ACTSNYC@cs.com on mon 8 nov 99
In a message dated 11/7/99 6:15:30 PM Eastern Standard Time,
eiblodge@freenet.edmonton.ab.ca writes:
>
> ---------- Forwarded message ----------
> Date: Sun, 7 Nov 1999 17:34:41 EST
> From: John Hesselberth
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Hazards of encapsulated cadmium stains
> Resent-Subject: Re: Hazards of encapsulated cadmium stains
----------------------------Original message----------------------------
> Ray Aldridge wrote:
> >However, since I can't imagine a mechanism by which an object (a grain of
> >encapsulated cadmium, say) could resist solution in a glaze at 2300
> >degrees, but be readily dissolved by roomtemp acetic acid, I would be very
> >interested in such a speculation, if it were at all plausible.
> >
Well for one, the encapsulated particle could crack/craze during cooling,
> due to different expansion coefficients between it and the glaze
> surrounding it, thereby releasing the Cd for leaching.
>
>
> >Do you know of a net resource that contains this regulation? I'd like to
> >see the actual language.
>
> Well I can give you an internet reference by which the FDA tests to
> decide whether or not to impound or take legal action for lead. While I
> haven't personally found an internet reference as to what is required of
> manufacturers, I would think it would be smart to be assured that your
> work passes the tests the FDA may use. It also goes into detail on
> definitions of hollowware, flatware, cups, etc. and specifies how pots
> must be labeled if it is unsuitable for food use.
>
> Go to www.fda.gov and search for CPG 7117.07 The specific URL is about
> 2 lines long so I won't try to reproduce it here.
> I haven't found a similar reference for cadmium.>
> John Hesselberth
> Frog Pond Pottery
> P.O. Box 88
> Pocopson, PA 19366 USA
> EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
>-----------------------------------------------------------
I'm getting up at 4 am and catching a plane, so this has to be very short.
You can't use "commonsense" here with this scientific problem. Stability of
a color at high heat is utterly unrelated to its stability in acid at room
temp.
The cadmium isn't really "encapsulated." It's just sort of included into
crystals of zirconium silicate as they form. There's essentially no toxicity
data on ingestion by animals of the cadmium in this form. But neither
stability in high heat, nor acid solubility are related to toxicity. And
once fired, there is absolutely no guarantee at all that the cadmium will not
leach and be soluble in acid.
As soon as cadmium is present in the glaze, it is the obligation of the
company to test. And yes, there are a set of cadmium leaching levels just
like those for lead for different types of ware, e.g., plates, cups, jugs,
etc.
Hope this helps. I talked to Degussa reps and the US distributor about this
process back a few years ago. Very interesting.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@cs.com
Ray Aldridge on tue 9 nov 99
At 04:47 PM 11/8/99 EST, Monona wrote:
>----------------------------Original message----------------------------
>
>You can't use "commonsense" here with this scientific problem. Stability of
>a color at high heat is utterly unrelated to its stability in acid at room
>temp.
>
>The cadmium isn't really "encapsulated." It's just sort of included into
>crystals of zirconium silicate as they form. There's essentially no toxicity
>data on ingestion by animals of the cadmium in this form. But neither
>stability in high heat, nor acid solubility are related to toxicity. And
>once fired, there is absolutely no guarantee at all that the cadmium will not
>leach and be soluble in acid.
I keep asking if anyone can cite a reference for a high-temp glaze colored
with encapsulated cadmium that actually did leach cadmium above the
acceptable limits, but I'm beginning to suspect that this is a chimera.
"They could be monsters in them thar woods." Well, they certainly could
be, no doubt about it, but I want pictures.
Monona, I don't think you're following the line of argument I'm pursuing
here, which is probably my fault for being unclear. But to reprise: If
there is free cadmium present in an encapsulated stain, whether due to
imperfect processing or imperfect encapsulation or breakdown of the
encapsulation in the glaze solution, does it remain in a high temperature
glaze? Or is the only cadmium present in such a glaze (after firing)
completely encapsulated? Otherwise would it not vaporize from the glaze,
just like an unencapsulated cadmium pigment?
>
>As soon as cadmium is present in the glaze, it is the obligation of the
>company to test.
