Opening the clay ...

Rest your finger near the center of the clay, find the place where it no longer wiggles. Slowly press a small indentatioin, place both your thumbs into the space and press down stopping about 1/4" from the wheel head

Place your hands back into the center and slowly open outwards. Start with your finger in the center of the bowl and form the bowl's bottom shape now. Then compress the bottom with a wooden rib working towards the center to help prevent "S" cracks later.