Drying Stages of Clay

 

Ceramics can be described as greenware (unfired) bisqueware (fired) or glazeware (fired a second time, with glaze). Unfired clay naturally dries in the air, over time. You can extend the time by bagging the clay and/or spraying it with water. Clay dries in different stages, each with its own characteristics. All are considered greenware:

 

Slip – This is a liquid clay with a milky consistency. It can be used like glue to attach two pieces of clay together. You can also mix different chemicals with slip to change the color, and use like paint as an “underglaze”.

 

Plastic – This stage is when clay is softest and easiest to work with, completely changing its form. You can add and remove pieces easily at this stage. If your piece starts to dry and harden, you can spray it with a water bottle. You can also use a special heater/blow drier to speed the drying process for increased strength and rigidity.

 

Leather Hard – At this point, the clay has lost about half its moisture. It is still like a block of cheese and can no longer be molded. At this point, it’s the perfect stage for trimming, burnishing, adding textures, and attaching handles, spouts, and decorations. It’s still cold to the touch. If you break a piece off while it’s leather hard, you can add slip to each edge and carefully glue it back together.

 

Black Hard – a short transition before becoming bone dry, the vessel still shows some indication of internal moister, but is highly fragile – you can’t trim or cut into it now or it can easily break.

 

Bone Dry – The clay has lost all of its moisture. It turns a pale, chalky color, and is no longer cold to the touch. This is when it’s most fragile, and ready for firing. It must be placed carefully into a kiln.