Gas Firing Stoneware Pottery at Cone 10: Natural Variations in the Copper Red Glaze

My most recent gas firing produced some amazing color variations. The kiln was filled top to bottom with pots only glazed in my Copper Red glaze. About half of the pottery had great red colors, ¼ had great red but with color variation, and the remaining ¼ were mostly green, pink or gray.  The natural gas flame paints the glaze surface, and potters are blind to this process.

Thanks to my intern Samantha Thury for shooting these images. I many never know exactly how to produce the reddest of reds, but here are some of my guesses:

Bright red/red-orange: consistent reduction and temperature throughout the firing, slower flame path, less oxygen entering the kiln.

Burgundy: heavier reduction. Often gradates to violet, black and then clear.  Seen in areas of the kiln where uneven reduction causes flame to become trapped, and then simultaneously over-reduce and oxidize different areas of the same pot.

Gray-Pink: somewhat of a mystery…consistently seen on the left side of this kiln, and in certain other areas of the kiln. The flame could be slower, causing more reduction. Perhaps there is heavier reduction during a certain point in the firing. This color is often seen next to bright red, but rarely seen next to clear. This could mean that reduction is achieved before cone 5, but perhaps too much reduction is achieved.

Gray: transition color mostly seen from bright red/burgundy to clear, but seen here on a more red/pink to clear transition.

Clear: oxidized. The bottom shelf of most kilns usually results in clear, sometimes with hints of red or violet. Achieving medium reduction before cone 5 and through cone 10 could eliminate clear. I also see clear closest to the burner ports and target bricks, where the flame path is faster and more turbulent.

For all you potters interested in producing your own Copper Red glazes, check my previous blog post for my glaze recipes and firing techniques:

Copper Red Glazes: The Elusive Bright Red Pottery

Also check out “Copper Red Glazes: A Guide to Producing These Elusive Glazes” by Robert Tichane. Read the book, then re-read it! It’s been an enormous help in developing my red, and especially my firing techniques.

Glazing Handmade Ceramics at Cone 10: Painting with Fire

While I use brushes for much of my glazing decoration, the kiln does just as much painting as me. Unlike painters, potters have to give up some control of their artwork by using fire to finish the surface.  I brushed iron stain onto the rim of the mugs below, then the iron dripped down the walls during the firing.

Each pot is first dipped in a bucket of glaze. I chose glazes that move and drip during the firing. The image below shows how I brush colorants like iron or cobalt onto the surface.  This adds color contrast, and encourages drips and movement.

After glazing, my pottery is loaded into a natural gas kiln. This is basically a huge oven with no windows that heats to about 2400 degrees F. for about 12 hours.  After 2 days of cooling, I open the kiln with fingers crossed, hoping that the “kiln gods” gave some good colors to the pots.


The images below show how I use iron, cobalt and copper stains to add color and movement. I brushed them on as a vertical line, then the stains melt down the pot during the firing.  This big pot barely fit in the kiln- we had to take out a few of the floor bricks!


The Copper Red glaze is very responsive to the flame path in natural gas kilns.  The gaseous atmosphere produces red colors, while the clear/green colors show up where the pot was more oxygenated.  The flame naturally paints the glazed surface.


Rustic Pottery, Part 2: Wood Ash Glazes

Guest Posting by Laura Fuller


I’m not Joel, but in third grade, we spent Mrs. Sullivan’s class scheming on the fort we wanted to construct around our desks.  Joel doesn’t remember or deny this, but he does confirm that he had a “fort phase.” Naturally I now write about his pottery.


I’ll teach six more weeks in Dubai, UAE, which is ultimately an airport:  Being unsafe takes effort, you can get what you need but with preservatives, and jewels and gadgets of all countries attempt to constitute a style of one’s own.  If flying through O’Hare is not visiting Chicago, being in Dubai isn’t the definitive Middle Eastern experience.

Ski Dubai: Where Arabia goes to ski and shop and the environment goes to die.
Jacques Peak, photo by Joel while skiing at Copper Mt. Colorado.









