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bruce, i am sorry that i do not read chemical formulas. please, what does this really mean in ordinary terms?


just in case Bruce doesn't see this I'll jump in. In ordinary terms Roy reformulated it and his version was tested for cobalt leaching and Hesselbreth says it should be okay for functional pots. The main change Roy made was decrease the cobalt and add a titch of strontium.

Roy's recipe as on the link Bruce posted is:


Ferro Frit 3134............. 37.00

Custer Feldspar............. 16.00

Strontium Carbonate......... 4.00

EP Kaolin................... 26.00

Silica...................... 17.00


Cobalt Carbonate............ 2.50

Rutile...................... 4.50




I'm in stitches over a titch of Strontium! :P

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Cobalt Carbonate when fired turns into Cobalt Oxide and Carbon Dioxide. The same way that we use Calcium Carbonate to add Calcium Oxide you can use Cobalt Carbonate to add Cobalt Oxide.


'The theoretical oxide form has 93% CoO while the carbonate has 63%. So if you want to switch from the oxide to the carbonate in a recipe, multiply by 93 and divide by 63. To switch from carbonate to oxide multiply by 63 and divide by 93.' 


Joel - I just love these technical glaze chemistry posts despite the fact that they make me realise how much you know that I never will! Oh to be young again..........

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Knew a potter who "blessed " many of her glazes with a pinch,( not snitch, or was that titch), of Rutile.... Can only get away with this level of science when you know what you're doing.

Or perhaps she had a heap of rutile she was trying to use up before departing the planet, I don't think so though.

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well, after all these days, the plate with the vinegar test appears to be unaffected by that acid.  good news!  i think i will wash it and use it for french toast with a titch of maple syrup.  guess what?  spellcheck doesn't raise an eyebrow over titch. :blink:

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