Potter's Journal

Woodstove raku

2012-01-12T11:21:00.026-05:00

It's winter in Keene, NY. Winters here are long. Temperatures can get down to -20 F or less.

This is my second winter of heating this house with wood. I like the physical and repetitive and traditional qualities of heating with wood. You cut it, split it, stack it, bring it into the house, stack it again, feed it into the stove, clean out the ashes, sweep up the bark and ashes that collect around the stove, find uses for the ash, keep the chimney clear.

I've been firing and smoking pots right in the woodstove, pulling them out when they seem "done". It's raku.

The results may not be as functional as stoneware - but the process is good for small sculpture. It's fast and easy, invites experimentation. Smoking emphasizes marks and structure. There is the excitement of unplanned firing effects. Multiple firings - no problem.

This is fun. It's play. Science would spoil it's best features. But, I do intend to put a cone pack in there (one of these days) to see just how hot it gets. I will report my results.

This is the most economical of all ways to fire pots. I am already burning wood to heat my house; there is no additional cost for firing little pots buried down in the ashes in the woodstove.

Also, this way of firing uses a renewable resource for fuel and adds no more carbon to the environment than the amount produced by heating my home.

High fire adds technical difficulties and uses a whole lot more fuel. If the work is non-utilitarian, high fire does not necessarily contribute important visual qualities that cannot be achieved in low fire. Low fire is easier on the wallet, easier on the environment, and capable of producing work with powerful visual presence.

To smoke these pots, I put them into a covered tin can along with paper or sawdust ... and stick the can with pot and combustibles back into the woodstove for 15 minutes or so. I've been pulling the can back out if smoke stops coming from the can. If the pot didn't get enough smoke, I put it back with more combustibles for a while longer. The smoke that escapes the can goes right up the chimney ... or you can see the wood gas burning where it escapes the can and finds more oxygen.

After the firing, the pot is likely to have some crusty ash on the surface. This is easily scrubbed off using an abrasive scrubber and scrubbing compound (e.g. Comet).

Decoration

In using colored slip on this work, I found that the slip I usually use for high-fire work sticks well to the earthenware pot. However, because it remains porous like the body, it will take up the carbon from the smoke just as readily as the white earthenware body of the pot ... meaning the slip and the body both turn black and you lose the color. In order to keep the color, I found that adding borax to the slip will cause it to become a low-temperature glass in the initial part of the firing (in the coals, not yet in the smoking can). Then when I expose the pot to smoke, the glassy colored slip seals out the smoke ... and the color shines through the surrounding black. Cool beans.

Speculation

I'm guessing that I could paint on a solution of borax to seal the surface of the claybody or porous slip and cause these borax-painted areas to resist the smoke. This would be the reverse of the effect of sealing in carbon by painting a high fire carbon trap glaze with soda ash; I would be using the borax to seal the carbon out, not in. The soda ash causes the glaze to get glassy after the carbon is already absorbed and keeps the carbon from getting burned out as the temperature climbs. In this raku process, the borax causes the glaze to get glassy before the carbon is absorbed and keeps it from getting absorbed during the smoking.

After a while I will probably want to experiment with terra sig and burnishing.

I can envision an ever-expanding low-fire career unfolding.

That's all for now. It's snowing outside. I have to stack the firewood that I split yesterday before it gets buried under the snow. The wood will be stacked outside to dry for a year - to be fuel for next winter's heating/firing season.

Saturday, January 14, 2012 1:08:20 PM

I got the wood stacked and then started up the snow-blower ... only to discover that the snow-blower wouldn't move. After tearing the machine apart (something I've never done before), I found a broken weld in the mechanism that thrusts the drive plate against the friction wheel. (You could use a mechanism like this to make a variable speed potter's wheel using a constant-speed motor. I should be possible make a good potter's wheel from an old snow-blower transmission.)

I discovered online that you can weld steel using 2 or 3 car batteries connected in series (link). I was tempted to explore these new heights of resourcefulness, but I decided that my time would be better spent trying to get the help of someone with a welding machine and experience. I brought the broken part to a local auto repair garage ... and the guy did a very nice job of welding the two pieces back together - better than the original. It took him less than 10 minutes. He charged me $10.

