Roll the round handle of any of the tools over the clay coil to compress it.

Use the fettling knife to flatten the coil further (Figure 1) , and a thumb to smooth any remaining rough spots. (Figure 2)

This next step is very important.

With a narrow, pointed object (I used the handle of a paint brush), poke a hole on each end of the form. To ascertain that they reach into the hollow middle, blow through one of these holes. Air should exit though the other hole. These openings are imperative, for they allow expanding hot air to escape during the firing. If air is trapped, the pressure will blow apart the mold.

Finished mold. Leave it loosely wrapped in plastic for 24-48 hours, then uncover completely to air dry. It must be completely dry before it can be fired. Otherwise, the small amount of residual water turns to steam, and causes the clay to explode.
If you don't plan on firing the mold, it still needs to be DRY before use. If it is still damp, the soft clay that is molded around it may stick and be difficult to remove.