Why is there no glaze on foot rings?

I guess the answer is so obvious to those who already know, but here I go:

Why is there no glaze on the foot rings of commercial pottery but glaze on the bottom?


Likewise, there is no glaze on the base of slipcast pieces without foot rings.


The question came to me while looking at Hobby Ceramics pieces which generally have allover glaze on their bases.

Glaze is actually a thin layer of glass that melts when fired in the kiln. If you fire the pot with glaze on the base it will stick to the kiln shelf and both pot and shelf will be ruined. The other way of overcoming this is to used stilts to sit the piece on and then it can be glazed all over the base. When the stilt is removed there will only be pin pricks left where they were. Stilts can only be used at lower temperatures. There are racks for firing plates that use a similar method.