Now I've got to put the blower back together and blow the snow. Then I'll need to bring in firewood. Then I need to go buy some food. (There is nothing in the refrigerator but a single bottle of beer, a partial thing of celery, and 7 eggs. However, there is enough rice, pasta, and sardines to survive for a week or more. And there is a turkey in the feezer.)

I wish I didn't have so many different non-clay jobs to do and could just do clay. But then, I would have a different life, be a different person, and make different pots. Writing this blog is actually helping me think through and do all my non-clay tasks ... without getting discouraged or side-tracked.

The blog-writing process helps me remember and develop the real Bill. In part, this is because I am imagining that there is at least one reader out there who would like to know who I really am.

Note: Yesterday, I found my old Nikon 55 mm f/3.5 macro lens which will work fine on my Nikon D200 digital camera for photographing these little woodstove pots. The macro lens will let me get close enough to fill the frame.

Sunday, January 15, 2012 12:48:20 PM

Of course, I overestimated my abilities. It took me until late last evening to get the snowblower together. There was not really a whole lot of snow to blow ... and much of it was wet and glommed together. I went to bed without trying to blow, and woke up with the temp outside of -5 F and the driveway iced up, leaving mostly ice and little white stuff that would go through a snow-blower. I threw wood ashes on the driveway hoping it would add some traction.

I still have to bring in wood and shop for food and make my cone pack.

Sunday, January 15, 2012 5:44:56 PM

Wood in - made a big double-row near the woodstove.

Cone pack drying. I will be testing from cone 010 to cone 03.

Mouse

I was going out the door to go grocery shopping when I heard a scratching sound. It was coming from a plastic bucket near the door in which I keep salt for melting the ice on the walk outside the door. A little mouse had fallen into the bucket and was struggling to get out - very cute, but not a creature that I wanted to share my house with.

What to do? I tried to think of a humane way to get rid of the mouse. If I threw it outside it would slowly freeze to death. Drown it in the toilet? - ughhh. Try to clobber it with a stick or stomp on it? - I might miss or just wound it ... and cause it to suffer. Then it occurred to me: Why don't I toss it into the woodstove where the heat should kill it almost instantly? That seemed pretty humane ... so I opened the stove door and flipped the mouse in. The mouse landed on a recently-added piece of wood that was not yet burning ... and immediately ran out of the stove and hid under the wood I just stacked next to the stove. Curious, brave, lucky little creature lives another day (just like me).

I'm not sure if there is a lesson to be learned in this experience. Does it mean that I am indecisive, unable to carry out tasks about which I am ambivalent, that I have a cruel streak, that there is a higher power looking out for the mouse and/or me, that my best intentions were ill-conceived and perhaps immoral, or just that life is full of surprises? Maybe all of those. I dunno.

Monday, January 16, 2012 12:34:07 AM

Eggs

I returned from Lake Placid with groceries. The temperature was about -5 F. In trying to carry too many bags at once while wearing heavy mittens, I dropped one of the bags - which turned out to be the one containing two dozen eggs. (Apparently, this is the fate of those who throw mice into the woodstove.)

Only 6 of the 24 eggs were broken (lucky me, cursed only 25%). I decided to have a rather large omelet for dinner.

Temperature inside the woodstove; frozen pipes

After dinner the cone pack seemed dry enough to go into the woodstove. I stuck it in, being careful to keep it level and very close to the coals. It did not blow up (proof of dryness).

I thought I'd take a shower while the cone pack was absorbing heat. It turned out that the hot water pipe to the shower was frozen (the apparent fate of those who throw mice into the woodstove and drop eggs). So, I didn't take a shower.

Interesting but in no way helpful to me: It has been known for centuries that hot water can freeze before cold water. I found explanations for this counter-intuitive phenomenon online (link, link, link). I now have to deal with plumbing issues before the other non-clay jobs I have to do ... which leaves me even less time and energy to do clay.

