R&D

We the potters in an effort to build a more perfect kiln...

I've been researching materials to build a newer type of salt kiln consisting of inner protective plates of high refractory something like used kiln shelves, wrapped in fiber blanket or board. Cordierite seems to be one of the cheaper materials on the market, but it's not the most resistant material in a caustic environment. In my current plan I chose to use both 2" fiber blanket and vermiculite board for the two outside layers. All of this is pinned down to a steel frame made of angle iron and expanded metal grate. I have yet to test the vermiculite board against caustic materials such as wood ash and soda vapor. I may end up going with just plates inside and two layers of blanket outside. I've found many different companies that produce plates that could be used, at the point it all comes down to cost v.s. useful life in the environmental kiln. I plan to make a small test kiln consisting of these materials. A lot of these materials I've found listed on alibaba.com.

One other thing I plan to try is a glass material from the UK which can be painted on the plates to create a barrier layer of glass that inhibits the corrosion of the caustic vapors from eating away at the kilns liner. All of this will go on the back of a small trailer so that it can be toted around to where ever I go. 

What ever kiln I build will be fire with waste vegetable oil (WVO) or a combination of WVO and propane. I've done some extensive web research on how some of these burners are made. In the end after trying to build my own I may decide to purchase some commercially made burners. They are extremely expensive but seem to work exceptionally better than anything I've seen. They also can burn just about anything in the lubricant isle.

Aside from the music this is a good video showing the afore mentioned commercially made burner.

http://www.youtube.com/watch?v=q4ZriEMN0FQ

Another video showing the set up and start up of the same type of burner in a furnace.

http://www.youtube.com/watch?v=4SX1lNvUjZg

Here's a good example of a nice homemade liquid propane gas burner

http://www.youtube.com/watch?v=KKtKn3l2U1c&feature=related

Here's an example of a dual fuel burner utilizing liquid propane gas for initial start up.

http://www.youtube.com/watch?v=Sw4qsOWSjrg

This last example is more like what I've been leaning toward in my own design.

Sodium kiln research

As a desire to continue some research I'd done at MHCC returns to my focus, I've been investigating materials to be used in the construction of a small soda test kiln. I stumbled on this article which I found particularly fascinating. It would appear that the majority of the research has been done for me already. I must express my gratitude to Peter Meanley for providing an excellent paper to base my future investment in salt kiln materials against. Below is a link to the article in question for those of you who might wish to build a soda kiln that lasts long enough to pay for itself.

http://kilnshelf.publishpath.com/Websites/kilnshelf/Images/Insulating%20Materials%20for%20Salt%20Kilns%20Article.pdf

Space...the final frontier

Building a gas kiln has proven to be a difficult thing in my current situation. Primarily because I'm a renter, not an owner. It comes down to an issue of space because I don't have a space which would be acceptable as a kiln site. Lately I've been looking into fiber because of it's ease of use and lightness. I had planned on making a small basket style kiln for a while as a test. Something like the Simon Leach raku kiln video on youtube linked below.

http://www.youtube.com/watch?v=OQB7bDAYWL0&feature=fvsr

After looking at many, many... many videos and blogs about fiber kilns an idea struck me to build the kiln on a trailer. So as I'm planning this, shopping for a metal flat bed trailer and compiling a materials list I stumble on a website of Steve Davis, who makes trailer kilns and does workshops. I had been thinking how clever of an idea I'd just come up with, and been really excited because I'd never even heard of this idea before. I can't say I am dead set on his entire design of the kiln, but it's certainly great. It's pretty much what I'd already designed except I'm using different burners and my flow path is not a straight cross draft but a down draft. Because of the type of burners I've designed I need a larger firebox than this kiln has designed. There's really no better way to conquer the space issue for me personally.

I will be building one, with a completion time of mid summer hopefully. I've really been itching to get back into stoneware temperatures. I am contemplating building a smaller mock up design that will only require about a two rolls of fiber and a cart instead of an entire trailer to save on initial costs considering I don't know if I like the fiber as a kiln material.

Linked below is Steve Davis's website showing his designs for what he calls a Kazegama.

http://www.kazegamas.com/kazegama.htm

Break it down

I've got a few hundred pounds of cone 10 clay in my basement. I'm not currently nor in the near future am I firing to cone 10. I've decided to try and reformulate these clay bodies to cone 1ish. Looking at the clay recipes for cone 3 most have a mixture of similar components. One major component to these clays is talc. Some cone 6 clays have about 10% talc or less. Cone 08 clays have near 50% talc. So a happy medium is a low talc body I've been using that's white stoneware mixed with a nice ball clay and about 25% talc as well as a little bit of soda spar. So what I'm doing is cutting the clay up into thin slices and laying it out to dry. Once the clay is dry I'm going to mix in about 25% talc and rehydrate in about 100lb batches. I have several plaster and bisque molds with which I will dry the clay back out down in my basement. It will probably take me about a week and a half to get the clay dry and reformulated. I'm hoping to have 300lbs of clay ready to throw by the end of the month.

