Bert Gibson on wed 28 jul 04
I found out the formula for one of the glazes we use at school calls out =
for Barium Carbonate. I suggested to the instructor that maybe it should =
be mentioned to the class that it might not be food safe. He told me =
that all the barium is burned out at cone 10 temperatures and not to =
worry about it. He almost seemed agitated that I was even asking the =
question.=20
I have a person who asked me to make them a mug with this glaze, but I =
am going to explain that it is not a food safe glaze. Below is the glaze =
formula.
Geff's Orange
Pot Feldspar 32.0
Dolomite 22.0
Barium Carb 22.0
EPK 15.0
Silica 9.0
Rutile 1.5
RIO 4.5
You can see a couple of examples of this glaze on my website, you just =
need to click through the cone 6 pictures to get to the cone 10 =
pictures. Am I right about the suitability of this glaze for food use?
Bert Gibson
http://home.comcast.net/~lazybpottery
=20
Paul Lewing on wed 28 jul 04
on 7/28/04 5:59 AM, Bert Gibson at lazybbeefmaster@COMCAST.NET wrote:
> I suggested to the instructor that maybe it should =
> be mentioned to the class that it might not be food safe. He told me =
> that all the barium is burned out at cone 10 temperatures and not to =
> worry about it. He almost seemed agitated that I was even asking the =
> question.
Bert, the data on barium is not conclusive, but it's probably wise to avoid
it on food surfaces. I know I wouldn't use it that way, and not many
responsible potters would. And that glaze has a lot of it.
And as to its being burned out by cone 10? Sorry, Professor, you're wrong!
Maybe he's defensive because he's not sure about his information.
Paul Lewing, Seattle
Ivor and Olive Lewis on thu 29 jul 04
Dear Bert Gibson,
Some years ago, and you will have to check the archives the paper ones
for this, there was an article by Janet De Boos relating to the
behaviour of Barium Carbonate. It may be in Ceramics Monthly, Pottery
in Australia or Ceramics Technical but I am not sure which. Before
she became a ceramist of some note, Janet de Boos qualified as a
Chemist and has a BSc.
Now a lot may be said about the nature and behaviour of Barium
Carbonate, but unless what is said is compared to the information she
gives and to that given by Edouard Bastarache
() I would treat information with
suspicion and scepticism.
Regarding the Chemical properties of Barium Carbonate, Kaye and Laby
give a melting point of 850=BA C but are uncommitted about the
temperature at which it decomposes to Barium Oxide and Carbon dioxide.
CRC Disagree giving 1555=BA C as the melting point. So there is clear
need for some investigation into conflicting information. However,
accepting that decomposition happens then the oxide will melt at 1923=BA
C which casts some doubt on the information given to you about
volatalisation at Cone 10.
Just looking at your recipe and without resorting to calculating the
Unity formula, it seems to me to be deficient in Silica and might have
insufficient to take into solution the large amount of Group 2
compounds so that they are sequestered in a glassy phase.
This recipe could be a candiadate for a Lab determination if you are
determined to use it.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Hank Murrow on thu 29 jul 04
On Jul 28, 2004, at 8:42 PM, Ivor and Olive Lewis wrote:
> Dear Bert Gibson,
> Some years ago, and you will have to check the archives the paper ones
> for this, there was an article by Janet De Boos relating to the
> behaviour of Barium Carbonate. It may be in Ceramics Monthly, Pottery
> in Australia or Ceramics Technical but I am not sure which.
> murrow.biz/hank
>
Dear Barium lovers;
Here is Ron Roy's note about the article:
"The article is in Ceramics Technical issue #3. She did not publish all
the
results - none on what happens when you add in 3% and 6% copper. You can
get the full results fron Janet DeBoos, at The Ceramics Workshop,
Austrailian National University School of Art, PO Box 804, Canberra ACT
2601, Australia.
The cost is $A10. I tried an international money order but it was
expensive
so I just gave them a credit card authorization.
Don't have it yet but the published results for cone 10 and 11 (30
glazes)
are in the CT article."