Annoyed and stubbornly ignoring the frozen pipes, I sat by the woodstove, noodling around on my harmonica and watching the cone pack through the little glass window on the woodstove door.

After a while, the results became clear. The first cone, which was cone 010, corresponding to approximately 1620 F, was the only cone that actually bent. The second cone (cone 08) had only the slightest hint of softening.

Speculation ... Intellectualization

If you wanted to be get a highly vitrified clay body from a woodstove firing, the stuff cone 07 is made of might do it. However, actual cones are formed in a mold with materials that are unlikely to be plastic enough to use for hand-building.

Vitrification might not be all that desirable, anyway. A more vitrified body would take up smoke less readily. Also, it would probably be more vulnerable to cracking from uneven heating and cooling.

It might be interesting to try to develop a vitrified, low-expansion woodstove body fluxed with lithium which would expand and contract less. Hmnn....

The clay I used to make the cone pack was stoneware. The stoneware clay got hard in the woodstove just like the earthenware clay. Either clay body withstood the shock of being taken from room temperature, placed on hot coals, and then pulled back out into room temperature. Either clay body is durable enough to be washed with water and scrubbed with a brush and cleanser. This work does not need to hold food or tolerate freeze-thaw cycles outdoors ... so who cares how vitrified the clay is?

Real Bill says

Art is purposeful play. It's a performance fixed in time. The process is more important than any talk about it. Too much intellectualization undermines the work's freshness and spirit, ... the visual evidence of spontaneity that gives a piece of work its energy. Art needs science ... but science is not art.

Do I want to do art? Yes.

Do I want to do science? Nahh. Science is no fun. It stresses me out. It's like going into medicine when I should have become a potter. I'll do science if I run into a snag. I should keep outside of the science box as much as possible: I'll be more true to myself, happier, more imaginative, more productive.

Tuesday, January 17, 2012 1:04:19 AM

More images

I got my frozen pipes thawed out. Lucky me they didn't break. And now I can take a shower. What a luxury!

It warmed up to +30 F (balmy) ... so I have time to figure out how to insulate the pipes better and keep cold drafts out of the crawl space. I will crawl around looking for gaps between the stone foundation and the sill plate to fill with insulating foam. I will look for cold drafts. I can cover a lot of the cold stone foundation with fiberglass. I can put some styrofoam behind the little door to the crawl space. I can put a little heater down there or wrap the pipe with a heating tape.

My next big project (after I finish doing the sheetrock, painting, and floor in the downstairs bathroom) will be to replace all the corroded water supply lines in the house. I will use PEX which is elastic enough to withstand freezing without breaking. From what I've read, this job doesn't seem too hard. However, I've never done this sort of work before, so I expect it to be stressful and full of surprises and trips to the hardware store.

I will be getting another load of green firewood sometime soon. My wood guy, Jeff, said it would be today but that didn't happen. The wood will need to be split and stacked when it comes.

In between all this non-clay stuff, I will keep making, firing, and photographing pots. I will share images of this work with you ... along with snippets of what my life is like.

Testing and developing glazes

2010-12-25T11:44:00.031-05:00

I've been gearing up for some serious glaze testing. I've been watching the struggles of my friend, Kim, who is developing slips and glazes for soda firing.

Building on multiple sources, I have a plan for how to proceed with my own testing. In this blog, I will share my ideas and any good glazes I develop. Comments or suggestions are welcome.

Why is testing necessary?

Glaze recipes do not travel well - often need to be adjusted for local conditions. Making a single test tile of a recipe is a shortcut that often misses the mark. Likewise, trying to use glaze calculation software to create a one-shot cure is also a shortcut that often misses the mark.

What sort of local conditions can affect glaze features? Hot oxides interact with each other, the kiln atmosphere, and the clay body ... and have complex effects on the glaze melt. There is a lot of variability in raw materials, clay bodies, solubles in the water, kiln atmosphere, and firing schedules - any of which can affect the glaze. Glaze calculation is no more accurate than the analyses of the materials - should be taken as a rough approximation. Your working recipe will be the result of systematic testing. Use the software to narrow the scope of the testing.

