Robert Wilt on sun 2 aug 98
Laura Conley writes:
>Hamer states that strontium is not toxic. I've heard rumors otherwise.
>Does anyone know?
Also in "The Artist's Complete Health and Safety Guide" 2nd edition
(by Monona Rossol) it says of strontium carbonate "No significant
hazards".
At MIT we got 5 pound bags of strontium carbonate (some labeled
strontium oxide) last year. These were rebagged by our supplier.
No particular warnings on the bags. All of our rebagged
supplies have the same generic warning.
Just recently we ordered a full bag. It is labeled "Strontium
Carbonate Type D", made in Cartersville, GA by Chemical Products
Corp. "CONTAINS 1% BARIUM CARBONATE". The bag had strong warnings about
not breathing the dust. I was a little surprised, and not happy.
(Not that I blame the manufacturer - their bags are clearly marked.)
I went to another studio where I teach (Radcliffe) and checked their
strontium supply. They keep their bags in big blue bins with covers -
good for keeping down the dust, but not conducive to reading the
outsides of bags. Their strontium is labeled "Strontium carbonate B",
made in Germany by a company called Solvay (?). "CONTAINS 2-3%
BARIUM CARBONATE". Similar warnings about the dust.
It's not that I breathe strontium carbonate dust on a regular basis.
But, there is the EPA, there is OSHA, there are students who can't
get simple safety precautions into their heads, there are occasional
material spills, there are customers who want to be reassured that
their glazes are safe... Despite these issues, I'm not going to ask that
we pull strontium carbonate from our shelves (as we did barium
carbonate), and I'm not going to stop using strontium carbonate in
my glazes. I will, though, test the strontium matt glazes for barium
release before using them on food surfaces (I'm 95% sure they'll pass,
but better to make it 100% if possible). And we will put up some
warning around the strontium, especially since anyone who reads the
books may make the same false assumptions about its safety.
Geochemical association plays some part in this - barium and strontium
ores are closely associated in nature, so it is natural for the
strontium ore to contain some barium. The refining process probably
removes some of the barium ore, but removing it to an acceptably
safe level may be prohibitively expensive for potters (but maybe not -
does anyone know?)
I think that this can be generalized - many pottery materials are
relatively unrefined and may contain various contaminants you might
not see in the "generic" formula. For example, look at the difference
between a generic clay formula (Al2O3 2SiO2 2H2O) and an actual
clay analysis, where you start to find titanium, iron, and various
fluxes. Even that analysis may not tell the whole story - if you go
down into the parts-per-million range, you can start to find things
like chrome, vanadium, lead, arsenic, uranium, etc. These extremely
minor contaminants are not a problem as far as we know, but they are
there. Some of these same contaminants play a much larger role in the
geochemistry of the coloring oxides, and depending on the refining
process, could be present in significant quantities. (Not that most
of these oxides aren't already toxic by themselves.) But, I rarely
see detailed analyses of colorants, so don't know for sure.
Here are two things I'd like to see done:
- materials rebagged by the supplier should have a label that
repeats all the warnings we would have received had we purchased
a full bag
- books talking about toxicity and safety should point out that
materials sometimes contain toxic contaminants, and be specific
when possible
By the way, the Pinnell Strontium Matt glazes seem to work much better
when I mix them at Radcliffe than when I mix them at MIT. Possibly the
different strontium sources are the cause of this.
>Also, I have heard that uranium, strontium, vanadium are all a bit
>radioactive. Is this true? How radioactive? Are there any others?
Uranium has naturally-occurring radioactive isotopes (U-234, U-235,
U-238). Strontium and barium have none. Vanadium has one (V-50).
Potassium has one (K-40). Carbon has one (C-14). Lead has one (Pb-204).
