Re: Even Bonsai Potters like to do something a little different...

irene_b Sat Jul 24, 2010 6:59 pm

prestontolbert wrote:Irene-
To make this as short as possible, what we call raku is a firing process that is usually thought of as Japanese. In Japan the Rakurisan family produces work that is fired to 2300 F which is true Raku. It is glazed and wood fired with a deep black finish. American raku which was pioneered by Paul Soldner in California, is usually done in small gas kilns, fired to about 1800 F, and produces a rainbow spectrum of color, from lustrous black, red, gold, blue, to white crackle, as you see on Andy's work. ( I do very much like the raku piece with the vertical stripes. It makes me want to do some more raku!) After quickly firing to 1800 F or so, the red hot pottery is removed with hot tongs and placed in an airtight can filled with combustible. The absence of oxygen allows carbon to form in the unglazed clay turning it black, and making the colors appear in copper glazes and black cracks show in white crackle. Sadly raku is only suitable for teaware and tropicals, as it will spall in freezing conditions. I hope this makes sense.

Edit: I just remembered the background in my avatar was a massive raku sculpture. Nina Hole from Denmark built a 14 foot clay sculpture and fired it with wood. At top temperature we unwrapped it and threw sawdust and salt on it. It was the most beautiful fireball I've ever seen.

It cracks faster?

Stone Monkey Mon Jul 26, 2010 5:46 am

Preston

Thanks for the kind comments. I must admit I do love a Raku firing now and again. Also thanks for answering Irene's Raku question.

Irene

Raku is a low fired ceramic process as Preston described. Raku in Japanese means " To have fun, enjoyment". Because there pots are not vitrified they are not frost proof. So yes they would crack in the freeze / thaw if left outside over winter

Regards to you both

Andy

Stone Monkey Wed Jul 28, 2010 8:57 am

Peter

Thanks for your kind comment. Will you be at the Noelanders Trophy next year?

Regards

Andy

DWThomas Fri Jul 30, 2010 4:37 am

For what it's worth, upthread someone asked about raku firing. I have a (somewhat random sequenced) series of shots online taken during some raku firings at my local community college. This is done outdoors on a concrete deck with a stone wall around it, a sort of courtyard just outside the ceramic studios. The raku kiln and two Bailey gas kilns for the the regular work are all out in this courtyard under a shed roof to keep the elements off them.

You'll find the raku shots here.

It's pretty exciting, lots of action, smoke and smells. Somewhere along the way I expect to take this class myself (before I get too old and decrepit to handle stuff hot enough to glow orange ) affraid

The activities at the college are slowly sorting out after a major remodel and expansion. There is/was supposed to be a salt kiln and a small bronze foundry on this deck at some point. But the two gas kilns were supposed to be inside, alas, thanks to an architect who didn't like advice, the inside space created was ruled dangerously small and unsuitable and is now occupied by the electric bisque kilns. At least, after a two year hiatus, we can do high firing again.

DaveT

irene_b Fri Jul 30, 2010 7:39 am

Dave thank you for the link to the pictures!!! Very interesting!
Irene

graham walker Fri Jul 30, 2010 8:21 pm

Hi All,
I keep reading in these pottery threads about cone6 etc. or coning
I assume this is referring to temperature of vitrification?, could one of the potters please explain what it all means (in simple terms please!!!)
I have also seen reference to cones in clay types, is this the same thing
Is this term only used in USA, or do potters in the UK use the same terminology?
Thanks in anticipation
Graham

DWThomas Fri Jul 30, 2010 10:28 pm

Yes, it's a reference to firing temperatures, recommended and measured. The cones are pyrometric devices that slump over at their rated temperature and are often placed in a series of three in the kiln at target, target-1 and target-2 temperature ratings so one can see the temperature approaching the desired goal.

There is a reference chart here (from one of their makers).

I think they're universal, but perhaps I'm a victim of American ego, I'm sure someone will fill us in.

Compared with some numerical work they are a little tricky, as a "Cone 06" and a "Cone 6" are radically different temperatures.

