[Jewelry making - Article 00122] - Re: [Orchid] Cobaltocalcite pink to blue?

[Noel Yovovich]

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    Wayne, Actually, ceramic glazes with cobalt will come out blue
    whether you start with oxide or carbonate, fire in oxidation or
    reduction, at low temps or high (1500 to 2400 degrees F). I don't
    know what the minimum is, since ceramic clay bodies don't mature (at
    least, the ones I know about) any lower than that. What this
    suggests to me is that cobalt "prefers" to be oxide given half an
    excuse. For what it is worth, Mg can be used to produce purple
    glazes, with some difficulty. It tends to do dark brown. So, if
    turning the cobalt blue turned the Mg brown...yuck? And, dolomite
    (also used in ceramics) *is* pretty soft stuff...  I should leave
    this whole area to the experts!if you'll tell me the kiln
    tempaerature used to oxidize the cobalt carbonate to the oxide, I'll
    experiment with some pieces of the pink material and pass the results
    on to the Orchid network. I bought a couple boxes of it a few years 
    ago in Tucson! My guess is that the dolomite will just break down... 

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