I'd like to know if this is a legal obligation ( in other words, is
pre-marketing testing required, and is failure to do so illegal on its
face, whether or not the glaze actually leaches cadmium.) According to
what I've found on the FDA site, it isn't. Do you have other references?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
ACTSNYC@cs.com on wed 10 nov 99
> ----- Forwarded message ----------
> Date: Tue, 9 Nov 1999 12:53:26 EST
> From: Ray Aldridge
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
>
> ----------------------------Original message----------------------------
> At 04:47 PM 11/8/99 EST, Monona wrote:
> >----------------------------Original message----------------------------
> >
> >You can't use "commonsense" here with this scientific problem. Stability
> of
> >a color at high heat is utterly unrelated to its stability in acid at room
> >temp.
> >
> >The cadmium isn't really "encapsulated." It's just sort of included into
> >crystals of zirconium silicate as they form. There's essentially no
> toxicity
> >data on ingestion by animals of the cadmium in this form. But neither
> >stability in high heat, nor acid solubility are related to toxicity. And
> >once fired, there is absolutely no guarantee at all that the cadmium will
> not
> >leach and be soluble in acid.
>
> I keep asking if anyone can cite a reference for a high-temp glaze colored
> with encapsulated cadmium that actually did leach cadmium above the
> acceptable limits, but I'm beginning to suspect that this is a chimera.
> "They could be monsters in them thar woods." Well, they certainly could
> be, no doubt about it, but I want pictures.
>
> Monona, I don't think you're following the line of argument I'm pursuing
> here, which is probably my fault for being unclear. But to reprise: If
> there is free cadmium present in an encapsulated stain, whether due to
> imperfect processing or imperfect encapsulation or breakdown of the
> encapsulation in the glaze solution, does it remain in a high temperature
> glaze?
There may be some free cadmium that was not washed off the surface after
crystallization, but that is a minor issue. The major issue is the cadmium
*in* the zirconium crystal. The crystal resists--but imperfectly--breaking
down at high temperatures. This resistance will be dependent on the
efficiency of the fluxes at dissolving zirconium silicate, the temperature,
and the time the glaze is in a liquid state. Don't get a false picture in
your mind of this little crystal as invincible under all conditions.
> Or is the only cadmium present in such a glaze (after firing)
> completely encapsulated? Otherwise would it not vaporize from the glaze,
> just like an unencapsulated cadmium pigment?
>
The cadmium is not completely encapsulated since some of the crystal will
dissolve and be incorporated into the glaze with the other ingredients. And
some will vaporize, some will leach with acid and so on. The theory is that
these crystals resist dissolving and much less cadmium will be dissolved into
the glaze or fumed. But if ingredients are used in the glaze that are very
good at fluxing zirconium silicate, those crystals are toast.
Remember, the resistance of zirconium silicate to heat will be altered if
those crystals are not by themselves, but are being acted on by fluxes.
> >As soon as cadmium is present in the glaze, it is the obligation of the
> >company to test.
>
> I'd like to know if this is a legal obligation ( in other words, is
> pre-marketing testing required, and is failure to do so illegal on its
> face, whether or not the glaze actually leaches cadmium.) According to
> what I've found on the FDA site, it isn't. Do you have other references?
FDA usually only gets involved after there is a compliant or problem. They
don't have the budget for much preventative work. However, after there is a
problem, they can pop in on the manufacturer and ask to see their lead and
cadmium leach tests. If they don't have them, they can seize and destroy
the ware and fine the manufacturer.
Read 21 CFR 109--the whole thing. Obviously, if you do not use cadmium, you
do not need to test for cadmium. And just as obviously, if you use cadmium,
don't test, and by some luck no cadmium leaches from your ware, no one is
going to cite or fine you. They wont even know you exist.
Today though, if you sell through most big stores or in the state of
California, you will be expected to provide proof that your ware doesn't
leach lead or cadmium.
But forget FDA--you have bigger problems if someone claims they were injured
by your ware. If you used cadmium or lead in any form and have absolutely no
test data, it is clear you were negligent and did not exercise due care in
protecting your customers. Then you and the crystals can be toast.