You might also find some rubidium (Rb-87) in your materials, maybe
a few others. How radioactive? That depends on the intensity and type
(alpha, beta, gamma, x-ray) of the radiation. The intensity depends
on the abundance of the isotope, the energy of the emitted particle(s)
and/or photon(s), and the half-life of the isotope. The effects on
organic tissue depend on the type and energy of the radiation, the
location of the isotope (internal or external), and a great deal of
probability (luck) as to what molecules the radiation hits (if any)
and what happens afterward.
Remember that your body is a constant shooting gallery for background
radiation from the earth below and sky above. I wouldn't worry too
much about radiation from any non-concentrated sources (uranium I'd
keep in a lead-lined box, but forget the rest). The chemical toxicity
issues are of much greater concern.
bob wilt
Earl Brunner on mon 3 aug 98
In a message dated 8/2/98 8:42:51 AM Pacific Daylight Time,
rjw@studiopotter.org writes:
<< Despite these issues, I'm not going to ask that
we pull strontium carbonate from our shelves (as we did barium
carbonate), and I'm not going to stop using strontium carbonate in
my glazes. >>
Am I missing something here? I was not aware that we were pulling barium from
our glaze palette. I see little in any of my resource books that suggest that
we should eliminate this material altogether. I will admit to some reluctance
to use glazes that appear high in this material. Short of laboratory tests,
and from a glaze calculation standpoint, are there suggested limits for barium
in say the cone 5-6 range and the cone 9-10 range that would minimize or
prevent leaching? Do we know that leaching takes place?
Edouard Bastarache on mon 3 aug 98
Hello Bob,
Strontium:
The greatest danger to humans is that from artificial isotopes 89Sr and 90
Sr produced in nuclear reactions;fallout of 90 Sr mainly from atmospheric
nuclear explosions (and power-plant reactor accidents) has caused great
concern.These isotopes are deposited in bones, acting as a source of
internal radiation.The 90 Sr has a half-life of 28 years and emits beta
particles that damage the blood forming cells in the bone marrow.
Obviously,as can be seen, this is not the case of strontium carbonate
I belong to the generation who protested against nuclear testing and
warfare.
Later,
Edouard Bastarache M.D.(Occupational & Environmental Medicine)
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
----------
> De : Robert Wilt
> A : CLAYART@LSV.UKY.EDU
> Objet : Re: toxicity of strontium
> Date : 2 ao{t, 1998 11:41
>
> ----------------------------Original message----------------------------
> Laura Conley writes:
> >Hamer states that strontium is not toxic. I've heard rumors otherwise.
> >Does anyone know?
>
> Also in "The Artist's Complete Health and Safety Guide" 2nd edition
> (by Monona Rossol) it says of strontium carbonate "No significant
> hazards".
>
> At MIT we got 5 pound bags of strontium carbonate (some labeled
> strontium oxide) last year. These were rebagged by our supplier.
> No particular warnings on the bags. All of our rebagged
> supplies have the same generic warning.
>
> Just recently we ordered a full bag. It is labeled "Strontium
> Carbonate Type D", made in Cartersville, GA by Chemical Products
> Corp. "CONTAINS 1% BARIUM CARBONATE". The bag had strong warnings about
> not breathing the dust. I was a little surprised, and not happy.
> (Not that I blame the manufacturer - their bags are clearly marked.)
>
> I went to another studio where I teach (Radcliffe) and checked their
> strontium supply. They keep their bags in big blue bins with covers -
> good for keeping down the dust, but not conducive to reading the
> outsides of bags. Their strontium is labeled "Strontium carbonate B",
> made in Germany by a company called Solvay (?). "CONTAINS 2-3%
> BARIUM CARBONATE". Similar warnings about the dust.
>
> It's not that I breathe strontium carbonate dust on a regular basis.
