Forming processes and techniques
Porcelain differs from other ceramics such as terra cotta,
stoneware and earthenware by its whiteness, translucency,impermeability, durability and resonance.
THE PASTE :
Composed primarily of three natural occuring rocks ;
Kaolin (Chinese for "high hill") :
Base ingredient in porcelain (55%), a very pure and plastic clay.
Quartz (20%) :
A degreasing substance enabling the porcelainto
hold its shape under firing.
Feldspar (25%) :
Soft element allowing for the fusion of the mixture.
THE MANUFACTURING :
Early methods of transforming these raw materialsinto objects
were done by hand.The paste was moulded, turned or stamped.
This was a difficult process and is still used todaywhen making prototypes or artistic objects.
Casting :
The paste in its liquid form is poured into a hollow plaster mould,
leaving a layer of clay on the surface of the mould.
The cast is then removed after a period of time.
This method is used to make hollow or sunken piecessuch as vases, soup-tureens and coffee/tea pots.
Jollying/Jiggering :
Used to make round objects such as plates, saucers, cups, etc.,
this method uses a semi-soft round shaped paste
set flaton a spinning mould.
A blade is set at the desired thickness and any excess is cut off.
Pressing :
Hardened granular paste is injected by steam pressureinto
the two sides of the mould.
the FIRING :
After the piece is dried and finished, it is ready for its first firing.
It is placed in an electric kiln at 980°.
The piece becomes dehy-drated and porous
and is nowentirely dipped in glaze.
A second and final firing is done in a gas kiln at 1400°.
The piece is now vitrified and has lost 15% of its original
volumeand dimensions.
The porous gray mixture has become white, translucent,
impermeable and resonant.
THE DECORATION :
The piece is now ready for decoration.
Enamels and precious metals (i.e., gold, platinum) can be appliedover
the the fired glaze.
This can be done by brushstrokes, chromo-lithography
or by engraving (inlay).
In order for the colors and metals to adhere to the glazeone
or more successive firings
between 780° and 1350°may be necessary. |