Monona
ACTS
181 Thompson St., # 23
NYC NY 10012-2586
Ray Aldridge on thu 11 nov 99
At 12:12 PM 11/10/99 EST, Monona wrote:
>----------------------------Original message----------------------------
(snip)
>The cadmium is not completely encapsulated since some of the crystal will
>dissolve and be incorporated into the glaze with the other ingredients. And
>some will vaporize, some will leach with acid and so on. The theory is that
>these crystals resist dissolving and much less cadmium will be dissolved into
>the glaze or fumed. But if ingredients are used in the glaze that are very
>good at fluxing zirconium silicate, those crystals are toast.
The thing I'm trying to pin down here is: how much leachable cadmium can
remain in a glaze after it's reached a point 400 degrees C above the
boiling point of cadmium. Is there some mechanism that prevents this
vaporized cadmium from evolving completely from the glaze?
Also: what kind of high temperature glaze do you think would be most
suitable for these encapsulated stains? Michael says the worst kind of
glaze would be a high-alkaline type, since this would be most active in
dissolving the zircon crystals.
>
(snip)
>But forget FDA--you have bigger problems if someone claims they were injured
>by your ware. If you used cadmium or lead in any form and have absolutely no
>test data, it is clear you were negligent and did not exercise due care in
>protecting your customers. Then you and the crystals can be toast.
>
Monona, could you speculate on why Cerdec and others selling these stains
have not, it appears, taken any steps to ensure that their customers
understand the legal issues you allude to above? The corporate stance
seems to be that these stains are safe. It strikes me that in any lawsuit,
the supplier and manufacturer would be much more vulnerable than the
typical starving potter, since their pockets are so much deeper. I'm just
wondering why they don't appear to be concerned about safety, in the
current litigious climate.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Don & June MacDonald on thu 11 nov 99
Somewhere I seem to have missed something. Just how toxic, poisonous
etc. is cadmium? I know that it is used in the paint world for cadium
yellow, cadmium red. I have a student who is using these colours to put
little fish all over her pieces, a glaze inlay process and very
creative, and I hate to tell her not to use the colours, but I have 100
other students putting things in the kilns, all fired to Cone 6, and I
do not want to take risks with their work.
Thanks for any information you can give me,
June
ACTSNYC@cs.com wrote:
>
> ----------------------------Original message----------------------------
>
> > ----- Forwarded message ----------
> > Date: Tue, 9 Nov 1999 12:53:26 EST
> > From: Ray Aldridge
> > Reply-To: Ceramic Arts Discussion List
> > To: CLAYART@LSV.UKY.EDU
> > Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> > Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> >
> > ----------------------------Original message----------------------------
> > At 04:47 PM 11/8/99 EST, Monona wrote:
> > >----------------------------Original message----------------------------
> > >
> > >You can't use "commonsense" here with this scientific problem. Stability
> > of
> > >a color at high heat is utterly unrelated to its stability in acid at room
> > >temp.
> > >
> > >The cadmium isn't really "encapsulated." It's just sort of included into
> > >crystals of zirconium silicate as they form. There's essentially no
> > toxicity
> > >data on ingestion by animals of the cadmium in this form. But neither
> > >stability in high heat, nor acid solubility are related to toxicity. And
> > >once fired, there is absolutely no guarantee at all that the cadmium will
> > not
> > >leach and be soluble in acid.
> >
> > I keep asking if anyone can cite a reference for a high-temp glaze colored
> > with encapsulated cadmium that actually did leach cadmium above the
> > acceptable limits, but I'm beginning to suspect that this is a chimera.
> > "They could be monsters in them thar woods." Well, they certainly could
> > be, no doubt about it, but I want pictures.
> >
> > Monona, I don't think you're following the line of argument I'm pursuing
> > here, which is probably my fault for being unclear. But to reprise: If
> > there is free cadmium present in an encapsulated stain, whether due to
> > imperfect processing or imperfect encapsulation or breakdown of the
> > encapsulation in the glaze solution, does it remain in a high temperature
> > glaze?
>
> There may be some free cadmium that was not washed off the surface after
> crystallization, but that is a minor issue. The major issue is the cadmium
> *in* the zirconium crystal. The crystal resists--but imperfectly--breaking
> down at high temperatures. This resistance will be dependent on the
> efficiency of the fluxes at dissolving zirconium silicate, the temperature,
> and the time the glaze is in a liquid state. Don't get a false picture in
> your mind of this little crystal as invincible under all conditions.