Buff color body made from ball clay, fireclay, soda spar, talc.
Porcelaineous Body - porcelain, ball clay, soda spar, talc
Red Body - stoneware, ball clay, redart, soda spar, talc

I'm going to try one of the Porcelain cone 10 bodies I have in a line blend with soda spar to try and bring it down to cone 6 nice and tight.

Basket Case

In Pat Horsley's workshop he showed many slides of what he called baskets. These oval shaped pots had extruded handles spanning the their tops and resembled baskets in form only with no woven character. In his slides the remarkable thing was that even early on his glazes were good. He seemed to almost perfect the formation of color and surface quality very rapidly. The only thing that had some lacking in his early work were his forms themselves were somewhat bleak or spartan. He quickly remedied this as well soon producing pots that were dynamic in both glaze color and surface quality as well as intriguing forms.

Here is a greenware pot inspired by Pat Horsley, but the form itself is influenced by Don Sprague, Wally Schwab and a little of my own ideals thrown in to complete the functionality of this pot. This pot is entirely wheel thrown from top to bottom. The main body is constructed of a bottomless cylinder wider at the bottom, pressed into an oval. The bottom is a wheel thrown slab cut off the wheel and immediately slumped into a bisque form to start the concave form and to more rapidly dry it for attachment. About 20 minutes later I attached the bottom slab to the upside down oval cylinder. The foot and handles are thrown and taken from the same ring of clay.

The handles are my only real complaint on this pot. They need to be longer and attached at the sides for increased strength. Ethically I cannot sell this pot because the handles may fail the user with hot liquids causing someone to get burned. I will end up using it as a fruit bowl since mine was given away as a gift recently.

Clean Slate

This is a slate blue glaze on a red clay. The high iron content of the clay gave the glaze a greenish appearance where thin. Where thick it's a deep blue like the paint used on submarines. It's glassier than the original recipe description, which I'm thinking is because of a substitution of 3134 for 3124. It also might be because I'm using Unispar instead of Kona F-4. All in all I call this pot a success, it's got acceptable color response, and on the red clay the glaze stopped bubbling and healed over. I will probably reformulate this glaze with 3124 and apply it dipped on white clay in my next test.

This picture was taken with light from an open window. The sunlight brings out the green, inside the pot is blue.

The Blues

Cadwell's Base is a strontium crystal matte glaze that has a zirconium opacifier. The zirconium opacifier tends to make colorants lighter and more pastel in color. The strontium should form a matte crystalline structure on the surface of the pot giving a nice muted matte look over all. The mottled appearance in the glaze on these pots is my application not the glaze. I had decided to use a hand pump sprayer to apply these glazes allowing me to make less than if I were to try and dip these pots. The sprayer was a failure, but this base is a success in several ways. Color response is exactly what I was expecting, muted softer colors. Texture is a bit shinier than I had anticipated, I'm not sure why yet, but all my glazes came out much glassier Three other colors are formulated, but not fired yet, a yellow, gray and a rust red.

• Here are two versions of the glaze in testing. 
• The bottom is copper carbonate giving a powder blue. 
• The top is cobalt carbonate giving a periwinkle blue. (picture is much darker than glaze)

• Here is the periwinkle by itself, not the liner on these pots is a soft cream yellow. This liner glaze is formulated to be tough to stand up to wear and feels like teflon.

• Here is the powder blue copper glaze note the stronger color on the rim where it overlapped the liner .

• Here you can see the powder blue on a textured pot. The zirconium opacifier mutes texture, if this glaze were thick it would have greatly reduced the visual effect of the chatter marks from my tool.

Substitution

In the last post I mentioned some glaze testing I've been doing. I've been using digital fire (glaze calculation software) to try and formulate glazes that have materials which are no longer available or are cost prohibitive. For instance Redart is a cheap material commonly used in glazes. I tried to formulate a couple glazes with Redart in place of Barnard. Of course these two clays are not even close to the same. In manipulating the other materials I hoped to get something close. 

The pot pictured to the left is what I got, and it is actually color response wise pretty much exactly what I was expecting. However I had added another variable to the mix, trying to adapt a cone 3 glaze to cone 1. I believe what I have here will actually melt out closer to cone 4 - 6. It has small bubbles that did not heal through out the entire glaze. It's a mustard yellow that breaks chocolate brown.

I tried to apply this glaze thinly to give the two tone brown yellow, however I wanted stripes of yellow in the tool lines left behind from my shur-form. My haste with the application gave me brown with patches of yellow.