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G200 In Ohata Glaze

glaze ohata g200 custer

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#1 annschunior

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Posted 03 January 2014 - 05:38 PM

I've used this ^10 Ohata recipe for years.
G-200 43.4
whiting 6.5
Talc 5.7
EPK 5.7
bone ash 9
flint 19.5
iron 9.7 
 
I've made the change from the old G200 and I don't like it. I've tried both Custer and the G200HP/minspar combination. They look about the same as each other, but not the old Ohata. The new formulation isn't nearly as bright and firey as before; more of a purple tone than orange.
 
Has anyone else noticed this and tried to formulate it back to its old look? If anyone else has been working on it, I'd just as soon not start from scratch. Or, could someone suggest where I might start with a reformulation.


#2 bciskepottery

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Posted 03 January 2014 - 05:47 PM

The recipe I use contains only Custer:

Kaki ^10
43 Custer
19 Silica
6 Talc
7 Whiting
6 EPK
9 Bone Ash
100

10 Red Iron Oxide

#3 JBaymore

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Posted 03 January 2014 - 05:48 PM

Or, could someone suggest where I might start with a reformulation.

 

Insight glaze calculation software. Demo version is free at Digitalfire.com.

 

best,

 

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


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#4 Mark C.

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Posted 03 January 2014 - 05:50 PM

I have not used Ohata in many years and it was made with Kingman feldspar which I have a lifetime supply of. I switched over to another iron red recipe. The new custar is a bit different than the old-you could look for some old G200 from retired potters or maybe a backstock at suppliers.

Once you find a potash feldspar that you like I suggest buying enough to last a long time. Mined materials always change over time as the deposit is worked into new areas.

Also is your clay body the same as well as the firing atmosperes and fuel sources (natral gas vs propane)

I know that these two fuels make the same glazes look very different depending which is used.

M


Mark Cortright
www.liscomhillpottery.com

#5 bciskepottery

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Posted 03 January 2014 - 05:52 PM

You can also run a piece through a bisque firing to brighten up the kaki . . . like to a tomato red. Have done that on a couple pieces that came out more liver red or dull in color.

#6 Mark C.

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Posted 03 January 2014 - 07:09 PM

Another thought is your talc? the same or some newer different talc-talc sources have changed radiically through the years.

I have a few glazes that do not at all work well with the newer talcs.

M


Mark Cortright
www.liscomhillpottery.com

#7 Venicemud

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Posted 04 January 2014 - 10:35 AM

The advice to refire in your next bisque firing will probably do the trick.  A brighter red  is generally obtained if O'Hata is fired in oxidation rather than reduction. - in my experience.

Joan.



#8 Wyndham

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Posted 04 January 2014 - 10:53 AM

you might try a line test by  boosting the bone ash to 10% cut the iron to 9% and/or subbing some of iron with Spanish red iron ox.

When and how much reduction do you do, purple sounds like reduction issue. Anyway, just a few ideas to try.

 

Wyndham



#9 JBaymore

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Posted 04 January 2014 - 11:48 AM

Purple says heavy reduction to me.

 

I fire Lyon's Ohara Kaki (the original name) in the nobori, and becasue I fire each chamber differently can get different results all in "one" firing. Heavy early reduction and maintanined throughout the climb, ...... purplish for sure. In my oxidatiion chamber (oxy. after a light reduction in the bisque range) get the best kaki (persimmon) reds.

 

best,

 

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


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#10 bciskepottery

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Posted 04 January 2014 - 04:16 PM

Here's a couple links of possible interest:

http://www.clayworks...e1234374884.pdf

Looks like G-200HP is being discontinued and will be replaced with an EU substitute from Spain:

http://www.highwater... on Feldspa.pdf

#11 annschunior

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Posted 09 January 2014 - 11:32 PM

Thanks for all your ideas. That gives me some things to work with. However - It isn't the firing. I've fired both the old bend G200 and 200HP with minspar side-by-side in same kiln and see the difference. I'm using the same talc. I know that mixing 70/30 G200HP/minspar is supposed to be the same as the old G200, but is isn't. I'm almost wondering if there's a particle size difference. I'll be contacting Axner for the old blend, and you can bet I'll buy a LOT of it. Thanks for the warning that G200HP will be discontinued, too. 



#12 Wyndham

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Posted 10 January 2014 - 12:34 PM

Another area to explore is adding some fireplace ash, which has some basic fluxing materials and start to look back to the origins of this type of glaze.

I think we may have refined our glazes too much from the original early (red)clay/ash glazes and lost some of the natural spontaneous effects that simple materials can give.

It might be worthwhile to explore this area.

Wyndham







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