Pi Plate

Size (width x height): 5-7/8" x 1/2"

Glazing*: An iron oxide under-glaze was painted into the numbers on the rim, then the entire plate was dipped in honey-butter.

The iron-oxide under-glaze was a waste of time, as the honey-butter glaze is not transparent enough to let it show through.
The numbers around the rim are pi to 20 decimal places: 3.14159265358979323846...
The three circles (which show only partially through the glaze) amplify the reference to pi.

*Note that glazes are identified by the names used in the Santa Fe College Pottery Studio; they are not universally recognized glaze names.