Today Michael Wallace was on site to set up for the archaeobotanical field school next week. The blogger caught up with him whilst he wrestled with his equipment:
Michael, what are you setting up here?
It's called a water separation or flotation machine.
And what exactly is the function of the machine?
Basically, it separates out things that float from things that sink. What this allows you to do is to clean the sample by removing the silt, and collect floating material and heavy residue for analysis.
And what sort of things are you hoping to find when you process these samples?
When you dry sieve on site, you lose almost all of the archaeobotanical material. With the flotation machine we can find things such as charred crops and seeds, as well as non-archeobotanical material like small bones, that may not have been found during excavation. The most common type of charred material found is residue from cooking or the processing of cereals and other crops. So, for instance, the by-product of processing wheat (chaff) may be burned (for instance as tinder) and then found in our sample. So we may be able to infer things about dietary habits or crop processing from the flotation samples. Similarly, finding charred weeds can help to build up a picture of the environment of the area and context we are excavating. Sometimes, if there is a destructive fire such as a barn burning down, we may have a wider range of charred material, as more things are burnt.
What difficulties do you face when doing the flotation?
As you've seen, setting up the machine is always a bit of a challenge, but once you've got a system the operation is easy. The main difficulty then is establishing a sampling method. In an ideal world obviously everything would be sieved but its not practical. The best practice is a combination of targeted sampling and systematic sampling. So anything that, for instance, contains large amounts of charred material, such as a fireplace, would be sampled, but you would also do some systematic samples in case a context that looks less promising contains interesting material.
And you'll be doing some work with archaeobotany students next week, is that right?
Yes, I'll be doing a combination of practical field schools and lectures, teaching the theory and practice of flotation, how to select samples, and how to identify samples in the lab.
Excellent, we look forward to it!
As part of our archaeobotanical special, we also have:
Water separation: a pictorial tutorial!
|Firstly, a three-way splitter was added to the mains water supply, so that finds processing and equipment cleaning can take place without disconnecting the hosepipe from the machine|
|The hose is run through the trees to an elavated area (so that the water will drain downhill) ...|
|... and is attached to the machine.|
|Michael improvised a funnal and wide hose system ...|
|... to further encourage the water to flow away from the flat areas.|
The next step was to turn the water on and test the pressure:
|... for the pressure to be sufficient to clean the sample it should jump around one metre in the air.|
|With the water pressure tested, the barrel was filled with water.|
|The water comes through holes in these pipes, which are submerged, to clean the sample.|
When the barrel is full, the water flows over the top...
... and into the two fine seives stacked on top of one another:
|Niagra Falls, ON, Canada|
|A mesh was then added, which would allow the silt to pass through, but catch the heavy residue.|
|The sample is then added.|
|The archaeologists then run their hands through the sample to ensure that it is all cleaned ...|
|... and the water drains off and runs away down the hose, leaving the floating material in the two seives.|
|The mesh was then gathered ...|
|... drained ...|
|... tipped onto a sheet ...|
|... and left to dry in the sun.|
|The floating residue in the seive is then rinsed to remove any remaining silt ...|
|... tapped out onto a paper towel ...|
|... rolled up ...|
|... and hung up to dry in parcels!|
Object biographies have also begun for third year students - Matt and Callum spent the day in the library researching the lead ingot found in week one.
And finally, we close this archaeobotanical special with an archaeobotanical top trump: