Common Problems With Utah Wild Clay (And What I’m Learning So Far)
People talk about wild clay like it is romantic. Nobody mentions the cracked test tiles on the shelf.
Over the past year I have been collecting and testing small samples of wild clay around Cache Valley. Four problems keep showing up: cracking while drying, warping in the kiln, melting too early, and staying too porous. Each one tells me something about what that clay wants to be.
- Cracking usually means high shrinkage or too little temper, so I add sand or grog
- Slumping at cone 10 can mean a clay is better as a slip or glaze ingredient
- Wild clay rarely works straight from the ground without adjustment
When people talk about wild clay, it is usually romantic. Dig it up, process it, fire it, connect to the land. What they do not always talk about are the cracked test tiles on the shelf. Or the bowl that split clean in half while drying. Or the sample that melted into a warped puddle at cone 10.
Utah wild clay is beautiful in theory. In practice, it is humbling. I am still early in the process, but a few problems keep showing up.
1. Cracking while drying
This has probably been the most common issue. Some deposits have high shrinkage. They feel plastic when wet, promising even, but as they dry, fine cracks start to form. Sometimes it is surface cracking. Sometimes it is a full structural split. That tells me there may be too much clay content without temper, uneven particle sizes, or simply high shrinkage.
I have started adding sand or grog to reduce the stress during drying. Sometimes it helps. Sometimes it just reveals the next problem.
2. Warping in the kiln
Even when a test tile survives drying, firing brings a new variable. Some samples warp badly at higher temperatures. Edges lift, surfaces twist, and you can see the stress lines in the clay. That usually means the clay body is not balanced and does not have enough structure to handle high fire conditions. Just because clay exists in the ground does not mean it wants to become a pot.
3. Melting too early
Iron rich clays can be beautiful, with deep reds and warm browns, but they can also melt faster than expected. A few of my tests have slumped at cone 10, especially when used too thickly. That is useful information. It may mean the clay is better as a slip or glaze ingredient than as a full throwing body. Failure, in this case, is just data.
4. Staying too porous
At the other end, some deposits barely vitrify even at high temperatures. They stay chalky and porous, which limits their use for functional pottery. That does not make them useless, but it changes the conversation. Maybe they are better for sculptural work. Maybe they need blending.
Why keep going?
There have been more failures than successes so far. But every now and then a test tile comes out of the kiln and surprises me. The color deepens, the surface tightens, the iron freckles just enough, and it holds together. Those moments make the cracked tiles worth it.
Working with wild clay makes me slow down. It makes me pay attention to shrinkage, mineral content and firing temperature in a way commercial clay never asks for. I am not trying to prove every hillside in northern Utah can make functional pottery. I am just learning what this ground wants to be.
Mark a 10 centimeter line on every wet test tile before it dries. Measure it again when dry and after firing. Shrinkage is the number that explains most cracking, and it takes about ten seconds to record.
The cracked tiles stay on the shelf on purpose. They are the notes that tell me which clay to try next, and how.
