Good question CW. I throw a round shape on the wheel and after the clay is centered I open it all the way to the wheel head, leaving no clay on the bottom. I make the walls the shape I want and let it set up, then remove it and alter the shape into an oval. For the bottom I roll out a slab and connect the ring to the slab. There are other ways, but this way I get to throw on the wheel and use hand building techniques. Getting a symmetrical oval that holds it's true shape all the way thru the process is difficult as things can easily get warped and wonky. I won't say I'm after perfection as these hands are not capable of such feats. But the pursuit of better and better keeps me coming back for more. Thanks for looking.