Help! I am having issues with underglazes disappearing in spots during glaze firings. I paint the underglazes (usually Duncan or Speedball) onto greenware and fire in a bisque kiln to cone 06. Then I dip my pieces in a clear glaze and fire to cone 6. When the pieces come out of the bisque firing, they are totally fine. After the glaze firing however, some pieces will have small round spots that look like the clear glaze and colored underglaze just JUMPED right off the pot. All my pieces are wiped down before applying the clear glaze, and as I already stated, they look perfect after the first firing.. I have had this happen on the inside of bowls, as well as the outside. Why would this be happening? Thanks in advance!