You want the clay and the firing temperature to match for proper maturation/vitrification, but also to avoid:
Even Bonsai Potters like to do something a little different... - Page 2 Medium

Even Bonsai Potters like to do something a little different... - Page 2 Medium

A low fired clay vessel fired to cone 10 -- one can bet the owners of the adjacent pieces were not too happy, not to mention the studio assistants having to deal with the cleanup.

graham walker Fri Jul 30, 2010 11:31 pm

Thanks, DWThomas
It still seems to me, as an engineer, somewhat primitive.
Surely in modern times a temperature gauge would more accurately determine temperatures for firing etc??

Graham

DWThomas Fri Jul 30, 2010 11:57 pm

Well, sometimes simpler is better! I think one problem is that thermocouples and the like aren't all that happy inside a kiln at 1200ºC, especially in a salt/soda fire atmosphere. But another factor is there is apparently a bit of time/temperature related effects in firing, and the response of the cones is such that they tend to track that. We're in territory where I know just enough to be dangerous, so hopefully we'll hear from somebody who really knows! bom

Dale Cochoy Sat Jul 31, 2010 12:12 am

Graham,
The cones respond to heat work, not just heat. It's a composite of heat and time and other differences.
Yes, thermocoupled meters are used to read temps but you can't just heat a kiln to a "X" temperature and then shut it off. It is a combination of, mostly, time and temp.
What I do is use a temperature meter with a probe in the top AND bottom of the kiln and adjust air, gas to try to keep the temp at top and bottom raising at the same rate and temp. Once I get close to the temp I know my cones are rated for I remove the meter probes and look inside the kiln peep holes at the cones and watch them drop until the one drops that I am firing to. You often have to make adjustments to the kiln gas/air to keep them firing the same top and bottom.
Yes, cones are used commonly all over the world.

Here is a good shot of my gas kiln with the two meter probes in the peep holes I use top and bottom. ( I use a FLUKE meter). You can see the meter better in the 2nd shot sitting on top of two pieces of 4x4. and a shot of the two cone packs removed from my kiln top and bottom. They are almost identical which is exactly what you want. These two packs are fired to about cone 9 1/2. 9 is down ( actually they are caught on the #8 cones in front of them so they stopped bending) and 10 about half way.

Even Bonsai Potters like to do something a little different... - Page 2 Kiln_h10

Even Bonsai Potters like to do something a little different... - Page 2 Kiln_n10

Even Bonsai Potters like to do something a little different... - Page 2 Cones10

Having said all that.....many newer kilns are micro processor controlled such as my electric bisque kiln. I don't even use cones with it any longer as I have the computerized firing down so well that I merely make a few adjustments to the temp increase/hr as I fire. Even newer kilns are almost walk-away ( although I wouldn't! ). There's not much tricky to bisque firing but often with high firing/glaze firing you need to make different adjustments due to clays, glazes, finishes, etc.
Gas firing is a completely different animal than electric firing BTW. You have to keep a better watch on everything you are doing when an open flame is involved!

Sounds pretty easy doesn't it?

You can see in DW's picture.....'Stuff' Happens!

DWThomas Sat Jul 31, 2010 3:37 am

Thanks Dale! Nice setup.

It occurs to me another consideration is --- act surprised now --- MONEY! Twisted Evil

In my previous life I was entangled with computerized industrial control systems. With the right sensors, equipment and system configuration it's possible to specify temperature profiles vs time, air/fuel ratios and all sorts of things. Only problem is, the control system could cost way more than the kiln (maybe more than four or five kilns!) And, as Dale suggests, the computer system still can't look inside and see how the pieces look.

DaveT

graham walker Sat Jul 31, 2010 9:45 am

Thanks, Dale and Dave for the concise and clear explanations
I now understand much more

Graham

prestontolbert Mon Aug 02, 2010 11:00 pm

Why don't we start a firing thread?

rock Wed Aug 04, 2010 11:26 pm

prestontolbert wrote:Why don't we start a firing thread?

or just start a fire Shocked

rock Wed Aug 04, 2010 11:35 pm

DWThomas wrote:Thanks Dale! Nice setup.

It occurs to me another consideration is --- act surprised now --- MONEY!

