Recently I made the pot shown below, painting the design on with underglazes. After I painted it, I fired it to make sure the design did not smear when I applied the glaze. Needless to say, the underglaze still smeared (Mostly the black). Why? I investigated and found this answer on a ceramics message board:
It doesn't really matter how high you fire your glaze kiln but
you have to fix the underglazes at a HOTTER temperature to keep them from
moving under the glaze. So if you bisc to 04 then your glaze firing is
supposed to be at a lower temperature. That's if you want your
underglazes to stay put.