PROSPECTORS: A Conversation with Alex Thullen & Matt Fiske

CG: What was your first experience with clay, and what was it that “grabbed” you?

Thullen: I grew up in a house where handmade functional and decorative objects were ubiquitous.  Reed Baskets, Ceramic Figurines, Cross-Stitch, Ukrainian Easter eggs, and a plethora of other meticulous, detailed objects were my everyday surroundings. The small electric kiln in our basement was the first introduction to clay, long before I even knew what it was used for. I was exposed to these objects from a very young age, but it wasn’t until my first experience with clay in Junior high school that I really understood the potential of the material. Or, the possibilities that it would open up for me to fill my need to make things with my hands, and in some way, shape my own surroundings.

CG: You are both prospecting glaze materials, yet very differently from one another. What is your approach to prospecting, and how has it changed since you began?

Thullen: My interest in working with locally sourced materials began years ago when I began working with atmospheric firings, and started looking into more traditional, historic methods of creating glazes. After spending so much time testing and experimenting with traditional reduction glazes, I was ready to move beyond the conventional “crayon box” of the materials that I had at my disposal from ceramic suppliers, and to see what could be achieved with materials sourced from my own surroundings. This began with more conventional choices akin to the material that were used by early potters to create their glazes, such as wood ash, locally dug clay, and numerous materials derived from traditional geological sources, and the landscape around us. I was interested, as I began to develop my own personal aesthetic, in carrying this idea through to my glaze materials and palette as well.

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More recently, I have begun what I refer to as “Urban Prospecting”. In thinking about the process of sourcing my materials and how this related to the work that I was making, I began to consider the source of my aesthetic. I am heavily influenced by, and interested in the application of ceramics to architecture. The patterns and texture used to decorate my pots began by looking at pattern and geometry in architectural embellishment and decoration, including brick, tile, and other uses of ceramics in constructing our environment.

I started to realize that I could be using these materials themselves physically, and not just as inspiration, by processing these materials to create my glazes themselves. Additionally, in thinking about the origins of my materials, we all derive sourced material from our surroundings. Living and working in an Urban (and suburban) environment, I don’t have landscape or geology readily at my disposal. My landscape is the urban environment that I work in, and drive through every day. This is where I have begun to draw from to create my glaze palette. The materials that I use are essentially the detritus from Architectural and Industrial sources in my surroundings. Old building bricks, broken glass, industrial slag, and chunks of concrete contain the necessary chemical makeup to make glazes just as beautiful as any that can be derived from the rocks and minerals that shape the natural world around us.

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Specific Glazes I Use:

Clay Bodies: I use a very simple porcelain body, mainly Kaolin, Feldspar and Silica and a few small additions for workability. This is the basic clay that I use to make the majority of my pots. Three of the pieces in the exhibition are made with an iron-rich version of this clay body that contains Iron-rich slag which I found on a beach in Northern Michigan last summer. The clay body has such a high thermal expansion and contraction rate as a result of the iron that only my shino glazes can be used on this clay without causing significant glaze fit problems. The resulting clay body has a beautiful deep brown color, and a metallic sheen from the reduction firing.

Beach Glass Celadon: This glaze starts as a traditional celadon, but incorporates beach glass as a pigment, rather than the traditional Iron oxide compounds. Being related closely to glaze, glass uses virtually identical pigments to create color. By taking a combination of blue, green and brown glass washed up on the shores of the Detroit river, I can grind these materials into a fine powder, and essentially create a “stain” of my own. Because this material contains cobalt and chrome from these glasses, the colors are more intense, and a bit more reliable and true than a traditional celadon glaze.

Angle Iron Celadon: This is a very traditional celadon glaze. In this case, I have taken sheets of rust from the Angle Iron supports of an old salt Kiln that was torn down and re-built during my first year at Pewabic Pottery. This was my first kiln-building project, and is full of nostalgia for me because of the friendships that we made while working on it. The rust sheets were ground and ball-milled to create a very fine iron oxide that is used to color this glaze.

