What do you call it when somebody spends the whole day making pottery?

Kiln time or Kiln day, most likely. I guess you can also call this day "productive", if we go to a general answer.

Explanation:

A Kiln is a furnace or oven for burning, baking, or drying, especially one for calcining lime or firing pottery. It's not unusual for people in the pottery business to refer to the time that they work with a kiln as "Kiln Time".

jefferson introduced the idea that one does not change a government for "light" causes because he wanted to emphasize the seriousness of colonists' reasons for declaring independence.

each morning i wrote my name

on the dusty cabinet, then crossed

the dining table in script, scrawled

in capitals on the backs of chairs,

practicing signatures like scales

while mother followed squirting

linseed from a burping can