How to dig and process clay: part 1

PART 1: acquiring the clay

There’s a *lot* of great clay around Oregon. I first started on this mission because I found some veins of perfect, thick, sticky grey clay on our land, and it just looked like what you’d buy in a bag from a craft supply shop.

I met a ceramicist once who argued that there is no hard line between mud and clay. Mud, or soil, always includes a certain proportion of clay particles. Soil is a composed of five ingredients: minerals, soil organic matter, living organisms, gas, and water.

That mineral component is the largest, and is divided into three size classes: clay, silt, and sand (Figure 1). The percentages of particles in each of these three size classes is what makes up the soil’s texture. Because of their size, those tiny clay particles make for a very dense, sticky substance.

Source: “Different Types of Soil – Sand, Silt, Clay and Loam,” The Constructor, September 26, 2018, https://theconstructor.org/building/soil-types-sand-silt-clay-loam/25208/.

If you want to produce something that is easy to work and is strong, you’ll want to look for a soil with a high clay content, and then do some filtering so that you end up with a greater proportion of those tiny particles.

Look for areas where water sits on top of the ground and doesn’t drain away easily. That’s a sign of a high clay content, because it suggests that the soil isn’t very porous. There’s usually somewhere between 8 and 18 inches of topsoil before a layer of dense clay, so if you’re digging for some reason, that’s a good opportunity to acquire some clay-rich soil. Here in Oregon, there is a lot of clay-rich soil, and I happen to have a piece of ground that got totally turned over recently, which has given me a great opportunity to access good clay. You can see that the section in the middle is grey and sticky-looking, and isn’t supporting as many plants as the areas around it!

There are better and worse soils to start with, but actually I’ve had awesome success with quite different kinds. My stepdaughter found some amazing black mud on a hike and we gave that a try, and it was weird as anything to shape but it fired beautifully, with some obvious texture and some amazing red hues. If there’s a lot of organic matter in it that’ll give you problems (though we’ll get the biggest bits out in the next step), and the grey sticky stuff is the easiest to model with and will give the strongest results, but I encourage experimentation.

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