Underglaze bleeding

[milkymoonceramics]

Apologies in advance for the supidity of my question, I am a complete beginner who loves sculpting but hates the technical side of firing! I have been making very small porcelain pieces of jewellery for  a while, which I decorate with underglaze  before bisque firing, then covering with a clear brush on glaze. I have been taking my pieces to a local shop to fire them, and they have always come back perfect and no bleeding of underglaze colours. I have recently moved to a new area and took them to a new kiln to be fired. This time, the underglaze bled after they were glaze fired, and ruined the pieces. I have since bought my own little electric kiln and have fired some more pieces, (to cone 6, standard speed) and the same bleeding has happened.  As my materials and techniques when making the pieces is identical, I can only assume it is the firing that is making the difference. Does anybody know what is likely to be causing this bleeding? Could it be caused by the temperature of the firing or the speed?  I have tried contacting the original shop that did such a great job but they have not  replied to me. Thanks in advance for any tips! 

[oldlady]

i would continue to ask the original shop BY TELEPHONE!  get to a technical person or whoever fires the kiln.  only that person can tell you what may be different about your firings in the past.   

perhaps your kiln is different in some way.   what do you mean by standard speed?  have you tested the heatwork with cones?

[neilestrick]

Cone 6 is not necessarily the same in every kiln unless they have all been calibrated, which many aren't. Assuming you're using the same clear glaze and the same underglazes and the same glaze thickness, firing them cooler will probably stop the bleeding.