather than separated as the whole of the level goes through the screen.  What I mean by that is that this soil is bagged and tagged and taken to the lab rather than just sifted at the screens in the field.  This allows for a more contextual and wholesome understanding of the soil, permitting us to not only date the organic material but also have an even closer look to what is found in the soil as we go along.  Regardless of the facts, flotation is an important method for dating and equally messy as being out in the field.