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Raku - Leaving Pots In Kiln


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#1 jpdes

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Posted 24 July 2014 - 11:53 AM

I am planning to convert an old electric kiln to a raku kiln.  I am wondering if there is any reason not to introduce the smoke and reduction atmosphere into the kiln rather than remove the ware and reduce in separate containers.  Combustibles would be added to a chamber built underneath the kiln (after turning off electricity to the elements) and any openings in the kiln closed up.  It would then be left to cool on its own and opened the next day.

 

In my research so far most of the reasons not to use an electric kiln as a reduction kiln are not applicable

 

- the kiln will be outside on a large rural property with lots of airflow so toxic gases, carbon monoxide and upset neighbors should not be a concern.

- I'm not worried about element deterioration.  When they no longer function adequately the kiln will be further converted to operate with a gas burner

- there is no need for rapid and/or multiple firings

 

I've read the postings here and found other sources that describe how to create a reduction environment in an electric kiln but all the sources I found dealing with raku using an electric kiln involve removing the items and reducing in containers.  Do raku glazes require a fast cool to effect their color reactions or would the results be similar if left in the kiln after an adequate reduction environment had been created?

 

Any insights or suggestions will be greatly appreciated.

 



#2 TwinRocks

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Posted 24 July 2014 - 12:04 PM

I have limited experience, but part of the point is to expose the ware to combustibles when it is at its peak temperature, and then cool the ware rapidly to capture the colors we associate with raku firing. If it was cooled more slowly, in theory you may end up with less color.

I also like the effect alcohol has on raku, it can lead to some of the most eye dazzling results and leaving it in wouldn't allow for alcohol application.

Also, if you are using glazes and want crackling, you would want to take it out for that reason as well.

Long story short: I am pretty sure it has to be taken out hot or it isn't considered raku.

#3 Tyler Miller

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Posted 24 July 2014 - 12:18 PM

Yeah, quick cooling combined with the post-fire reduction is a part of the process.  A copper pigmented glaze gets its rainbow effects, for example, from the combustion in the reduction chamber paired with rapid cooling (and maybe burping the chamber).  The reduction only partially takes hold.  Introduction combustibles to the kiln would give you reduction and colour change, but not the wild effects of raku.

 

Crackle effects and horse hair/naked raku also need you to remove the pieces from the kiln.



#4 Marcia Selsor

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Posted 24 July 2014 - 12:58 PM

The glazes would be completely different because they would be oxidized and not reduced. A simple description would be a copper luster would turn 

green or turquoise and the body would be white not black.



#5 neilestrick

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Posted 24 July 2014 - 01:02 PM

In addition to the issues of reduction posted above, dumping a bunch of combustible material into the top of a hot kiln is a very dangerous thing to do. It ignites so rapidly that there's good chance of catching a fireball in your face.


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#6 Benzine

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Posted 24 July 2014 - 01:42 PM

There would also be the issue, with the carbon build up.  On on of my first firings, I had too much fuel going into the kiln, so I had some carbon build up on the walls afterwards.  This easily burned off, in subsequent firings.  However, based on that, and what my reduction bins look like, I would imagine repeatedly dumping combustibles, in the kiln, and letting them sit there and reduce, would cause the interior of the kiln to look like that of a meat smoker.


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#7 Idaho Potter

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Posted 24 July 2014 - 06:38 PM

I agree with all comments/replies to your question.  To me the most important part of raku is the post-firing reduction.  As Marcia said, a copper based glaze can give you so many iridescent  colors and luster if the pot is removed from the kiln and placed in the reduction can.  If you want to let it cool gradually, do it in the reduction can with the lid tight  so the glaze doesn't re-oxidized--'cause then you'd just have a green pot.

 

Also, try under-firing and/or over-firing to get different effects with the same glaze.  What a difference of two minutes either way can make in the outcome.

 

So, if you don't like the outcome, just re-fire (maybe even layer on a different glaze) raku is fun and surprising, so enjoy it.



#8 John Hertzfeld

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Posted 24 July 2014 - 07:49 PM

as Niel said, there is a huge difference between placing a hot item into a room temp chamber filled with combustible and trying to jam enough combustibles into a 1000F chamber before you ignite yourself and the building you are in, and go out in a blaze of glory. these aren't oven temps, these are a dangerous environments that must be respected.

 

get a metal trash can and fill it with leaves or whatever, have a hose ready in case things go awry.



#9 jpdes

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Posted 24 July 2014 - 07:53 PM

Thanks for the thoughtful replies.  I thought that might be the case.  

 

Can anyone suggest a book or reference source that gives a technical description of raku glaze behavior ie. at what temperatures various reactions occur, how rapidly does cooling have to happen to maximize color effects, etc.?  So far I've mostly come across the "do it this way" descriptions.



#10 jpdes

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Posted 24 July 2014 - 08:01 PM

Thanks for the safety warnings.  I assure you safety of person and property will get full and proper attention at all times.    



#11 Marcia Selsor

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Posted 25 July 2014 - 06:19 AM

There are many books out there.

Steve Branfman's Raku; A Practical Approach 2nd Ed. or Mastering Raku

Robert Piepenberg Raku Pottery (1970)

Advanced raku Techniques by Bill Jones

Raku Art and Technique by Hal Riegger , 1970

There are many newer books out there. Also you can go to CAD and look up the subject.

I will be having a dvd coming out soon covering Raku and some other techniques. 

Marcia



#12 jpdes

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Posted 25 July 2014 - 10:04 PM

Thanks Marcia.  I'll track down those I am not yet familiar with.  Having been enlightened by many of your responses on the forum I look forward to your dvd.



#13 Marcia Selsor

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Posted 25 July 2014 - 10:06 PM

Thanks. it is being edited as we speak.. So to say.
Marcia




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