Clay Body COE of 4.6??? How on earth to Glaze that without crazing?

[kraythe]

I am sick of my current clay because the supplier wont tell me jack about it and I cant get it to fit any glaze without crazing so I was browsing through the Laguna site looking for an alternative and then I looked at some of their cone 10 clays and some have COE down to 4.6. How on earth can you glaze to that clay. Every glaze recipe I know STARTS at 6.0 and goes up from there and the most common is in the 7's.  Clearly I am missing something. Can someone help me out here ? 

[Callie Beller Diesel]

I think you're maybe getting too hung up on glaze calc numbers.  Coe is a starting point, and not always helpful. Neither glazes or clay expand or contract in a linear fashion, particularly if there's something like lithium in the mix.  You'll have a glaze that fits like a glove, but the numbers will say that it shouldn't be.  You don't have to match exactly the Coe of the glaze and the clay body, although having them close can sometimes help. Stop getting hung up on numbers, and just test something to get a starting point. 

 

Also, not all clay bodies are meant for production pottery and the avoidance of crazing or shivering. Aesthetics, ease of use for sculpture or teaching purposes, price and material availability are also factors when manufacturers come up with a clay recipe. 

[Min]

What Callie (and others) have said on this thread and others.

On the thread "What's your mug?" I posted a picture of a simple white glaze on a red clay. I test the heck out of my glazes, this glaze fits this clay. The clay is this one, it has a COE figure of 4.6 and my glaze calc program has the glaze at 5.72  I've been using a set of mugs and bowls with this clay and glaze for most of this year, the glaze doesn't craze even though the COE figures have a fair spread.

I'm posting my glaze recipe for you to see but please don't use it on regular COE clays as it will likely shiver.