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Kathy321

Firing Organic Additions To Clay

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Kathy321    0

I have been reading Katheen Standen's book 'Additions to Clay Bodies'. Although it sounds like she is using an electric kiln in at least some cases, she doesn't talk much in the book about firing clay containing organic or combustible additions. I would like to try some of the ideas in the book but am wary of ruining my electric kiln by firing combustibles. Can anyone with knowledge of this book or the techniques described comment on this?

Thanks,

Kathy

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JBaymore    1,432

It will take SOME life off the elements. How much is hard to estimate. Less than many people will tell you. It is not "death incarnate" to elements. Do a cle an bisque between "carbonaceous materials " firings to get as much life out of them as you can.

 

Reduction electric kilns are common everywhere I work and go in Japan. They depend on either wood fireboxes (not for heat), on charcoal trays, or on small gas burners. They are designed with small flues that are used to vent the CO and other byproducts of combustion. They typically have THICK elements. Way thicker than the usual US standards. This is to give them a bit more longevity before replacement. Some have surface mount strip / ribbon elements.

 

Replacement of the elements more often than straight oxidation firing is the "cost of doing business" for having reducing conditions in an electically heated kiln.

 

Be aware of the potential VENTING issue there; lots more gunk stuff produced than in "clean" firings.

 

best,

 

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

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PeterH    87

John,

 

Firstly, total agreement. Most kiln elements rely on a protective layer of oxide to avoid corrosion. So if a mildly

reducing firing reduces the thickness of the protective oxide layer, it makes sense to re-establish the oxide layer

by ensuring that the next firing is in oxidation.

 

My question is: does it need to be "a clean bisque", or will a glaze firing do as well?

 

Regards, Peter

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JBaymore    1,432

Could be either... just not a firing with a lot of reduction. Doesn't have to get all that hot... just enough t re-establish the oxide coating.

 

Years ago there was a US produced reduction electric made by some friends I knew .... Reduction Productions "Stoker". Used a charcoal tray at he bottom. Worked well. Was not well recieved .... because everyone "knew" that you can't do that and get good results :rolleyes: . (tell that to Kondo Uzo)

 

best,

 

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

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Kathy321    0

I was thinking of pre-firing, to burn out the combustibles in say an old propane gas oven outdoors since that would be easy to set up. The idea being that 400 or 500 degrees would be hot enough to do the trick.

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I use combustibles in my electric kiln but only clean stuff like nut shells, leaves, rice, coffe ground etc. to get a volcanic surface. I would never use oxides in the el. kiln! Here in Switzerland one cannot buy el. kilns with reduction possibilities. You have to throw moth balls into the kiln if you want reduction. Imagine the stink :angry:

Never in my life!

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JLowes    28

Russel Fouts in a PMI article was showing how he gets smoking effects on pots in an electric by wrapping them with paper and then in aluminum foil and firing them to around 1,000 F.  Perhaps this could be an avenue to explore.  In my saggar firing for fuming I use aluminum foil (heavy duty commercial kitchen foil) and it starts to break down around 1,000 F, but I fire to as high as 1,350 F with the shell of foil intact, but I don't stay at that temperature for long.

 

Hey, I'm getting an idea here....

 

John

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I fire combustables periodically in my clay bodies (rice, sticks, clean cat littter, etc) and 'accept it' as part of the usual wear and tear of the kiln, if you really want the effect then element wear is part of getting it.............but having said that......

 

-I vent the kiln throughout a slow bisque fire to 1000C to clear off all the carbon,

-most of my firings are regular wares with my interest in combustables going through a phase periodically when I'm trying to achieve something I really want,

-kiln elements will be replaced when they need to be replaced and is part of the business of making ceramics and is built into the costs of doing ceramics

 

I guess worrying about the elements of a new kiln for a few firings is like worrying about using the 'good' china.......enjoy using it and risk a chip or crack or don't use it and let it sit pretty

 

Peepholes and vents open for a long bisque, give the chamber time to clear out and fire combustables intermittently.....your kiln will be fine

 

Irene

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Kathy321    0

Thanks for suggestions! Unfortunately my kiln is in my house (seemed like a good idea at the time) so venting is a problem. It is vented with ducting and a fan but a bit leaky around the lid - may have to add a hood vent.

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JBaymore    1,432

If stuff is leaking out in general "normal" firings.... your kiln vent is not installed or adjusted correctly.

 

best,

 

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

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Marc: yes, exactly. And thank you for the compliment! Very kind of you.

 

Kathy: awwww, a hood vent or a bendable "chimney" out the window is a must! Don't endanger your health.

 

Evelyne

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alabama    144

I have been reading Katheen Standen's book 'Additions to Clay Bodies'.   but am wary of ruining my electric kiln by firing combustibles. Can anyone with knowledge of this book or the techniques described comment on this?

Thanks,

Kathy

 

Hey,

     I have had 11 years of fire science and 24 years of primitive pottery.  Paper, an organic material, burns at 451 degrees.

Hence the movie 451 Farenheit, I think it was about the Nazis mass burning of books.  So, I'm thinking that pre-heating combustibles in a oven up to 500

degrees would only make it carbon and for you to burn the organic material out would have to be in the heat range of about 800 degrees which should burn

anything organic to ash.  Since ash isn't a vapor like salt or soda it should vent itself out the kiln or settle in the bottom of the kiln, not on the elements.  Carbon can be deposited on pottery between 500 - 700 as the vessel is cooling down.  Have you ever watched carbon burn off a very hot pot doing raku?  If the pot is too hot, the organic material burns off leaving no marks, then as the vessel cools the hair or other organics leave carbon traces until the vessel cools beyond the point carbon can collect.  So there is a small window of opportunity carbon can be put on vessels.  But since it is carbon and carbon burns, it can be burned off and tried again if the desired effect isn't achieved.

     Anyway, I don't think burning anything pertaining to organic material will hurt an electric kiln.  It should and probably will smoke as the organic

material breaks down.  Some independent testing may apply and since you're dealing with physics results should be constant with no variation.

Hope this sheds some insight.

Thanks,

Alabama

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