Mind the Gap

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Details matter! The image is of the gap between the kiln shelf & the bottom of the pot, which is raised up by three wads of high-refractory clay material (called wadding*) which prevents the pot from sticking to the kiln shelf when the soda coats everything in the chamber with soda glass. After the firing, the wadding just pops off, leaving pale marks where it previously stuck. 

I find the higher this gap is, the more glaze gets deposited on the bottom, creating some color & sometimes a bit of shine. The wad marks - pale dots where the pot rested on the wadding where no soda vapor could get deposited - are often quite handsome. 

Wad marks on a mug

Because the wadding is basically wet clay, the weight of the pot tends to squish it almost flat. It will still do its job of preventing the pot from sticking to the shelf, but the bottom won't get any soda, so will just be white. Not the end of the world, & not the end of the pot, but I do like the ones with more distinct wad marks better. 

To achieve this, I find I have to make the wads ahead of time, so they are a bit drier & stiffer when I place them on the pot. I can't make the wads too early, because if they dry to much, they won't stick to the bottom long enough to get the pot into the kiln. Like a lot of things in clay, the pots are fine if I don't do it, but they are just a little bit nicer when I do. 

Speaking of things that I should really remember to do ahead of time: I was supposed to fire today, & I would have, except my cone packs exploded! Regular readers must get tired of hearing all the ways I manage to screw up, but maybe you can draw inspiration from it: If a ginormous fuck-up like Lori can do this, so can I! Actually I don't know if I screw up more than most people, but since I am a ceramic educator as well as a potter, I believe in being open about my mistakes. I make em! A lot. But then I fix em & move on. 

The culprits. You can just tell they are plotting something.

I fixed the exploded cone pack by unloading the entire kiln to dump out the little bits of debris inside the pots, then reloading the whole thing. I was mad at myself at first - the exploding cone pack was definitely caused by my dumbness - but it's summer in Maine, I was outside, the birds were singing, & loading kilns is fun! If that's the worst mistake I make this week, I can live with it. Anyway, the last firing was absolutely picture-perfect, the cones falling in synchronicity, so I was overdue to have a Murphy's-Law firing. 

Anyway, once I got over calling myself a moron & started enjoying the work, I decided that, far from a moron, I am in fact a genius! (LOL ALL DAY) Or at least reasonably clever in this instance, as I realized that when I scheduled the firing I built in some time in case something goes wrong! So I'm still on schedule. 

Barring some other mishap, I'll be firing this load on Friday, probably unloading Monday. I hope to have new work in the online shop on Wednesday! 

*Wadding Recipe

1/3 Kaolin

1/3 Alumina Hydrate

1/3 Coffee Grounds

Fire Down Below

Because my propane-fired kiln is outside, I am often asked how I can fire in the winter. Doesn't the cold prevent the kiln from heating up? Internally I chuckle at these inquiries. The difference betweencomfortable and uncomfortable, for people, is less than 100 degrees, and the first 100 degrees are the easiest for the kiln to achieve. I'm regretting those chuckles now, because, at -5°, the winter cold does in fact make s difference. Not to the ability of the flame to heat the kiln; that's still a negligible effect. The problem is getting enough propane to the burners to burn! Propane's phase shift from liquid to gas is -44°. It's stored as a liquid by keeping it under great pressure. When some of the pressure is relieved by opening the valve, some of the propane turns to gas and escapes out the valve, down the pipe and to the burner, where it (hopefully!) is burned to create heat for the kiln. This phase change - from liquid to gas - is endothermic, meaning it consumes heat energy to happen.

The closer the external temperature is to the liquid-point (there's some chemistry term for that, can't think of it right now) of propane, the less pressure is required to keep it in a liquid state. The tank loses pressure as it empties anyway, and the endothermic phase shift makes the tank even colder than the air around it.

If the air around the tank is -9°, as it was when I got up this morning, I would still be able to grill a steak using my propane tanks. The firing, however, takes hours - 11 hours even if everything goes perfectly. The tank is getting colder and losing pressure the whole time. The burners wouldn't stop burning, but it would be as if I were turning the valves down, down, down.

I might be able to finish the firing... I do have completely full tanks, which matters (pressure!). But it's possible that I will attempt to do the firing and just burn a bunch of propane and stall out before I reach temp.

Also - not that this affects my plans! - loading in the sub-zero suh-hu-huhuhucks. The my hands hurt, the wadding keeps freezing, the wax on the bottoms is brittle and flakes off.

