Category Archives: salt-fired porcelain

Ginger, terrified, plays with fire again…..

It’s been twenty-four hours since I salted my kiln and shut it down last night, and the temperature is still about 900 degrees on top.  It was a good firing, with a steady climb to 2250 F, the temperature I like to reach for salting.  Last evening, I had a friend over who has worked with clay for many years.  It was fun to explain my process and a bit about the history of salt firing as I understand it.  She also took some pictures while I was at work… here’s the best one.

Salting the Kiln

 

I’ve got my respirator on, and the port brick is in my left hand. I just pushed the burrito of salt into the kiln with the stick in my right hand.  Usually there’s not so much flare-out, but my delay in stuffing the port brick back in made for a more dramatic photo.  At that point, it was about 9:30 at night, many hours since I began the firing at 6:00 AM.

The first hours of the firing are quiet.  It’s dark, and the grass is crisp with frost when I go out to the propane tank to turn the gas valve full on.  I have placed the burner stands and burners in position, and their needle valves are firmly closed.  Righty-tighty..  The main ball valve that supplies the kiln is checked closed as well; my Mom’s pipe wrench at the ready to open it.  Dear readers, are any of you fortunate enough to possess your Mothers’ pipe wrench?

Little Blue TongueIn the first hours, the burners are quiet and the kiln makes no sound.  I have nice Hones nozzles that make for a beautiful flame.  I keep a firing log where I record every detail of the firing, logging in the temperatures returned by the top and bottom thermocouples every thirty minutes.  I have cone packs in the kiln, but rely on the thernocouples and the state of the kiln to conduct the firing.

All the protocols of the firing must be carefully observed each time I fire.  It helps me to not be afraid.  I have blown up a kiln; a natural gas caternary arch kiln, and the memory comes to fire with me each time I light up another kiln.  Intellectually, I understand what happened on that Sunday morning long ago, and know that I will never blow up a gas kiln again.  Still, I think of it.  With this kiln, I am most apprehensive at top temperature, when tiny flames lick out of cracks here and there, and I try to estimate the temperature of the 2 x 6’s just a few feet about the arch.  An insulating brick layer and generous kaowool blankets swaddle the arch, providing nearly 15 inches of insulation between the hardbrick hot face and the top of the kiln.  My next kiln shed will be framed with metal; one less thing to worry about.

This load is half stoneware, decorated and painted in my usual manner, and half pure white porcelain.  It’s my little experiment; pots for the Making White show at Valley Art this coming weekend.  I’ve been blogging about these pots, and have really enjoyed making them in spite of the usual problems with porcelain – mostly, a narrow time window to do attachments.  The clay  – Georgie’s Crystal Springs – is obedient, and is a very pleasant throwing clay.  It reclaims well.  I’ve lost quite a few handbuilt pieces, though. It doesn’t like to stay bent and must be dried very slowly.  Nonetheless, half the kiln is white porcelain work.  There isn’t even a flashing slip on it, and it’s glazed within with beautiful flambe blue glaze that yields a glossy, functional lining for cups and casseroles.

A couple of years ago, I fired about six porcelain pieces made in this manner in my salt kiln. Everyone who comes to the studio admires them, so I thought I might someday make enough to sell.  I don’t feel that I can take the porcelain pots to my juried shows, because they will be so different from my jury images.  Some may make it to Showcase, where we OPA members get to show whatever we like.

I kept the white pots together in the kiln, as much as I could, because I  am concerned about all the cobalt that circulates in my kiln during a firing.  Some of the first few porcelain pots show signs of copper flashing, which is rather pretty.  The main source of copper was actually from the flambe blue liner itself, which contains a lot of copper carbonate. I am really eager to see how much pigment moves onto these pots, even though it may spoil them.  Ah, science….  It’s got to be wild in there; 400,000 BTU’s per hour rearranging the molecules of mud.

Here’s the stack – you can see the white pots at the top and bottom.

Stack

Tomorrow about 11:00 AM, I will take out the thermocouples, and with a mallet knock the channel iron bars that hold the door shut out of their rests.  I’ll pull the door, which hangs from a heavy iron I-beam,  carefully out of the kiln about 5 inches so a space is made at the top for heat to escape,  The kiln temperature will still be over 500 F when I start to move the door.  It’s very hard not to pull it out far enough to have a peek into the chamber, but I’ll be resolute.  At 5 PM, I will draw the work and see what useful, and hopefully beautiful, pots have come into the world.

Stiff slab handbuilding with porcelain….

I’m still working on pots for my March show of white salt-fired porcelain.  I’ve got just about enough, but thought I would make a few more handbuilt vases for the load.  I’m working with Georgie’s Crystal Springs cone 10 porcelain, which has turned out to be a decent working clay if dried carefully.  Last night, I sliced a bag into three thick slices and let it start drying – or conditioning, if you will.  I am very particular about the stage of dryness for my handbuilt work.  I work with much stiffer clay than anyone else I know, and make just one pot at time so my clay stays just right.

