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I myself joined the WAYWO group last month and posted a diary in which I documented my big project for this autumn-- I built a kiln. Now I've returned to show you all how well it works.

I've tried to keep the photos fairly small so they'll load quickly and kos won't hang me up by my tufted ears. Please join me under the Itzl-flavored, elegantly whorled hairball.

Well, when last I wrote about this project I was still unsure whether or not it was a kiln I was building. You see, the whole thing was very experimental. But I wrote about most of that last time. I had left my mound of iron, clay, chaff and the occasional bit of firebrick for a couple of weeks and when I came back to it--

All that clay was getting green with moss and little seedlings.
I decided that perhaps I should seal up the firing chamber and start a small fire in the firebox just to dry things out a bit more before I actually put any pots at risk.

The chamber sealed -- kinda like bricking up the entrance of a tomb really. Although this wall does have a window. Yes, I'll have to tear this wall down when I want to open the kiln and build it again for the next firing.

A small fire in the firebox that I maintained for an hour or two.

And the next day I tore down the wall. I set a pot on a small slab of firebrick just to test things. The temperature was quite low. I perhaps could have baked some bread but it was not hot enough for clay.

Although it seemed to be working, I could see a problem or two with my kiln already. Even at these low temperatures the uneven mixture of concrete for my floor had popped and cracked. I smeared some fire-resistant mortar over it and started preparing for a proper firing-- to really see what this kiln could do.

Here you can see the firing chamber while I'm loading it. I just decided to take my chances and put almost everything I'd made from clay over the last few months into the kiln. In the center there you can see the three colorful, pyrometric cones I'd picked out for this firing in a row, stuck into a lump of clay. They're a clever sort of thermometer. Each type of cone is made to melt at a certain temperature and by using a range of different cones you can get an idea of how hot your kiln is. Before I sealed things up though, I had to put a little bit of firebrick under my cones to get them up where I could easily see them through my little window.

And here is the kiln resealed-- note the sheets of metal I'd used to cover it and protect it from the rain. Those are actually used offset printing plates! I inherited all sorts of treasures...

And now the firing can begin. I set a couple of candles to burn in the kiln overnight. Warming things up very slowly. I partially block the air-intake pipes to keep my candles from blowing out. Then, in the wee hours of the morning, I light a fire in the firebox. I start slowly like I did to begin drying the kiln. I have a variety of pieces inside; some are pieces I'd already had fired elsewhere in electric kilns, most of the pieces are just dry clay, greenware. If I don't proceed slowly the greenware pieces will explode. They may seem dry but there is still a fair amount of water even in dry clay. This water is bonded to the molecules of clay and during firing these bonds are broken. Fire something too quickly and you form pockets of steam INSIDE the walls of your pots. Yeah, "boom!"

I maintain a small fire all morning. Around lunchtime I begin to increase the amount of wood that I'm adding.

You can see the iron rod I'm using to brace the door to the firebox. Every time I toss in more wood I pull the door open and push it closed with this rod. The insulation I'd attached to the inside of the door begins to fall apart in the heat and the top of the door eventually begins to glow. I managed to drop the door on my hand once during firing. Ouch! instant blisters. Should have had both of my special impregnated leather gloves on.

A peek through the window shows that the first cone has fallen -- we're over 650˚ Celsius. It's already after three o'clock in the afternoon. I decide to increase the pace.

I wired up a small ventilation fan to help increase the flow of air.

But my fan is too close to the firebox! While repositioning it I notice how hot it is and add a curved section of pipe to set it back from the firebox. Cracks are developing in the kiln as it dries out better and actually becomes fired itself.

The kiln steams. Here you can see the wet clay patching the cracks and the extension pipe for the fan-- that red glow was a bit much for the fan. I'm wishing that there had been more wind that day.
Well, the friends who were going to be helping me out with the firing either couldn't make the long trip out to the kiln or had to leave early. So, with my supply of wood dwindling I continue on as the sun sets:

And night falls:

Firing a wood-fire kiln is just the sort of thing to warm the heart of any pyromaniac. In an effort to improve the heat retention and get the temperature to rise more quickly I do a couple of things during the firing. I mound dirt up against the back and one side. And I cover the top and remaining side (my temporary wall) with some mouldering fiberglass insulation that had been used as nesting material for the local martin.

But after stumbling around in the dark for a few hours scrounging more wood to burn I decide that I've had enough. My second cone should have fallen by now. My goal of firing to over 1200˚ Celsius is perhaps unrealistic. Oh well, I know I've managed at least a good bisque firing. My glazes will just be well dried at this point but I figure that all-in-all it's not too bad for a first attempt. As snow begins to fall I allow the fire to die down. I block the intake pipes, cover the kiln with those sheets of metal, and cap the chimney to prevent the kiln from cooling off too quickly. It's about eleven o'clock when I leave the kiln and go to bed.