>
> > Or is the only cadmium present in such a glaze (after firing)
> > completely encapsulated? Otherwise would it not vaporize from the glaze,
> > just like an unencapsulated cadmium pigment?
> >
> The cadmium is not completely encapsulated since some of the crystal will
> dissolve and be incorporated into the glaze with the other ingredients. And
> some will vaporize, some will leach with acid and so on. The theory is that
> these crystals resist dissolving and much less cadmium will be dissolved into
> the glaze or fumed. But if ingredients are used in the glaze that are very
> good at fluxing zirconium silicate, those crystals are toast.
>
> Remember, the resistance of zirconium silicate to heat will be altered if
> those crystals are not by themselves, but are being acted on by fluxes.
>
> > >As soon as cadmium is present in the glaze, it is the obligation of the
> > >company to test.
> >
> > I'd like to know if this is a legal obligation ( in other words, is
> > pre-marketing testing required, and is failure to do so illegal on its
> > face, whether or not the glaze actually leaches cadmium.) According to
> > what I've found on the FDA site, it isn't. Do you have other references?
>
> FDA usually only gets involved after there is a compliant or problem. They
> don't have the budget for much preventative work. However, after there is a
> problem, they can pop in on the manufacturer and ask to see their lead and
> cadmium leach tests. If they don't have them, they can seize and destroy
> the ware and fine the manufacturer.
>
> Read 21 CFR 109--the whole thing. Obviously, if you do not use cadmium, you
> do not need to test for cadmium. And just as obviously, if you use cadmium,
> don't test, and by some luck no cadmium leaches from your ware, no one is
> going to cite or fine you. They wont even know you exist.
>
> Today though, if you sell through most big stores or in the state of
> California, you will be expected to provide proof that your ware doesn't
> leach lead or cadmium.
>
> But forget FDA--you have bigger problems if someone claims they were injured
> by your ware. If you used cadmium or lead in any form and have absolutely no
> test data, it is clear you were negligent and did not exercise due care in
> protecting your customers. Then you and the crystals can be toast.
>
> Monona
> ACTS
> 181 Thompson St., # 23
> NYC NY 10012-2586
Michael Banks on fri 12 nov 99
Ray Aldridge wrote; November 12, 1999 04:36 NZ time:
> (snip)
>
> The thing I'm trying to pin down here is: how much leachable cadmium can
> remain in a glaze after it's reached a point 400 degrees C above the
> boiling point of cadmium. Is there some mechanism that prevents this
> vaporized cadmium from evolving completely from the glaze?
No, I don't think there is Ray. Unencapsulated Cd would be expected to be
totally fugitive, although any gas bubbles entrapped in the cooled glaze
could conceivably contain some, if the the soak period was too short to
clear it. Cd is a chalcophile (sulphur-loving) element and is not capable
of bonding significantly with silicates. Even it's sulphides and sulphosalts
are volitile above red heat and are immiscible in silicate melts, analogous
to oil and water.
Butting-in,
Michael
Elke Blodgett on fri 12 nov 99
from Monona
MORE FROM RAY---
> The thing I'm trying to pin down here is: how much leachable cadmium can
> remain in a glaze after it's reached a point 400 degrees C above the
> boiling point of cadmium. Is there some mechanism that prevents this
> vaporized cadmium from evolving completely from the glaze?
>
Please read the previous post where I explain why the *melting* point of
cadmium is closer to the temperature at which cadmium starts to fume than the
*boiling* point.
To illustrate an answer to your question, imagine that you have mixed a
solvent that boils at 150 o F with water which boils at 212 o F. At room
temperature, there will be evaporation of both the solvent and the water, but
the solvent will predominate. As the temperature rises to 150 o F, the
percentage of solvent will continue to be greater until most is boiled off.
But even at 212 o F there will still be some solvent in the evaporate.
This is why to get really pure water, the temperature must be very controlled
and the water must be double or triple distilled.
The solvent that remains is just that which physically didn't get to the
surface of the liquid or to a bubble surface and it stayed in the liquid.
