I've been throwing with Standard Clay 630 (^6 white stoneware) this year and have really been enjoying using it. However, I used a few different commercial glazes with it and have found that some of them are crazing. For example:
Amaco HF-9 Zinc Free Clear
Amaco PC-40 Celadon
Amaco Sahara Yellow
Coyote Light Blue Gloss
All of these are translucent, so maybe that's the common thread? Because Amaco's Ultramarine, Amaco's Amethyst, and Coyote's Buttercup didn't craze at all. But I tried my local studio's zinc-free clear, and it didn't craze.
It's not the cooling, because nothing is being fired any differently than other pieces that don't craze. So I'm thinking it's a COE / glaze fit issue...but I am a total newbie at glaze chemistry, so I bow down to the collective knowledge of the forums and ask if there's anything I can do to my commercial glazes to make them fit.
Other than changing clays, of course. Which is probably what I'll have to do, but I like the 630 the best out of the ones I've tried and I really love the celadon and light blue glazes...
Also, how serious is this breed of crazing? Is it really *that bad* when it comes to using them for food/drink??
(Regarding clays.....I know some of you swear by clays made by Highwater, Laguna, etc., but I live in Pennsyltucky and getting anything other than Standard isn't an option right now. Also, I am a hobby potter and porcelain is out of my current league.)