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Hello all  : )

I just bought some cobalt oxide, I'd like to paint it directly on some leather hard stoneware vessels before bisque.

Can I ask if anyone knows which percentage of cobalt to amount of water should I use for best results? 

Thank you!

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KIf just starting out on this you could make different dilutions to see how it turns out.

Some mix the cobalt oxide with a little iron oxide for a softer blue.

Cobalt oxide ,a strong colourant,  little goes a long way.   

What is your next move? Clear glaze?  White glaze?

Should make a tile with stripes of your strengths of CoO

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just FYI, cobalt oxide can sometimes leave tiny specks of really dark color wherever you apply it.   cobalt carbonate is more easily dispersed in water or slip or whatever you like as a medium.

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On 7/28/2019 at 11:46 AM, missflo said:

Hello all  : )

I just bought some cobalt oxide, I'd like to paint it directly on some leather hard stoneware vessels before bisque.

Can I ask if anyone knows which percentage of cobalt to amount of water should I use for best results? 

Thank you!

I haven't used cobalt oxide, but for my blue slip, I use 97.5% porcelain and 2.5% cobalt carb. I put sodium silicate in and find that it works really well. The water ration for this slip never matters as long as it isn't super, super fluid. 

I used to just do oxide+water on leather hard pieces, but find the slips to work much better.

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I agree that cobalt crab is a bit more refined and does a better job with no extra strong blue spots. I have some mixed in a jar of water for the past 40 years it evaporates and I just add a bit of water when needed. I use it to draw and band a few pots a year.

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I'm not finding the reference just now, thought that oxide is soluble, carbonate is not - in terms of handling the powder, not after firing...

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34 minutes ago, Hulk said:

I'm not finding the reference just now, thought that oxide is soluble, carbonate is not - in terms of handling the powder, not after firing...

 

34 minutes ago, Hulk said:

I'm not finding the reference just now, thought that oxide is soluble, carbonate is not - in terms of handling the powder, not after firing...

I rule is to not eat on an unglazed surface that has colorants on it.

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45 minutes ago, Hulk said:

I'm not finding the reference just now, thought that oxide is soluble, carbonate is not - in terms of handling the powder, not after firing...

I see, well they are both insoluble in water, but the carbonate is a salt, it's just less concentrated than the oxide.    I think it's important to use caution with both

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9 hours ago, Hulk said:

I'm not finding the reference just now, thought that oxide is soluble, carbonate is not - in terms of handling the powder, not after firing...

Think the soluble one is cobalt sulphate or nitrate. Think some folk use it as onglaze washes. Not to be played with

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Another option is cobalt alumina...it's a bright blue and easy to see how much you are using. I used to use the cobalt oxide to do Chinese brush on pots.....on the glaze. It needed to look like the ink would look if you were doing the drawing on paper....that was my guide. I liked it better than carbonate because I could see the result better than with the carbonate. 

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