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Published Apr 18, 2022

Like many potters, I have entertained the idea of digging the clay from my backyard to make pots—especially during gardening season when I am fighting to get things to grow in the clay-saturated soil. But like many potters, I have not pursued it because it seems like a herculean effort. 

But in today's post, an excerpt from the April 2022 issue of Ceramics Monthly, Matt Fishman offers tips to make digging and processing clay manageable. And as you can see from Matt's finished pots, the results of the labor can be uniquely beautiful. –Jennifer Poellot Harnetty, editor

PS. To learn more about Matt's labor of love, check out the full article in the April 2022 issue of Ceramics Monthly.

Local Materials: Foraging and Processing

Ready to try out wild clays in your own work? Here are some tips for getting started with foraging for local materials then processing and testing them.

  • Start simple: Backyards of friends and family may have limited geologic diversity but offer a simple and safe first collection point to familiarize yourself with the process. Gathering several pounds of clay or rock will provide enough material for ample testing. 

  • Use the web: Online mining databases can point you in the direction of more specific minerals. Search in your area for kaolin or fireclay mines to use for clay bodies, as well as limestone, granite, or other rocks to use as glaze materials. Google Earth images can help pinpoint accessible deposits; look for large outcroppings, which stand out as white or stone-colored surfaces against the surrounding vegetation and dirt, or the remnants of old roads/structures where mines once were. 

  • Know the legality: Regional, state, and national parks are generally off limits, while collecting on Bureau of Land Management or Forest Service land is sometimes allowed. Know what jurisdiction you’re in and the rules pertaining to that particular place before you go. Private property is illegal to collect on without permission from the owner. To request permission, find an email or mailing address and give an honest and accurate picture of what you’d like to collect and why. Offers of finished work made using resources from the property can sweeten the deal. 

  • Stay safe: Use a respirator while collecting and processing dry clay and other materials, especially if the chemical makeup is unknown. Bringing a partner is advised as well, as locations may be on rough terrain and have limited cell-phone reception. Avoid digging in areas known to contain dangerous materials such as lead, asbestos, or mercury. Stay out of both abandoned and active mine shafts and structures, as both pose serious dangers. 

A This is an area of iron-rich laterite clay with visible veins of white kaolin. B Matt Fishman examining the materials at various levels of an outcropping. Photo: Kate Gibbs.

C Fishman collecting an iron-rich rock for use in tenmoku glazes and iron decorations. Photo: Kate Gibbs. D Fishman collecting clay. Note the variation in color and texture in the relatively small area. Photo: Kate Gibbs.

E Closeup view of a granite boulder with large feldspar crystals. F  This is a piece of feldspar weathered loose from the granite.

Processing and Testing

Clays can sometimes be used right out of the ground. Oftentimes, however, stones and other large objects need to be screened out. Slaking the clay down to slip consistency, then running through a mesh of desired fineness, followed by re-drying to plastic consistency will make a more manageable product. Rocks that are collected for use can be crushed first with a hammer and then with a large mortar and pestle. Some rocks are significantly easier to crush after a run through a bisque firing. A rock tumbler fitted with porcelain balls as crushing media, or a ball mill, if available, can work the rock into an even finer product, though it is not necessary to start with one. 

It is difficult to discern how refractory a clay is by visual inspection of the raw material. Instead, hydrate and then pinch a small form from the clay. Fire it to bisque, then to mid-range, and then high-fire temperatures to see how it responds, making sure to have a catch tray underneath it to protect the kiln shelves in case of melting. Glaze materials are best tested by line blending, where two materials are blended in various ratios (e.g. 100% rock, 90% rock and 10% ash, 80% rock and 20% ash, etc.) to see how they respond to each other. Easy blends to start testing include: any wood ash and any clay, wood ash and any crushed stone, and any natural material with a store-bought feldspar. 

Keep an open mind. The fired results from foraged materials won’t resemble the clays and glazes many of us are accustomed to, especially in early tests. Rather than trying to fit the materials into what we know ceramics to be, look at them with fresh eyes and appreciate the unexpected effects that they offer. Note: Many of the beautiful but rough surfaces will not be as suitable for eating or drinking from.

G To prepare the wild clay for slaking and screening, roughly crush the pieces. Photo: Kate Gibbs. H Screen the wild clay slip through a relatively large mesh to filter out twigs, leaves, and large stones, while leaving as much texture as possible. Photo: Kate Gibbs.

I This is the face of a wild clay body after cutting it with a wire tool. Note the red streaks of iron-bearing material and the particles of various sizes leaving marks across the surface. Pinched and stamped sake cup, 2 in. (5 cm) in height, wild stoneware, Chosen Karatsu-style ash glazes, reduction fired to cone 10, 2021.

the author Matt Fishman has been a studio potter for several years after leaving a career in restaurant kitchens. He works out of Berkeley, California, making functional ware and teaching at The Potters’ Studio. He and his partner, Kate Gibbs, have been collecting and using local materials for the past five years. To learn more, visit

Topics: Pottery Clay