> But, there is the EPA, there is OSHA, there are students who can't
> get simple safety precautions into their heads, there are occasional
> material spills, there are customers who want to be reassured that
> their glazes are safe... Despite these issues, I'm not going to ask that
> we pull strontium carbonate from our shelves (as we did barium
> carbonate), and I'm not going to stop using strontium carbonate in
> my glazes. I will, though, test the strontium matt glazes for barium
> release before using them on food surfaces (I'm 95% sure they'll pass,
> but better to make it 100% if possible). And we will put up some
> warning around the strontium, especially since anyone who reads the
> books may make the same false assumptions about its safety.
>
> Geochemical association plays some part in this - barium and strontium
> ores are closely associated in nature, so it is natural for the
> strontium ore to contain some barium. The refining process probably
> removes some of the barium ore, but removing it to an acceptably
> safe level may be prohibitively expensive for potters (but maybe not -
> does anyone know?)
>
> I think that this can be generalized - many pottery materials are
> relatively unrefined and may contain various contaminants you might
> not see in the "generic" formula. For example, look at the difference
> between a generic clay formula (Al2O3 2SiO2 2H2O) and an actual
> clay analysis, where you start to find titanium, iron, and various
> fluxes. Even that analysis may not tell the whole story - if you go
> down into the parts-per-million range, you can start to find things
> like chrome, vanadium, lead, arsenic, uranium, etc. These extremely
> minor contaminants are not a problem as far as we know, but they are
> there. Some of these same contaminants play a much larger role in the
> geochemistry of the coloring oxides, and depending on the refining
> process, could be present in significant quantities. (Not that most
> of these oxides aren't already toxic by themselves.) But, I rarely
> see detailed analyses of colorants, so don't know for sure.
>
> Here are two things I'd like to see done:
> - materials rebagged by the supplier should have a label that
> repeats all the warnings we would have received had we purchased
> a full bag
> - books talking about toxicity and safety should point out that
> materials sometimes contain toxic contaminants, and be specific
> when possible
>
> By the way, the Pinnell Strontium Matt glazes seem to work much better
> when I mix them at Radcliffe than when I mix them at MIT. Possibly the
> different strontium sources are the cause of this.
>
>
> >Also, I have heard that uranium, strontium, vanadium are all a bit
> >radioactive. Is this true? How radioactive? Are there any others?
>
> Uranium has naturally-occurring radioactive isotopes (U-234, U-235,
> U-238). Strontium and barium have none. Vanadium has one (V-50).
> Potassium has one (K-40). Carbon has one (C-14). Lead has one (Pb-204).
> You might also find some rubidium (Rb-87) in your materials, maybe
> a few others. How radioactive? That depends on the intensity and type
> (alpha, beta, gamma, x-ray) of the radiation. The intensity depends
> on the abundance of the isotope, the energy of the emitted particle(s)
> and/or photon(s), and the half-life of the isotope. The effects on
> organic tissue depend on the type and energy of the radiation, the
> location of the isotope (internal or external), and a great deal of
> probability (luck) as to what molecules the radiation hits (if any)
> and what happens afterward.
>
> Remember that your body is a constant shooting gallery for background
> radiation from the earth below and sky above. I wouldn't worry too
> much about radiation from any non-concentrated sources (uranium I'd
> keep in a lead-lined box, but forget the rest). The chemical toxicity
> issues are of much greater concern.
>
> bob wilt
Tom Buck on tue 4 aug 98
Earl Brunner:
Janet DeBoos of Australia has reported on the leachability of
glazes containing Bairum Oxide (from BaCO3 usually). Her data appears in
Ceramics Technical 3 (an ofshoot of Ceramics Art and Perception, Jane
Mansfield, Editor). Her studies continue, I believe, yet she urges caution
-- some innocent-looking glazes will leach barium ion on contact with
acidic foods. And barium ion is toxic at low levels...see M Rossol's
manual on hazards in the arts.
If a potter uses barium-based glazes, she/he would be wise the
avoid their application on vessels that could find their way into the
fridge. Even a dryweed pot may be safeguarded by placing holes near
the bottom so it won't hold liquid.
