I was experimenting with the option of using glass with pottery.  Here are the results.

We used red potters clay and fired mini-bowl designs shaped as pinch pots.  These are only 2" in size.  Then we glazed them and placed marbles, glass pebbles and chunks of all sorts inside the forms.  We fired them again at glaze temp. A few bubbled up and were sharp- so I used hot glue to fill in a few 'boo-boos.'  Most were great.

The students used them as lucky pocket charms.