When to test

Test all new glazes and test working glazes any time something changes, such as a change in raw material, glaze density, water supply, clay body, firing schedule, kiln atmosphere, colorant combinations. You also may need to test for suitability for leather-hard, bone-dry, or bisque application.

How to test

Instead of testing a zillion recipes to find a few that work for you, your time will be better spent if you select a few glazes and test them systematically ... on the faith that you can probably get any of them to work.

You will want to do either a line blend (varying one oxide) or a square blend (varying two oxides). Rather than weighing out all the ingredients of each test, you weigh out just the ingredients for each boundary point of the blend (such as the corner glazes of a square blend or the ends of a line blend), add water to make them have equal volumes, then use volumetric means to proportion out the boundary mixes to create the mix for each test tile.

After the tiles are fired, glaze software can instantly provide the recipe for every tile in the blend based on the recipes of the corner glazes and the number of intermediate points.

The commonest variables that require testing are alumina and silica - something that should be done with any untried or problematic recipe.

You have to keep things simple in order to make sense of the results. In every test (even a square grid that changes two variables) you are really always examining a change in single variable at a time while you keep everything else the same.

A Currie blend (or grid) is a type of square blend that fixes the proportions of a set of glaze ingredients while systematically varying the alumina and silica to create a family of different glazes. This grid is usually 5x7 (35 tiles). Silica increases by 4 increments left-to-right. Alumina increases by 6 increments bottom-to-top. Using the same size grid helps you visualize a tile's position in the grid and understand how the glaze changes as you vary alumina and silica.

A more general concept is the square blend in which you systematically vary one oxide in each of two axes. You create corner recipes that determine the oxide levels in the corners. You determine the number of increments in each axis. You can customize the scope and granularity of the grid any way you want.

I believe that the best use of glaze software in solving glaze problems or in developing new glazes is in the design of tests. Reality is what is recorded in the tiles. Your working recipes will be the recipes of the mixes you actually put on the tiles - not something you came up with using software to juggle ingredients while you check the calculated effects on oxide levels.

You can design the corner glazes of your test to make the range of oxide levels being tested as broad or narrow as you wish. You can determine the granularity of your testing by defining the number of intermediate points in each axis of the test.

If you are trying to fine tune an almost-working recipe you want to narrow the focus of your test. If you are trying to discover a glaze nobody that has never seen before, you can make the scope as wide as you want. If you are a functional potter, you can use the software to keep the oxides in the four corners close to the known limits for durable glazes.

In constructing a square grid, you define a set of ingredients that will be constant in all 4 corner glazes. Then you add ingredients to the corner glazes that will systematically change only one variable in each axis.

Labels, registry, computer records

Each test set and each tile must have unique identifiers. The computer can be used to define the tests before they are run ... as well as the labels that identify each test and it's corresponding set of tiles. There should also be a hand-written registry for recording date, test, and tiles.

The hand-written registry will only show what tests were done and when. The details are all in the computer in records that can easily be backed up. If the registry book were lost, it would be no big deal because the information originated in the computer records. (If the computer records were to be lost, the registry information would be nearly useless.)

The test set identifier will consist of a letter corresponding to the year plus a sequential number representing the number of the test set during that year. For example, if "A" represents "2010", then "A46" would be the 46th set done in 2010, "B19" would be the 19th set done in 2011, etc.

There are difficulties involved in labelling tiles being tested in salt/soda firings. Identifiers painted on the bottoms of these tiles are easily obscured by kiln gunk. One solution to this problem is to stamp or inscribe the identifier on the tiles during the leather-hard stage. Another way would be to paint the identifier onto an unglazed area on the back or side of the tile, rather than on the bottom.

The most precise and error-free way to identify the tiles in a set would be to paint a label on each tile immediately after it is glazed, using a combination of set identifier plus the sequential number of that tile in that set. For example "A46-21" would identify the 21st tile in the in the 46th test set of 2010.

