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changing cobalt based colors in glazes?

updated sat 9 mar 02


Ian Currie on fri 8 mar 02

Hi Gary

I caught your post by good luck... You are almost right - it is magnesia
(MgO) that will change cobalt blue to a more purple colour, especially in
low alumina magnesia glazes. So you will need some magnesium carb., or
talc, or dolomite... in there to get the effect. The "redish" is coming
from pyroxene crystals that are usually pink with cobalt. Same crystals
will give lovely golden yellows with a little iron oxide (~2%?).

See plates F, H and I on page 78 of "Revealing Glazes".

And thankyou for the comments!



> From: Gary Elfring
> Organization: ESF
> Reply-To: Gary Elfring
> Date: Thu, 7 Mar 2002 12:53:20 -0600
> Subject: Changing cobalt based cors in glazes?
> I went to an Ian Currie glaze class last year and have
> since made a number of grid tiles. I have the perfect
> (for me ) Celadon glaze and a great standard base
> glaze (all cone 10 R).
> I want to do some simple line blends using, Cobalt Carb
> as a colorant, with my base glaze.
> I remember seeing pictures that showed that some ingrediant
> altered the color produced by Cobalt, from the vivid blues to
> a more redish blue. I think it was either Manganese or Magnesium,
> but it could be something else. I can't find this mentioned in
> either of the 2 books I have from Ian. Anyone know what metal
> alters the color of Cobalt in glazes, and maybe what percentage
> would be a good place to start my line blend at?
> PS: I strongly recommend Ian's class for anyone interested in
> making their own glazes!
> --
> Best regards,
> Gary
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Michele Williams on fri 8 mar 02

Is there any chance of getting the new glaze recipe for red with cobalt that
seems to be developing in this thread? I'm a newbie, have only one semester
of kiln/studio availability to me before it's all over (sob!) and I have a
design that begs for a blue glaze that breaks red at rims and edges. I'd
love to have a bit of a head start....

Michele Williams