So, firing this week is a big ol' nope. Instead, let's enjoy some Sonny Boy Williamson!

NCECA Wrap UP

Yikes! Is it too late to do this? It's a week now since I returned from Providence, and I hit the ground running, getting ready for Mug Season, the Maine Pottery Tour, and of course firing and delivering work.

Here's a quick highlight reel:
Wednesday was the gallery day. The bus tour was...spotty. The shows (the ones I saw!) were great, but there was one that the bus couldn't get to (WAT??) one where nobody was home, one that had an additional cost to get into (yes, I am the world's cheapest human. But after paying for the conference, and then paying additionally for the bus tour - didn't that used to be included?? - I was cranky about being asked to pay an entrance fee for a show. So I didn't.)
I took a boatload of photos on the gallery day, with my little iThing; you can see them here. (I was going to post them all here but time just does not allow.) My most favoritest piece that I saw all week was the giant wall of porcelain panties at Brown University.

Misty Gamble is the artist. The panties are cast porcelain with added beads and rhinestones. Hilarious and masterfully done. The subject matter of her work - not just panties, but femininity - mirrors some of my interests back when I was sculpting, and maybe even now.

Frederick Douglas Opie gave a non-traditional keynote, about the role of ceramics in Incan, Mayan, and Columbian cultures. Opie, a professor at Babson College, is more a food guy than a clay guy, and the address was like a college lecture. Some people didn't enjoy the departure, but me, I'm always up to learn something new. I think, too, the point about ceramics being a marker of status made people uncomfortable. We want to think we like what we like because that's what we like, but in fact the possession of handmade claywork - the more esoteric the better - marks us as people who have the education and sophistication to appreciate it, and the disposable income to purchase it. Yeah. Uncomfortable. Sounds like snobbery, among people who think of themselves as the very earth of the earth. But status is what makes us humans go 'round, and every human culture has had status markers. Doesn't mean your preferences are fake - quite the opposite, your preferences (and mine) and the status they denote are very real, and you will have markers of some status - high, low, or in-between -  no matter what.

It's an interesting thing to think about, but a discussion for another day.

Though I spent most of my time watching demos - they are why I go to NCECA - there were some good discussions as well. Here are the ones I would have gone to, if I weren't busy ogling pots in the gallery expo, where the largest collection of inspiring functional pots could be found.

• Heidi McKenzie, The Basics of Business in the Arts
• Dustin Miyakawa, Become Your Own Photographer
• Paul Lewing, Teaching and Selling as Performance
• Panel discussion: The Social (Media) Experiment 

My fellow travellers attended discussions of injury treatment & prevention in the ceramists' hands; ceramics in psychiatric healing, and clay and community in the St. Croix valley.

I was in New Bedford, at an opening featuring former staff, residents, and Salad Days artists from Watershed on Thursday evening, but had I not been, would surely have attended the Pottery Slam: Claystories - and maybe even told a story myself. I am shy in crowds but put me at the front of the room, and I can fly with it. Strange but true.

And now: the demos. SO AMAZING, so inspiring.

• Martha Grover was the first one I saw. You can see a similar demo here; and I'm told that all of the NCECA demos will eventually be on youtube. I was delighted to learn that Martha, a Maine native, will be returning here soon. I managed to elbow my way through the throngs to give her a business card and invite her to do the Pottery Tour, when she completes her move. Martha was part of a series on quick-hit, 30 minute demos in the Process Room, about which more later.
• Linda Christenson! Watching Linda work was just..soothing. She has a lovely personality, and makes very serene pots. I used to live in Minnesota, even met Linda on the St. Croix Valley Pottery Tour a couple of times, and her accent really brought me back there. She threw, and talked about clay and life as a potter.
• Gustavo Perez - in the same ballroom with Linda. I didn't respond to his work at all, but learned a lot from watching him. My favorite quote of the conference came from him: "It can feel like there is no energy to work, and it is then, exactly then, that you must go work." And also, related: "It is a matter of discipline to work when you feel it, and then, when you don't." These are nudges that I needed!
• THE PROCESS ROOM! was where I spent the majority of my time. I don't know if this is a new thing, but it is the best. ever. I watched Martha Grover, Jason Barnett (? Not sure. Margaret Bohls was scheduled, and Jason substituted, so his name is not in the program), Jennifer Allen - though I was in the hall, peering in for much of that one - Shawn Spangler, Amy Santoferraro, Winnie Owens-Hart, and
• Chris Dufala. Chris demostrated  method of image transfer using undergalzes painted on plaster that I had never seen before. I was amazed and determined to learn it, if not for my own work, for my students. There is a link to instructions of Chris' monoprint process on his website.
• Like everyone else, I was disappointed that the process room was too small to accommodate the interest.  The overflow room set up the next day even overflowed! My suggestion: next yer put it in one of the ballrooms: three tables, one active, one being cleaned up, one set up for the next artist. It'll be full every hour of the day. 
• This is an out-of-the-box item on my wish list, inspired by the morning yoga: Let's have a fitness room, with exercise bikes & ellipticals, and a loop of past NCECA demos playing on a video screen.

