Once visitors have left the Pottery having had a fabulous time creating their clay masterpieces, they may be interested to know what happens to their ‘makes’ left behind. Aimee is the key person responsible for the aftercare of customers work as it makes it’s journey from clay to ceramic. She describes part of the process below:
“After our customers have made their pots and decorated them, there are a few processes they will go through before customer and pot are re-united.
Clay is left to dry out until it is bone dry and there is no moisture left. This can usually take several days but we use the assistance of radiators and fan heaters during winter and the sun’s rays during summertime to speed up the process a little bit. Whilst clay dries, it shrinks by a small amount of about 5-10% so it’s also important not to expose clay to too much heat too quickly as this can cause it to crack.
Once pots are dry, they are ready to be fired. They have to be fully dry as any moisture still within a pot when being fired will evaporate, potentially creating air bubbles which may cause a pot to ‘explode due to there being nowhere for the air to be released to. This is why clay can’t be made too thick or projects such as pinch pots need an airhole. One way to tell they’re dry is how they look visually. With the grey stoneware and red terracotta clays we use, pots dry a lighter shade compared with when they are freshly thrown off the wheel. Another way is the ‘cheek test’ by placing the base of a pot to your cheek. A dry pot is usually cold and you can’t feel any moisture on you cheek.
All pots go through 2 firings. The first firing is known as a bisque where pots go through the change from clay to hard pottery. At this point, pottery is still quite porous which means it will later absorb glaze easily. A bisque firing reaches a maximum temperature of 960 degrees – very hot! This firing gives a matte, pastel-like effect and can be chalky at this point. 573 degrees is the temperature point in a bisque firing where clay changes its state to hard pottery and becomes irreversible. The term is called Quartz Inversion.
The second firing pottery goes through is a glaze firing. We use a clear glaze which is what makes pots waterproof and functional. Pots are dunked in the glaze and their bases are wiped. The reason for this is so that they don’t become stuck to the kiln shelf. A glaze firing has a maximum temperature of 1080 degrees – even hotter! Between 1000 and 1120 degrees is where the pottery changes state again from bisque to the final product. This final firing produces the final product making your pots functional, dishwasher proof and usable
Fun fact: When packing kilns, pots can touch each other in a bisque but not a glaze. The reason for this is because as the glaze melts, any pots touching will become stuck together during the cooling down process of the firing.”