Preparing Stoppers for Bottles

I have created a few bottles intended for olive oil and created ceramic nobs that fit the form. I wanted to create a glass stopper that is inserted in the ceramic nob, so when you go to open the bottle, you are surprised to find a glass stopper inserted inside.

Here is a nob for one of the bottles,

I cut out a hole or insert at the bottom of the nob piece in order to fit the glass stopper after it has been bisqued and glazed.

I then measure the diameter of the insert before it is bisqued and take into consideration the shrinkage that will happen once the piece is bisqued and then again once the piece is glazed. It's important to know how much the piece will shrink in the firings in order to create the correct size for the glass that will fit into it. The glass will not shrink as much as the clay.