I can’t curse it, though. Safety, convenience, dreamy beaches, solid job, and good friends — not torture. And there are little glimpses of an older-than-me culture here if I bother to look.  You can hear the call to prayer from five mosques at once at Kite Beach.  Graffiti and Iranian merchant ships frequent the creek in Diera.

But these joys are fleeting, up against the cranes, malls, Maseratis and TGIFridays.  It’s mostly contrived to look Arabian. Give the people what they want: stucco, marble, huge doorways–literal smoke and mirrors.  Look at our fancy Arabian-esque mall! It’s just like Arabia, but big! And with retail! It’s like Arabian retail Inception!

People list Dubai’s location as a reason to stay here. “Well, it’s just so easy to travel from here.” The place’s value is attributed to the ease with which residents can escape it? Huh.

But it’s true. I hopped to Jordan for spring break this year to reorganize my self. I traveled with a kind family of hippies and a lumberjack, the best travel crew I’ve ever known.

Jordan is even more Westerner-friendly than Dubai but doesn’t abandon its culture to be this way.  Like a family dinner instead of a fancy restaurant meal, Jordan offers what it has instead of what it thinks you want: its own food, open air markets, monolingual Arabic signage, and even locals who groom their own facial hair.

The whole week gave off an aroma of chance as we took in seemingly private moments, decidedly uncontrived.  I felt snug and small as I watched them, un-special myself but privileged to see something special, like a rare phenomenon of nature.

We took a scenic route and would fall short of Petra by sunset.  Hani, driver and guide, consoled us with an iPod adaptor cord.  Banjos and guitars and wailing harmonies crowded into all the van’s empty spaces, and we howled out open windows as the afternoon began to droop. At sunset, we unloaded on the side of the road.  A fresh wind bloomed from a vast gorge.  The sun resolved down in the valley and a mist settled below.  Our hair swirled in the continuous gust, and we laughed our exhilaration, maybe at the implied joke of possibly passing that moment anywhere else. The unexpected wind swept upward, not threatening to knock us into the gorge but to blast us far from it — Southeast Asia, New York, Seattle. We threw our arms wide to catch air that was left off our itinerary.

I slept with my windows open in Petra.  At 4:30 AM I popped awake, panicked by the bullhorn fervor of a grown man hollering at full voice. I laid back down and let the loud, emphatic call to prayer steamroll into the room.  The snoring cut out abruptly from the next bed, startled into a hush. If he was awake he didn’t say anything.  Neither of us rose to shut the window. The curtains undulated with the breeze, giving the illusion that the invitation to prayer was a physical thing, one that could move fabric and make noise and feel cold. I smiled, flat on my back, that someone’s job was to wake us up to be grateful. It would have happened without me. The call would have sounded and Petra’s men would have walked to the mosque with their prayer mats even if I had slept in my Dubai bed.

Joel explains two reasons for using wood ashes in his glazes: philosophy and aesthetics.

The philosophy bit carries a sense of participation in a community or cycle. His ashes come from a family in Collegeville, MN, who heat their home with a wood burning stove. This wood is entirely deadfall or dying trees, which the family harvests from the St. John’s Arboretum. The ashes then are “an expression of the landscape,” he says. They reflect the types of trees from which they come and where those trees grew.

But wood ashes are harder to work with. It takes “dozens of hours” to sift through them and special glaze chemistry to mix custom glazes, which are ever-changing: “When the ashes change from year to year, so must my glaze recipes. Pine ashes differ from Oak, Walnut, etc.” The trees don’t really care that Joel has a glaze to make.  They live and die on tree watches, and the Nuka glaze takes from them what it can get. The pots that use this glaze are simply reflections of the small moments that Joel catches — a season heavy with pine or oak, a stop on the side of a Jordanian mountain.  Things happen, and sometimes we’re both lucky enough to see them and crafty enough to capture them.


The second bit is the aesthetics.  Joel says of his ashes, “I’m curious how this earthen material often creates an earthen aesthetic.” He points to “complex glaze surfaces, rustic tones, natural color variation, spots, drips, asymmetrical patterns that” remind him of “colors and surfaces in nature.”

