Earl Brunner on mon 8 oct 01
Isn't Merrie talking about using this glaze in a wood fire? (I can't
remember the original post and no longer have it on my computer) If so,
then don't we have to factor in the potential glaze altering affects of
the ash in the firing? Depending on the quantity of ash, the chemistry
of the glaze could be pushed off quite a bit I would think. If we are
talking wood fire, I haven't read anyone addressing that consideration.
Craig Martell wrote:
> Merrie wanted to know:
>
>> ORIBE ......cone 10 to 13
>> custer feldspar 49
>> whiting 15
>> kaolin 12
>> flint 25
>> copper carb. 7
>> Is it food safe, stable, does it have too much copper for a lemonade
>> cup?
>
>
> Hello MB:
>
> This glaze is good to go according to Insight and Matrix. Everything is
> a-ok on the molecular level and the expansion is good too. That's without
> copper though. At 7% the copper is probably going to increase the
> solubiltiy of the glaze and it will most likely leach. If you drop the
> copper to 4% there is a much greater chance of food safety. 4% is about
> the limit for copper in glazes for functional ware from what I've read via
> John Hesselberth who has done exhaustive testing. Ron Roy too.
>
> regards, Craig Martell in Oregon
>
--
Earl Brunner
http://coyote.accessnv.com/bruec/
bruec@anv.net
Merrie Boerner on mon 8 oct 01
Hi Yall,
One amusing thought, then One glaze question........
Tony Blair ; British Prime Minister ...powerful man/great speeches.
Tony Clennell ; Canadian Prime Choice Meat ....great
potter/writer/comedian.
Tony the Tiger ; US Prime Choice Breakfast .....cartoon
character/GREAT voice.
On a perfect day, I'd have Frosted Flakes for breakfast, with coffee in a
Clennell shino mug, while listening to Tony Blair deliver an eloquently
written speech.
Now, let's talk about this glaze.........
ORIBE ......cone 10 to 13
custer feldspar 49
whiting 15
kaolin 12
flint 25
copper carb. 7
In the wood firing, it can turn mauve with green, or green with bright red
on high spots, or green with mauve, or mauve breaking bright green on high
spots with bright red, or bright green and bright red. It is so full of
surprises ! What do yall think ? Is it food safe, stable, does it have too
much copper for a lemonade cup?
Merrie in Mississippi
HA ! My spell check wants to turn "Clennell" into "cleanness" ! It would
take much more than a mere suggestion from a computer !
Craig Martell on mon 8 oct 01
Merrie wanted to know:
>ORIBE ......cone 10 to 13
>custer feldspar 49
>whiting 15
>kaolin 12
>flint 25
>copper carb. 7
> Is it food safe, stable, does it have too much copper for a lemonade cup?
Hello MB:
This glaze is good to go according to Insight and Matrix. Everything is
a-ok on the molecular level and the expansion is good too. That's without
copper though. At 7% the copper is probably going to increase the
solubiltiy of the glaze and it will most likely leach. If you drop the
copper to 4% there is a much greater chance of food safety. 4% is about
the limit for copper in glazes for functional ware from what I've read via
John Hesselberth who has done exhaustive testing. Ron Roy too.
regards, Craig Martell in Oregon
John Hesselberth on mon 8 oct 01
on 10/8/01 4:21 PM, Merrie Boerner at boerner@TISLINK.COM wrote:
> Now, let's talk about this glaze.........
> ORIBE ......cone 10 to 13
> custer feldspar 49
> whiting 15
> kaolin 12
> flint 25
> copper carb. 7
> In the wood firing, it can turn mauve with green, or green with bright red
> on high spots, or green with mauve, or mauve breaking bright green on high
> spots with bright red, or bright green and bright red. It is so full of
> surprises ! What do yall think ? Is it food safe, stable, does it have too
> much copper for a lemonade cup?
Hi Merrie,
Too bad it is such a a neat glaze. Unfortunately it also a very unstable
glaze. Although it has enough silica and alumina to be stable, no glaze I
have ever seen will hold 7% copper carbonate without significant leaching.
Another Oribe glaze (different from yours) was tested by Betsy Price and Tom
Wirt and the results are posted on my web site. It only had 5.5% copper and
leached 52 ppm of copper. That is a lot and certainly enough to make food
taste bitter and color to fade whether or not it poisons anyone. I would
not use a glaze like this on functional pottery. Soak half of one of your
pots in vinegar for 3 days and see what happens. If, by chance, nothing
happens have it leach tested and tell us the results. I suspect it will
fade in vinegar testing.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Timothy Sullivan on mon 29 oct 01
When I run this through INSIGHT, I get the following for the base glaze:
custer feldspar 49.00 CaO 0.683*
WHITING 15.00 K2O 0.218*
EPK KAOLIN 12.00 Na2O 0.094*
FLINT 25.00 Al2O3 0.518
======== SiO2 4.220
101.00
I limit most of the glazes that I use (cone 10 reduction) to between .35 and
.38 Al2O3. I've found that my glazes are consistently stiff if I go higher
than that. By the way, the Si:Al ratio is usually above 9 or so (glossy).
My question is what advantages would I see if I were to drive the Al2O3
higher ( harder glaze surface etc.) and would ball milling or adding GERSTLEY
BORATE to the mix make the glaze surface less stiff?
Thanks in advance for the help.
Tim in Atlanta where today I was freezing and glazing in my COLD kiln room.
Ron Roy on tue 30 oct 01
Hi Tim,
Your alumina is already high for a cone 10 glaze - what is it you want from
this glaze?
As you raise the alumina the glaze will get less glossy. If you add boron
(I would recommend frit 3134) you will counteract the tendency for the
glaze to become less glossy - but it will melt better.
Ball milling will increase melt up to a point but they say the tendenct to
crawl will increase if you do too much. Maybe a combination of both would
be worth a try.
The other option is to decrase the silica - there is a lot - but you have
to watch for crazing - again - boron additions will tend to stop the
crazing - up to amounts of 12%
RR
>When I run this through INSIGHT, I get the following for the base glaze:
> custer feldspar 49.00 CaO 0.683*
> WHITING 15.00 K2O 0.218*
> EPK KAOLIN 12.00 Na2O 0.094*
> FLINT 25.00 Al2O3 0.518
> ======== SiO2 4.220
> 101.00
>
>I limit most of the glazes that I use (cone 10 reduction) to between .35 and
>.38 Al2O3. I've found that my glazes are consistently stiff if I go higher
>than that. By the way, the Si:Al ratio is usually above 9 or so (glossy).
>
>My question is what advantages would I see if I were to drive the Al2O3
>higher ( harder glaze surface etc.) and would ball milling or adding GERSTLEY
>BORATE to the mix make the glaze surface less stiff?
>
>Thanks in advance for the help.
>
>Tim in Atlanta where today I was freezing and glazing in my COLD kiln room.
>
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Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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