There was much more, but I am realizing it's just too much to type up this morning, so going to wrap up the wrap up. It is extremely unlikely that I will be in Kansas City next year - unless a money-anvil drops out of the sky - but if you are there, enjoy!




http://nceca.net/2016-nceca-invitational/

The Veil Lifted: The Magic of the Bisque

Sometimes I feel like we give the bisque firing the short shrift. Who gets excited about unloading a bisque? Who invites people to watch, or posts pictures? The glaze firing with its shiny surfaces and appealing colors gets all the attention, but really, the bisque firing is when all the magic happens.

The ware is just dried mud when it goes into the kiln. If it wasn't coddled, it wouldn't last a single rainy afternoon. Then by some hot miracle, it becomes permanent ceramic material. Ware exists over 25,000 years old that has undergone this change. Bisqued pottery laughs at rain!

It's enough for most ceramicists to know that it does happen, but did you ever wonder what, exactly causes those changes to occur? I can't say I completely understand the process, but here's as much as I do get:

1. In the early part of the firing, the remaining physical water is driven off. You may think your ware is perfectly dry when you load it in the kiln, and it may be damn close, but - surprise! - there's always some water left hiding between the clay platelets, because the clay can never be drier than the atmosphere. So unless we have literally zero humidity for an really extended time- in which case your greenware is the least of your worries -  there's always going to be some water to drive off. This is the water that can cause your piece to go boom if too much of it turns to steam while still deep in the walls. That's why we candle below 212° F. But you knew that.
   The next few things happen concurrently, or at least, their temperature ranges overlap. 
2. The carbon and sulfides begin to burn off around 575°, and continue to do so until 1500° or so. You want all these gone before the glaze firing, because they can cause pinholing and other glaze flaws if they have to push out through a layer of glaze. They are what make the bisque smell so noxious. 
3. Between 840° to 1110°, the heat breaks apart the kaolinite (clay) molecules into metakaolin and water. Metakaolin lacks plasticity, has smaller platelets, and is more absorbent than kaolinite. At this point the ware could no longer be slaked down; it's a part of history, now. But wait, there's more:
4. At 1060° F, quartz inversion occurs: the room-temperature stable form of silica - alpha-quartz - changes its crystalline structure and becomes beta-quartz.  It's funny, but more potters are aware of quartz inversion than of the conversion of kaolin to metakaolin, which is the really significant event of the firing. But quartz inversion is a hazardous time for the bisque, because the ware will go through a sudden 2% increase in size. Cracking and splitting (aka dunting) can occur if parts of a piece go through quartz inversion ahead of other parts. All this happens in reverse as the firing cools.
5. Beginning about 1600° F, the points of the hexagonal-shaped clay platelets begin to fuse whereever they touch. This is why bisqueware is stronger and harder to break apart than greenware. 

I lied, before, when I said all the magic happens during the bisque. There's still vitrification, and all the wonderful events within the glaze. Still, bisquing is a pretty amazing process. All of that Alpha Quartz and MetaKaolin stuff sounds like little, molecular superheroes in the kiln. And they are, for us; if it weren't for them, we couldn't do what we do. And we'd all have to eat off of deer shoulder blades, yuk.

Oh, yeah. I unloaded my bisque today.

I Did Not Know That: The Feldspar Edition

While mixing up test glazes, I came upon a recipe calling for G-200 Feldspar. Well, hmmm. I have Custer, a potash feldspar. I have Kona F-4, a soda feldspar. As far as I know, for our purposes, there are only potash and soda 'spars. Wrong! G-200 is 75% potash, and 25% soda feldspar. So, I should be able to achieve the same thing by substituting the appropriate proportions of Custer and Kona.

