Category Archives: salt kiln

In Praise of Wadding…

Without wadding, there would be no salt firing.  I believe that most atmospheric firers wad their pots to some degree, and I know that there is great variation in how wadding is made among potters.  For those of you who have not taken part in salt firing of pottery or other atmospheric firing, the vaporous kiss of the salt (or wood ash, or soda….) is what creates the special effects we seek on the surface of our work.  That same vaporous kiss will fuse your pot right to the shelf upon which it sits, where it may shatter into dangerous shards as the kiln cools and it cannot shrink at the same rate as the shelf.  What to do?

Each piece that goes into the kiln must perch upon balls of wadding.  This wadding leaves small white circles where it has been adhered to the pot.  Many buyers hate these white dots, and want pots that don’t have them. They are particularly incensed by the wad marks – usually long ovals – that remain from where wads are placed when casserole lids are fired in place.  Sigh…  Here are some typical wad marks on a salt pig from my recent load.

Salt Pig 1 Bottom

I have used a lot of different combinations of materials to make my wadding.  At this time, I use a 50-50 mixture of alumina hydrate and Helmar kaolin BY VOLUME.  Wearing my respirator, I measure the materials out into a plastic dishpan.  I use about 8 cups of each material, which makes about 10 pounds of wadding.  I mix the two materials by hand, and then add water.  It’s okay to make it too sloppy; just add more of each until you get it right.

I like to make wadding one batch ahead during a firing.  That way, it has time to become more plastic and easier to roll out into coils.   I often mix up the wadding, and then cover it with plastic for a few days before wedging.  I prefer to wedge it on the formica top of my slab roller table rather than on my plaster wedging table.  The alumina hydrate makes it into un-clay, and it sticks to the plaster in an untidy way, even as it is being blended.

When it is smooth and uniform, and still a bit wetter than I would like when I make my wads, I pack it into a tightly covered plastic container from the restaurant supply store and put it in my storage area.  It’s good to keep it on the wet side, because unlike clay, I can’t seem to rehydrate it by spritzing or sprinkling water into it.  Other wads have been easy to rehydrate, but this wad has specific properties that are more important.

What are the properties a salt-firer requires from wadding?  First, and most important, is how the wadding comes free from the pot after firing.  The first wads I used required much hand sanding to make the places where wads had been adhered smooth and attractive.  This quickly becomes wearisome!  I have been known to describe myself a a connoisseur of abrasives, and this is sadly true.  Shelves must be sanded after each firing, kiln posts too; you have to be a little bit nuts to do all this work when you could snatch soulless but serviceable cone 6 pots out of an electric kiln with none of these annoyances…

My first hands-on experience with salt firing was as observer of Craig Martell’s salt-firing process.  Craig has a big salt kiln that he fires occasionally, and agreed to let me come when he was setting up to fire, and even put some of my first pots for salt in his kiln.  I helped with wadding, and learned that a person has to stick the wads on with Elmer’s. Craig has vast technical knowledge, and without his help, I would have given up on learning to salt fire and returned to red earthenware, most likely.  Here’s a pot of mine from that firing in Craig’s kiln. I have never been able to duplicate some of the effects on this humble piece – I still use this gold slip, but it hasn’t been willing do this in any of my three salt kilns….

Pot from CRaigs Kiln

The first wadding I made myself incorporated flour along with alumina hydrate and EPK kaolin.  It was okay to roll out, made decent balls/spheres/bollitos of wadding.  It also soured quickly and needed to be used with a day or two.  I used to put the leftover bits of wadding into the freezer, and still find a small,  mysterious bag of frozen dough once in a while.

James Tingey, another fine Oregon potter, came up and fired with me once,  and introduced me to wadding made with wood sawdust.  This took less sanding, but made a larger minimum wad which didn’t work for my small pieces such as butter boxes.  I am not sure at what point I switched to my present mix, but it’s clearly the best for ease of forming and removal, and keeps forever.  It becomes much more plastic as time goes on, too.

There are two principle uses for wadding in the kiln; setting up the pots, and wadding the furniture.  I may also use wadding for chinking in the kiln, especially since I am laying up a brick door again.  It shrinks, and probably doesn’t really stop that much flame, but it makes me feel like I am doing something.  Better to stuff shreds of kaowool in; but I worry about fibers.  I should research this hazard…

I like to make all the wads for the firing before I start stick them on, and have become surprising good at guessing how many will be needed.  I need two full plates of 1/2″ balls for general use, about 100 3/4″ balls for wadding the contact point between my silicon carbide barstock and the shelves, and about 32 big fat wads of wad for the tops of the posts I use top separate the shelves – 4 per shelf.  Here’s a plate of small wads ready for wadding pot bottoms and lids as well.  I fill up rectangular plastic plates, which are tucked into ziplock bags.

Waddimg

Potter friends contact me from time to time to tell me about new ways to make wads.  A potter somewhere rolls wadding into a small slab, then presses a straightedge into the slab at intervals, in two directions, to create small regular cubes connected at the base,  It’s bisqued, snapped apart, and glued onto pots.  Is this easier than what I do?  Maybe…

How does a potter learn this stuff?  I have been extraordinarily well mentored, not only by Craig, but also by longtime friend and ceramic engineer Barrett Jackson, who regularly introduces me to all sorts of high tech materials.  From him, I got boxes of ceramic cam rollers – diesel engine parts – rejected products of a high-tech manufacturing firm where he worked for years.  These make the all-time best ever kiln posts for salt.  From him I also got – free, for picking it up in LA – my barstock that I use to set the load.  Here’s a shot of early stages of stack building.