Molasses: This glaze started as an amber-colored, high-iron ash glaze. I’ve incorporated concrete dust into it as a source of calcium. Processing the concrete so that it is usable requires calcining the material to break down the chemical bonds that hold it together, and then carefully screening out the sand and gravel that is added to the concrete during the original mixing process. It is quite a caustic material, so care needs to be used when handling and spraying the glaze, much like an ash glaze.  I have carefully adjusted it so that it is fluid enough to highlight the carved decorations on my pieces, but is still stable enough to keep it from running badly.

Belle Isle Black: This is one of my favorite glazes. It’s a high-magnesium matte black glaze that is based mainly on a red local clay that was sourced from Belle Isle, a state park in middle of the Detroit river. The majority of my glaze materials wash up on the shores of the island.

Brick Powder Slip: This is a simple flashing slip that I use for soda firings, made by blending ground brick powder with Kaolin, and small amount of feldspar. The brick powder deflocculates the slip, making it ideal for bisque application without cracking, and the Iron in the original brick clay gives the slip a beautiful color when flashed by the wood ash and soda in atmospheric firings. Coming from a city with a northern climate, the small chunks of brick that wash up out of the river have been exposed to possibly over 100 years of freeze-thaw, making them extremely porous, and easy to break down into a very fine powder.

Slate Shino: This simple shino glaze contains powdered slate from the roof of Detroit’s old University Club, now demolished. This historic gem was an incredibly beautiful building full of intricate architectural details. Tragically, it fell victim to urban decay, corruption and looting, and had to be torn down several years ago. I was lucky enough to salvage some of the old roof tiles from the grounds just before it was demolished, and used a ball mill to grind them down to a fine powder. The iron in the slate gives the shino it’s rich red-orange color over the porcelain clay that I use.

Luster Shino: This glaze is a layering of a high-alkali Shino over a dark iron-rich slip containing ground brick powder. The high iron concentration combined with the carbon trapping caused by the high soda content of the glaze causes the intense metallic luster in the fired glaze surface. This is one of my favorite, but most unreliable and variable glazes.

Fiske: It’s no coincidence that all of my best prospecting spots are in close proximity to good fishing, hiking, or camping spots. I will occasionally set out to go digging for a specific material and a mission to go collect it – but usually my discoveries come about from rambling around backroads, or driving into the mountains with my eye out for color and texture. More than anything, the main objective is to get the hell out of the studio and go exploring. This approach has evolved quite a bit over the years, and wasn’t really a thing until my time in Graduate School in Utah. For those who haven’t been, Utah is a kind of geology and ceramic material paradise. At the time it was hard to justify driving out into the desert or up into the hills just for camping and hiking, or just for research and studio work. These days, it’s critical for me to step away from the studio and get outside and recharge.

locations. I learned a lot hanging out with him and few other rockhounds – and pretty much everything I’ve learned since then was the result of going out and doing it. As far as I’m concerned, you can’t really learn rockhounding or prospecting from a book (although Falcon Guides have a really good series of books on Rockhounding – I have 5-6 of them from all the different states Ive lived in!). I think the best way to go about it is to just get out there and start picking up stuff. The real trick is to then put it straight into a kiln. Early on I often made the mistake of collecting a bunch of material and then never getting around to using it. Getting results immediately is super important. It seems that the longer you wait to test something, the likelihood of never using it increases dramatically.

Clay Body: For the past few years I’ve used Laguna 550 Porcelain. Although it’s on the pricier end of the spectrum, I’ve had really great results in a wide range of firing atmospheres and temperatures. It looks good in cone 6 electric, it holds up in cone 12 oilspot firings, it’s a beautiful translucent bright white in reduction, and it’s not too yellow or grey in oxidation. In addition to it’s fired characteristics; it also throws really well and is reasonably resistant to warping and cracking. My best guess is that it’s a Grolleg Kaolin based recipe with soda feldspar, silica, and white bentonite. It looks almost identical to the porcelain recipe I use when I have access to a good mixer and a pugmill: 55 Grolleg, 30 Minspar, 15 Silica, 2 Macaloid.

