Kiln time!

Yesterday it finally happened, we loaded the first batch of our bone-dry greenware for bisque firing (the first time the pots go through high-temperature heating).
 Greenware is really fragile and must be loaded into the kiln with a great deal of care.

While we were loading our works in, our teacher Kirsti explained to us the proper way of using the school’s electrical kilns. In this instance we were using two out of six. She said that all the kilns have their own personalities – they all even had funny names! These names were easier to remember than the factory generic codenames. We were introduced to a small kiln called ”Nabero” (front loading) and a bigger one called ”Lätsä” (top loading). The latter was an older model.

We all started from the basics with kilns and firing, so our teacher needed to explain to us all the little details – how to load the kilns, how to place pillars into a triangle formation on which the boards are put on, and how to program the firing timetable. Kilns are always fully loaded to make the firing economical and with bisque firing it’s possible to lay works on top of each other. Just to keep in mind that with cup shapes there should be space for hot air to flow if you put something in it – keep it loose.

The kilns were programmed to warm up slowly, 100°C/hour until the temperature reaches 500°C (the chemically bonded water will begin to evaporate at this stage). The slow ascent is vital, as there is still some moisture inside the clay body even though they seem dry. This slow process makes sure that the clay objects stay whole and doesn’t burst into pieces.

After the first firing part the kiln was ”free” to reach 850°C on its own pace, which is the highest temperature for our earthenware clay. Stoneware clays and porcelain are fired at higher degrees. When the highest temperature is reached it stays in this temperature for 5 minutes – this stage is called braising. After this the kiln starts to slowly cool down. The cooldown process is really slow, it takes hours. Cooling down rapidly could also break up the ceramics. Now the clay is changed forever, from humble soft beginnings into a new substance  –  a ceramic material.

Later on today we’re hopefully able to unload the kilns and see the fired pieces – are they intact, did our joinings hold. This is always exciting! The next step after bisque firing will be smoking – an interesting technique – but more about that later.


Fingers crossed that all my works are in one piece.

 //Jenni//