Sometime back in the 60’s I took Soils 200 at Oregon State University; part of my education as horticulturist-to-be.  I remember that the Cove clay soil – which I was soon to know intimately –  was considered to be the archetypal Oregon clay soil, “2:30 Soil.”  At 2:00, too wet to plow…  at 2:30, too dry to plow.  My handbuilding clay is like that, with a teeny perfect window of time to work.  It has to dry enough to stand, but moist enough to flex a bit and join to itself on demand.

If I am stamping, or using texture mats, I will apply texture when the slab is still a bit soft; then dry it to the same stage as my clay to be carved. If you a reading this because you’d like to try this stiff-clay handbuilding stuff, you’ll have to find your own way with it.  At workshops, I pass bits of clay around so everyone can get a sense of how stiff is just right.

So here’s some just-right clay, twiddled around, covered and uncovered for a couple of days, and rolled out just a hair under 1/4″ thick.  I use paper SlabMat, so I don’t have to remove the canvas texture.1 Layout toolsHere are some of my layout tools, a big right triangle and a quilters’ rule.  The rule is 18″ long.  I want to make some tall standing rectangular vases, so I cut front and back each about 7″ x 12″. The end panels are 3.5″ x 12″.2 Score and Moisten

I don’t use magic water, vinegar, or any of that goo for joining.  I score all edges to be joined with a serrated rib, which is much quicker than one of those silly little metal brushes.  I line the pieces up and stick them together.  You can see that I have dressed the inner seam at the right of the image with the black water-buffalo horn tool – it’s better than a finger.

3 Stand it Up

Here are the two sides and the back, stuck together and standing up.  The clay has to be stiff enough to stand!  I do not use coils, they are a colossal pain and way too much work. These are approach joins, and they work well for me.  I have also beveled the edged in various ways, with various tools that I have gleefully invented, but in the end this method is faster, stronger, and looks just as good.4 Applying the Base

It’s easy to put the bottom on – you can see the slight distortion where the serrated rib has roughed up the clay.  No sweat!  We will fix that in an hour or so when the box/pot has set up a bit.  You can also see that there is a finished pot right behind that has already had strips of clay applied to the top edge to give a more refined appearance and strengthen the pot.  When I was learning to handbuild, seemed like everyone wanted to whack on their pots with wooden tools to strengthen the joins; all that has ever done for me is distort the pots.  Here’s a picture of how the strips go on the top.  If I am in a fussy mood, I will miter the corners by eye, but it works just as well to lay them in square.5 Trim the Top

I did put a couple of stamps on each front and back slab, couldn’t help myself.

Here’s that same pot about an hour later – er, part of it.  I used to try to finish all the surfaces at the time I did the building but have learned to leave the pots alone for a while and clean them up when they have set together strongly – at least 1 and maybe 2 hours.  I  keep a toasty studio in winter  and I keep the pots well away from the stove so drying is even.  6 Rough Joins Ready to Scrape

As you can see, I work on lots of clean newspaper and often on an old bath towel.  These edges are ready to clean up.  I will also take care of that little nick in the pot too, don’t need that….7 Microplane Smooth

The first tool I use is a fine microplane from the cookware store.  These tools are super for handbuilders.  I use mine for dozens of tasks, and they are especially good for working on square work because they are so flat and plumb. It’s fine if joins – or feet – extend a bit; they clean up fast with one of these tools.

The next image is a bit hard to understand, but it shows the tool I use to finish up the joins; a smooth oval rib.  Carefully applied, it scrapes away the texture left by the microplane.  I do like the microplane texture – and use it sometimes to surface small objects.  But I want a smooth surface on these standing vases.8 Oval Scraper

With all the edges finished, it’s time to apply the surface imagery.  Gotta start somewhere.9 Start Somewhere

I’m getting a bit weary of these flowers, but since people still want to buy  the pots I will keep making them.  I am a slave to commerce! 10 Handbuilt Dogwood Fin

Done with this one…  a similar design on the reverse, and geometric figures on this sides.

12 Finished HB Vases

Here’s the group from the work session, about 5  hours in at this point.  You can see that the one on the right is wearing a little bandage to compress the top…  I noticed that the top trimmers were separating a bit, so I filled the void with some very heavy body paste and bound it up with nursery flagging tape.  Every potter should have some on hand….   That pot came out of the bisque a couple of days later with the top tight and perfect.  Incidentally, I always make these pots last to fill my kiln, because they dry super-quick compared to thrown pots.  They are so even in section that they can dry overnight if needed.  I dried these under plastic just because they are not my usual compliant grey stoneware clay.

Here’s the one I like best….11 Geometric Box Fin