Working on a new glaze and I decided to look at their COE's as I had slight crazing. First I put in the one that had the least crazing.
Cornish Stone - 50
Whiting - 50
COE = 848
This recipe has the least crazing.
Cornish Stone - 45
Whiting - 45
China Clay - 10
COE - 769
This recipe had the middle amount of crazing, only small but still there.
Cornish Stone - 40
Whiting - 40
China Clay - 20
COE - 691
This has the most crazing.
So I thought that must be right, so to check I put in a glaze I have that I know doesn't craze. That came out to be 400ish. Can't remember the exact figure as I didn't right it down. Tested another glaze I know doesn't crazy with my clay. Same thing, around 400ish.
Why is the first glaze test with the highest COE got the least crazing
To my knowledge you want a glaze with a slightly higher COE than your clay to have slight compression in the glaze. Too high and it crazes, to low and it shivers.
Correct me if I have F'd up somewhere.
I don't know the COE of the clay.