I should have known better. The bottom of that jug was heavy; I’d convinced myself I liked it that way and scaled back the amount I’d trimmed from the bottom. The problem was that I’d fired it along with the other ware that I had thrown on the same day. So, why I was surprised to see that shattered form in the kiln on Sunday morning was anyone’s guess.
Having taught high school ceramics for a few years, I’ve learned to read green ware (un-fired dry clay) for its readiness to be fired. Occasionally, student work blows up in the kiln, but it’s usually due to attachment mistakes – where air becomes trapped between two pieces of joined clay. Every once in a while a piece is fired that is not quite ready and that little bit of moisture remaining in the clay seals its doom. When firing hundreds of clay forms a week, a system is needed to determine which pieces are ready and which are not quite bone dry.
The surface of dry clay will feel dusty, but more than that it won’t feel cool, unless it’s been stored in a very cool room. Sometimes comparing the hand held temperature – as the form feels against the palm of your hand – of one form that you’re sure is completely dry with the questionably dry form, will reveal the difference. If I still can’t tell if a from is dry, I place that questionabe form against my cheek, a telltale cool sensation will reveal an ever so slightly damp form. I usually only use this technique when the hand held comparison method hasn’t helped me to decide on a given form’s readiness to be fired. This usually happens when I’ve unloaded a couple of kilns and my hands are very warm from handling all that warm pottery.
Working in an outdoor studio has its own set of challenges when drying pottery. Many humid days in a row can delay drying time significantly, and cool damp nights can have the same effect. Additionally, when the ware has taken on the ambient room temperature it can feel deceptively warm, as if it’s dry and ready to be fired.
I (finally) decided to create a system to address the extra drying time needed for that outlier form that is more dense than the rest of the lot. I’ve designated a section of a drying shelf for that one or two pieces of heavier ware to remind me to delay firing.