Glaze software

Glaze software is indispensable for understanding and developing glazes, and for keeping records.

The different available glaze software products vary considerably in their ability to store and organize information. GlazeChem is a good one for storing and retrieving records.

The records in GlazeChem can include images of glazes and detailed notes. You can keep all your tests in special folder. Each test can be kept in a separate glaze datebase file on the computer. Each database can contain detailed notes, the recipes of the boundaries of a blend, and the recipes of all the tests in the set. It is possible to predefine and label each test set and print out the corner recipes before you go out to the studio to mix the glazes. The printouts can be used in the studio to check off glaze ingredients as they are added to a batch. After the tests are run, the print-out recipe lists can be discarded. You can use the program to determine the recipe of any of the tiles that interest you. You can go back to the computer and record your results ... even including images of selected tiles. You can give descriptive names to tiles/recipes that worked well and copy them to a collection of working glazes.

Hard to please #1

2010-12-16T02:54:00.003-05:00

A recent sculptural vessel I'm calling "Hard to Please #1"... The height is about 20 inches. Stoneware.

IFB kiln for Soda

2010-11-02T17:16:00.018-04:00

November 2, 2010

The following is a summary of a series of email messages which I recently exchanged with Nils Lou regarding his current recommendations for constructing a soda kiln using insulated brick coated with ITC100HT.

Coated IFB Soda Kiln

In *The Art of Firing* (1998), I read your preliminary report of using refractory coatings to protect IFB from the erosive effects of sodium atmosphere and to increase emissivity. I would be grateful if you would answer a few questions....

More than a decade has passed since the publication of The Art of Firing. Would you now recommend building a new soda kiln of coated IFB ... or should I stick with hard brick?

Sure, I am still using the original kiln, but made the mistake of salting a couple times with "burritos". After repair I only introduce salt by spraying the salt/soda solution. All IFB were totally dipped.

Is that kiln made of K23's coated with ITC100HT?

Yes.

Do you fire to cone 9-10.

Yes.

Are you saying that as you constructed the kiln, you totally immersed each brick in ITC100HT - ie coating all six sides, not just the hot face?

Yes.

Do you dip the bricks into a bucket of ITC ... or paint it on?

Dip.

Do you have a specific gravity or some other measure of how thick the ITC100HT should be to coat the bricks?

No, thin with water to thin paint consistency.

How much of the ITC would I need to coat the bricks for a 40 cubic foot kiln?

5 gallons

Would I need to buy 5 gallons of the concentrated ITC100HT? ... or do you mean that I would need 5 gallons of the diluted mixture used for dipping bricks?

5gals. of ITC, diluted to 10 gallons or so.

Do you use the ITC as a sort of mortar, laying the bricks up with the ITC still wet? ... or do you let the ITC dry on the bricks before you lay them up?

No, let dry.

Is there a benefit to coating the side of the bricks that faces away from the heat?

Yes. If you dip the brick completely you don't have to fool with orientation. Otherwise, no heating benefit.

Composition of ITC100HT

Is "ITC100HT" anything more than a good kiln wash that I could make myself using commonly available raw materials?

It is much more, and is a proprietary formula.

Are you saying that some of the material contained in ITC100HT is specially manufactured - not something I could buy by the bag from a ceramic materials supplier?

Yes.

Topcoat to increase emissivity

Would a topcoat of HUC be as effective in increasing emissivity as ITC296A?

HUC is no longer available to my knowledge.

It appears that I don't have many options to select from.

Apparently so.

In *The Art of Firing*, you said HUC was a slurry of silicon carbide and various suspending agents. How about a kiln wash composed of kaolin and silicon carbide powder?

You could experiment with SiCo3, sodium silicate, and clay--might be interesting.

I don't know how I would measure the benefit of an emissivity coating other than showing a reduction in gas used in firings. Once a kiln is coated, you would have to build a new kiln to test another coating formulation. Is there an inexpensive way to accurately measure the amount of gas used in a firing?

I got a used meter from the gas company, so I could measure the gas. Otherwise, if the firing time is reduced you could assume you were using less.

