How Clay Cracks

Following the success of the Young Scientist project 'How clay Cracks' by Aiden Bowen and Fraser Pock, we invited the boys to submit a summary of their project which came first in the Junior Group, Chemical, Mathematical and Physical sciences section.

 

The basic idea of out project is to investigate how the conditions clay is dried in changes the way it cracks.


We decided on this as the best project after making a list of all the ideas that we had had. After that we decided on what we were going to do in what order, and decided the best thing to do would be to simply get some clay from the art room and put it in an oven to dry.


We came in the next morning to find the clay hadn’t cracked and on closer examination we found that art clay had added fibres to stop it cracking. After two weeks trying to find someone who supplies raw clay or somewhere we could get it for ourselves we had nothing. It came up in conversation with my grandfather that there was a potter that he knew called Steven Pearce  who uses completely natural, local clay. We gave him a call and they agreed to give us as all the clay we needed.

 

Meanwhile we had decided on the variable conditions we were going to use on the clay and we decided to test weight, humidity, amount of water in the clay and temperature baked at. After testing all of these we found that water and humidity wouldn't work so we worked with weight and temperature. We weighed the clay out into the various weights and put them in Petri dishes, and dried them in the school science oven or on a windowsill. We then   photographed the results and numbered them.

 

During the Christmas holidays we studied the  photos and measured the width of the thinnest and widest cracks visible as well as the longest and shortest cracks.


We also counted the various joints and gave the general idea of the amount of cracks. We found that it was effected by the speed the water left the clay, which was effected by the mass-surface area ratio (no matter how the mass changes they all had almost the same surface area) and temperature, which dries it faster by evaporating the water faster. Of those two mass-surface area ratio made the biggest difference. The main difference was with the clay whose water evaporated faster (the lighter hotter ones) had a large amount of both small “hairline” and larger cracks, with complex nets of smaller cracks in the centre of the dishes.


On the other side the ones that had a higher mass and a lower drying temperature had fewer cracks but they were larger. This rule was almost constant throughout until we got to the samples that were the heaviest and that were not baked at the highest temperatures, these had one or two stout cracks or non at all. These aren't anomalies though because as the drying speed decreases there is a point where the size of the cracks decreases quickly and they disappear.


The other findings that we made are mainly about the shape of cracks.