Studio pottery bowl, unknown maker, possibly Scandinavian.

even the underside is lovely, it looks like reduction firing

not temperature but oxygen supply which tends to give that metallic shine and vibrant colours.
I think the oxygen is actually pulled out of the clay body of the pot to feed the flame.
Raku also uses reduction but immediately after firing while the pot is still red hot.

the best way to learn about all that is to attend a big pottery fair and talk to the potters .there you can see and feel the difference between all the potting techniques.
I have often turned up an hour before the punters so I can talk without buyers interrupting