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How To Turn Cobalt Blues Into Something Much More Subtle?


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#1 oly

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Posted 18 March 2014 - 04:10 AM

I've been experimenting with cobalt blue, even at 1/2 percent it's very strong colouring and I want to produce something much more subtle (hopefully saleable!), like a sort of pale duck-egg blue or pale grey-blue, perhaps even with a tiny hint of jade to it. 

 

I think I will have to reduce the cobalt down to something like a quarter or an eighth of a percent.

 

I will soon be firing some more test pieces with differing percentages of oxides this week and hoping someone can give me some ideas, to help set me in right direction.

 

If it was a paint, I'd just be adding a little grey or pale green I suppose, but with glazes I'm finding most don't seem to do what I expect!

 

Appreciate very much any ideas to set me on the right sort of path! 

 

By the way my kiln is electric oxidising and firing to 1230 with 45min soak.



#2 TJR

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Posted 18 March 2014 - 07:49 AM

You could try adding tin or zircopax, you can also cut it with iron oxide. Give me a day and I will send you a recipe for my blue colourant. I am not in the studio right now. Actually, I am on my way to teach my bad Gr.10's.

Tom.



#3 neilestrick

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Posted 18 March 2014 - 09:09 AM

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.


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#4 oly

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Posted 18 March 2014 - 09:34 AM

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?



#5 Dick White

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Posted 18 March 2014 - 11:33 AM

We have two things going on here in color theory - saturation and hue. Cobalt is a very powerful colorant. The only way to reduce the saturation, i.e., intensity, and make it more pale is to dilute it's concentration. This can be done either by using less per unit volume of glaze or using cobalt carbonate rather than cobalt oxide.(There is less elemental cobalt in a gram of cobalt carb than cobalt oxide). To shift the bright harsh blue of pure cobalt to a more pleasing hue, other oxides like iron, rutile, copper, or chrome can be mixed in to take the bright edge off the blue. It is also possible to get to a turquoise or robin's egg blue without cobalt, through a high alkaline copper glaze.



#6 neilestrick

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Posted 18 March 2014 - 02:28 PM

 

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?

 

 

I've used very few glazes over the last 20 years that looked good with just cobalt. It's too bright, intense, flat. Deeper, more complex colors are achieved by adding other oxides.


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#7 Min

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Posted 18 March 2014 - 03:30 PM

 

 

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?

 

 

I've used very few glazes over the last 20 years that looked good with just cobalt. It's too bright, intense, flat. Deeper, more complex colors are achieved by adding other oxides.

 

I agree with Neil on diluting the harshness of the cobalt with other colorants. Gosu, or asbolite, used in Japan is an impure cobalt. It had manganese and iron in it. Much more subtle blue.  Used in brushwork with matcha green tea as the medium for brushwork but the same toned down blue is achieved in glaze or slips.



#8 oly

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Posted 18 March 2014 - 05:33 PM

 

 

 

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?

 

 

I've used very few glazes over the last 20 years that looked good with just cobalt. It's too bright, intense, flat. Deeper, more complex colors are achieved by adding other oxides.

 

I agree with Neil on diluting the harshness of the cobalt with other colorants. Gosu, or asbolite, used in Japan is an impure cobalt. It has manganese and iron in it. Much more subtle blue. It is used in brushwork with matcha green tea as the medium for brushwork but the same toned down blue is achieved in glaze or slips.

 

 

 

 

 

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?

 

 

I've used very few glazes over the last 20 years that looked good with just cobalt. It's too bright, intense, flat. Deeper, more complex colors are achieved by adding other oxides.

 

 

I am going to do some serious testing this week with smaller percentages of cobalt and other oxides as suggested. I've now got a good idea of where to start so very many thanks for the information.



#9 Pres

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Posted 20 March 2014 - 09:41 PM

Base glazes that have Strontium in them as replacement for Barium will also do a little different color with cobalt.


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#10 Mudslinger Ceramics

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Posted 20 March 2014 - 10:33 PM

 

 

 

I almost always cut my cobalt with either red iron oxide, rutile or copper carbonate, sometimes more than one. Depends on the base glaze as to which one gives me the color I want. Most of the time I use 0.3%-0.5% cobalt, and about 2% iron, 2-4% rutile, 2-3% copper.

