iandol on sun 4 nov 01
Dear Gail,
I have taken up your point about the inclusion of Barium Carbonate in =
glazes following reading Eduard's comments on the toxicity problem. I =
would also suggest that you search out the articles written by Jan De =
Boos several years ago which record her research on this chemical. In =
addition, I am caused to ask why it is necessary to the function of a =
glaze. When presented with a glaze recipe perhaps we should question the =
function of each of the constituents and eliminate those which are not =
making a valid contribution to our own design intention.
As I understand things from reading the major glaze commentator of =
recent years; Rhodes, Cooper and Royle, Daly, Parmellee, Chappell, I am =
left with the feeling that adding Barium Carbonate is done to achieve =
three distinct and separate functions, though all may occur within a =
particular glaze.
The first is to modify the hue of a glaze, for example; create a =
turquoise from copper in an oxidising or neutral atmosphere or intensify =
a red under reduction; Intensify the blue of an Iron Celadon; Encourage =
violet and green hues from Nickel oxide or carbonate.
The second function is to opacity and/or matt a glaze surface and is =
achieved by adding greater, even massive, proportions of the chemical.
The third common function attributed to Barium Carbonate, or its oxide, =
after the presumed decomposition under the influence of heat is that of =
a high temperature (Stoneware heats) auxiliary melting flux.
Rather than causing melting under the influence of rising heat, I would =
firstly speculate that small amounts of Barium Carbonate react first by =
dissolving in the melt provided by Frits, Borates, Lead silicates or =
Alkali silicates and that on cooling it reacts with the vitreous =
material to create coloured compounds or change some other physical =
characteristic such as viscosity or optical brightness. (Though I do not =
mean to cloud the simplicity of this proposal it is possible to think =
that an acid base reaction takes place between carbonates and silica, =
which is presumed by some people to have acidic qualities. This is an =
implication which can be drawn from calling the columns in the Unity =
formula "Basic", "Amphoteric" and "Acidic". Such terms imply the =
potential for chemical reactions) Secondly that when large amounts are =
present it dissolves to saturation to be reconstructed on cooling and =
come out of solution as an alumino silicate substance similar to a =
felspar (Celsian ??). Thirdly, excess which does not dissolve (though =
one might suppose it may react and discharge carbon dioxide) remains as =
insoluble particles which opacify the depth and matt the surface of a =
glaze.
Given that the first two situations would create relatively insoluble =
substances and that only small proportions of Barium Ions are trapped in =
the glassy silicate matrix of the glaze then perhaps it is only when =
excessive quantities of Barium carbonate are added into a glaze that =
concern need be given regarding potential hazards. But confirmation of =
that would be in the province of qualified chemists and toxicologists =
and I have neither expertise.
I would suggest that Barium Carbonate be avoided as a glaze constituent =
unless the colours it imparts are part of the design brief. Opacity and =
mattness can be achieved with less expensive and more reliable =
materials. If a student or worker choses to employ a recipe which =
contains Barium carbonate they might question the originator of the =
recipe as to why it is included.
<various conclusions?>>
Only one implication. We know precious little about the materials we =
use. I do not have the facilities of a University Library available =
nearby to search for information, nor a Materials Laboratory where I =
could go to test, or have my ideas tested. But I think it important to =
put ideas to students, be they informal, undergraduate or post graduate =
scholars, so that they can carry the quest for knowledge forward and =
have access to alternative possibilities.
Best regards,
Ivor Lewis. Redhill, South Australia
Cc: Edouard Bastarache edouardb@SOREL-TRACY.QC.CA
Cindy Strnad on sun 4 nov 01
Hi, Guys.
I hate to ask a stupid question--really I do. But
here goes. For as long as I've been in clay (5
years--not long, compared to many of you), I've
heard that barium is bad, bad, bad, and that we
must not put it into our glazes. So I just figured
"everyone" knew what they were talking about (as
I'm still sure they do), and never used it in
glazes intended for food use. But I've been
wondering about this off and on for quite a while.
