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“The land is the real teacher.
All we need as students is mindfulness.”
– Robin Wall Kimmerer,
Braiding Sweetgrass
Today, buying glaze ingredients is as easy as ordering takeout or booking a ride. At the click of a button, potters can purchase bags of highly processed materials from all over the world. It’s convenient, and we don’t need to think too hard about it – but it makes us beholden to large industries. Mines close, and veins of materials run dry, forcing potters to make substitutes. Material prices can also rise or become unavailable as a result of demand from other industries.
We are seeing this right now with lithium-bearing minerals, such as spodumene, being bought up for the battery industry. When replacement materials enter the market, their chemistry is never quite the same, forcing potters to retest and adapt their recipes.
Often, we have little idea where our materials come from, who is involved in mining and processing them, and what their working conditions are like. Many are aware that cobalt mining in the Congo is problematic, but what about the conditions of the people who extract other glaze materials and the environmental implications of those processes? We overlook such questions, just like we do with much of our supermarket produce.
There is a growing "wild clay" movement in the ceramics field, with professional potters and amateurs harvesting their own clay. I celebrate this, and I want to encourage others to try using the rocks and minerals in their backyards to make wild glazes, too.
This is not a new idea. Until globalization sharpened its claws, this was the traditional way of making pottery; it was a necessity. Clay and rocks are difficult to transport, and pots are generally inexpensive. It did not make economic sense to transport pottery materials over long distances.
When I began potting, as a young lad at Winchcombe Pottery, I read Pioneer Pottery. Michael Cardew’s pioneering spirit turned me on to the idea of using local materials. It wasn’t until I apprenticed for Mark Hewitt, though, that I saw these ideas in practice. Mark uses a local gravel as the base of two of his standard glazes, and it was one of my jobs to process it. We also gathered and tested other local rocks, and came up with a lovely celadon whilst I was there. Since then, further inspiration has come from articles, books, and pots – most notably by Wili Singleton, Ian Currie, Steve Harrison and Matt Blakely – and travel to places such as Mashiko, Japan, where potters make gorgeous glazes from local materials.
Making wild glazes is like growing your own tomatoes. The raw rock in your hand is like the seed; it needs cultivation to produce fruit. The tomatoes you buy in the store are never as tasty as the ones you grow. They can’t be. Partly, this is because they aren’t picked at peak ripeness, but it’s also because you have not turned the soil yourself and watched the tomato ripen from green to yellow to red. You haven’t squeezed it to see if it’s ready to pop off the vine.
The same goes for turning rocks and minerals into glazes. It is a process. It takes trial and error, time and energy, intention and mindfulness. In the end, this work makes the glazes and the pots that they coat that much more satisfying.
Local materials offer endless possibilities and variety. A couple of years ago, I set out on a quest to make a palate of four stoneware glazes from one locally sourced rock. I did not want four shades of beige, but a palate of distinctly different glazes. The parameter I set was to use at least 50% of one single source rock in each of these glazes.
In the beginning of this quest, I foraged for rocks from all over Utah and Idaho, performing simple melt tests to cone ten in a small gas kiln. These initial tests showed me that at stoneware temperatures, one can melt most rocks, but often the results are muddy pond-like greens or uninteresting browns (as potters, we know there are some spectacularly interesting browns out there).
I chose to base my palate on one particular granite from Devil’s Playground in northern Utah. Why this particular rock? It contained lots of quartz, some feldspar, and a little iron. Once it was powdered, it melted into a glaze at cone ten without any other additional materials. Admittedly, at 100% granite, it was a fairly uninteresting gray glaze, but it provided a good canvas for further experiments. Also, I was totally enamored with the place.
The Landscape
Devil’s Playground is on the western edge of the Great Salt Lake. It is a remote area in the high desert. No cell service, no settlements. Quiet. Granite slabs jut out of the barren plain. The rock has weathered in fabulous patterns, from cavities that look like honeycombs, to seams and cracks, arches and pillars, all the way down to dust. These structures have eroded over millions of years.
On my first visit, I climbed up one of the tallest granite slabs with my bulky 4x5 Speed Graphic film camera. A wide, desolate basin expanded below. The edge of the Great Salt Lake was so far off that I couldn’t see the water. It was exposed. Vicious winds threatened to blow me off the peak. I set the tripod and made a photograph anyway.
The Playground is so dry, yet it teems with life; desert plants like sagebrush, Utah juniper, pinyon pine, and cheatgrass thrive. Their cracked limbs show the struggle of survival.
On various trips, sitting quiet and still, I marveled at the wildlife: spying lizards and birds, a jackrabbit, an owl, and a snake. Rarely a human. I saw the detritus of humans, though: old ammunition casings, food wrappers, rusty metal. In a small act of thanks and reciprocity, during each visit, I collected these human things and removed them.
From Rock to Powder to Glaze
I always tried to impact the landscape as little as possible when I was collecting the granite. I’d pick pieces of rock that had weathered off larger boulders and were loose on the surface. For my initial tests, I collected half a bucket, but came back for more with my trusty Prius when I saw its potential and needed to run more tests. Devil’s Playground is BLM land, and its website states you can collect “a reasonable amount of material.” A Prius trunk-full of five-gallon buckets seemed reasonable to me.
