02 Slips and Glazes
Finding My Way to Glazing
When I first started making pottery, I didn’t think too much about glazing. I was taking classes at a community college and a local ceramic center. I wasn’t afforded much of a voice in the glazing realm, aside from choosing my color. As for the firing, it was a mystery I had no part of. This was okay for the first couple of years: I was learning how to make pots and that consumed me. But I got to a point where it dawned on me that I loved making pots, but I didn't love pottery. The glazes finished the process but left me with a shiny, coated form that smothered the life out of it: a thick, opaque frosting that erased any marks or voice in the clay.
About that time, when I had begun looking for more control in how my finished pots looked, my teacher, Becca Floyd, gave me the opportunity to take a wood firing workshop taught by Michael Hunt and Naomi Dalglish. She knew how much the experience of an intense workshop would benefit me and evolve my making process. This week-long workshop at the John C. Campbell Folk School has proved to be the most defining moment in my pottery career. It opened the door to a whole new world of making pots. It was what I was looking for but didn’t know it.
I learned about wood firing, wild clay, Hamada, Korean pottery, ash glazes, rocks, imperfections, crazing, and pots that look alive. I discovered I did like pottery. In fact, I loved it. I went down the rabbit holes of glazing, firing, and clay. I assisted Shawn Ireland and Bandana Pottery in wood firing and clay making. I joined a small studio with interesting working potters who generously answered my never-ending questions and encouraged and critiqued my work. I made as many pots as I could every chance I got. Life became what I imagined it would be when I was a kid—when you find the thing that gives you purpose, you matter.
I experimented constantly. I made and tested countless glazes, slips, and washes. Slowly, my voice started to emerge through my pots and they started to look and feel like me. I still experiment regularly.
Pottery is exciting and the more I learn, the more motivated I get. It is a cavernous craft with no limits. The explorations in form, method, firing, and glaze have no end. The more I make and learn, the more I feel inspired and full of ideas. I feel grateful and lucky that such a fire has been lit inside of me, marrying heart, head, and hands. As I work, I tend to this flame and it lights every aspect of my life.
I approach glazing as I do every other part of the process. Glazing is as important as the choice of clay and the type of kiln firing. Each of these aspects that go into making a pot are equally deserving of attention. I think of glazing as a contributing layer that enhances and showcases the slip and/or the clay underneath. The materials have a symbiotic relationship, all working together to let their individual qualities shine and become one finished piece.
“Pottery is exciting and the more I learn, the more motivated I get.”
Making and Using Slips and Glazes
ROTARY SIEVE
IRON- AND ASH-GLAZED VASE
YOU’LL NEED
Talisman rotary sieve or sieve with 60 and 80 mesh screens
Empty 5-gallon (19 liter) buckets with lids
Quart mason jar, Tupperware, or other equivalent container with lid
Electric drill with a mixer attachment
Assorted bamboo brushes
Assorted hake brushes
Oil-based wax, such as Aftosa blue wax
Water-based wax, such as Amaco or Forbes
Sponge
Large whisk or wooden spoon for stirring glazes, slips, and iron wash dry ingredients, according to desired recipes
Digital scale
4-cup (1 liter) plastic measuring cup scoop
Respirator
ABOUT ASH GLAZE
My main choice is a simple ash glaze made with ash, kaolin, and feldspar. I got the basic recipe from a Japanese potter on the Internet who informed me that the feldspar in Japan is much different than the feldspar in the United States. The type of wood burned for the ash is important, as is the type of kaolin. It’s a simple recipe of three ingredients, but the variance in the materials can completely change the look and feel of the glaze.
I did a lot of testing and, depending on the type of materials I used, the glaze came out shiny, matte, dry, yellow, or pink—that's how much it can vary. The way you apply the glaze also matters greatly: thin to thick make almost entirely different glazes.
I honed in on the ingredients that imparted the qualities I was looking for—a matte finish with a satin feel and a slightly bright white color. Every batch of glaze varies slightly because the ash is not a controlled ingredient—I like that about it. This glaze is very versatile, which is important to me. I use it over slip for a warm white, over slip with iron for a spooky and nuanced black, and over slip decorated with wax and iron for a contrast of black and white. I use it over raw clay and it varies from a finish reminiscent of stucco to concrete to metal to rock.
Essentially, I'm able to get many glazes from my single ash glaze, and they relate one to another. This is important to me because I don’t want a bunch of colored glazes complicating things and sending my pots all over the place visually. I want the work to be cohesive, with neutral tones so the wild clay looks at home. Here are some of my glaze recipes. The processes for mixing them follows.