The same thing happens in glazes, except that they are MUCH more complex
mixtures.
>
Don't think of all the little cadmium atoms as soldiers lined up and waiting
for the exact right temperature when they will all take off running. It is
more like a disorderly retreat. Some run way ahead of the pack and
stragglers remain behind.
> (snip)
>
> >But forget FDA--you have bigger problems if someone claims they were
> injured
> >by your ware. If you used cadmium or lead in any form and have
absolutely
> no
> >test data, it is clear you were negligent and did not exercise due care in
> >protecting your customers. Then you and the crystals can be toast.
>
> Monona, could you speculate on why Cerdec and others selling these stains
> have not, it appears, taken any steps to ensure that their customers
> understand the legal issues you allude to above? The corporate stance
> seems to be that these stains are safe. It strikes me that in any lawsuit,
> the supplier and manufacturer would be much more vulnerable than the
> typical starving potter, since their pockets are so much deeper. I'm just
> wondering why they don't appear to be concerned about safety, in the
> current litigious climate.
If they are selling only to business customers and if they provide MSDSs,
they are pretty insulated from suits like this. You, on the other hand, set
up a business and have a legal obligation to know what you are doing--how to
protect yourself, your workers, and your customers. That's part of your job.
You are what is called in the law, a "sophisticated user." Cerdec has no
obligation to educate a sophisticated user. They can even be a little
extravagant in their claims of safety because it is assumed that you will
check out the safety of their product with tests of your own--as liability
and the laws direct you to.
However, if they sell to hobbyists, grade schools, etc., they are vulnerable.
That's one reason Duncan, Mayco and Amaco were vulnerable to the lawsuits
in which I was retained in 1997. We even entered into evidence their
advertisements and product literature that was aimed at these unsophisticated
users.
If Cerdec is making their stuff available directly to people without a
business tax number, then they are fools. And Degussa--who I understand is
the primary manufacturer--will not be pleased.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@compuserve.com
Gerald Durbin on fri 12 nov 99
Reference The Artist Handbook - Cadmium is considered toxic: do not ingest;
do not breath dust.
Cadmium is actually a silvery metal, the same as sodium. potassium and
barium.
This is a good reference as it contains a lot of information concerning
chemical composition of various colors etc.
Gerald Durbin Ph.D
Pontotoc Pottery
----- Original Message -----
From: Don & June MacDonald
To:
Sent: Thursday, November 11, 1999 4:12 PM
Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> ----------------------------Original message----------------------------
> Somewhere I seem to have missed something. Just how toxic, poisonous
> etc. is cadmium? I know that it is used in the paint world for cadium
> yellow, cadmium red. I have a student who is using these colours to put
> little fish all over her pieces, a glaze inlay process and very
> creative, and I hate to tell her not to use the colours, but I have 100
> other students putting things in the kilns, all fired to Cone 6, and I
> do not want to take risks with their work.
>
> Thanks for any information you can give me,
>
> June
>
> ACTSNYC@cs.com wrote:
> >
> > ----------------------------Original message----------------------------
> >
> > > ----- Forwarded message ----------
> > > Date: Tue, 9 Nov 1999 12:53:26 EST
> > > From: Ray Aldridge
> > > Reply-To: Ceramic Arts Discussion List
> > > To: CLAYART@LSV.UKY.EDU
> > > Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> > > Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> > >
> > > ----------------------------Original
message----------------------------
> > > At 04:47 PM 11/8/99 EST, Monona wrote:
> > > >----------------------------Original
message----------------------------
> > > >
> > > >You can't use "commonsense" here with this scientific problem.
Stability
> > > of
> > > >a color at high heat is utterly unrelated to its stability in acid
at room
> > > >temp.
> > > >
> > > >The cadmium isn't really "encapsulated." It's just sort of included
into
> > > >crystals of zirconium silicate as they form. There's essentially no
> > > toxicity
> > > >data on ingestion by animals of the cadmium in this form. But
neither
> > > >stability in high heat, nor acid solubility are related to toxicity.
And
> > > >once fired, there is absolutely no guarantee at all that the cadmium
will
> > > not
> > > >leach and be soluble in acid.
