Operation gabbro/Hembury bowl.

The reenactment  of a ceramic chaine operatoire is a lengthy labor intensive  business. I’ve been  teaching my prehistoric pottery course over the last 2 weeks and this has involved going out prospecting for clays, on Crousa Down, Lizard, Cornwall.

So as a team we have dug out gabbro clay in the Lizard, Cornwall from 3-4 locations. This  involved  deturfing, digging a hole and then auguring out the clay.  We took a bucket from each location.  The second step is then processing the clay until it is plastic enough to make pots.  This is done either by wet or dry processing. Robin and Mallory, in the picture,  did all the work (heroes)

Mallory is dry processing by crushing and sieving the clay and we wet processed the clay and then had to sieve it to remove all the stone. The wet slip is then dried on a plaster or wooden bat. My colleagues at Flameworks have remarked on the amount of work that is required to make this clay I to a material plastic enough to make a pot.  Contemporary studio potters normally use co mmercial bagged clays.  we’ve made shrinkage and temperature test tiles. 

When a new Clay is dug test need to be performed to test its plasticity, it’s shrinkage rate and it’s firing/ maturing temperature. Most clays will likely fire to 750*C before melting so we’ve made four tiles to test each clay. They dill be fired successively higher each time starting at 750*C , then 950*C , 1150*C and maybe  , if they don’t melt before this last high temperature to 1250*C. If it is possible to fire them up to 1250*C maintain shape, performance with a fairly low shrinkage rate then we would have found a good potting, stoneware clay. 

                                              

Once the test tiles have been fired the various shrinkage rates  be worked out for dry ware, totally dry ware, shrinkage once fired at the successive temperatures. Most shrinkage occurs between wet/plastic  stage. The best way to achieve plasticity is age the clay for over a year butwe don’t have time for that b