The next morning I can't resist and peek inside:

The snow is still falling:

Well, things are much too hot to open the kiln and I've got to be getting back to the big city for my regular work week. In another week though, I come back--
I begin by peeling the fiberglass insulation off the kiln:

Underneath the insulation the clay of the kiln has baked to a rosy orange color. I've managed to bisque fire my kiln!

These dark, shiny, stringy blobs are proof that fiberglass is glass. The area around the chimney got so hot it melted the insulation.

While firing in the dark even more cracks opened up. This one had been belching a bit of smoke.

And this lovely moth that had been hiding under the insulation had obviously moved in some time after things had cooled off.

Here you can see how beautifully orange the parts of the kiln that had been under the insulation became. I dramatically left my chisel sticking out of the first hole I poked through the side of the kiln (can you spot it?)

And here is a hunk out of that wall and the little door I used for a window. You can see how the clay on the innermost (top) edge of the hunk has gone from orange to more of a yellow ochre color. When I quit I was actually beginning to high fire the walls.

But what about the inside you say? Perhaps you've had enough already? At any rate I shall muddle on--

Yes, a horrible scene of destruction. One of the last things I tossed into the kiln was some old cardboard and the ash from that was everywhere. You can see that pot I put into the kiln when I dried it. remember how it was all black and sooty? Now it's burnt clean. But I'm mostly looking at the warped metal bar and the iron sheets that I'd used to reinforce the roof of the firebox melted! They've dropped into the firebox. I took them out and set them against the wall of the garage:

I guess I won't be putting those back into the kiln.

Still, everybody loves bubbles!

Here are the pyrometric cones:

The one on the left is for 1221˚ C (Cone 6), the middle cone is for 1046˚ C (Cone 05) and it seems about ready to melt, and the third cone is... um, completely melted into a puddle of goo that had glued the blob of clay onto the chunk of firebrick under it.

Sigh, and the floor popped again. I'll have to buy some sheets of firebrick to line the floor with.

Maybe you're more interested in how the pots and sculptures survived?
Well, here ... I'll move this piece out of the shadows of that last picture:

A big pot with a hinged lid, decorated with lizards. This piece was put in the kiln as sort of an experiment. When friends of mine fired it for me in their electric kiln they had broken the lid and I tried gluing it back together and patching it up. Here I wanted to see if it would survive re-firing-- and it kinda did.

Here I've removed a large teapot decorated with dragons and I've noticed that the high fire glaze that I'd applied lightly with a brush is still chalky. Maybe next time.

And this little cup was wounded. I suspect this is damage from the popping floor.

Here's some of the other pieces that fared better:

This is a coil pot (front and back views) that I made for the base of a floor lamp. The heat and smoke did strange things to the bit of glaze that was already on it.

And this is a-- well, you can see what it is:

Still hadn't brushed the ash off of it. The teeth are painted with a bit of casting slip. That's a special kind of goopy clay, almost a porcelain, used exclusively for pouring into plaster molds-- well it used to be, until I decided to use it like an engobe and paint something with it. I like it.

Full disclosure:

The skull was directly in the path of the flames and perhaps heated up a wee bit too fast. Remember that steam I mentioned earlier building up pressure inside the walls if you fire clay too quickly? It fractured this side of the skull. This crack does not go through to the inside. It's just a plate that has popped up because of the pressure caused by the water inside the clay being released as steam too quickly. Oddly enough, it is just a crack and the plate is not in danger of falling off. I think it almost looks like the seams between the bones of a real skull.

And to finish, another look at that dragon:

I can see some areas for improvement on my kiln. I still want to be able to fire it up over 1200˚ Celsius. My clay should develop lovely speckles at those temps and there are some interesting glazes I'd like to play with. I'm going to need to build an outer ring of my insulating clay and chaff mixture around my chimney. I may even finish it off with bricks and mortar. I think the pipe I was using was used as a chimney liner but at temps over 1100˚ C it's going to need some help. I'm going to rip out part of my firebox and increase the size and number of spaces between the parts of my grating. I'll probably need to get a second fan into working order as well.

Perhaps if I'd stuck with things through the night and fired until the wee hours I'd have gotten the temp up a bit more but with the iron plates dropping out of the ceiling of my firebox it was perhaps best that I stop then.

I hope to be firing it up again in the spring. Time to save up for some more shelves and get to work on some more sculptures...

Originally posted to Marko's Litterbox on Sun Nov 18, 2012 at 02:04 PM PST.

Also republished by What Are You Working On? and Community Spotlight.

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