SERVING DISH WITH ASH GLAZE AND CARVING
Recipes
My recipes are formulated for cone 10 reduction fired pots.
SLIP
Slip is a clay in liquid form. I use it to brighten my glazes because my clay is very iron-rich and dark. The use of the slip adds another layer of movement to the pot. I use it thin to enhance the marks and character of the clay, rather than masking them. This gives the glaze a lighter backdrop to make it appear white. I use this slip before bisque on leather-hard pots.
USING TONGS TO GLAZE A PLATE BY DIPPING
Basic Process for Making Glaze and Slip
TIPS TO START WITH
Making glaze and slip follows the same process, except that you generally use a 60-mesh sieve for straining slip and an 80-mesh sieve for glaze. Slip usually needs to be sieved more times.
I always make a test batch of glaze to see how it's going to work with my clay and firing technique. A test batch should be no less than 500 grams.
Once the test is done, I generally make batches of glaze in 10,000 grams, which is about a 5-gallon (19 liter) bucket's worth. The exception is my ash glaze. Because I use so much of that, I make 30,000 grams and store it in a 20-gallon (75.7 liter) tub. I can also easily dip large pieces in the bigger bucket, instead of having to pour out the glaze into a wider trough.
Note: If you add too much water and your glaze becomes too thin, set it aside for a day to let it settle. Pour off the excess water and mix again to a heavy cream consistency.
MIX A BATCH
Make your glaze outdoors or in a well-ventilated area and wear a respirator. For a 10,000-gram batch, you'll need:
Your dry ingredients
Respirator
Digital scale
Scoop measuring cup
Two 5-gallon (19 liter) buckets
Water
Drill with mixer attachment
Sieve
Note: An easy way to convert your recipe to 10,000 grams is to move the decimal point twice to the right—20 grams becomes 2,000. Important: Write down your conversion, and after you weigh and add each ingredient to the bucket, cross it off the list. A mistake could cost you an entire kiln load of pots, and perhaps kiln shelves too. Glaze mistakes can be costly and ruin months of hard work. If I get interrupted while making a glaze, I can be sure of what has been added so far because I have crossed it off my list.
1. Carefully weigh the glaze ingredients one at a time and add them to a 5-gallon bucket.
2. When you have added all the dry ingredients, add enough water to mix the glaze easily with the drill. It should be on the thick side of a heavy cream consistency.
3. When thoroughly mixed, pour the bucket of glaze through a sieve into an empty bucket. Use an 80-mesh sieve for glaze and a 60-mesh for slip. If you are not using a Talisman (rotary) sieve, you will need to use your hand or a rubber spatula to push the glaze through the sieve.
4. Use a small amount of water to rinse out the original bucket. Repeat step 3, pouring the glaze back into the original bucket. Check to make sure the glaze is smooth and free of small, chunky particles. If it’s not, sieve it again. You can add more water at this point and mix it in if the glaze is too thick.
5. Label your glaze and keep it in a bucket with a secure lid. Stir or mix the glaze with the drill prior to use.
Steps for Making Ash Glaze
WASHING ASH
Washing ash before using it in a glaze is not a requirement, but it's important for a couple of reasons. First, ash is caustic and can give you chemical burns. Washing the ash minimizes this risk significantly. If you don’t wash the ash, you will need to wear gloves or use glaze tongs as you work with it. And if you do wash the ash, you will still need to be careful with it when washing the glaze off your hands, especially if you have sensitive skin.
The other reason for washing it is that glaze made with washed ash will keep for many months. If you don’t wash it, you will need to make a new batch for each kiln load.
For my recipe, I weigh the ash dry, then wash it. The weight from chunks and unburned pieces isn’t significant enough to matter for my purposes. If you need a more exact amount, you will need to wash your ash first, let it dry, sieve it, and then weigh it.
To wash ash, put the amount needed in a 5-gallon (19 liter) bucket and fill it with water. Make sure there is room for half to one-third of the bucket to be filled with water. Let the ash sit in the water for 12 to 24 hours. A stinky, yellow liquid will rise to the top; carefully dump this water off without losing the ash particles. Refill with clean water and repeat three to four times, or until the water stays clear. You can leave this water once it's clear, to make your glaze.
COLLECTED ASH BEFORE WASHING
MIXING THE ASH GLAZE
1. Add the weighed-out feldspar and kaolin to the bucket of washed ash.
2. Add enough water to give it a thick cream consistency. Use a drill with a mixer attachment to fully incorporate your ingredients.
3. When fully mixed, pour the glaze through an 80-mesh or higher sieve into a clean bucket. If you need to add a small amount of water for the glaze to pour and sieve, that’s okay. Just keep your glaze at least as thick as heavy cream.