Horizontal tubes

2010-09-15T14:58:00.001-04:00

Here are a couple of recent pots based on horizontally positioned cylinders. I call them tube pots.

(My next series will play with horizontal cylinders that have been folded and collapsed.)

Train Engine with Pink Wheels

Stone Pony

Images of recent work

2010-08-26T00:00:00.005-04:00

In a previous post I talked about getting inspired by a video on origami. I found that by putting folds in the walls, it is possible to cause a controlled vertical collapse of the soft clay with visually striking results. Below is a selection from the first set of pots I did playing with this idea.

Links

2010-07-29T10:11:00.009-04:00

My collection of links has gotten big - a lot of good stuff - valuable resources, opportunities, and sources of inspiration. These links fill a void for me - help me feel connected to the huge number of people working in this medium.

I've added JavaScript to the page that will automatically alphabetize the various lists and eliminate duplications.

Kiln wash, wadding for soda, refractory coatings

2010-07-23T13:40:00.049-04:00

I'm building a new soda kiln with my partner, Kim. I've scrounged the best information I can find on refractory coatings for sodium atmospheres. I will update this post if I learn more.

Kiln wash recipes

	A	B	C	D	E	F
alumina hydrate	50	50	20	30		60
calcined kaolin		25
zirconium silicate			40	30	90
kyanite				30
kaolin	50	25	30			30
ball clay			10
bentonite				10	10	10

Notes
Kiln wash is nothing more than a layer of highly refractory material used to coat surfaces you wish to protect from glaze runs, kiln atmosphere, and ash deposits. The wash should adhere, lie flat, not form dust, not form chips or flakes. It should be easily removed with hand tools.

If the kiln wash shrinks too much on drying, it will crack and tend to fall off the shelf in flakes which can fall onto work being fired on a lower shelf. To decrease shrinkage, increase the proportion of non-shrinking refractory material. The choice of non-shrinking refractory material should be based primarily on cost of material. It can be alumina, calcined kaolin, zirconium silicate, kyanite, etc. The non-shrinking refractory material can be up to 90% of the kiln wash recipe.

You can buy calcined kaolin as Glomax or Molochite. You can make your own calcined kaolin by heating to bisque temperature (red heat) in a bisqued bowl. Calcining of clay eliminates the physical property of shrinkage without changing the chemical and refractory properties of kaolin.

To control swirling kiln wash dust in kilns with high turbulence, add 1-2% feldspar (source of info = John Britt). If you add feldspar, make sure you don't add too much. After firing, you should be able to scrape off kiln wash with a finger nail. If you need a tool to scrape off the wash, it has too much feldspar.

Recipe D is essentially the same recipe posted on Clayart by Tony Clennell as the "working potter's ITC". It has been applied to kiln walls and used for repairs (tony.clennell@gmail.com).

According to John Britt a soda kiln wash recipe should not contain silica.

Silica in kiln wash is ok at lowfire or midfire temperatures without salt. Silica is not so good at high fire - especially for wood, salt, and/or porcelain.
Silica is a glass-former. If a lot of glaze drips onto the shelf, it can melt the silica in the kiln wash and form a glaze on the shelf.
When you scrape your shelves to clean them, you create a lot of silica dust, which is a known carcinogen.
If you use a wash containing silica in a salt or soda firing, the kiln wash becomes a glaze. This is because silica is a glass-former. When sodium oxide, which is a strong flux, is introduced atmospherically, it can easily melt the silica in the kiln wash into a glass.

For applying kiln wash with a brush or roller, it should be mixed to the consistency of heavy cream. For application with a sprayer, it must be mixed thinner.

Using a roller or spray gun are faster than using a brush. If you are using a brush for doing a whole shelf, use a 4- or 5-inch house-painting brush. If you are touching up bare spots after scraping off glaze drips, use a 1–inch glaze brush and just dab it on in the spots that need it.

If you use a brush, work very fast because the shelf will suck up the wash as soon as the brush touches it, making areas of uneven thickness.

