I also underglazed a bowl with a bunch of different blues. I'm not too happy with how it's looking, but will paint a few more things on it that will hopefully make it better.
Underglaze is basically pigment and clay in a very liquidy form. It's meant to be applied "under the glaze", hence its name.
I will be re-bisque firing these before applying the clear glaze over them. This will hopefully prevent the underglaze from streaking or getting messy especially with the cone 10 clear glaze since it's so watery. It might not matter with the phoenix pot as I will be brushing the glaze on it and smudging the underglaze might make it took cool. I shall have to think about it. I plan to do a few more pieces that will require a cone 6 glaze so I might wait until I get all those pieces made before I fire up the Phoenix pot.
No pictures tonight, maybe tomorrow or Tuesday.