He appreciates the unpredictability and experimentalism of every firing when he uses these materials, especially when he incorporates iron, which reacts with the ashes to create dark contrast. The more labor-intensive and unruly work is rewarding.

He boils it down to this: “Constant challenge helps the artwork learn and grow.” I like the idea that the art itself is being challenged, that art learns. I like even more that he goes looking for this challenge because art’s learning is a worthy pursuit.

It’s a human tendency to tuck that learning into a classroom, a box, or a fail-proof glaze formula to use for all time:  This is how we learn about culture. This is how we make the Nuka glaze. But it’s not that simple, and that’s why it’s so valuable.  The end product is at the mercy of all the calls to prayer and winds from Jordanian valleys and fallen Minnesota branches from any family of trees — nothing we can plan or reign over. And the statement that forms won’t ever be said that way again, not for us and not for as long as we live, which makes that mug seem like quite a privilege for your coffee refill, no?

Copper Red Glazes: The Elusive Bright Red Pottery

I’ve been exploring Copper Red glaze recipes for about 2 years now, and I still don’t know exactly what causes the reddest of red glazes.  Some recipes are consistently dull liver color, yet they will blush orange-red from time to time, like the mug pictured to the left.  It was in a firing that did not have enough reduction.   A lot of the pottery was mostly green, like the right side of this mug.   For some reason this pot has an awesome red-orange racing stripe down the side right where the green transitions to red.   Was it because the flame was hitting it in a weird way?  It wasn’t even close to the burner ports….

“Copper Red Glazes” by Robert Tichane is the best resource I’ve found for Copper Reds.   If you want to learn about reds I say read it, then read it again.  He suggested that any base glaze can be adapted to a Copper Red glaze by adding 2% Copper Carbonate and 3% Tin Oxide and then firing in a reduction atmosphere.  This inspired the above glaze, which was originally an Elaine Coleman Celadon that I found in an old Ceramics Monthly.  I added the Copper and Tin, as well as a bit of EPK to raise it from cone 9 to cone 10.  Here’s the recipe, and don’t forget to glaze very thick!!

Copper Red/Elaine Coleman Celadon
Custer Feldspar
EPK Kaolin
Silica (325-mesh)
Ferro Frit 3134
Zinc Oxide
Copper Carbonate

Another book that’s super helpful for Copper Reds, and just about every other glaze at Cone 9-10 is “The Complete Guide to High-Fire Glazes: Glazing and Firing at Cone 10” by John Britt.  Buy this book, seriously.  I learned most of what I know about glazing from this book.  John also describes a bunch of his techniques all over Youtube, here’s a great one for glaze testing:

Easy Glaze Testing (color blend) (part 1)

The images below show the “John’s Red” glaze on stoneware. It’s also important to note that John’s Red glaze is much more vibrant than the above glaze (Copper Red/Elaine Coleman Celadon), which is often liver colored, or muddy brownish red.  I wonder why???

The left image shows John’s Red at cone 9 over Fireclay Stoneware with iron.  I really like these dark burgundy reds, but recently I’ve switched to “Tableware- No Oxide” clay from Continental Clay, which is a white stoneware with very low iron content.  It helps brighten up the reds, like the cup shown on the right.  The rim was also dipped in a Nuka glaze, which ran down the pot during the firing.

Here’s the recipe I’m working with.  It’s John’s Red, but I increased the EPK from 5.4% to 8.4% to stiffen up the glaze for cone 10 firing:
John Britt Red, cone 10
Custer Feldspar
Silica (325 mesh Flint)
Frit 3134
Zinc Oxide
Tin Oxide
Copper Carbonate

Nuka is an ash glaze.  Check out “Ash Glazes” by Phil Rogers for some great recipes and info on ashes.  Nuka’s are so awesome that they deserve an entirely different blog post, so I’ll just give you the rundown on the recipe I’ve developed over about 2 years.  I get wood ashes from a friend with a wood stove and dry sift them through 12 mesh, then again through 40 mesh.  The glaze recipe changes with the type of wood ash and the sifting process, but here is my current cone 10 recipe…although it’s likely to change because right now it looks a lot better at cone 11:

