The next step is to open the clay on the wheel. While the clay is rotating at top speed and continually lubricated, lay your right thumb across the top (through the center axis). Push down on the end of your thumb with your left hand. Because your thumb is crossing the center, opening the clay this way ensures the opening will be centered as it is created.
Open the clay down to its final depth. You want to keep approximately half an inch of clay at the bottom of the opening. (Some of this will be lost when the pot is cut off the bat.) This forms the floor of your pot. If you aren't sure how thick the bottom is, stop the wheel and use you potter's needle to measure it.
Reduce the wheel speed down to about half. Use your left hand to guide and brace your thumb. Pull your thumb outwards, keeping your right palm controlling the outer surface of the clay. Widen the opening to the size you would like for your pot's inner floor. Don't make the base too narrow. Keep in mind that you need to be able to move your hand up and down in the pot's interior.
Opening the clay is a fairly complicated process in itself. For more detailed instructions, see How to Open Clay.
