Kiln wash flaking/cracking

[Jenna]

Hi all.
Lately, I've been having a problem with my kilnwash flaking off during firing. Here is what I can't figure out... I frit cast in two part molds, the base part which creates the design and a "lid" to press the glass. I use the same refractory plaster to make both parts of the mold and the same kilnwash (from the same mixed batch) as my release. Only the kilnwash on the lids flakes, resulting in sticking glass and a fine spiderweb pattern which shows the cracking/flaking. I apply the wash in a very thin layer. I have tried applying more layers, same result. Everything is thoroughly dry before firing although I do vent to 1000deg.
I have only recently started having this problem and besides buying some new kilnwash (same brand as before) I haven't changed anything else in my process or firing schedule. The kilnwash on the other part of the mold stays perfectly intact, enough so that I can even get a second firing out of them without applying new kilnwash.
Any insights much appreciated.
Cheers, Jen

[Valerie Adams]

I'm not well versed in casting, but it sounds like the wash on the "lid" mold is being fired upside down to press the glass? If that's the case--and I could be misunderstanding, so keep this in mind!--wouldn't gravity be the issue in the wash not sticking? Once the wash is fired, elements of it burn out. The reason it remains on our shelves is its own weight holding it there.