Ron Roy on sun 4 jan 98
Hi Marjory,
Vanadium is one of the nastier oxides in terms of toxicity. The durability
of the glaze is a factor in how much will be released into food. If the
stain is encapsulated I think the danger is less but there still might be
problems. I have asked - on this list before - if anyone knew under what
circomstances encapsulation breaks down. There was no reply that I saw.
Vanadium is not something I would have in my studio - if you must use it
make sure you don't breath or ingest it.
The durability if glazes does not depend on what cone they are fired at.
The balance of fluxes and amounts of silica and alumina present determine
how good the glass is. Each temperature requires different "limits." Hi
fired glazes are more easily made safe because the alumina and silica can
be present in higher amounts - in relation to the fluxes. This does not
mean that all high fired glazes are durable - it's just easier to make them
safe. Low fired glazes are more difficult simply because you are restricted
in the fluxes that work down there - and because alumuna and silica are
hard to melt - you just can't have as much.
>Another question for the glaze gurus, is 6% vanadium stain added to a base
>glaze fired to cone 6 too high to be food-safe?
>
>Thanks,
>
>Marjory
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Mark Sweany on mon 5 jan 98
Ron Roy wrote:
>
> ----------------------------Original message----------------------------
> Hi Marjory,
>
> Vanadium is one of the nastier oxides in terms of toxicity. The durability
> of the glaze is a factor in how much will be released into food. If the
> stain is encapsulated I think the danger is less but there still might be
> problems. I have asked - on this list before - if anyone knew under what
> circomstances encapsulation breaks down. There was no reply that I saw.
>snip
Since I have been on the list, I've read a number of posts
about using the various metals in glaze and I too would like to
get some kind of difinitive answer as to their safe use. I know
when we had the big deal about the lead compounds many years
ago, the belief at that time was that their use in high fire
glazes was safe, but at lower temperature firings, if the ware
was used for food service, the lead could leech out of the
glaze. Has that been proven wrong? Does the lead leech out
regardless of how it was fired? I'm also assuming that what
holds true for lead is true for the other metals? Is that a bad
assumption? Somewhere, someone has to have done a study on
this. Can anyone help us out?
Craig Martell on tue 6 jan 98
At 10:47 AM 1/5/98 EST, Mark wrote:
>----------------------------Original message----------------------------
> Since I have been on the list, I've read a number of posts
>about using the various metals in glaze and I too would like to
>get some kind of difinitive answer as to their safe use. I know
>when we had the big deal about the lead compounds many years
>ago, the belief at that time was that their use in high fire
>glazes was safe, but at lower temperature firings, if the ware
>was used for food service, the lead could leech out of the
>glaze. Has that been proven wrong? Does the lead leech out
>regardless of how it was fired? I'm also assuming that what
>holds true for lead is true for the other metals? Is that a bad
>assumption? Somewhere, someone has to have done a study on
>this. Can anyone help us out?
Mark:
I think that Ron already gave you a very definitive answer to your question.
He said that the composition of the glaze AND the firing were both
important, with the composition being the most important factor. He also
mentioned that high fire glazes could be considered more durable because of
higher contents of alumina and silica. As far as using lead in hi fire, I
think it becomes fairly volatile above cone 5 or 6 and is generally not used
in high fire glazes. Actually, why would anyone want to use lead in a high
fire glaze when there are so many other non toxic fluxes available at higher
temps.
A general rule for lead and other potentially harmful oxides is that there
needs to be at least 3 times the amount of silica present in the molecular
formula to chemically bind the material into a silicate chain and hold it
during attack from acids etc. Even if the glaze is within durable limits on
the molecular level it should be tested for nasty oxide release.
There is a ton of info about lead and other oxides in Parmelee's book,
Ceramic Glazes. There are also references to papers and studies done and
published by the American Ceramic Society and others. Lawrence and West's
book Ceramic Science for the Potter has good info as well.
regards, Craig Martell-Oregon
Judith Enright on tue 6 jan 98
I know I'm beating a dead horse, but....
In talking with Ann in the lab at the Mason stain company this
morning, she insisted that their colors are foodsafe to ^10 in
oxidation, ASSUMING THAT THE BASE IS BALANCED AND FIRED CORRECTLY.
This includes their chrome pinks, reds, yellows and purples. I use
12% stain in my base and she assured me that this amount is not
excessive (she reminded me that Fiestaware colors are created with
Mason stains, and this ware is high-fired).
If anyone would like to go the source, Mason's number is (330)
385-4400.