Thanks Neil, I'm guessing that gives richer, more three-dimensional colours?

 

 

I've used very few glazes over the last 20 years that looked good with just cobalt. It's too bright, intense, flat. Deeper, more complex colors are achieved by adding other oxides.

 

I agree with Neil on diluting the harshness of the cobalt with other colorants. Gosu, or asbolite, used in Japan is an impure cobalt. It has manganese and iron in it. Much more subtle blue. It is used in brushwork with matcha green tea as the medium for brushwork but the same toned down blue is achieved in glaze or slips.

 

 

 

Hi Min

 

Any idea of the proportions of cobalt to iron and manganese in the Gosu?    

 

 

ta,

Irene


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#11 Babs

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Posted 21 March 2014 - 01:24 AM

Bernard Leach

 

Bernard Leach in A Potter's book has a formula for "Chinese Cobalt".
It is:

Manganese oxide 40
Black Iron Oxide 30
Black Cobalt Oxide 20
Calcined Ochre 10

I read this recently in his book, refined when he was living in Japan.

Haven't tried it but may be close to Gosu if that was the colour he was pursuing.

Perhaps John would know of this.

 

 

 

 

 

 

 

 

 

I agree with Neil on diluting the harshness of the cobalt with other colorants. Gosu, or asbolite, used in Japan is an impure cobalt. It has manganese and iron in it. Much more subtle blue. It is used in brushwork with matcha green tea as the medium for brushwork but the same toned down blue is achieved in glaze or slips.

 

 

 

Hi Min

 

Any idea of the proportions of cobalt to iron and manganese in the Gosu?    

 

 

ta,

Irene

 



#12 PeterH

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Posted 21 March 2014 - 06:49 AM

In http://en.allexperts...rglaze-gosu.htm it says

Gosu is the Chinese name for Black Cobalt Oxide. It is a pure cobalt pebbles with a hint of manganese that

is rarely found even in China. If you are trying to achieve the gosu that is found on the ware from the Meiji

Period, you should try a process designed by Leech entitled Chinese Cobalt. (Recipe as given by Babs).

... it also gives a contact name, if you want to follow this up.

 

In Pioneer Pottery Michael Cardew gives his recipe for a subdued/less-strident cobalt blue:

20% Cobalt carbonate

20% white tin oxide

10% black manganese oxide

10% talc schist

15% plastic red clay ------------------- corrected

20% china clay ------------------------- corrected

05% red iron oxide

... mixed and ground well. With a warning that cobalt gives a reddish colour if applied too thickly.

 

Personally, I would like to know the recipe that Sam Scott uses.

http://media-cache-e...3c6aeef932d.jpg

 

Regards, Peter

 

Thanks to C Banks

 



#13 C. Banks

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Posted 21 March 2014 - 07:28 AM

I'm wondering if a decimal got misplaced on a few ingredients.


*unfortunately my upbringing did not allow acess to art schools but this idea of 20 coc03 20 sn02 and 10 mn is less than subdued and not something id want to mix up nvm test or even pay for

**please excuse the tone - I envy folks who are able to post with 'warm' tones

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#14 Min

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Posted 21 March 2014 - 12:03 PM

When I used to do mocha ware I mixed parts by volume of 1 manganese dioxide, 1 red iron oxide, 1/2 cobalt oxide in the vinegar then put that over a slip containing 10% red iron oxide. An opacified white glaze overtop. More blue, more cobalt, less blue more iron and manganese. The white glaze turned the iron slip to gray which helped tone down the blue a bit more.



#15 Babs

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Posted 22 March 2014 - 02:52 AM

Mocha ware? I thought that involved nicotine?



#16 Min

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Posted 22 March 2014 - 10:39 AM

Mocha ware? I thought that involved nicotine?

 

I believe it originally used a tobacco tea but vinegar works too, I used apple cider and it works really well. 



#17 smastca

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Posted 23 March 2014 - 02:44 PM

Hey Oly - found this on pinterest.  Not sure who was the originator but does this help?  You will have to translate the ingredients though.

http://media-cache-e...1752834af90.jpg






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