will edwards on wed 4 oct 00
Mmmmmm. I was after a different kind of response but here's what I found =
so
far. (BTW- More in the form of an answer to; is this a viable glaze where=
it
knowingly could be used as a food bearing glaze?)
Unity Formula as I have it. (Since we all use many programs and calculati=
ons I
could be very wrong about this I suppose?)
0.063 K20 0.111 Na20 .0460 CaO 0.144 MgO 0.222 ZrO 0.153 Al203 0.49=
2
B203 0.004 Fe203 1.925 SiO2 0.001 TiO2
Percents - 42.47& SiO2 5.75 Al203 12.58 B203 2.19 K20 2.53 Na20 9.47=
CaO
2.14 MgO 8.74 ZrO.
Recipe: 43.50 GB
43.50 PV Clay
13.00 Zircopax (Zirconium silicate)
I was alarmed at several things regarding this glaze but I wondered where=
it
might have came from? I see some issues with it but thought perhaps some =
of
those guru's out there could add to these findings. Would it hold H2O? (O=
urs
didn't) Would it hold Copper? What about a high boron level as this? Low =
SiO2
for a cone 6. Was this the original formula for a ^6? I actually recentl=
y
recieved a piece that looks pretty since I posted the original and we nee=
ded a
vase so we stuck some flowers in it and left for a few hours. It was leak=
ing
like a sieve when we got back. (A member of their studio brought it in) W=
e
still have an ample supply of GB but had reserved it for raku.
I was already in the midst of looking at it for potential use for some of=
our
members but then I saw the formula and then I got the piece and now I am =
still
wondering if anyone else out there could clear up this subject any better=
than
I have. (Its time to move on I suppose?)
However I have decided I am not going to use this one at all and since I =
know
it is widely used in another setting I was only pondering should I say
something to them based on my findings? I felt like I was intruding but t=
hen
of course wouldn't anyone that was worried about safety and their childre=
n? =
William Edwards
Opelika Arts Center Director
____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=3D=
1
amy parker on thu 5 oct 00
Will - I will put some of this on a container in the next load & let you
know if it leaks for me or not - could be the clay body interaction, of
course. As for the cobalt & copper & leaching - well, since no more GB I'm
not going to have my test batch analyzed, but I will say that the color is
stable - no paling in vinegar.
Amy, wishing I'd bought more than 25 lbs of GB!. Drat. I had some nice
color interactions with this glaze too!.
At 09:12 PM 10/4/00 MDT, you wrote:
>Mmmmmm. I was after a different kind of response but here's what I found so
>far. (BTW- More in the form of an answer to; is this a viable glaze where it
>knowingly could be used as a food bearing glaze?)
>I was alarmed at several things regarding this glaze but I wondered where it
>might have came from? I see some issues with it but thought perhaps some of
>those guru's out there could add to these findings. Would it hold H2O? (Ours
>didn't) Would it hold Copper? What about a high boron level as this? Low SiO2
>for a cone 6. Was this the original formula for a ^6? I actually recently
>recieved a piece that looks pretty since I posted the original and we
needed a
>vase so we stuck some flowers in it and left for a few hours. It was leaking
>like a sieve when we got back.
>William Edwards
>Opelika Arts Center Director
Amy Parker
Lithonia, GA
Chris Schafale on sat 14 oct 00
I tried to send this message before, but I think it got lost last
weekend. Trying again because I think we may be discussing this
glaze with some inaccurate information. Makes a big difference in
the numbers whether you include the boron in unity or not.
> Hi Will,
>
> I put this glaze in Insight, and got the following:
>
> GERSTLEY BORATE 5/99 analysis ...1000.00 43.48%
> PLASTIC VITROX...... 1000.00 43.48%
> ZIRCOPAX............ 300.00 13.04%
> ========
> 2300.00
>
> CaO 0.74* 9.94%
> MgO 0.03* 0.24%
> K2O 0.11* 2.44%
> Na2O 0.13* 1.89%
> TiO2 0.00 0.05%
> ZrO2 0.33 9.85%
> Al2O3 0.40 9.71%
> B2O3 0.77 12.85%
> SiO2 3.66 52.78%
> Fe2O3 0.01 0.24%
>
> Cost/lb 0.24
> Si:Al 9.23
> SiB:Al 11.17
> Expan 6.11
>
> As you can see, the unity numbers are quite different from yours. I
> think that most of the difference is probably because you are
> including B203 in unity, and I am not (per John Hesselberth's
> research on limit formulas).
>
> Anyway, what I see is a glaze that has plenty of alumina and
> silica, but lots of boron. It might be worth testing for boron release,
> as I understand there are water standards for boron, to use for
> comparison. Also, testing with different oxides and looking for
> leaching would be worthwhile. But I don't think it should
> automatically be dismissed as a dangerous glaze -- it might be
> fine, and likely is no worse than many other glazes being used in
> community studios.
>
> As for the leaking, it's always hard to tell whether that is a result of
> the glaze, the clay, the firing, or some combination. Seeping can
> be caused by crazing of a glaze over a body that is still somewhat
> porous (as is often the case with cone 6 clays, and even more
> often the case with so-called "wide-range" clays that are fired at
> the low end of their range). The expansion of this glaze is very low,
> so I would not expect it to be crazing, though. On the other hand,
> Ron has remarked that very high levels of boron can actually raise
> expansion, and I don't know if Insight reflects this.
>
> Anyway, that's my take on it.
>
> Chris Schafale
>
> > Mmmmmm. I was after a different kind of response but here's what I found so
> > far. (BTW- More in the form of an answer to; is this a viable glaze where it
> > knowingly could be used as a food bearing glaze?)
