It may seem a bit odd that you create the unfired one at a trivial of 36, and the fired one at 21.. BUT keep this in mind:
The unfired ones are unsellable - cannot give it back to vendors. BUT for a mere 2sp more you can get the firing sheets needed to make the fired ones.
Once you make the fired ones 1. They are stackable and 2. You can sell it back to the vendor at roughly 9s 5c per - which is just over how much it cost to make in the first place.
There are a couple of advantages to going the extra step, if money is not an object, then dump them and press on.
Just my 2cp