When applying wash to clean shelves, apply several thick layers, allowing each to dry before applying the next. Then, with a wet sponge, wipe the wash off the edges and a 1/4-inch band around the top border of each shelf to prevent chips of kiln wash from falling onto the ware stacked below.

The best way to clean shelves that have glaze drips or salt build-up that has eaten through the kiln wash is to use a "diamond grinding cup" on an angle grinder. These cups come in a diameter of 4"-5" with prices ranging from $13 to $150. Use a dust mask and goggles when using this tool.

Wadding
For WADDING... use the same recipe as for kiln wash with less water so it has the consistency of dough. You can add 40% or more of sand and/or sawdust. Sawdust burns out leaving crumbly material, easily crushed with pliers.

Wadding is used in salt/soda/wood/gas reduction firings to allow the kiln atmosphere to reach surfaces that would otherwise be excluded. Wadding is necessary in salt/soda to prevent pieces from being glued to kiln shelves by atmospheric sodium or glaze runs.

The kiln atmosphere will reach around the wadding everywhere except the surfaces in direct contact with the wadding. The surfaces in contact with wadding are masked from the atmosphere. This will result in pale wad areas surrounded by expanses of atmospheric glazing and/or flashing.

It has become part of the mystique and tradition of these firing techniques to use wadding in creative and decorative ways.
Examples:

Wad bottoms in order to glaze/flash bottoms.
Lay tall pieces sideways on wadding to get ash/glaze runs to pool on the gravity side.
Stack bowls rim-to-rim to get atmospheric effects on the rims and inside ... while conserving kiln space.
Wad lids in place so that they are exposed to the same atmosphere as the nearby pot surfaces ... and allowing flashing of lid contact surfaces.
Stack plates or bowls separated by wadding ... resulting in interesting flashing effects on inner and outer surfaces, as well as conserving kiln space.
Apply wadding purely as a decorative masking technique (i.e., regardless of whether wadding is required for placing or stacking the piece in the kiln).

Refractory Coatings

We are thinking of building a larger kiln. According to Nils Lou, a kiln made of hard brick will use four times as much fuel as the same size kiln made of insulating firebrick. In the past, most salt/soda kilns have been made of hard brick because uncoated insulating brick does not hold up well in the soda atmosphere. If you could put a protective coating over soft brick, there would be a huge savings in fuel costs.

We are aware of various refractory coatings that have been recommended to enable insulating firebrick to withstand the erosive effects of a salt/soda atmosphere. Thus far, I have no personal experience with any of these coatings. I would greatly appreciate comments from others who have experience with any of these coatings.

In The Art of Firing (1998 edition), Nils Lou devotes a chapter to refractory coatings and discusses his experience using these coatings in salt/soda kilns. It is now many years since he reported his preliminary findings with HUC and ITC coatings. I wrote to Nils Lou to find out what his current thoughts are about these materials. I contacted him by email ... and he patiently answered my questions. I summarized this correspondence and have put it on this blog with his permission (link).

Recipe D above is essentially the same recipe posted on Clayart by Tony Clennell as the "working potter's ITC". It has been applied to kiln walls and used for repairs (tony.clennell@gmail.com). Whether or not it can protect IFB from soda vapor, I dunno.

Here is the contact information for International Technical Ceramics ("ITC"):

Delkich International Technical Ceramics Inc

325 Mealy Drive

Jacksonville, FL 32233-6901

Phone:(904) 285-0200

(ITC has no website.)

Here is a link to an ITC vendor named anvilfire.

Nils reports that a salt kiln made of 23K brick and coated with ITC100HT has held up well in repeated cone 9 soda firings over many years. He also recommended applying a topcoat of ITC296A which is a denser material which will raise the emissivity.

Instead of paying an arm and a leg for these ITC coatings, I wonder if I could substitute Tony Clennell's working potter's ITC for commercial ITC100HT. I wonder if I can mix up my own working potter's HUC (containing silicon carbide, clay, and maybe some sodium silicate) as a substitute for ITC296A.