Note: If you add too much water and your glaze becomes too thin, set it aside for a day to let it settle. Pour off the excess water and mix again to heavy cream consistency.
4. Sieve the glaze twice, then test for chunks or unabsorbed particles. You will need to sieve until the glaze is completely smooth.
5. Test your glaze at different thicknesses.
ASH-GLAZED MUG
The Glazing Process
Pots are ready for glazing after they've been bisque fired. When the pots are bisqued, I wipe them down with a damp sponge to clean off any dust that might interfere with the glaze adhering. I brush on a water-based wax called Forbes wax on the bottoms of the pots and anywhere else I do not want glaze.
Ash Glaze by Itself
My ash glaze is formulated for bisque ware. I apply it by dipping a pot in the glaze. Whether I use the glaze thick or thin depends on the desired outcome. By thick I mean heavy cream consistency—any thicker and it may crawl, or shrivel, when it's fired. By thin I mean milk consistency. Typically, when it’s applied, the glaze appears darker where it’s thinner.
Ash Glaze with Iron Wash
I use a thin ash glaze when I’m combining it with iron wash.
1. After dipping the pot in the ash glaze, I wait a few minutes for it to dry.
2. I decorate the surface with a wax resist technique, using an oil-based wax such as Mobil or Aftosa. I pour the wax into a cup and add about a fifth of the volume in hot water. This helps the wax flow and prevents it from gumming up.
3. I paint the wax on with a brush and let it dry. This generally dries in about 10 minutes if it’s not too thick. If I don’t like my wax design, I can wash off the glaze and wait a day for the pot to dry and start over.
4. The iron wash needs to be stirred after decorating each pot because the iron particles sink to the bottom. I use a wide soft-haired brush to apply the wash, being careful not to brush over the same area too many times, add thicker layers, or let it pool up. If the iron is too thick it can bubble, crust, and run, ruining the pot.
VASE WITH ASH GLAZE AND AN IRON WASH
Notes on Glazes
I typically glaze a kiln load of pots, decorate them with wax, and then apply the iron all at once. This takes me two to three days. The ash glaze and the iron can be tricky. I’ve been using them together for years and I still encounter issues. If the ash glaze is too thick it can be a problem. If the iron is too thin or too thick it can be a problem. If the reduction is too much or not enough it can be a problem.
CIRCLE DESIGN CUP WITH IRON AND ASH GLAZE
I've put years of testing, adjusting materials and firing schedules, and continued tweaking, into the process to figure out how to make the pots come out the way I want, with interesting and exciting surfaces. Each kiln load can differ dramatically. The iron might come out gray, brown, red, purple, black, shiny, matte, or with other differences in color and texture. I choose to control this to a point, but so many factors are involved that it is not in my interest to subject my work to a rigid, tightly controlled environment where the results are the same each time.
The slip, glaze, iron application, kiln load, and oxygen reduction during the firing and cooling in the kiln are all contributing factors. I enjoy opening the kiln and not knowing exactly what I will see. I like discovering the variation in each kiln load, with some pots shiny and black and some matte and red, and all the colors and surfaces in between. Each pot is significant and interesting on its own, and as a group, the pots display all of the variance of their materials and process.
SHINY GLAZE
I use a couple of shiny glazes to break up the surface decoration and create contrast. These pots tend to be elegant and quiet on their own but fit in nicely with the majority of matte and darker ash-glazed pots. The shiny glazes I use regularly are a celadon and a shino. Celadon glazes originated in China and are known for their subtle green tones that range from a pale gray-green to jade. Shino is a satiny, white feldspar-based glaze that originated in Japan in the sixteenth century. Both glazes have vast categories on their own.
SHINO
The shino recipe I use is named Sprague Shino. I got the recipe from a potter named Steve Lloyd. I bought a beautiful tea bowl from him made from a local clay that he had dug. The glaze was what I was looking for, lending itself beautifully to the imperfections in wild clay. He generously shared the recipe. Sadly, he died a few months after I met him. Every time I use this shino, I think of him and the moment of buying the tea bowl and talking about wild clay.
CUP WITH SHINO GLAZE BY STEVE LLOYD
CELADON
The celadon recipe I use is called Ru Celadon. Ru ware is a famous category of Chinese pottery from the Song Dynasty. This glaze has been reformulated with modern ingredients to evoke the original Ru glaze. The glaze is a greenish-blue color, and has a shiny texture when it comes out in gas reduction. When I first tried this glaze, it didn’t resemble Ru ware. It wasn’t until I started reduction cooling that the glaze took on the palest and richest shade of blue and a satin-to-matte surface. This was closer to the colors of Ru ware pottery, but really not even that close! Regardless, the glaze evokes a calm and fragile utilitarian feel in the finished pot—simultaneously ancient and new.
