Turquoise Matt Glaze Recipe, Cone 10

[TJR]

Had a bucket of it.

Here's the recipe I have;

Neph Sy    58

Barium Carb  27

EPK             6

Flint             7

Lith Carb.    3

Total         101

Copper carb10

Bentonite    2

I'd rather use Strontium Carb instead of barium carb

I think I got this recipe out of Ceramics Monthly. Hadn't used it in years. Now I have a bucket with 2 inches of glaze in it.

Thanks for your help

TJR.

Does this glaze look familiar to anyone? Of course I will test it.

[Mark C.]

This looks similar to my recipe cone 9/10 barium matt from memory(not a good gauge)

I can look in studio this weekend

I will add Strontium Blue is always lighter for me as well-I use the barium on non food surfaces

Mugs and cup outside -white on inside and lips.

Mark

[Marcia Selsor]

Alisa had one I sent her too. She sent it back to me when I couldn't determine which one I had sent her.I call it "the one".

She has done a huge amount of testing.

Marcia

[TJR]

Thanks you guys. This is pretty fast service. What is the ratio to convert from barium to strontium. I know you need more. Maybe I should look at the wedsite.

TJR.

Mark, I've seen your glaze on your ware shelves. This might be the same glaze? It's called Carmen's Turqoise Blue. I do not know Carmen.

T.

[PeterH]

I've always read the substitution is gram for gram.

 

But a Molar substitution (molecule for molecule) would be 75% of the weight of the Barium Carbonate, as barium weighs more than strontium. 74.8% actually.

 

That makes a lot of sense, as I believe that the Cu++/Cu+ balance is different because of the different redox chemistry of

Ba & Sr. Which means that you need more total Cu to get equal amounts of the colourant Cu++.

Regards, Peter

I can probably chase up a reference if anybody wants to see one.

[TJR]

 

I've always read the substitution is gram for gram.

 

But a Molar substitution (molecule for molecule) would be 75% of the weight of the Barium Carbonate, as barium weighs more than strontium. 74.8% actually.

 

That makes a lot of sense, as I believe that the Cu++/Cu+ balance is different because of the different redox chemistry of

Ba & Sr. Which means that you need more total Cu to get equal amounts of the colourant Cu++.

Regards, Peter

I can probably chase up a reference if anybody wants to see one.

 

The scary thing is that I think I understood what you both said.

T.

[Babs]

WHy are you substituting the Barium for Strontium? Is it only for the toxicity factor?  Strontium toxicity? 

[Guest JBaymore]

WHy are you substituting the Barium for Strontium? Is it only for the toxicity factor?  Strontium toxicity? 

 

Other way around.

 

best,

 

..................john

 

PS:  While barium carbonate toxicity has been studied a good bit... strontium not so much.  So we may be substituting one issue for another.  Laguna Ceramics MSDSs list the same TLV TWA as that of barium carbonate 0.5. and the LD50 is >2000 mg/kg.  Some scientific MSDSs show lack of study data but are more cautious in their language about personal protection and ventilation.  Some say it is purely a "nusience dust" and l;ist stuff like "OSHA Permissible Exposure Limit (PEL): 15 mg/m3 total dust, 5 mg/m3 respirable fraction for nuisance dusts. - ACGIH Threshold Limit Value (TLV): 10 mg/m3".  All sources I've seen except the best chemical grade type list between 1/2 %  and 1.5 % barium carbonate IN the "strontium carbonate".

[Babs]

Ouch!

So A Calcium substitute would not result in the colouring sought?

Go test lazy one?? OK

Have a Barium rich glaze with the name Alex Luff attached... Can't seem to find out about this guy. Would be an early potter as I've had this glaze since the 70s.

I read in a post somewhere that someone was placing a glaze with Barium on outside of mugs. Is this considered, if not best practice, at least acceptable? I used to use the above mentioned glaze for this but veered away from it because of the hype around Barium. Not diminishing  the dangers by stating it  thus.

[Guest JBaymore]

The biggest issue with barium is the use of barium carbonate in the studio for the potter.  The raw material barium carbonate has some significant toxicity issues.  Being aware of this is more for the potter than the customer.

 

The predicting of the possible leaching of barium compounds out of glazes is complicated by the fact the the dissociation of barium carbonate (a raw material source) to the oxide form (a flux acting on silica) is affected by firing conditions.  If it does not convert from carbonate to oxide, it remains as little tiny pieces of barium carbonate "trapped" in the glass matrix. IF this happens..... then there is greater potential for the leaching of baruim carbonate from the fired glaze. Barium oxide leaching out of a fired glaze is less common. 

 

(When you see BaCO₃ in low fire glaze recipes... it is likely always more of an opacifier than a flux... and a toxic opacifier to boot.) 

 

best,

 

.....................john

[Babs]

Thanks John, at C5/6 it would have some fluxing action but I'm going to work at replacing it. Or at least most of it as the glaze I used to use has fair load of it....30ish % from memory.