Thanks, Professor Google!

Clay is Rusted Feldspar

Guest blogger Douglas Watts writes:Lori asked me to explain in a fairly simple way what clay is, where it comes from, and how it got here. So here's an attempt at a non-technical explanation.

Clay is feldspar rusting. This is an analogy, but not that far from the actual process. We all know what happens if you buy a nice, shiny piece of cast iron from the hardware store and leave it outside in the sun and rain. It quickly rusts. If you leave it out long enough, it turns to almost all rust. So what is rust?

Rust is primarily the minerals limonite and goethite, created when iron combines with oxygen from the atmosphere and oxygen in water. We all know that iron things tend to rust faster when wet than when dry. Moisture hastens rusting.

Feldspar is not iron. Iron is one element, iron. Feldspar is a large family of minerals made from oxygen, silicon, aluminum, sodium, potassium and calcium. Feldspar does not form on the Earth's surface. It only forms miles beneath the Earth's surface, where solid rock is naturally in a semi-liquid, molasses-like state.

Feldspar is only released from its 'natural' home and to the Earth's surface either when it is forcibly ejected from a volcano as lava or when, after hundreds of millions of years, the 2-3 miles of solid rock above the feldspar is eroded away, leaving the feldspar nakedly exposed on the Earth's surface. This is usually in the form of granite, which is a rock made of feldspar and quartz and some mica.

To add another analogy, just like a piece of fine pottery on the edge of a shelf 'wants' to fall on the floor and smash, feldspar 'wants' to turn to clay when it is exposed to the Earth's surface. The agent for the pot on the shelf wanting to fall down and smash is gravity (in outer space, pottery does not break, it orbits). The agent for feldspar wanting to turn to clay is a bit more complex, but similar in design to iron rusting. In both, the agents are primarily air and water.

In the presence of air and water at the Earth's surface, the most natural and restive state for feldspar is to re-align its molecules into clay molecules. Clay is a mineral, just like quartz or feldspar. It has a very regular and ordered crystalline structure, like a diamond or a cube of salt. The three predominant clay minerals are kaolinite, illite and montmorillonite. With a scanning electron microscope you can get pictures of very nice, well formed, plate-like clay crystals growing right next to a crystal of feldspar.

Feldspar becomes clay by slowly bringing water into its crystal structure, like a sponge left in a puddle of water. This water becomes part of the very fabric of the feldspar; like how iron becomes part of your blood cells. The feldspar wants the water. It likes it. Which brings us back to rust.

What we call rust is the natural state of iron on the Earth's surface. Iron readily combines with oxygen to make rust. It wants to become rust. In fact, we have to do all kinds of crazy things to prevent iron from becoming rust. We coat it with oils, with paint (like Rust-Oleum) or galvanize it with zinc, all to keep the iron from contacting oxygen in the air and oxygen in water, sort of like teacher chaperones at a high school dance. Left to its own device, feldspar becomes clay because it wants to; that is its most stable and natural state on the Earth's surface. Like a thrown ball 'wants' to come back down, feldspar wants to become clay. Clay is rusted feldspar; and the actual chemical reactions are not that different.

In Maine, where I live, from 1880-1930 there was a flourishing industry where large feldspar deposits were quarried and mined for use as ceramic pottery glaze. This was feldspar that had not yet had time to weather into clay. It is still solid enough to make a house foundation. But if you crush into a fine enough powder, it works beautifully as a glaze ingredient. Most of the feldspar mined in Maine was shipped to pottery works in New Jersey as a basic glaze ingredient for everything from fine plateware to toilet bowls. It was an 'industrial mineral,' as the saying goes.

The only reason Maine does not have deposits of natural, 'primary' clay is because for the past million years Maine has been scoured by successive, mile high glaciers every 100,000 years or so, which like a steel plow on a snow-filled driveway, scraped away all the clay and softened rock right down to hard bedrock and dumped the residue in the Atlantic Ocean. In the U.S., you have to go south of the line of glaciers, ie. Kentucky or Tennessee, to find clay deposits still intact and near where they were first formed. What we in Maine call 'marine clay' is actually the finely ground-up residue from the glaciers' scraping and grinding that has partly altered into true clay minerals and is on its way to doing so, give another 10 million years. That said, it is still perfectly usable as a slip or a low-fire earthenware body. Be patient, Maine !!!