In my previous life I was entangled with computerized industrial control systems. With the right sensors, equipment and system configuration it's possible to specify temperature profiles vs time, air/fuel ratios and all sorts of things. Only problem is, the control system could cost way more than the kiln (maybe more than four or five kilns!) And, as Dale suggests, the computer system still can't look inside and see how the pieces look.

DaveT

Right Dave Thomas (wendy's? ). All those are available especially in industry. The home grown potter is very happy for the most part with cones, we dont need that kind of pinpoint temps. Cones are interesting check out..Orton more than you would ever care to know...http://www.ortonceramic.com/resources/video/

rock Wed Aug 04, 2010 11:38 pm

Even Bonsai Potters like to do something a little different... - Page 2 Confuc10

prestontolbert wrote:Why don't we start a firing thread?

Rob Addonizio Thu Aug 05, 2010 9:24 pm

Ah cones....

Did a bisque load in my gas kiln last night. Having cones is a necessity unless you have a kilnsitter. The load got overfired by two cones. It was hard to see them in the kiln, and in hind sight I will have to place them higher and farther away from the peep hole for visibility.

Note to self:
If cones are not visible and you are within 100 degrees of final temp., shut it down!!!! The reason must be attributed to the fact that the cones have melted......DOH! Rolling Eyes

prestontolbert Mon Aug 09, 2010 5:42 am

All this talk about cones and thermocouples gets me thinking about the color of temperature. I know potters who only use the color of the kiln and the look of the pots to gauge temperature. I'm not one of them. I use both cones and a pyro in my kilns, but I'm trying to learn the art of color reading. On another subject, what do you other potters do about eye protection. I use dark shades to peek in the kiln, but some seasoned pros(Tom Coleman, Paul Geil) claim that light from even stoneware temps isn't harmful to the eyes. What do you all think?

Stone Monkey Mon Aug 09, 2010 12:19 pm

Preston

I have always used dark glasses to peer into the kiln. Just to be on the safe side Very Happy

as you never know. I fired my gas kiln this Saturday gone up to cone 10/11 as I was doing some firing for a friend to wanted a Celadon Glaze on some ceramics. I threw in some Ash Glazed Tea Bowls and they came out a treat. I thought I would also put some of my normal cone 6 - 8 glazed pots in the firing and over fire the glaze to see what the result would be. There was some good and some not so good, but hey thats the joy of experimentation.

As Rob said I also have a hard job of seeing the cones tipping over in the bright heat, even with my glasses on, so perhaps I should learn to fire by colour instead of cones & pyro. Will post pics of the high firing stuff when I have put my photography head on and taken some pictures.

Regards

Andy

prestontolbert Mon Aug 09, 2010 7:19 pm

Andy-
One way to see cones is to use a flashlight. It sounds counterproductive but it works. For gas firing, especially celadons, I wouldn't try to fire to color, they're just to finicky. I can't wait to see your results.

Stone Monkey Wed Aug 11, 2010 5:50 am

Thanks for the tip Preston Very Happy

I have changed my tack on the tea bowls and took them a little step further to what I think is a better and more Japanese inspired finish which has captivated me for a while now. Just loved the idea and Stone Monkeyed it Wink

Even Bonsai Potters like to do something a little different... - Page 2 Img_0511

Even Bonsai Potters like to do something a little different... - Page 2 Img_0512

Even Bonsai Potters like to do something a little different... - Page 2 Img_0513

Thanks for looking

Regards

Andy

landerloos Wed Aug 11, 2010 6:53 am

Peter

Stone Monkey Wed Aug 11, 2010 9:53 am

Cheers Peter cheers

LANCE Wed Aug 11, 2010 11:36 am

Et Al, I have found this thread very useful, and the pots are excellent.
As a relative beginner I would be most interested in a thread on glazing and firing.
Simon Leach was mentioned, I recommend his videos on YouTube to anybody interested in kiln building , ceramics or pyromania in general.

Stone Monkey Wed Aug 11, 2010 12:27 pm

Phil

Start a new thread on what you would like to know and I am sure we will all give you our two penneth worth Wink

Ditto about Simon Leach videos. I have been watching them since he first started, about 2 years ago now, they are very beneficial indeed for all level of people crazy about mud Shocked

Happy potting

Regards

Andy

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