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Patsu

Can Electric Kiln Peak Temp Be Raised

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If you wrap the aluminum foil on the outside of the stainless jacket, you are going to increase the temperature of the interface between the stainless and the firebrick.  How much.... hard to say.  This might cause the stainless to rust out faster than normal.  Ditto things like screws and clamps and such.

 

Another consideration is what refractory choice the manufacturer made for the brickwork.  Taking it higher might be exceeding the use rating of the bricks.... ther by causing the dead air spaces to slowly crake into largfer spaces... and decreasing the insulating value of the bricks.  Is this kiln solely one type of refractory?  If you cut the heat losses on the outside, you rais the interface temperature at every juncture of materials in the wall section.... possibly exceeding the use ratings opf them.

 

Third, what are the elements made of?  Was the alloy selected for durability at the higher temperatures?

 

An additional layer of low rated insulating firebrick under the floor and on the lid can work wonders.  1600 F rated bricks would be just fine.  Block insulation also.  RCF board is overkill.  RCF blanket is a health hazard.

 

best,

 

.....................john

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First, why do you want to go to cone 10? It's unnecessary. Cone 6 is plenty hot for most anything. You can soak from cone 4 to cone 6 in 60-75 minutes. Cone 8 or 10 could take many hours and waste a lot of energy.

 

That kiln is only rated for cone 4 because it runs on 120 volts and is too big for a 120 volt kiln. It just doesn't have enough power to get it above cone 4 without soaking. I'm confident that it uses the same bricks as all their other cone 10 kilns, and likely uses the same type of element wire as well. It's made for folks who do low fire work.

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With the exception of a couple of special glazes that require a reduction firing like copper reds and shinos, in terms of clay body vitrification and durability, cone 6 is great. You don't have to go to 10 to get a vitrified clay body. Just make sure you're using a cone 6 clay body so that it fully matures. Stay away from bodies that are rated cone 6-10, as they are under fired at 6. and make sure you're using actual cones to verify your findings. Cones measure heat work, thermcouples only measure air temperature.

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That Potter's Choice shino is not a true shino. It's similar to a shino in that it's kinda orange, but beyond that it's not really even close to the real deal. That's not to say it's not a nice looking glaze, I just wish they wouldn't call it a shino.

 

Cones have become much more expensive since digital kilns came into fashion. But you won't need to use them forever. Once you've used them to confirmed the soak time needed to get to cone six, you can stop using them. Keep them around in case you run into issues in the future and need to re-confirm.

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That Potter's Choice shino is not a true shino. It's similar to a shino in that it's kinda orange, but beyond that it's not really even close to the real deal. That's not to say it's not a nice looking glaze, I just wish they wouldn't call it a shino.

 

Cones have become much more expensive since digital kilns came into fashion. But you won't need to use them forever. Once you've used them to confirmed the soak time needed to get to cone six, you can stop using them. Keep them around in case you run into issues in the future and need to re-confirm.

to be honest, anything in american ceramics called a "shino" lacks the geologic pedigree to be called a shino--but semantics.

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  There would still be kiln heat loss overall, but less radiant energy loss.  

 

Maybe you should stop thinking of these as somehow separate things in the more global overall concept. They are all components of the energy being applied.  Radient heat energy transfer is still heat energy transfer.  You are completely correct that if you decrease the radiant transfer, you will need less energy input in a unit of time to achieve a given application of heat energy to the load.

 

best,

 

.................john

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to be honest, anything in american ceramics called a "shino" lacks the geologic pedigree to be called a shino--but semantics.

 

In lectures and teaching situations I always refer to "American Shino" when talking about the non-Japanese veriety of the glaze here.  Ditto for "American Raku".  Both have roots in Japanese traditions,.... but are far removed as we practice them.

 

I have a small supply of the ground stone that is the sole basis for the Shino glaze in Japan which I have brought back with me from when I am working in Japan.  (I treat it like gold and replenish it from time to time. ;) )  Time spent with a shino ware potter gave me a recipe for obtaining nezumi (mouse gray) and also explained the glaze preparation process. 

 

Many Japanese potters use the stone alone as the glaze, suspended and fixed by the use of a decomposed seaweed solution binder.  That is it.  Some add a SMALL percentage of what would be a kaolin type clay..... like 5 to 10 percent.  The amount of clay added, if there is any, is varied to match the various batches of the stone on a batch-to-batch basis.

 

Aside from the chemical composition of the stone itself, the KEY here is the preparation of the stone.  It is ground in a stamper mill and is not water milled to round off the particles.  There is also a wide particle size distribution.  This allows the edges of the "chipped" particles to sinter early in the firing process well before tru fluxing and melting takes place. 

 

Japanese shino is also generally fired to a much lower endpoint than the American variety. More like about Orton cone 7-8.  BUT...... it is traditionally fired on LONG heating cycles..... like typically 48 hours on the up cycle.  The traditional body underlying the glaze is pretty white, open textured, and not all that mature.

 

Sometime in workshops and classes here in the US I will bring out a piece or two of actual Japanese shino glazed ware.  I'll tell the participants that its glaze name is something that they are very familiar with.  Many times.... they don't recognize it as Shino.  Most is quite different from the look of most American shinos.

 

American shino first got "derailed" from accuratlty modeling the Japanese precursor when lithuim was used in the mixtuire by Virgina Wirt.  Then the idea of carbon trapping from soluble soda compounds got started. (In Japan carbon trapping in shino is a defect.)

 

American Shino is to Japanese Shino what American Raku is to Japanese Raku.  Us Americans tend to like things "bigger and bolder and in-your-face".

 

best,

 

........................john

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Well that's the kicker isn't it. Use 'actual' cones.  I haven't been.  Therefore I cannot validate the state of vitrification of my test piece.  

 

Neil,

 

Moving forward, yes, use witness cones to verify heatwork. But for the test piece you've already fired you could do a porosity test to see if the clay is fully vitrified.

 

Make sure your piece is totally dry and take a very precise measure of its weight. Then soak the piece in water for an hour or so. Dry it off completely and measure the weight again. If there is no difference in the weight you're dealing with a fully vitrified piece. If the piece is heavier after soaking the clay is still somewhat porous. Porosity of .5%ish is acceptable, but the lower the better. 

 

Cheers,

 

Chris

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