Greenware clay should not crack when painting underglaze on it, but that’s what’s happening with my “new” clay, Kentucky Mudworks’ Elkhorn ^6.
Was it something I did?
I had wondered if my pieces were made weak at the corners. But no, the pieces were even enough all the way around.
And I actually watched one of the pieces crack from the outer edge.
How bad is this greenware cracking problem?
I had thought the cracking only happened about 25-40% of the time on the greenware clay.
Closer viewing of bisque fired pieces show every one of them had at least hairline cracks. This is so frustrating. If I were a beginner, I’d probably give up clay!
What I expect from my clay.
I had picked this clay because it seemed the closest to Highwater Clays’ Redstone ^6 in features, which I loved and used reliably for years.
Here are the features that I’m seeking:
- Cone 6 red clay (just for the esthetics and for best base coloring of skin tones under terra sig)
- Shrinkage rate around 11% to 12% (that’s just a personal preference for comfortable known proportions.)
- Absorption rate of 1% or less at cone 6 (I’m picky about this because my functional ware demands it for no-leaky-bottoms in functional ware.)
- Be useful for wheel throwing, hand building, and sculpting. (A strong requirement because I do all three, sometimes on the same piece.)
I thought the Elkhorn would do the trick. Yet, now I’ve learned that I also want it to - NOT dunt when I paint underglaze or terra sig onto the greenware clay.
Kentucky Mudworks has been very kind in acknowledging my situation and has offered me the option of trying out a different clay (Sheltowee) for my hand building. I will try it out as a possible temporary measure.
But I have that Requirement #4 of my clay, “Be useful for everything I make.”
I really dislike having multiple clays around, cluttering up the studio space. I want one red clay body for cone 6, and one white cone 10 clay body for my wood firing. That way my glazes can be formulated for the clay bodies I use, and I don’t accidentally high fire the wrong clay!
A Possible Solution to Cracking Greenware
My research tells me that Highwater Clays had added 6% Kyanite to their Redstone clay body. This stuff supposedly gave their greenware clay the strength to stay together for terra sigging and underglazing.
I’ve now purchased some Kyanite and will need to do some math and experimentations to figure out how much I will need to hand wedge into each pound of the 400 lbs+/- of Elk horn clay I have on hand. And then test, test and test again. I am hoping that if I can figure out the right percentage to use, I can talk Kentucky Mudworks into making me a batch of useable clay.
So, watch for updates on my tests here for a functional greenware clay.
Update: July 12, 2026
My testing of the Kyanite was successful… to a degree.
The splitting stopped on the greenware when underglazed (Yay!!!), but the clay became a bit less bendable showing the multiple mini cracks on the outside of the clay where the clay was bent. This is a common problem in any clay that’s become a bit short.
So now I will add a bit of extra bentonite to the recipe. I’m hoping the small amounts of .02% to .1% of bentonite I will add won’t too badly affect the absorption rate. Off to do more tests!
On a side note, I was told by an employee of Kentucky Mudworks that none of their clay body contains Kyanite. I’m not sure how that company has NO complaints (except mine) about the clay dunting when underglaze is added to greenware. There are so many techniques that require adding colorant to the bone-dry clay.
Does everyone who buy from KM bisque fire before underglazing?
That can’t be right. My recent purchase of underglaze specifically says that it can be safely used on greenware.
Anyway, I have been told that Kentucky Mudworks does make custom clay bodies in 1800 lb batches. So that is good.