> > >
> > > I keep asking if anyone can cite a reference for a high-temp glaze
colored
> > > with encapsulated cadmium that actually did leach cadmium above the
> > > acceptable limits, but I'm beginning to suspect that this is a
chimera.
> > > "They could be monsters in them thar woods." Well, they certainly
could
> > > be, no doubt about it, but I want pictures.
> > >
> > > Monona, I don't think you're following the line of argument I'm
pursuing
> > > here, which is probably my fault for being unclear. But to reprise:
If
> > > there is free cadmium present in an encapsulated stain, whether due
to
> > > imperfect processing or imperfect encapsulation or breakdown of the
> > > encapsulation in the glaze solution, does it remain in a high
temperature
> > > glaze?
> >
> > There may be some free cadmium that was not washed off the surface after
> > crystallization, but that is a minor issue. The major issue is the
cadmium
> > *in* the zirconium crystal. The crystal resists--but
imperfectly--breaking
> > down at high temperatures. This resistance will be dependent on the
> > efficiency of the fluxes at dissolving zirconium silicate, the
temperature,
> > and the time the glaze is in a liquid state. Don't get a false picture
in
> > your mind of this little crystal as invincible under all conditions.
> >
> > > Or is the only cadmium present in such a glaze (after firing)
> > > completely encapsulated? Otherwise would it not vaporize from the
glaze,
> > > just like an unencapsulated cadmium pigment?
> > >
> > The cadmium is not completely encapsulated since some of the crystal
will
> > dissolve and be incorporated into the glaze with the other ingredients.
And
> > some will vaporize, some will leach with acid and so on. The theory is
that
> > these crystals resist dissolving and much less cadmium will be dissolved
into
> > the glaze or fumed. But if ingredients are used in the glaze that are
very
> > good at fluxing zirconium silicate, those crystals are toast.
> >
> > Remember, the resistance of zirconium silicate to heat will be altered
if
> > those crystals are not by themselves, but are being acted on by fluxes.
> >
> > > >As soon as cadmium is present in the glaze, it is the obligation of
the
> > > >company to test.
> > >
> > > I'd like to know if this is a legal obligation ( in other words, is
> > > pre-marketing testing required, and is failure to do so illegal on
its
> > > face, whether or not the glaze actually leaches cadmium.) According
to
> > > what I've found on the FDA site, it isn't. Do you have other
references?
> >
> > FDA usually only gets involved after there is a compliant or problem.
They
> > don't have the budget for much preventative work. However, after there
is a
> > problem, they can pop in on the manufacturer and ask to see their lead
and
> > cadmium leach tests. If they don't have them, they can seize and
destroy
> > the ware and fine the manufacturer.
> >
> > Read 21 CFR 109--the whole thing. Obviously, if you do not use cadmium,
you
> > do not need to test for cadmium. And just as obviously, if you use
cadmium,
> > don't test, and by some luck no cadmium leaches from your ware, no one
is
> > going to cite or fine you. They wont even know you exist.
> >
> > Today though, if you sell through most big stores or in the state of
> > California, you will be expected to provide proof that your ware doesn't
> > leach lead or cadmium.
> >
> > But forget FDA--you have bigger problems if someone claims they were
injured
> > by your ware. If you used cadmium or lead in any form and have
absolutely no
> > test data, it is clear you were negligent and did not exercise due care
in
> > protecting your customers. Then you and the crystals can be toast.
> >
> > Monona
> > ACTS
> > 181 Thompson St., # 23
> > NYC NY 10012-2586
>
Ray Aldridge on sat 13 nov 99
>
>from Monona
>
>MORE FROM RAY---
>> The thing I'm trying to pin down here is: how much leachable cadmium can
>> remain in a glaze after it's reached a point 400 degrees C above the
>> boiling point of cadmium. Is there some mechanism that prevents this
>> vaporized cadmium from evolving completely from the glaze?
>>
>Please read the previous post where I explain why the *melting* point of
>cadmium is closer to the temperature at which cadmium starts to fume than the
>*boiling* point.
Yes, of course, but what we are discussing here is what happens *after* the
glaze has passed the boiling point of cadmium, not before. Let's assume
that those of us who are still interested in the discussion understand that
evaporation of a fluid begins before the boiling point is reached.