  The decision to use a single, commercial clay body came after the realization that my real interest was in glazes. With so many variables in the glaze materials and firing processes I’m interested in testing, the very last thing I needed was another variable to account for. There’s also the issue of scale. When prospecting glazes, I like that the scale of collection and storage is in the 10-20lb, 5 gallon bucket range. When it comes to prospecting for clay bodies, the scale is more like 1000-2000lb, pickup truck range. I wish that I had the time and energy to make wild clay bodies – but the truth is that I’m just way more interested in spending my studio time throwing, glazing, and firing.

Glazes: For the past year and a half I’ve been really interested in Soda Firing, and I’ve been exploring 3 glazes. To these glazes I’ve been adding a copper material that I prospected outside of an old copper mine in Millford, Utah. I’ve been calling it Copper Sand, because it looks a lot like a bright green sandy dirt. Rather than ball milling, I’ve been experimenting with adding very coarse material into my glazes, and brushing them on. When I go to glaze I have about 5 ziplock bags of material sorted by particle size (6-12 mesh, 12-24 mesh, 24-40 mesh, 40-60 mesh, 80+ mesh), my buckets of glaze, and 3 small bowls of glaze to mix in the material. In the first bowl I usually have very coarse material, in the second bowl is finer, and in the third bowl is a mixture of the two. After lining all of my pots and allowing them to dry, I brush on the glazes, paying attention to glaze thickness and the amount of material going onto the pots. As I go along, I’m constantly adding more glaze and copper material to the bowls.

Copper Sand:  From a commercial standpoint, this material is a mid-grade copper ore. Because it was collected from the tailings pile next a mine, there’s really no telling when and where it was dug up. That said, I’ve learned a lot about it through trial an error. To make a very long and complicated geologic story short, it was at one point, a limestone rock. This limestone rock moved over a volcanic hot spot in the earth’s mantle, and was subsequently covered in a very thick, very erosion resistant volcanic layer of rock. Millions of years later, the tectonic plate switched directions and moved back over the hot spot. As a result, the limestone layers underneath the cap of volcanic rock were steamed and stewed with a mixture of sulphides and metal-rich solutions. For the past few million years, the volcanic cap has slowly weathered away, and the underlying copper/silver/gold/lead/tin/tungsten rich rocks and minerals have been exposed to enterprising miners. My best guess is that the particular material I collected was unearthed in the 1960’s or 1970’s and has since been slowly decomposing and breaking down in the Utah desert. It’s an extremely variable combination of mostly calcium carbonate, pyrite, arsenopyrite, and hematite – but it’s also contains varying amounts of tin, zinc, molybdenum, tungsten, titanium, gold, silver, lead, cobalt, magnesium.

Turqouise/Oribe Glaze: This is a glaze commonly found in a lot of studios, and is characterized by additions of copper carbonate to make for a watery blue/green. In oxidation it can make for a bright Mediterranean blue, and in reduction is can form a metallic microcrystalline black/green surface. With the addition of the varying coarseness of my copper sand material, I sometimes see streaky, webby, ash-glaze-like blue fields with silver crystals. I usually see a lot of greens and turquoise with black spots and speckles. I also occasionally see bright pink and red lichen-like surfaces. It’s a really variable glaze, and a recipe called Turqouise, which is very similar to mine, can be found in John Britt’s High Fire Glaze Book. My variation has a range of about cone 8-cone 10, and much hotter than that, it runs like crazy.

Hayne’s White: A very standard white liner glaze. My own variation uses Minspar, +10% superpax, and EPK. In the soda kiln, it has a tendency to carbon trap very nicely as well as crystallizing in very interesting ways. It’s much more resistant to running as my other two glazes, although it is very susceptible to blushing pink and purple when it’s next to copper glazes in the kiln. This glaze has a range of cone 9-11.

Celadon Blue: Another classic studio glaze, my recipe uses prospected basalt for the colorant. It’s also on the low calcium, high sodium spectrum of Celadon glazes. (It’s basically a celadon/copper red hybrid) As such, it doesn’t go matte in soda firings, but remains bright and glossy. It also has a tendency to carbon trap and blush when it’s next to copper glazes in the kiln. With additions of fine copper sand, it develops a rich copper red, and with coarse additions, it forms black and bright blue spots and speckles. Because this glaze tends to flux early on, it has a really wide range in the soda kiln and looks good between cone 6-10, and like the oribe, it runs like crazy beyond cone 10.