Tuition and Classes in the Fine Art of Throwing
Centering is the process of getting the ball of clay to rotate perfectly evenly on the wheel.
If you don't center correctly, throwing will be extremely difficult as the piece will be off balance from the beginning.
After you have wedged the clay you slap the ball into the middle, bash it down to make sure it sticks firmly and then start the process of squeezing and pushing the clay.
It involves squeezing the ball, then bringing the cylinder up, then pushing it down again and then squeezing it into the 'beehive' shape.
Water is added frequently and a relatively fast wheel speed is used.
The process takes a bit of force and should be repeated a few times to ensure that all air bubbles are removed and the form is perfectly centered with no lateral movement (kicking).