However, this is irrelevant to the point we're considering.
>>
>Don't think of all the little cadmium atoms as soldiers lined up and waiting
>for the exact right temperature when they will all take off running. It is
>more like a disorderly retreat. Some run way ahead of the pack and
>stragglers remain behind.
I'm sure you are correct. But as a practical matter, considering that
cadmium boils below 800 degrees C and the glaze we're discussing matures at
over 1200 degrees C, how many of these little soldiers can remain behind if
this temperature rise takes several hours, and the glaze is a fluid melt?
If I'm reading Michael correctly, he's saying "an insignificant number."
Do you have an alternate view? To extend your analogy in a relevant
direction, if water boils at 100 C, how much water is going to be left in
the retort at 500 C?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Elke Blodgett on sat 13 nov 99
from Monona
>
> ---------- Forwarded message ----------
> Date: Thu, 11 Nov 1999 17:12:28 EST
> From: Don & June MacDonald
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
>
> ----------------------------Original message----------------------------
> Somewhere I seem to have missed something. Just how toxic, poisonous
> etc. is cadmium? I know that it is used in the paint world for cadium
> yellow, cadmium red. I have a student who is using these colours to put
> little fish all over her pieces, a glaze inlay process and very
> creative, and I hate to tell her not to use the colours, but I have 100
> other students putting things in the kilns, all fired to Cone 6, and I
> do not want to take risks with their work.
> Thanks for any information you can give me,
> June
>
You say you "have a student" using cadmium. If you are a teacher in a public
school or in a university, your administrators are obligated by law to
provide hazard communication training that would include assessing the
toxicity of your materials by reading MSDSs, by comparing threshold limit
values, and other means.
Comparative toxicity is not an easy question, and it takes time and
education. But in the case of cadmium, there is not many metals you can use
that are more toxic. By inhalation the air quality limits (threshold limit
values) for cadmium are even more restrictive than for arsenic. It is a
potent carcinogen and kidney toxin in particular.
And if the students are children, they have no business using cadmium or
lead. Only people who can understand the hazards, who can carry out
precautions effectively and consistently, and are of an age to be able give
legal informed consent to accept the risks should be using things this toxic.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
Don & June MacDonald on mon 15 nov 99
Thank you for the opinions given on my request for information about
cadmium. We were talking about cadmium inclusion stains which are
advertised as being "safe" in all the ceramic advertising, and when they
first came into the suppliers, no-one knew much about them, except that
it was now possible to make these bright colours, previously
unavailable. I try at all times to ensure that things are safe for
users, students, myself, and the end user of the product, however I
might point out that there are so many opinions as to the relative
safety of everything we use that it is sometimes difficult to determine
what is reality, and what is 'old wives tales'. It seems sometimes that
today's relatively safe ingredient turns into tomorrow's dreadful
poison. Also, when they take the lead out of gasoline and add manganese
instead, the small amount of adding to the chemical soup that a potter
does in comparison to all of the drivers on the road seems somewhat
irelevant.
I do appreciate and pay attention to the articles and warnings that
Monona gives us all. But as my daughter said, after a visit to Bangkok,
until the whole world pays attention to air and other pollution, lots of
that pollution caused by North American ownership, we in North America
are just spitting against the wind.
I still do not feel that I have a definitive answer about encapsulated
cadmium stains, which is of course what this discussion has been all
about.
June
Elke Blodgett wrote:
>
> ----------------------------Original message----------------------------
>
> from Monona
>
> >
> > ---------- Forwarded message ----------
> > Date: Thu, 11 Nov 1999 17:12:28 EST
> > From: Don & June MacDonald
> > Reply-To: Ceramic Arts Discussion List
> > To: CLAYART@LSV.UKY.EDU
> > Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> > Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> >
> > ----------------------------Original message----------------------------
> > Somewhere I seem to have missed something. Just how toxic, poisonous
> > etc. is cadmium? I know that it is used in the paint world for cadium
> > yellow, cadmium red. I have a student who is using these colours to put
> > little fish all over her pieces, a glaze inlay process and very
> > creative, and I hate to tell her not to use the colours, but I have 100
> > other students putting things in the kilns, all fired to Cone 6, and I
> > do not want to take risks with their work.