> >
> > Unity Formula as I have it. (Since we all use many programs and calculations I
> > could be very wrong about this I suppose?)
> >
> > 0.063 K20 0.111 Na20 .0460 CaO 0.144 MgO 0.222 ZrO 0.153 Al203 0.492
> > B203 0.004 Fe203 1.925 SiO2 0.001 TiO2
> >
> > Percents - 42.47& SiO2 5.75 Al203 12.58 B203 2.19 K20 2.53 Na20 9.47 CaO
> > 2.14 MgO 8.74 ZrO.
> >
> > Recipe: 43.50 GB
> > 43.50 PV Clay
> > 13.00 Zircopax (Zirconium silicate)
> >
> > I was alarmed at several things regarding this glaze but I wondered where it
> > might have came from? I see some issues with it but thought perhaps some of
> > those guru's out there could add to these findings. Would it hold H2O? (Ours
> > didn't) Would it hold Copper? What about a high boron level as this? Low SiO2
> > for a cone 6. Was this the original formula for a ^6? I actually recently
> > recieved a piece that looks pretty since I posted the original and we needed a
> > vase so we stuck some flowers in it and left for a few hours. It was leaking
> > like a sieve when we got back. (A member of their studio brought it in) We
> > still have an ample supply of GB but had reserved it for raku.
> > I was already in the midst of looking at it for potential use for some of our
> > members but then I saw the formula and then I got the piece and now I am still
> > wondering if anyone else out there could clear up this subject any better than
> > I have. (Its time to move on I suppose?)
> > However I have decided I am not going to use this one at all and since I know
> > it is widely used in another setting I was only pondering should I say
> > something to them based on my findings? I felt like I was intruding but then
> > of course wouldn't anyone that was worried about safety and their children?
> >
> > William Edwards
> > Opelika Arts Center Director
> >
> > ____________________________________________________________________
> > Get free email and a permanent address at http://www.netaddress.com/?N=1
> >
> > ______________________________________________________________________________
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
> >
>
>
Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh)
candle@intrex.net
http://www.lightonecandle.com
John Hesselberth on tue 17 oct 00
Hi Chris, Will and others,
This gives an excellent example of the variability of Gerstley Borate and
why it is such a difficult material. I have been using the 9/97 analysis
for GB. It has only 1/3 as much silica and about 20% as much alumina as
the 99 analysis. Using the 9/97 analysis this would look like a very
poor glaze. Depending on which analysis you use for PV (which must also
be somewhat variable) I get silica numbers ranging from 1.8-2.3 (all with
boron out of unity of course). Chris is right that using the 99 analysis
for GB it looks pretty decent and certainly worth testing.
This could also explain the big difference Amy and Will are seeing when
they test this--they probably have different lots of GB. Having good
analyses and stable materials is vital to making the same glaze twice.
Until Chris posted this message I really didn't realize how much
variability there is in GB. I knew it was variable, but the I had never
examined the extent of that variability. Thanks, Chris! And good
riddance to GB!!
Regards, John
Chris Schafale wrote:
>
>> Hi Will,
>>
>> I put this glaze in Insight, and got the following:
>>
>> GERSTLEY BORATE 5/99 analysis ...1000.00 43.48%
>> PLASTIC VITROX...... 1000.00 43.48%
>> ZIRCOPAX............ 300.00 13.04%
>> ========
>> 2300.00
>>
>> CaO 0.74* 9.94%
>> MgO 0.03* 0.24%
>> K2O 0.11* 2.44%
>> Na2O 0.13* 1.89%
>> TiO2 0.00 0.05%
>> ZrO2 0.33 9.85%
>> Al2O3 0.40 9.71%
>> B2O3 0.77 12.85%
>> SiO2 3.66 52.78%
>> Fe2O3 0.01 0.24%
>>
>> Cost/lb 0.24
>> Si:Al 9.23
>> SiB:Al 11.17
>> Expan 6.11
>>
>> As you can see, the unity numbers are quite different from yours. I
>> think that most of the difference is probably because you are
>> including B203 in unity, and I am not (per John Hesselberth's
>> research on limit formulas).
>>
>> Anyway, what I see is a glaze that has plenty of alumina and
>> silica, but lots of boron. It might be worth testing for boron release,
>> as I understand there are water standards for boron, to use for
>> comparison. Also, testing with different oxides and looking for
>> leaching would be worthwhile. But I don't think it should
>> automatically be dismissed as a dangerous glaze -- it might be
>> fine, and likely is no worse than many other glazes being used in
>> community studios.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
amy parker on wed 18 oct 00
Well, I guess I must have the '99 vintage GB at my house!
I guess this boils down to the same thing I keep telling the kids - only
eat stuff that you recognize the ingredients - Keep It Simple Stupid.
Flour, eggs, butter, salt, not partially hydrogenated, diglycerides,
dichlorides. Silica, feldspar, RIO, not GB, PV.
Amy
PS - Don't eat the glazes just because somebody says they are safe enough
that you could! (WG)
John Hesselberth wrote:
>This gives an excellent example of the variability of Gerstley Borate and
>why it is such a difficult material. I have been using the 9/97 analysis
>for GB. It has only 1/3 as much silica and about 20% as much alumina as
>the 99 analysis. ...
>This could also explain the big difference Amy and Will are seeing when
>they test this--they probably have different lots of GB. Having good
>analyses and stable materials is vital to making the same glaze twice.
>
>Until Chris posted this message I really didn't realize how much
>variability there is in GB. I knew it was variable, but the I had never
>examined the extent of that variability. Thanks, Chris! And good
>riddance to GB!!
>
>Regards, John
Amy Parker
Lithonia, GA
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