An Unintended Experiment

Last year, as part of an experiment, I had made three identically shaped bowls.  The only major difference between these bowls was the amount of burnt shell temper I added to the clay used to make each.  One of the bowls had a "high" amount of temper and was marked with an "H," another bowl had a "normal" or "medium" amount of temper and was marked with an "M," and the third bowl had an extremely "low" amount of temper and was marked "L."  Unfortunately, I did not keep any notes on the actual amount of temper each bowl had in it, so I can't really speak in any more precise terms.  The only additional information that I can recall is that the "medium" bowl had the same amount of temper as my normal pottery and that the clay used to make the "high" bowl had so much temper in it that it was difficult to sculpt.  My initial plan had been to use them in a comparative boiling experiment, in which I would test for a relationship between the amount of temper in a fired pot and that pot's ability to survive heat shock from boiling water.  Though I did fire the three bowls, I never did run the experiments, though, deciding instead to focus on other priorities.

As a result, the three bowls sat outside in the backyard for the entire winter.  During that time they filled with water, snow, and ice, which melted and refroze depending on the weather.  It wasn't until this spring that I noticed them sitting in my backyard and decided to examine them to see how the weather effected them.  The differences are quite apparent.  As can be seen in the accompanying images, the bowl with the highest amount of temper survived the freezing and thawing completely intact.  The bowl with a "medium" amount of temper was split into three pieces, and the bowl with a "low" amount of temper appears to have broken up in to many pieces which are indistinguishable from the other pot shards in my yard.  Though this experiment would definitely need to be repeated with more exacting measurement to be considered valid, it does seem to suggest that, for pottery made from the clay found in my area, a higher amount of burnt shell temperature may increase the odds of that pottery surviving the stress from freezing and thawing. 

The bowl made from clay with a "high" amount of temper. 

 

The bowl made form clay with a "normal" amount of temper.