Here is what Kim and I have talked about doing.... In our current little kiln lined with hardbrick, we will include a little piece of IFB coated with working potter's coatings ... along with an uncoated piece of softbrick as a control. We will place these pieces of IFB right in front a burner and blast them with heat and soda. If the softbrick seems to be holding up compared with the control, we will eventually use these coatings on a larger kiln made of softbrick. If the Clennell mixture doesn't work so good, we can use ITC. Another thought: Maybe we should not work so hard trying to develop our own kiln technology and just use what is commercially available; that way we will have more time to make pots.

Clay origami

2010-07-07T08:10:00.005-04:00

I recently watched a mind-bending video about origami, Between the Folds. The concepts of folding can be applied to a broad range of subjects. We are not just talking about paper airplanes and swans. The physical features of any line or surface can be defined in terms of folds. There are broad implications for 3d design, architecture, and chemistry. I started thinking about what I could do with folds in clay ... and exciting ideas came to mind.

I immediately understood how George Ohr was able to control the way some of his pots collapsed. He must have put folds (or pleats) in the walls before he squashed. Wow! I tried it ... and got interesting results every time. Now I'm working on a series of pots that employ pleat-controlled collapse. It is very cool! You get a very organic form from a thrown vessel. It is necessary to do hand building and/or complex construction of thrown parts to create a vessel or sculpture that utilizes the collapsed portion.

I'm having fun. Click to see some images of this work.

Recent work - fun teapots

2010-05-25T13:34:00.013-04:00

I want to share some images of recent cone 9 teapots. These were fun to make - functional but unusual, constructed from thrown parts.

This one has an air-filled double-bubble handle that stays cool to the touch when the pot is filled with hot liquid. It pours a smooth stream.

This was a fun assemblage of parts - five balls thrown as closed forms, two pulled and twisted hollow tubes, a pulled handle, a thrown neck with flange and lid-keeper, and a little perforated lid. Named "Teapot with Balls", this one was accepted to the Baltimore Clayworks exhibition "100 Teapots V", Jan 15 to Feb 27, 2011. Retail price $550.

3-spout teapot with ring handle. The middle spout pours hot liquid. The upper spout (on the handle) pours blessings. The lower spout is a handhold. The sand-blasted surface is soft like human skin.

Power to the Potter

2010-05-24T12:31:00.002-04:00

I was an insecure kid. I didn't know any artists or craft-persons. Pottery - unknown. Sculpture - nothing. No tradition. Television culture. Class clown settled down and pursued a career in medicine. Why? I knew that other people would value this choice ... and I couldn't think of anything else to do. I worked hard, went to good schools, became a competent physician, ... but came to see that I wanted another kind of life - a quieter and more creative one. I dropped out and had the good fortune of stumbling into clay.

I had gotten into medicine expecting that my efforts would be valued. In the first years in my own studio, I had the naive expectation that calling myself a "potter" would automatically give me a new identity, sense of community, and source of pride. It took a while to realize that changing my label was just a step in the right direction. I didn't find myself until I was able to see my place in a much larger context.

I'm at peace. I am humble without shame or worry. My past mistakes are lessons. I don't care about money or recognition. I'm open. I presume nothing. I'm learning. I share freely. My sense of well-being does not require certainty, familiarity, order, control, perfection, or justice. I always try to do the right thing.

I want my work in clay be loose and playful. I want to develop my ability to improvise spontaneously around my ideas as I'm working - to work without a precise plan, precise control, or the nerdy intrusion of my intellect. In order to be as loose as I would like, I believe I need to maintain skills that can only be acquired through the discipline of production work. I intend to continue cycling between production work and playful work.

An inner voice calls me to a creative life. Following that voice can be scary and lonely. I've learned that success is impossible without risk-taking and persistence. My trepidation, procrastination, detours, intellectualizing, idealizing, pretending, ... my studies of ceramic technology, ... my efforts to make safe pots to sell, ... my efforts to teach ... are all just ways of dodging the risks and labor of making original physical objects. A chicken potter is a very small potter. A secret potter is no potter at all. I will put myself out there every day.