Why is such a minute amount of barium as may leach
out of a glaze such a really, horribly, terribly,
very bad thing? I don't have a bottle of MOM (Milk
of Magnesia) on hand to check, but doesn't that
contain barium? And we used to make sick people
drink barium for medical procedures at the
hospital. Not just a couple of cc's, either. Great
gobs of the stuff. Yech! Not that that means it's
good for you, of course, but it must (I hope) mean
it's not too lethal or profoundly, permanently
damaging. So, will someone please explain this to
me?
Thanks,
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
Gillian Evison on sun 4 nov 01
Cindy, as an ex xray technician I can tell you that the barium we use for
xrays is barium sulphate - a very stable and therefore non poisonous
compound. We can't use this for glazes because of the sulphur content of
course, and the one we use, the carbonate, is not stable and will break down
into barium and whatever, and the barium is poisonous. As far as MOM is
concerned - isn't the active ingredient you are thinking of aluminium? I
stopped taking it because I heard that aluminium is suspected in connection
with Alzheimers, and goodness knows I have problems enough with aging,
without that!
Cheers, Jill
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
Edouard Bastarache on sun 4 nov 01
Hello Ivor,
here is an excellent text from Michael Banks written many months ago:
"Hi Edouard,
Here's my opinion on the barium question (for what it's worth) :)
I tend to think that barium in high gloss glazes is generally well
integrated into the silica melt. An examination with a hand lens will
also show up unmelted inclusions. True satin matt glazes should also not =
be
a problem as the well-balanced ones start out as glossy clear glazes whic=
h
become matted to some extent on cooling. The matting agents are micro
crystals of Ca feldspar, Ba or Mg silicates, all of which are essentially
insoluble.
Dry matt glazes are where potential undissolved inclusions of barium oxid=
e
or carbonate could conceivably occur. Firstly, dry matts are often
unbalanced (e.g.; flux heavy), immature, or both. If there is insufficien=
t
melt formed to attack and dissolve the BaCO3, or there is insufficient
silica or alumina to form barium alumino silicates, undissolved inclusion=
s
are likely. Normally dry matt barium containg glazes are only used on the
outside of decorative pieces, but insane things do happen.
The presence of BaO would be obvious as it behaves essentially like CaO,
hydrating, swelling and ultimately spitting out, or giving rise to white
surface efflorescence. BaCO3 inclusions could be detected by swabbing wit=
h
dilute hydrochloric acid causing evolution of bubbles of CO2. In fact,
free-BaCO3 could be sensitively detected by testing using HCl or acetic a=
cid
(or vinegar), soaking for some time, then adding some sulphate-bearing
solution (eg: epsom salts -MgSO4). A opaque white precipitate of BaSO4 is=
a
super-sensitive detector of Ba ions.
So, if people wish to know if there is free Ba in their glaze, an acid te=
st
should be diagnostic. Barium is classed as a =AB lithophile =BB element b=
y
geochemists. It prefers to enter stable bonding arrangements with silicat=
es
or aluminosilicates. The lithophile elements form the strongest bonds wit=
h
silica and form the most stable silica glasses. These bonds are stronger
than that formed by the siderophiles (Fe, Ni, V, Co, Mn, etc) and very mu=
ch
greater than that formed by the chalcophiles (Cu, Au, Ag, Pb) with silica.
Therefore I feel it is unlikely to be acid-leached from balanced glazes i=
n
more than infinitesimal amounts.
Cheers,
Michael"
Later,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://www.absolutearts.com/portfolios/e/edouardb/
John Hesselberth on sun 4 nov 01
on 11/4/01 10:20 AM, Cindy Strnad at earthenv@GWTC.NET wrote:
> Why is such a minute amount of barium as may leach
> out of a glaze such a really, horribly, terribly,
> very bad thing? I don't have a bottle of MOM (Milk
> of Magnesia) on hand to check, but doesn't that
> contain barium? And we used to make sick people
> drink barium for medical procedures at the
> hospital. Not just a couple of cc's, either. Great
> gobs of the stuff. Yech! Not that that means it's
> good for you, of course, but it must (I hope) mean
> it's not too lethal or profoundly, permanently
> damaging. So, will someone please explain this to
> me?