As for strontium, if the SrCO3 grade available to potters contains
up to 2% BaCO3, and the recipe calls for say 10% SrCO3, then 0.2% BaCO3
may enter the glaze on the pot. At this level, can barium ion be leached
from a balanced glaze on say a plate? I've no data that says aye or nay.
Only a standard leach test will prove the plate foodsafe. If one wishes to
avoid paying for a leach test, then one could buy "reagent" grade SrCO3
with its high-purity (99.9% usually). Strontium ion is listed as "low
toxicity" in my references.
Tom Buck ) tel:
905-389-2339 & snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Ron Roy on tue 4 aug 98
I would like to commend Bob for what I think is an excellent post. It is
true that Strontium Carb has Barium Carb associated with it - my materials
info says 1.0 to 2.5 %. It is also interesting to note that strontium
carbonate (1.3 to 2.2%) is also associated with barium carbonate when
produced by Cometal.
By the way Tayor and Bull recommend we use not the natural but the prepared
variety - which has no Barium - anyone know where to get that?
I would also like to add that in my experiments I have found SrO to be a
valuable auxiliary flux for cone 6 glazes and I am concerned that the
material will be seen as a significant hazard - I don't think so -
certainly not in smaller quantities in glazes. I hasten to add - I don't
think we should be breathing it or eating it.
Here is what Taylor and Bull say about SrO and I summarize:
In direct comparison to Barium it is brighter and more fusible in glazes.
Improves the chemical resistance when replacing zinc and lead.
It's primary role is to is to facilitate low temperature glazes - when
firing at 1145 (cone 01) it helps in making craze free glazes due in part
to the highly developed glaze-body reaction layer.
When substituting, on a molecular level, for Barium you need less Strontium
and therefore lower the expansion of the glaze.
Adding small amounts of a new material to a glaze always lowers the
eutectic (more melting.) Small amounts of SrO in cone 6 glazes seems to me
to be a worthwhile avenue to investigate.
RR
Part of Bob's original post -----------------------
>I think that this can be generalized - many pottery materials are
>relatively unrefined and may contain various contaminants you might
>not see in the "generic" formula. For example, look at the difference
>between a generic clay formula (Al2O3 2SiO2 2H2O) and an actual
>clay analysis, where you start to find titanium, iron, and various
>fluxes. Even that analysis may not tell the whole story - if you go
>down into the parts-per-million range, you can start to find things
>like chrome, vanadium, lead, arsenic, uranium, etc. These extremely
>minor contaminants are not a problem as far as we know, but they are
>there. Some of these same contaminants play a much larger role in the
>geochemistry of the coloring oxides, and depending on the refining
>process, could be present in significant quantities. (Not that most
>of these oxides aren't already toxic by themselves.) But, I rarely
>see detailed analyses of colorants, so don't know for sure.
>bob wilt
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Robert Wilt on fri 7 aug 98
Earl Brunner writes:
>Am I missing something here? I was not aware that we were pulling barium from
>our glaze palette....
"We" refers to the local "we" - meaning the places where I teach. These
are college extracurricular and adult education settings. Both the
Radcliffe and MIT studios took barium carbonate out of their regular
studio glazes several years ago, mostly due to the toxicity of the raw
material and the number of inexperienced people around, but also because
some of the studio barium glazes failed the barium release test (whatever
standard they used then). However, people were permitted to use it in
their own glazes. A few did. More recently, though, both studios have
stopped stocking barium carbonate. This was brought on by the EPA
cracking down on the universities. They are looking for lead, barium,
chromium, mercury, copper, etc. The EPA gave the universities plenty of
warning of impending inspections, so the universities were scrambling for
a while to come into compliance with EPA rules. At Radcliffe (Harvard) we
were encouraged by the university to remove any suspect material from our
shelves, especially if it was not strictly necessary to our standard
palette. In addition to barium carbonate, things like iron chromate and
vanadium were removed. Green chrome and other metals used in our studio
slips and glazes got to stay, though. And we decided to let people keep
small private stocks of any materials they want for their own personal
glaze batches.