Judith Enright @ Black Leopard Clayware
email: Bleopard@ricochet.net
Ron Roy on wed 7 jan 98
Hello all - I know this is getting tedious - I certainly don't enjoy the
negativity of it - I do think it is important so I am tied to this
particular wheel - round and round I go ...
How much leaches out - of any glaze - fired at any temperature - has to do
with the durability of the glass. Durability has to do with the ability of
the glaze (glass) to resist attack by acids or alkalies.
You can have a perfectly good glaze at cone 04 with lead in it with no
leaching of the lead - well no I can't say no leaching - there is always
some - but with lead - because it accumulates in you - you have to be very
careful.
We chose the glazes we use because of how they look - not because of how
"hard" they are - Our training has not prepared us for this aspect of our
craft. The information is hard to come by unless you know where and how to
look.
There is no easy answer here for the great majority of us - you can make
good glass -if you know what you are doing - at most of the temperatures we
work at - lets not consider trying below cone 06 - case the lower you go
the harder it is to do.
Most of the glazes in the books we buy - are not good glass - In fact there
are those who say you can't have good looking glazes that are good glass so
they don't even try - it's not true - some of the unbalanced glazes that
were published on this list have been made into food safe glazes by others
on this list.
Those of you who don't want to know about this - there is a simple answer -
find out what oxides are problematic - like lead, cadmium, vanadium and
others in decreasing toxicity and just draw a line somewhere and leave them
out of all your liner glazes.
> Since I have been on the list, I've read a number of posts
>about using the various metals in glaze and I too would like to
>get some kind of difinitive answer as to their safe use. I know
>when we had the big deal about the lead compounds many years
>ago, the belief at that time was that their use in high fire
>glazes was safe, but at lower temperature firings, if the ware
>was used for food service, the lead could leech out of the
>glaze. Has that been proven wrong? Does the lead leech out
>regardless of how it was fired? I'm also assuming that what
>holds true for lead is true for the other metals? Is that a bad
>assumption? Somewhere, someone has to have done a study on
>this. Can anyone help us out?
Just to repeat again - lead leaching (or any kind) is not related to the
cone the glaze was fired to. It is related to the ability of the glaze to
resist attack by acids or alkalies. You cannot tell that by looking at the
glaze or the recipe (well maybe some can make a good guess from the recipe
but they are not studio potters I'll bet.)
The molecular view point is very helpful - but if you are going to put
questionable (toxic) materials in your glazes -on which food will rest -
testing for leaching is the only sure way to know.
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Ron Roy on thu 8 jan 98
The key words here are BALANCED GLAZE and FIRED correctly. Most of the
published glazes I see are not balanced - how do you tell the difference
between a balanced and unbalanced glaze? Sounds like a joke but I think we
could come up with some interesing 2nd lines.
>----------------------------Original message----------------------------
> I know I'm beating a dead horse, but....
>
> In talking with Ann in the lab at the Mason stain company this
> morning, she insisted that their colors are foodsafe to ^10 in
> oxidation, ASSUMING THAT THE BASE IS BALANCED AND FIRED CORRECTLY.
> This includes their chrome pinks, reds, yellows and purples. I use
> 12% stain in my base and she assured me that this amount is not
> excessive (she reminded me that Fiestaware colors are created with
> Mason stains, and this ware is high-fired).
>
> If anyone would like to go the source, Mason's number is (330)
> 385-4400.
>
>
>
> Judith Enright @ Black Leopard Clayware
>
> email: Bleopard@ricochet.net
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Tony Hansen on wed 14 jan 98
> I am looking
> for a good clear or semi-clear crackle glaze for a cone 6 porcelanous
> clay body.
Just take nepheline syenite and add kaolin. Start with 20% and adjust
to get the amount of melting you want.
--
-------
T o n y H a n s e n thansen@digitalfire.com
Get INSIGHT, Magic of Fire at http://digitalfire.com
Tony Hansen on wed 14 jan 98
> In talking with Ann in the lab at the Mason stain company this
> morning, she insisted that their colors are foodsafe to ^10 in
> oxidation, ASSUMING THAT THE BASE IS BALANCED AND FIRED CORRECTLY.
That is one huge "IF"!
Yesterday a customer immersed a 4% cobalt blue piece in vinegar over
night and it was white in the morning. I'll wager Mason blue stain
would have done the same in the cone 6 base glaze being used.
The 1213X matte was unscathed on the same test even though it is
quite a stoney matte.
--
-------
T o n y H a n s e n thansen@digitalfire.com
Get INSIGHT, Magic of Fire at http://digitalfire.com
Joyce Lee on wed 9 dec 98
I noted from Ron Roy's post that vanadium is a major unfriendly.
