In zirliner? !! Even after it was baked?!!There must be some sort of contamination, either in your Zirliner or your Ceram porcelain.
It has to be about 5 years or more that I have been doing this.Glaze instead of zirliner?
This is news to me.
Is this acceptable?
sometimes firing an alloy in the same furnace as all ceramics can have a contaminating effect on them. Ask me how I know? You make have to decontaminate your muffle or fire in a separate furnace. Now would be a good time to eliminate metal from your diet.Well of course I did, how could that have any effect on other bakes!!
Sandblast first, wash and do not touch it with fingers, never blot zirliner, check your hand for cream or oil. Substitute zirliner with regular porcelain and check the results. Do not use porcelain out of the bottle, it has to mixed well. Use another furnace to check contamination, do not use same furnace on PFM and ceramics. Good luck.Emax ceram over zirconia.