The processing began with calcining the rock (to 1200°F in an electric kiln). This helped loosen the bonds holding the granite together. I had access to a ball mill, but the rock had to be broken down to pea-size or smaller to be effectively milled. Easier said than done. In the beginning, I was doing this initial step by hand and hammer with the help of my assistant, Jack Orgill. This was exhausting work. Our method sped up when I acquired the “Crazy Crusher,” a simple but effective hand tool that crushes rocks between two metal plates. The granite peas tumbled overnight in a ball mill with dense porcelain balls for bedfellows. By morning, the rock was a fine, usable powder.
Over the course of a couple of years of testing and by adding various ingredients, I managed to create four distinct glazes using the Devil’s Playground granite as a base: a celadon, tenmoku, yellow matte, and jun glaze. The way I fired these glazes changed the way they looked considerably. For example, the celadon is yellowy green in oxidation and a richer turquoise with more reduction. I won’t bore you here with the details of the testing process or further intricacies of the firing. If you are interested, my blog goes into detail about the thousands of tests it took to attain these surfaces.
This work all came together in my 2023 exhibition, Teatime with the Devil. You can take a tour here if you like. At the end of this article, I provide the recipes for my granite glazes and the analysis of my Devil’s Playground. With magic glaze calculation programs such as Glazy.com, you can substitute other materials (bought or found) for my Devil’s Playground granite to achieve the same glazes.
Practically any rock or mineral you find can be useful in glazes. Some, such as lower fire clays or lakebed sediments, have fine-enough particles to be used without any processing. Granite happens to be quite hard, so calcining helps a lot. A ball mill also speeds up the process, but it is not essential. I mostly sieve found materials to forty or sixty mesh, which is not super fine, so it doesn’t take too long to produce enough for tests, even with hand tools. Other avenues can be fruitful, too; quarries or countertop companies will sometimes share rock dust from their saws.
The Pursuit of Happiness
Sitting here, at home in Oregon now, drinking a cup of tea from a mug draped in yellow, I am reminded of Devil’s Playground. I remember the feeling of being out there in the high desert, wind whistling through the sagebrush – of picking up rocks and wondering at the promise in my hands, dreaming of ripe, juicy tomatoes. The difficulties of the process have faded away, and I am left with the satisfaction of really knowing where this glaze came from.
In my continuing studio practice, I want to further cultivate the connection between my pots and the landscapes where they originate. Foraging for local materials and producing wild glazes is a mostly enjoyable challenge that makes my practice more sustainable and less dependent on industrial products.
Increasing numbers of people are becoming conscious of where their consumables originate, from questioning single-use plastics to trying to eat more locally produced food. As potters, I ask us to do the same, to be mindful of where our glaze materials come from and what we use. To try the less convenient path!
And if you don’t already grow your own tomatoes, get on with that, too!
Granite Glaze Recipes
Hamish’s Granite Celadon
80 Devil’s Playground granite
20 Wollastonite
Hamish’s Granite Yellow
50 Devil’s Playground granite
20 Logan Canyon dolomite
15 Zircopax
10 Bone ash
5 Edgar plastic kaolin
Hamish’s Granite Tenmoku
57 Devil’s Playground granite
14 Wollastonite
10 Grolleg
5 Basalt (Craters of the Moon)
5 Silica
5 Red iron oxide
2 Zinc oxide
2 Bentonite
Hamish’s Granite Jun
50 Devil’s Playground granite
20 Wollastonite
20 Silica
10 Mahavir feldspar
+ 2 Bentonite
+ 2 Bone ash
+ 1.5 Logan Canyon dolomite
+ 1.5 Red iron oxide
Chemical composition of the Devil’s Playground granite (analysis from Washington State University):
SiO2 75.64
TiO2 0.20
Al2O3 13.37
FeO 1.34
MnO 0.03
MgO 0.38
CaO 1.38
Na2O 3.23
K2O 4.37
P2O5 0.06
A final note on the black and white landscape photographs:
I wanted to photograph the landscape of Devil’s Playground in a way that aligned with my investigation of traditional ways of making. Professor Jared Ragland at Utah State University introduced me to wet plate or tintype photography. This method was invented in the 1850s and was one of the first ways people made black-and-white photographs.
The process involves coating a glass, tin or aluminum plate with silver collodion, exposing a photograph and then developing it whilst the plate is still wet. It is about the most challenging way to photograph a remote landscape like Devil’s Playground. Much can go awry. The development must happen in the dark, and the chemicals work differently depending on temperature and atmospheric conditions.
We had a very cold winter in Utah, and we had to keep postponing the mission. The process would not work if the chemicals or plates froze. In the end, we only had one day in early April available to try to make photographs. We didn’t know if it would be possible as we drove through a snowstorm to get there. Jared discovered a single public bathroom in the midst of the granite boulders, and we quickly converted it into a darkroom. He worked the chemistry, I worked the camera, and my trusty pal Stillman ran the plates back and forth. It is miraculous we got these images.