Porcelain is built of two substances. Pentunse the flesh and Kaolin working as the bones.
One without the other will never make a body of porcelain. Like us, Porcelain has memory, and a complex make up requiring nurture to become strong, functional, effective. In fact its very identity as porcelain depends on a perfect mixture in its nature built of bone and flesh, and then its nurture from its handler.
Any discrepancy in thickness can lead to fractures as it cools from 1300 degrees Celsius. You can get away with more unevenness with other kinds of clay, but with porcelain, Your errors, are revealed. Firing too high, too fast, too long, left with bubbles will leave the piece in shards.