Friday, February 4, 2011

Thin-Section Sampling – or – the Invasion of the Sherds

Now that we have a basic handle on the seriation, we are picking samples of sherds from each phase to export for thin-sectioning and petrographic analysis. This analysis, which will be done by Dr. Jennifer Meanwell, will hopefully tell us two things. First, it will let us know whether the variation we think we are seeing in ceramic pastes is real at a structural level.

Second, we should be able to look at changes in the frequencies of the different paste types (provided that they exist!) over time, which could relate to changing patterns of trade.

Thin-sectioning and petrographic analysis is both expensive and time consuming, so we have developed a rather elaborated sampling strategy in an effort to get a representative sample of each phase. Julie Novic and I are taking rims sherds only, dividing them into categories based on vessel types (bowls, jars, and other vessels), and then dividing each of those categories into two groups, based on paste. (This has been a good opportunity for Julie to teach me how to recognize the various paste groups, but I clearly have a ways to go!) I then get a list of randomly generated numbers and use those to pick sherds from each of the six stratified groups.

So far the random selections seem to be a pretty good representation of their parent groups. Since we also have a couple of specific ceramic types that we’re interested in, I go and pull out examples of them if they weren’t chosen during the randomized selection process.

Because we are sampling by phase, our sampling unit is the stratigraphic layer, rather than the excavated lot, which is how our material is stored. Since the former usually consists of several of the latter, we have to have several different lots open at the same time, which means that we are labeling every rim sherd to avoid confusion. The practical result is that all the ceramics tables in the lab are covered with neat lines of sherds, and we are starting to eye the patches of open space on the lithics table enviously!

The photos show Julie with her trusty pliers for checking paste types, and a portion of the bowl rims from a single group.

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