To make a long story short, and despite the other measures we took, at
Radcliffe we now are required to have a toxic waste disposal barrel in
our glaze room. All the sediment from the glaze settling sink goes into
it, and we pay to have it removed as toxic waste. I don't know where this
situation will lead. Environmental regulations are bound to get tighter
rather than looser, and toxic waste disposal is quite expensive. It could
in future years have a major impact on the way we work in that studio,
and/or on the types of raw materials we can use.
This trend is for the best, I think. It often takes some tangible threat
like fines from the EPA to make us do "the right thing" - which to me means
cutting down on water pollution as much as possible. All of our studios
could probably reduce heavy metal discharge with a little extra work and
some ingenuity. For example, like many other people on this list, we
already recycle our old glaze remnants into scrap glazes, which generally
turn out quite well. Hopefully we will be able to to recycle our settling
residue also.
bob wilt
hal mc whinnie on sun 9 aug 98
what we need is a major effort on the part of those interested in glaze
research to idenity substitutions.
the issue is more for teaching situtations then individual studio were
one can use such compounds if you know what you are doing.
about 5 years ago I cleaned out a whole store room at a high school of
commericakl glazes with lead and casdmiun, hundreds of dollars worth of
materials. I still use these in my sculptures which are fired out of
doors in a low fire gas kiln.
hal mc whinnie
On Fri, 7 Aug 1998 08:20:58 EDT Robert Wilt
writes:
>----------------------------Original
>message----------------------------
>Earl Brunner writes:
>>Am I missing something here? I was not aware that we were pulling
>barium from
>>our glaze palette....
>
>"We" refers to the local "we" - meaning the places where I teach.
>These
>are college extracurricular and adult education settings. Both the
>Radcliffe and MIT studios took barium carbonate out of their regular
>studio glazes several years ago, mostly due to the toxicity of the raw
>material and the number of inexperienced people around, but also
>because
>some of the studio barium glazes failed the barium release test
>(whatever
>standard they used then). However, people were permitted to use it in
>their own glazes. A few did. More recently, though, both studios have
>stopped stocking barium carbonate. This was brought on by the EPA
>cracking down on the universities. They are looking for lead, barium,
>chromium, mercury, copper, etc. The EPA gave the universities plenty
>of
>warning of impending inspections, so the universities were scrambling
>for
>a while to come into compliance with EPA rules. At Radcliffe (Harvard)
>we
>were encouraged by the university to remove any suspect material from
>our
>shelves, especially if it was not strictly necessary to our standard
>palette. In addition to barium carbonate, things like iron chromate
>and
>vanadium were removed. Green chrome and other metals used in our
>studio
>slips and glazes got to stay, though. And we decided to let people
>keep
>small private stocks of any materials they want for their own personal
>glaze batches.
>
>To make a long story short, and despite the other measures we took, at
>Radcliffe we now are required to have a toxic waste disposal barrel in
>our glaze room. All the sediment from the glaze settling sink goes
>into
>it, and we pay to have it removed as toxic waste. I don't know where
>this
>situation will lead. Environmental regulations are bound to get
>tighter
>rather than looser, and toxic waste disposal is quite expensive. It
>could
>in future years have a major impact on the way we work in that studio,
>and/or on the types of raw materials we can use.
>
>This trend is for the best, I think. It often takes some tangible
>threat
>like fines from the EPA to make us do "the right thing" - which to me
>means
>cutting down on water pollution as much as possible. All of our
>studios
>could probably reduce heavy metal discharge with a little extra work
>and
>some ingenuity. For example, like many other people on this list, we
>already recycle our old glaze remnants into scrap glazes, which
>generally
>turn out quite well. Hopefully we will be able to to recycle our
>settling
>residue also.
>
>bob wilt
>
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