Hi Cindy,
I think the real answer is that no one knows and people are just cautious
after being burned by lead. Who among us hasn't been asked by a customer if
our glazes are lead-free? As Edouard pointed out, there is not a single
documented instance of barium leaching from glazes hurting anyone. That
doesn't mean it hasn't happened--if it has happened it just hasn't been
frequent enough for anyone to be able to pin it down. But it might not have
happened either.
There is a huge difference in the barium you drink before your CAT scan and
other forms of barium. You are drinking a slurry of barium
sulfate--yumm--it is very insoluble in water and passes through the body
without being absorbed. What would be leach out of pottery would almost
certainly be barium ions which are soluble (that's why they leach--if they
were insoluble, they wouldn't leach). If the water were taken away they
would probably be barium acetate or barium citrate, both of which are very
soluble in water and, therefore, toxic. Would enough leach out to do any
harm? Who knows?? So why not use less toxic materials when medical science
is forever finding more and more substances that do damage in small
quantities?
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.
potterybydai on sun 4 nov 01
Hi, Cindy - I'm sure you'll hear from the experts on this, but I'm sure that
the Barium used in enemas and drinks for x-ray purposes is NOT barium
"carbonate" (which is deadly poison in it's raw form), but another form of
barium. One workshop presenter told us that even a small amount ingested
could kill you, with symptoms like a heart attack (which started a great
conversation about ex-spouses and how could one get barium into their
coffee!). I thought, though, that once it was fired, it changed from
carbonate to something else less toxic. The other problem with glazes that
have a substantial amount of barium is that they are usually matt, which may
not be the greatest for food (staining, horrible knife sounds, etc). Just
my uneducated, Canadian 2 cents worth of probable misinformation.
Dai in Kelowna, BC, waiting to hear the REAL scoop on barium.
"There is no right way to do the wrong thing."
potterybydai@shaw.ca
Gail Dapogny on mon 5 nov 01
Pete Pinnell in a recent glaze calculation workshop put it very clearly and
sensibly. I paraphrase:
Is barium going to make you keel over on the spot? Of course not..that's
not the point. Breathing dust isn't going to cause you to collapse either.
HOWEVER ...THERE ARE LONG TERM EFFECTS ATTACHED TO GLAZE USE THAT WE NEED
TO SERIOUSLY CONSIDER, the kind of effects which can and will show up in
advanced age. Who wants to exacerbate joint problems, tremors, lack of
coordination, etc. etc. when a little care and common sense in our use of
glazes might at the very least relieve the problems if not preclude them.
When we go into denial because of no concrete proof, we sound like the
cigarette companies ten years ago. Do we really want to treat our
customers the way they treated theirs? While people are apt to claim that
there are no examples of barium poisoning, at the same time we don't really
know that because we don't seem to look at lesser effects than death !
All of the respected glaze and substance experts-- Ron, John, Monona, Pete,
and others say the same thing: Have your glaze tested if you really want
to consider continuing its use.
---Gail
>on 11/4/01 10:20 AM, Cindy Strnad at earthenv@GWTC.NET wrote:
>
>> Why is such a minute amount of barium as may leach
>> out of a glaze such a really, horribly, terribly,
>> very bad thing?
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
De ruyter jean on mon 5 nov 01
Hej Cindy
Concerning the leaching and use of medical Barium You certainly have the
answer.
When it concerns working with it to prepare our glazes, well that is in a
way risqué.
The information I have concerning the action of Ba in our body it is really
not "
a cat to handle without gloves "
For people working with it daily a maximum of 1.to.mug (milligram)
by inhalation of absorption Ba is first stored in the bone muscles and than
very fast and permanently
in the bones.
The Ba ions are destroying the Ca ions in the skeleton.
The first symptoms are diarrhoea and vomit.
0.2-0.5 gram is toxic
1-3gram is lethal.
You see that there is strong argument to be careful by handling Ba.