VASE WITH A CELADON GLAZE
Guest Potter Interview: Michael Hunt and Naomi Dalglish of Bandana Pottery
SLICING A BLOCK OF CLAY USING SLAB STICKS
MEASURING A SLAB
MW: WHO WERE YOUR MENTORS? HOW DID THEY INFORM YOUR POTS?
MH AND ND: Will Ruggles and Douglass Rankin were longtime mentors. We were deeply influenced by their process: using soft clay on a slow-turning kick wheel, layering slips, and wood firing. Every part of this process was all about communicating the feeling of wet clay.
They impressed on us the importance and expressiveness of the clay wall itself—it's not merely a line drawn in clay, but something with substance and depth. Whether in the pottery or around the dining room table, we were welcomed into searching conversations around life and clay that propelled the two of us onto the path we are on today.
Michael Simon was also a mentor who taught throwing and altering as a way to combine wheel- and handbuilding techniques. All three of these potters were masters at integrating pattern with the form of the pot—something for which we continue to strive.
MW: YOU HAVE AN APPRECIATION FOR MATERIALS THAT IS VERY EVIDENT IN ALL OF YOUR POTS. WHAT IS YOUR PROCESS? WHY USE LOCAL CLAYS?
MH AND ND: We have always been in love with the way funky, impure materials give life to the historical work that we admire, so we spend a lot of time exploring local materials for our clays, slips, and glazes. These materials can have their limitations, but as in any creative endeavor, those limitations can help give you a framework to explore an idea. Perhaps a clay isn’t plastic enough to throw a pitcher, but it reveals a beautiful texture when it’s carved at the foot or faceted. Each clay, with its own character, is teaching us to listen and respond, influencing not only the pots themselves but ourselves as makers.
We make our clay by mixing the raw local clay into a slip and pouring it through a screen into a feed trough. We consider the screening process to be one of the first aesthetic choices in making the pots—the size of rocks and sand that are allowed through will determine the final landscape of clay. To this slurry, we add a relatively small percentage of commercial powdered materials, and then pump it all into fabric-lined racks where it will dry out to working consistency.
Our pots are fired in a large, Thai-style wood kiln. Since our pots are mostly glazed, our firings aren’t aiming for intense ash buildup, but for moderate amounts of ash melting into the glaze, as well as the subtle fluctuations of atmosphere that happen within each stoke of the kiln.
MW: DESCRIBE YOUR MAKING CYCLE.
MH AND ND: Because we mostly fire in a large kiln that holds 600 to 700 pots, our making cycle usually lasts about two months. We often enjoy making a large run of similar pots at one time. This can lead to a freedom of expression that might not be as easy if each pot feels precious.
It also creates an environment where you can respond in the moment to what is happening—small details of one pot lead us to explore something new on the next pot.
Bandana Pottery
MW: HOW DO YOU EXPERIMENT WITH THE NATURAL MATERIALS YOU USE?
MH AND ND: When we find a new wild clay, we conduct a variety of tests to determine its shrinkage, porosity, and working properties. A clay might have a gorgeous bright color in its pure state, but not hold water that well. When we vitrify the clay, suddenly it becomes a duller brown. Thus, we are always trying to find the right balance between the beautiful wild qualities of the clay that inspire us and the functional demands of tableware.
MW: YOU USE A VARIETY OF HANDBUILDING TECHNIQUES TO MAKE YOUR POTS. CAN YOU LIST AND DESCRIBE THEM?
MH AND ND: Hump molding: Forming a soft slab over a bisque mold.
Carving off from solid clay: Sometimes we make a rough form, wait for it to become leather-hard, and then carve the outside and inside (e.g., for boxes). Other times, we make very thick slabs in the shape of the pot and scoop out the soft clay right away and then do more finishing of certain details, like the foot, after it is leather-hard (e.g., for triple trays or triangle bowls).
Press molding: We press a soft slab into a plaster mold to make plates and trays. After they come out, we carve the foot out of the generous amount of clay we had in the mold.
Constructing with hump-molded forms: Some vases are made by taking two hump-molded forms and sticking them together.
Coil building: Some vases are finished with coil building, and Naomi uses coil building for her sculptures.
CARVING SECTIONS OF A SLAB SERVING TRAY
CUTTING THE SIDES OF THE TRAY AT AN ANGLE
THE COMPLETED TRAY BEFORE BISQUING
“We have always been in love with the way funky, impure materials give life to the historical work that we admire.”