I made and carved some knob blanks a month or so ago, and then made a plaster cast of them to facilitate duplication. There were a couple of things about the first knobs that weren’t satisfactory – primarily, I made them too “deep,” so the knobs made from the press mold had to have a portion of their clay mass cut off after forming. I decided that I would throw and carve a new set of blanks that would be exactly the size of the finished knobs I wanted. Then, I could cut them to exact size with a wire right in the press mold.
I also wanted to correct the side plane and other details of all the knobs so there were no undercuts to complicate the plaster process.