Too bad for me! When I began experimenting with glazes, following my
usual inclination to let my nose lead me when it comes to pottery (not
elsewhere, thank goodness), I purchased a couple of pounds of
vanadium...obviously did not grasp the cost of chemicals either. Now,
opting for a little more moderation in my approach to clay, I'd like to
do safely whatever needs to be done to the vanadium. (I've never used
any of it, by the way.) Suggestions, I hope?
Thank you,
Joyce
In the Mojave smug because I "went to the snow" yesterday in the
Sierras...recharged and ready to retackle those largish bowls, with my
"Warped Bowl" file from Clayart in hand.
Joyce Lee on mon 10 sep 01
." I wonder if there has been a serious
study to substantiate the ill effects of vanadium, or whether they =
are
just so much hear say." Mia in ABQ.
-----------------------------------------------------
If someone has information that indicates it's ok to use vanadium, I'd =
very much appreciate it being posted to Clayart. I have quite a lot of =
vanadium..... have had it since my second month in pottery five years =
ago.=20
I had requested from potter acquaintances a list of chemicals for =
mixing one's own glazes ..... knowing absolutely zip ....
not yet having experienced Robin Hopper's two week glaze course..... nor =
having discovered Clayart. In my ignorance, and without thinking =
about price, I ordered a lot of vanadium ..... very expensive compared =
to other chemicals ..... but my friend, to make me feel less like an =
idiot .... informed me that I could get beautiful yellows with the =
vanadium and that the yellows were considered difficult to obtain in =
high fire, but that she knew I had the grit to stay with it and earn =
those yellows for myself..................... still waiting....... and =
no tellin' where my grit is........
THEN I discovered Clayart and learned that vanadium was an unsafe =
chemical for use in functional pottery......=20
Was that last bit of information incorrect? I still have the =
vanadium...... over a hundred dollars spent for it ...... so haven't =
discarded it..... didn't know how to discard it, anyway.
Thank you for any help you may choose ..... and have the time ...... to =
offer.....
Joyce
In the Mojave where the swamp cooler didn't activate even once last =
night! The studio is comfortable this morning with the doors open .... =
no cooler needed yet! Exciting news around here ..... means we can quit =
dashing in and out of the heat, feeling as if our faces are being =
scorched, even with massive applications of 38 spf sunscreen.... great!
Wade Blocker on mon 10 sep 01
Joyce,
Edouard has posted the findings about Vanadium twice. I am sure it is
available in the archives.
I have used vanadium in reduction and gotten some really interesting
results. As long as you are not around the kiln when it fires glazes made
with Vanadium, and you do not use the glazes on ware designed for food, you
should have no problems.
Many yellow commercial stains contain vanadium.
My remarks whether the so called "malaise"from Vanadium had actually
been verified experimentally and tested, rather than being hearsay or fear
mongering, refers to quotes from Ron. Mia in ABQ where Autumn has
arrived
Bill Edwards on tue 11 sep 01
Hello,
I have to agree with Mia's statement about our
sourcing information on toxicology. I am sure that the
book writer has had training and done research, but
what better way could we ask for when we do have
people like Dr. Basterache and Dr. Robillard watching
out for our best interests in this field? It would be
nice for Monona to include information and background
work as well for our referencing and sourcing live and
in person on our forum. (The more expert advice we get
the better in my opinion)...
Certainly they are others who qualify themselves well
in terms of research and writing, but it is pertinent
we take into accounting the professionals we already
have on hand who earn their living in industrial
hygiene and toxicology.
Dr. Basterache has always been ultimately able to
produce all referencing and follow ups on his remarks.
It is so important to have this since we do seem to
have times of anxiety regarding a potential toxin or
chemical that gets bad reviews for whatever the
reason.
The best information we have is not what we sometimes
get in a book thats 1 to 10 years old, but information
that comes direct from the source and up to the minute
evaluations.
I spent over 20 years working with chemicals and
evaulating the use of them in my work using
toxicologists. It didn't make me a toxicologist but it
made me wiser to information sources. I am sure we
have those who are well informed and enlightened but
it would do us all good to detail where we source our
information from if we are going to use any references
to the dangers of the materials we come in contact
with.
I admire Ron and John who I feel are most capable of
providing good information. I also know that like me,
they too, get caught in the middle of a firing squad
at times. However, please provide your sourcing data
and the remarks from it if possible. Or if you have a
link to this information I could use it!
William Edwards
I'm hazardous but non-toxic...
__________________________________________________
Do You Yahoo!?
Get email alerts & NEW webcam video instant messaging with Yahoo! Messenger
http://im.yahoo.com
| |
|
