How Bone China Works

Bone China: Casting

These four-piece molds are used to make small pitchers.
These four-piece molds are used to make small pitchers.

In the casting area, 18 small lazy Susans sit on top of a conference-sized round table. Upon each of the 18 discs rests a casting mold. Three hoses hang from the ceiling: one for air, one for white clay and another for ivory clay. These hoses are used to fill each mold with liquid clay or slip.

Slip and air hoses Slip and air hoses
Slip and air hoses

The casting process basically works like this:

  • You use the air hose to clean out the mold, making sure there's no excess plaster or remaining slip from a previous fill.
  • You aim the nozzle of the hose and fill the mold with the desired slip (white or ivory).
  • You allow the slip to set for about 10 to 15 minutes.
  • You pour out the excess slip and let the mold sit for about another 10 minutes.
  • You release the mold.

To release the mold, the giant red bands are removed and the four mold pieces are gently pulled away from the clay piece inside.

Because the mold is in several pieces, there are seams along the greenware where the molds fit together. Workers use damp sponges and finishing knives to smooth out the surface and remove the seam marks.

Raw clay pieces that have not been fired in the kiln are referred to as greenware -- not to be confused with the green-colored clay pieces that indicate an ivory finished product. Fired pieces are called whiteware. Once the greenware is complete, it's ready to be fired in the kiln.