Post #672507 by tigertail777 on Wed, Mar 27, 2013 12:10 PM

I'm reaching into the very far nether reaches of my memory its been many many years... but regarding the glaze getting old: if I recall correctly over time the suspended particles in it can separate to such a degree that it affects firing time and quality. I think my teacher said for the most part this can be remedied with a shaking for a long period. I believe he used to put his bottles in some kind of homemade shaking/vibrating machine for an hour at a time, letting them rest inbetween both upright and upside down at intervals. He used to be almost paranoid about the glazes; making us turn every bottle upside down or right side up every month or so... so take that for what it's worth.

However... if the glaze is working fine on other projects, then it may not be the glaze itself that is the problem. As you said there could be dusty particles it is not adhering to, or perhaps that particular batch of clay has some small amount of a mineral in it that is not reacting well to that particular glaze. In the end, half the time you kiln something its a mystery as to why the dang thing comes out correctly or not in the first place, thus the miracle of "kiln birth" as my teacher used to refer to it.

Been many years since High School, I don't believe I even remembered that much. I do remember clay goes "BOOM" when the air is not properly worked out of it though. :wink: Oh and the dangers of getting ones hand caught in the pug mill...ugh.