Cheers, Hank in Eugene
www.murrow.biz/hank
daniel on thu 29 jul 04
Hi Bert,
I don't have a lot to offer on this. Only this really. I had a copper red
cone 10 glaze leach tested recently as it contained a small amount of barium
carbonate. It leached a very small, but measurable, amount of barium. So it
is in there after a cone 10 firing. Like Paul said, you have a bunch of it.
I think my glaze was only in the 2-3% range, can't recall exactly.
Just a data point.
Thanx
D
Belmont, California, USA
(ex terra australis)
Edouard Bastarache Inc. on thu 29 jul 04
Barium naturally occurs at low concentrations in ambient air, usually < 0.05
µg/m3, but is found at relatively high concentrations in soils , nearly 500
mg/kg. In fresh surface water, concentrations may vary from < 5 to 15,000
µg/L. and it contributes to water hardness. Foodstuffs provide also barium
and the daily human intake has been estimated to be in the order of 1 mg.
The biological half-life of barium varies between 2 and 20 hours. Absorbed
barium is mainly deposited in bones, which accounts for 93% of the body
burden in man. It is mainly excreted in feces and a small part (1 to 10%)
in urine.
Barium carbonate is an acute toxicant.
Acute intoxication by ingestion :
The lethal dose in man varies, according to the barium compounds involved,
between 1 and 15 g. by ingestion. Acute intoxications are rare and generally
due to suicidal attempts with the chloride or the carbonate.
Some cases of collective food intoxications were reported, related to food
contamination, and to confusion between carbonate and barium sulphate at the
time of radiological examinations. Barium carbonate having been substituted
accidentally for potato flour during the preparation of sausages, 144 people
were poisoned in Israel in 1963. Two patients died.
We have yet to see an acute intoxication by ingestion of food served/stored
in ceramic wares.
Nor have we seen a suicidal attempt from the same type of wares.
Barium compounds are not reputed to penetrate by skin unless the cutaneous
barrier is broken as in chemical burns; a case has been described in the
relevant medical literature which had been caused by barium chloride
in fusion.
The carbonate and the sulphate of barium are irritating to the mucous
membranes of the upper airways, the carbonate can also be irritating
to the skin and the eyes.
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
----- Original Message -----
From: "daniel"
To:
Sent: Thursday, July 29, 2004 11:26 AM
Subject: Re: Barium Carbonate glaze/food safe?
> Hi Bert,
>
> I don't have a lot to offer on this. Only this really. I had a copper red
> cone 10 glaze leach tested recently as it contained a small amount of
barium
> carbonate. It leached a very small, but measurable, amount of barium. So
it
> is in there after a cone 10 firing. Like Paul said, you have a bunch of
it.
> I think my glaze was only in the 2-3% range, can't recall exactly.
>
> Just a data point.
>
> Thanx
> D
>
> Belmont, California, USA
> (ex terra australis)
>
>
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>
Ron Roy on mon 2 aug 04
Hi Bert,
Barium does not burn out of glazes - what kind of school is this?
This glaze is way short of silica so it will release Barium into food - and
it will craze on most clay bodies.
I remember some one bringing a mug into Tuckers - it was glazed with a high
barium glazes with cobalt. The outside was a brilliant blue which continued
down to about halfway on the inside - the rest and the bottom were
absolutly white.
Some one had left some "neo citran" (one of those cold remedy hot drinks
with lots of ciric acid) on the counter over night. Not only was some
Barium leached out - but ALL of the cobalt.
I wonder what customers would think about that?
RR
>I found out the formula for one of the glazes we use at school calls out
>for Barium Carbonate. I suggested to the instructor that maybe it should
>be mentioned to the class that it might not be food safe. He told me that
>all the barium is burned out at cone 10 temperatures and not to worry
>about it. He almost seemed agitated that I was even asking the question.
>
>I have a person who asked me to make them a mug with this glaze, but I am
>going to explain that it is not a food safe glaze. Below is the glaze
>formula.
>
>Geff's Orange
>
>Pot Feldspar 32.0
>Dolomite 22.0
>Barium Carb 22.0
>EPK 15.0
>Silica 9.0
>
>Rutile 1.5
>RIO 4.5
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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