Nuka, 4/23/12
Wood Ash
Custer Feldspar
Silica (325 mesh Flint)
Bone Ash

Firing is another crucial component to Copper Reds.  Currently I fire in a large natural gas kiln with about 30 cubic feet of stackable space in about 10-11 hours.  I essentially use John Britt’s Reduction 1 firing cycle with a few tweaks.  I fire oxidation until cone 010 drops (about 1700 degrees F) and then do 30 minutes of heavy reduction- the kiln usually stalls in temp.  Then, I fire in mild to medium reduction until cone 10 is very soft.  I’d say more reduction is better than less here. I’ve yet to see adverse effects from over-reducing but I have gotten green from under-reducing.  Lastly, I open the damper and put the kiln into straight oxidation for 30 minutes, until cone 10 drops and 11 is soft- then shut down with the damper closed.  Robert Tichane writes about the importance of peak temp. oxidation for bright reds, and I’ve seen great results with this technique.

Now go mix up some glaze and start chasing the red!

Rustic Pottery: Woodfiring

Copyright 2005 St. John’s Pottery

My interest in something I like to call rustic pottery began in high school, after my first visit to the St. John’s Pottery. I was impressed by the idea of harvesting pottery materials directly from nature, but even more blown away by the colors and surfaces achieved by Richard Bresnahan and his apprentices. I bought the book Body of Clay, Soul of Fire and it sat across from my pottery wheel for the rest of my senior year.  Richard’s pottery was glazed naturally by wood ashes and flame that floated through the 87 foot long kiln, painting the pottery over the course of a 10 day wood firing. He learned these techniques during his apprenticeship in Karatsu, Japan. I tried to replicate his glazes and surfaces in our small electric kiln at Xavier High School and this made for some bright colors, but I was thirsty for the juicy wood fired surfaces.

I finally got to experience the use of natural materials during my freshman and sophomore years at CSB/SJU, interning at JD Jorgenson Pottery.  JD, a former apprentice at the St. John’s Pottery, taught me how to use natural clays in both pottery and kiln building.  We built a 3 chamber wood-kiln over 30 feet long and fired thousands of pots in over a dozen firings.  JD’s kiln produced a huge variety of wood-fired surfaces, so I busted out as many little cups as I could to put them in every nook and cranny of the kiln.  Most pottery was loaded as just raw clay, and each firing taught me more about how flame and wood ashes paint the clay surface.


Even my advisor and ceramics professor, Sam Johnson, was interested in wood firing during his 4 years of my undergrad that he spent firing mostly in gas kilns.  Sam built a wood kiln at the University of Minnesota Morris, which fired he his work in occasionally; however, his gas fired pottery (he called it his “whiteware”) was meant to be shown with his dark, wood fired surfaces. Sam’s process really motivated my interest in gas firing, and his critiques of my glazeware helped me find parallels with my wood fired work.


The wood fired surface continued to influence my pottery for the remainder of college and shows up in my current work. Even with glazed pottery that’s fired in an electric or gas kiln, I look for glazes with rustic colors, surface qualities, and variation that occurs during the firing.  Copper Red glazes provide deep, intense color that reminded me of the bright colors and asymmetrical patterns that Richard achieves on his pottery. The Nuka glaze utilizes local wood ash as the main glaze ingredient, and the ashes make for juicy surfaces with rustic tones.  I brush iron onto the glaze, which drips during the firing as gold and brown streaks as it reacts with the wood ashes at 2500 degrees F.


I’m still amazed how elemental pottery can be: water, clay, wood, and fire are used to make tableware for everyday use, and the earthen materials create a rustic, earthen aesthetic.  Wood firing taught me to give up some control and let the process speak.  The pottery you eat and drink from at the Local Blend is fired in a gas or electric kiln, but it’s influence by the wood fired process and surface.