Porcelain clay is a clay body that draws in many a potter because of its bright white color, translucency, and the way glazes look oh so fabulous on it. But it’s a fussy little clay body susceptible to collapsing during the forming process (especially on the wheel) and warping during the firing.
But it’s so pretty and I, for one, still like to take my chances with it. With practice, you can learn learn how to work with this persnickity porcelain clay and minimize your loss rate. Today, Gwendolyn Yoppolo explains what porcelain clay will put up with from the wet phase to the bone-dry phase. – Jennifer Poellot Harnetty, editor.
Porcelain commands us to be attentive in our touch and responsive to its needs. Beyond the basic technical demands that clay bodies all have in common, porcelain clay also needs to be treated properly to avoid warping and cracking during drying and firing.
One of the most important things to remember is to watch your timing–this is best learned through experience.
Building onto a form that’s too soft causes slumping. Adding softer clay onto a form that is too dry results in cracking. Altering and/or bending a form that’s too dry or leather hard causes warpage and cracking.
Slow and even drying is critical. Periods of rest, where the pieces are wrapped in an airtight chamber to slow drying and redistribute moisture, do help. The clay has a chance to get used to its new form at each phase, without having one part dry too quickly for the rest of the piece.
Here is a loose guideline and timeline for when to do what while working with porcelain. The phases are not distinct, but are separated out from the continuum of the entire process for the purposes of discussion. In fact, they blend together in many ways, especially the “cheese” sections. Because porcelain is thixotropic, it has a nice way of resoftening once it has reached the hard cheese stage, so you can actually go back and perform some soft cheese processes. Porcelain also rehydrates locally to some extent, so you can go back in a concentrated area. These guidelines are designed as a starting point for you to figure out your own way to achieve success.