Starting the StackYou can’t see the 3/4″ wads under the shelves, but they are there.  And you can see the big wads on top of the kiln posts, waiting for the next pieces of barstock to be laid over the top of them.  You also can’t see the level that I keep at hand.  I check level on the shelves in both directions – at this point, I rarely need to make an adjustment.  All that wadding helps to keep things level…

I wad all pots that go into the kiln, but I don’t wad salt and pepper shakers, beads, tiny cruet lids, and suchlike.  Because my shelves are carefully cleaned after every firing, this works for me.  I’ve considered experimenting with un-wadded pots, but the potential for variation in vapor movement in the kiln makes me feel safer firing with wads.

So!  If you have gotten this far, thank you…  This is pretty dull stuff, Unless you want to fire a salt kiln.  It’s the only way I know to get effects like this….

Flower Panel

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Making a new lid for my old butter boxes…

Finish BB House Here’s  is a favorite butter box, slightly grimy from sitting around my studio with other pieces I like too much to sell.  I do like to make boxes.  Hand-building is is a guilty pleasure for an impatient person like me who sometimes doesn’t love the many steps of wheel thrown pottery in my process.   Thinking about it now, I realize that it’s probably just as complex if you take righteously prepping the clay into account.

I am very particular about readying my slabs for hand building.  I do have a nice slab roller, which speeds the process and yields up perfect slabs of various thicknesses.  For the butter boxes, an extruder prepares the molding which forms the lid seat.  Here’s a picture of the extruder die; it’s cut from sheet pvc and supported during extrusion by the round die shown beneath it.  Much trial and error in designing this extrusion… Box MoldingHere’s a bunch of extrusion prepped for box building.  It dries out – DIES! – super fast, so I put it on plastic as well as under plastic. Fresh moldingsThe boxes are just little rectangles.  I have sheet pvc templates that I use to build them. Sheet pvc is a great material for repeated-use patterns in studio.  Mine is salvage from a local electronics manufacturer – it’s used to ship exotic films for chip building – but you can buy it on line or a good craft stores. There are several thicknesses; it takes serious shears or snips to cut the good stuff. Waiting for moldingHere’s a set of little boxes ready to receive their lid-seat extrusion.  As you all know, the most important thing about joining hand built pieces is keeping all the components at the same stage of dryness, er more correctly, wetness. A condition were there is no color change; the clay remains easy to score and “goop-up” with a serrated rib; but is no longer flexible is just right for this clay, a slightly gritty cone 10 stoneware.  As you can see, I don’t perfect the base boxes at this state.  That is so much easier to do hours later, when the piece is ready for final carving. Applying the moldingsHere’s extrusion going on.  I use a little 6″ ruler to measure each piece individually.  There is always a little bit of variation  1/8″ off can spoil the box…  careful! I do not use any joining slip, magic water, or any other such stuff.  If the clay is correctly conditioned none is necessary.  I cut a tiny miter freehand…  decades of sewing prepared me for clay work…  and I can hit it right on every time.  You might like to use a tiny plastic right triangle until you are confident. So…  all the boxes are built; and some have stamping or texture applied in the “flat state” that will be part of the surface.

Now, the tedious part begins – or USED TO begin – the building of dinky lids from four little triangles of clay.  I had thought for sometime that I could press a nice little lid onto a form, but how should I make the form?  Gotta be quick; just a trial, of course.  Wood is a possibility, bisque of course, but how about that crazy pink foam?  I have gained a new appreciation of the stuff because of what my sweetheart Steve makes from it.  Check this out!   Never want to run into the rest of this critter….. Bug head I still have pink foam in studio from days of experimenting with hat-making, to which I will return someday, of course…. Roughing the Block Here’s the first whack at a form for the lids.  Consultation with Steve makes sandpapering the form down a bit the next step… Wearing a respirator would be a good idea; fine particles of this pink stuff are a respiratory hazard, and a potential mechanical irritant to the surface of the eye.  sANDED bLOCK Pretty dang nice!  Took about 10 minutes, mostly because I don’t measure or overthink.  No drying time, bisquing, or other fussing.  Can’t wait to slap some clay onto it…. Lid on Block with RibHere’s a first lid.  I like a very soft rib to smooth stuff; perfect to contour the clay down to the form.  Impatient Ginger!  pink crumbs all over my work area! Cutting the EdgeMy little Chinese wire tool is perfect to trim the slab down to size.  I anticipated that I would do some further fitting, with a small Surform plane tool, so the lid block is a little bit oversized. Built no carvingThe lids are perfect first time through, yippee!  I will dry these boxes under plastic for a few days, and then do final surface design on them.  Production time reduced by the lid form by at least 25%…..

Can you see the lid seat on the box on the right above?  I ran out of extrusion and had to build the lid seat from strips…  I will round and smooth the edges later and they will be just as nice. So it can be done if you don’t have access to an extruder…

Reading over this post before I hit the button and launch it into the world, I realize that what I want to do next is make the series of little architectural stamps that I have been imagining….  little windows and doors, arches and cupolas; all related by scale,  Ooooohh!

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.