> > Thanks for any information you can give me,
> > June
> >
> You say you "have a student" using cadmium. If you are a teacher in a public
> school or in a university, your administrators are obligated by law to
> provide hazard communication training that would include assessing the
> toxicity of your materials by reading MSDSs, by comparing threshold limit
> values, and other means.
>
> Comparative toxicity is not an easy question, and it takes time and
> education. But in the case of cadmium, there is not many metals you can use
> that are more toxic. By inhalation the air quality limits (threshold limit
> values) for cadmium are even more restrictive than for arsenic. It is a
> potent carcinogen and kidney toxin in particular.
>
> And if the students are children, they have no business using cadmium or
> lead. Only people who can understand the hazards, who can carry out
> precautions effectively and consistently, and are of an age to be able give
> legal informed consent to accept the risks should be using things this toxic.
>
> Monona Rossol
> ACTS
> 181 Thompson St., # 23
> NYC NY 10012-2586 212/777-0062
ACTSNYC@cs.com on tue 16 nov 99
In a message dated 11/14/99 9:51:49 AM Eastern Standard Time,
eiblodge@freenet.edmonton.ab.ca writes:
>
> Yes, of course, but what we are discussing here is what happens *after* the
> glaze has passed the boiling point of cadmium, not before. Let's assume
> that those of us who are still interested in the discussion understand that
> evaporation of a fluid begins before the boiling point is reached.
> However, this is irrelevant to the point we're considering.
>
> >>
> >Don't think of all the little cadmium atoms as soldiers lined up and
> waiting
> >for the exact right temperature when they will all take off running. It
is
> >more like a disorderly retreat. Some run way ahead of the pack and
> >stragglers remain behind.
>
> I'm sure you are correct. But as a practical matter, considering that
> cadmium boils below 800 degrees C and the glaze we're discussing matures at
> over 1200 degrees C, how many of these little soldiers can remain behind if
> this temperature rise takes several hours, and the glaze is a fluid melt?
Is there any color left? If there is, there is a lot. If the color is gone,
maybe the solders are gone, too.
Remember, that the zirconium silicate crystals are very stable with heat, but
heat stability is not related to acid resistance.
But its all speculation. That's why testing is necessary.
> If I'm reading Michael correctly, he's saying "an insignificant number."
> Do you have an alternate view? To extend your analogy in a relevant
> direction, if water boils at 100 C, how much water is going to be left in
> the retort at 500 C?
You've missed the point of the example. The glaze is not all going to
volatilize like the water. I just used it to indicate that there can still
be low boiling materials left in solution well above their boiling point.
Also as I said, the glaze mixture is much more complicated than the water.
There are many substances. Materials can complex with other things. And the
thick viscous nature of the glaze impedes outgassing.
We don't need to theorize like this. We need to test. If the tests on a
particular glaze indicate that no cadmium present, then that's the end of it.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@compuserve.com
ACTSNYC@cs.com on wed 17 nov 99
> --------- Forwarded message ----------
> Date: Mon, 15 Nov 1999 14:27:55 EST
> From: Don & June MacDonald
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> Resent-Subject: Re: Hazards of encapsulated cadmium stains (fwd)
> ----------------------------Original message----------------------------
SNIP
> I do appreciate and pay attention to the articles and warnings that
> Monona gives us all. But as my daughter said, after a visit to Bangkok,
> until the whole world pays attention to air and other pollution, lots of
> that pollution caused by North American ownership, we in North America
> are just spitting against the wind. <
Fuzzy thinking that. We in North America are polluting on a per/person basis
a great deal more than they are in Bangkok. We just don't throw it in the
clongs. What do you want to do? Pollute at will until Bangkok stops?
Change begins small. And it begins with each of us.
Besides, this glaze question has little to do with pollution. It has to do
with potential harm to your customers and students.
> I still do not feel that I have a definitive answer about encapsulated
> cadmium stains, which is of course what this discussion has been all
> about. <
Good. That's exactly as it should be. And now that you clearly state that
you do not know for sure, you are ethically obligated to test if you use the
stains rather than put customers or students at potential risk.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@compuserve.com
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