(Sorry for my BENGLISH) I hope it is understandable
Jan
----- Original Message -----
From: "Cindy Strnad"
To:
Sent: Sunday, November 04, 2001 4:20 PM
Subject: Barium...Why?
> Hi, Guys.
>
> I hate to ask a stupid question--really I do. But
> here goes. For as long as I've been in clay (5
> years--not long, compared to many of you), I've
> heard that barium is bad, bad, bad, and that we
> must not put it into our glazes. So I just figured
> "everyone" knew what they were talking about (as
> I'm still sure they do), and never used it in
> glazes intended for food use. But I've been
> wondering about this off and on for quite a while.
>
> Why is such a minute amount of barium as may leach
> out of a glaze such a really, horribly, terribly,
> very bad thing? I don't have a bottle of MOM (Milk
> of Magnesia) on hand to check, but doesn't that
> contain barium? And we used to make sick people
> drink barium for medical procedures at the
> hospital. Not just a couple of cc's, either. Great
> gobs of the stuff. Yech! Not that that means it's
> good for you, of course, but it must (I hope) mean
> it's not too lethal or profoundly, permanently
> damaging. So, will someone please explain this to
> me?
>
> Thanks,
>
> Cindy Strnad
> Earthen Vessels Pottery
> RR 1, Box 51
> Custer, SD 57730
> USA
> cindy@earthen-vessels-pottery.com
> http://www.earthen-vessels-pottery.com
>
>
____________________________________________________________________________
__
> 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.
>
claymom on tue 6 nov 01
I'm sure you'll hear from the experts on this, but I'm sure that
> the Barium used in enemas and drinks for x-ray purposes is NOT barium
> "carbonate" (which is deadly poison in it's raw form), but another form of
> barium. ___________________________________________________________
>
Yes, it is different. In fact it is Barium Sulfate I think. One of the
funniest experiences I've ever had while undergoing an "Upper G.I. series"
which requires drinking a liter of the nasty stuff was when I asked the
technician why they were making me drink what I understood to be a toxic
substance. She blanched and scurried out of the room. I could hear
mutterings and shuffling papers and was suddenly surrounded by a covey of
hospital types......nurses, radiologists, technicians, interns,
residents.......about 15 or so.........all assuring me that it was quite all
right for me to drink the stuff; nothing bad would happen; everything was
absolutely safe. All of this delivered with very serious, concerned
expressions. Of course the main thing I was thinking was that their
professional insurance rates must be absolutely astronomical for me to rate
such a rush of attention. A little levity was good in an otherwise not very
hilarious situation.
Gerry T. aka claymom@palacenet.net
Ron Roy on wed 7 nov 01
This is a complicated subject and it will help those of you who are trying
to decide if you want to use Barium in glazes if you consider the following
points.
White glazes do not need Barium -if you need another mid range flux
Strontium is a better choice because - you need less of it and because of
that you get lower expansion rates - which help avoid crazing. Strontium
for Barium subbing is not a good choice if your expansion is already low -
if that is the case sub in calcium but do it by calculation.
I'm sure it is possible to keep barium in a glaze if the amounts are on the
lower side and the glaze is stable. Lower side in my estimation is below
10%. Keep in mind - shiny (well melted) with enough alumina and silica can
mean stable but you can't tell by looking - have the glaze tested.
When crystals form - some rob the surrounding glaze of silica making that
part of the coating less stable - adding copper affect glaze leaching badly
- so increases the chance of all ions getting into many foods.
Then you have to decide how much barium - leaching into food is too much.
You may be able to make a good guess for the average adult but what about a
small child or a one month old fetus? Keep in mind - Barium Carb is an
effective rat poison - how does the soluble barium in the carbonate compare
with the barium ions leached out of a glaze into food?
Barium kills by paralyzing muscles - particularly heart muscles - the
effect is like a heart attack - so it may not be suspected as barium
poisoning. An important factor when you think that some who use your ware
may already have heart problems. I don't know what the long tern effects of
barium are - I do know it replaces calcium in bones.
