I made my first knobs about a month ago, and cast them in plaster to make a press mold, so that I could make as many as I needed. The first knobs I made were too deep, and had to be hand cut after forming. I decided to make a new batch to carve and cast in plaster, and include this fun process in my blog.
I started out to throw some new knob blanks off the hump with my regular stoneware clay. I brought up a narrow column of clay, and formed a small knob with my fingers that was about 2 inches across. I added a little dimension to it, based on which of the first knobs I liked. The idea is that these new knobs will be just about the size that I want the finished knobs to be, accounting for shrinkage, so that I can just cut the knob to the finished size with a wire while it is in the press mold. I plan to shape the sides of the knob blanks when I trim the knobs in a tiny chuck later in the process. This will eliminate any undercut that might complicate the plaster process.
When these knobs have dried a bit, I will trim them and carve a little extra pattern into them. After that, I will join a section of extruded coil to the back to form the shaft. I am going to glaze these with the green lowfire glaze that I have used for my tile project, but also plan to finish some in the salt kiln.
You can see that I am cutting the the small knob off the hump of clay with a thread tool. This is a small bamboo knife - about 5 inches long - with a hole drilled in the rounded end. Then, a piece of stout linen thread (buttonhole twist from the fabric store also works....) is threaded through the hole and tied. I like about 6" of thread.
These knobs are finished by adding a 1/2 inch plug of clay at the back, and drilling a hole about about 1/2 inch deep into the extension to make a shaft to receive a threaded brass sleeve after firing. This permits the knob to be attached to the cabinet door just like you attach those boring (and expensive!) knobs from the hardware store.

Hmmmm........ that will be fun.