Barium favours turquoise from copper and vivid blues from Barium - used a
lot in high barium glazes - chances are they are going to leach a lot of
barium - and change colour with some foods. Remember - heat makes the
leaching happen faster. These types of glazes - unless proven stable -
should not be used on food bearing surfaces.
Strontium with iron gives richer yellows and browns in my limited experience.
I won't use Barium simply because I don't know the answers to these
questions - I do know it's toxic and I can't find any data that says there
is no problem.
What I do know - there are lots of Barium glazes in use - on functional
ware - that are unstable. If there is ever a case of death or injury traced
to one of those glazes we are all going to suffer loss of sales. As it is -
I have seen cases of high barium glazes which have lost their colour after
sitting over night with acidic liquids in them. I am sure that customer did
not run back to the potter and buy another to replace it - or any more of
any kind from that potter. It may even be so that they never bought another
hand made pot again.
I don't know when it will happen here - it has happened in some countries
already - that barium will be on the restricted list. It is surely not in
the same category as lead and cadmium and maybe even some of the oxides we
use - but it is being misused in many functional glazes and it is toxic.
Well that feels better having said all that - thanks Cindy for asking an
important question.
RR
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
Edouard Bastarache on wed 7 nov 01
Hello Ron,
there is no known effect of "chronic" exposure "by ingestion" in man
in my books.
Only acute effects by the same route of entry have been described.
Barium acute intoxications are rare and most of them are suicidal
attempts with the chloride and the carbonate.
Even BaCO3 is insoluble at neutral pH, it becomes soluble in an
acidic medium like the stomach where it is transformed to BaCl,
a very soluble compound, more than the carbonate.
Will enough soluble barium be leached from a ware to cause
the acute intoxication? I doubt that very much.
Moreover, there is not a single case described in the toxicology
literature of an acute intoxication due to using wares covered
by barium containing glazes.
>From a born-optimistic one,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://www.absolutearts.com/portfolios/e/edouardb/
Ababi on thu 8 nov 01
I have this rule. Barium lithium chrome. Only in special
occasions, when there is not another possible way.
Iron chromate I got with the studio. Since I am in clayart. hardly
touch it.
My turquoise with Strontium carb.
I had a beautiful clear Barium base. I have it now as a beautiful
Strontium and a nice whiting base.
I think from my humble experience, that firing a high (10^) glaze into
^6 gives kind of Barium dry look. I talk, write actually about none
barium glazes.
The next words are following Ron's words:
My teacher said once: "LEAD is a poison by law, so we are not using
it."
Sometimes the laws are made by politicians. The politicians need points
to re be elected.
Let us be responsible. let them find other reasons to make laws and .
regulations. Do not make politicians decide for us what to use and what
to excommunicate. We will be the ones who will have to go around and
around to find hard solutions
Keep the barium, chrome,lithium mangnese and what ever is needed to art
and use
for domestic wares safer materials.
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
sharon@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
---------- Original Message ----------
>Hello Ron,
>there is no known effect of "chronic" exposure "by ingestion" in man
>in my books.
>Only acute effects by the same route of entry have been described.
>Barium acute intoxications are rare and most of them are suicidal
>attempts with the chloride and the carbonate.
>Even BaCO3 is insoluble at neutral pH, it becomes soluble in an
>acidic medium like the stomach where it is transformed to BaCl,
>a very soluble compound, more than the carbonate.
>Will enough soluble barium be leached from a ware to cause
>the acute intoxication? I doubt that very much.
>Moreover, there is not a single case described in the toxicology
>literature of an acute intoxication due to using wares covered
>by barium containing glazes.
>From a born-optimistic one,
>Edouard Bastarache
>Irreductible Quebecois
>Indomitable Quebeker
>Sorel-Tracy
>Quebec
>edouardb@sorel-tracy.qc.ca
>http://sorel-tracy.qc.ca/~edouardb/
>http://www.absolutearts.com/portfolios/e/edouardb/
>_______________________________________________________________________
_
>______
>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.
| |
|
