Paul Lewing on mon 21 apr 03
on 4/21/03 8:39 AM, Hannah Brehmer at hannah.b@MINDSPRING.COM wrote:
> Thanks to Lily about the possible toxicity of a spodumene glaze, since =
> it contains lithium.
So what =
> I'm hoping is that Ron or others might be willing to say whether they =
> think the spodumene glaze is food safe or not.
Hannah, there are a couple of points to be made about this glaze and
lithium.
1. No one can tell if a glaze is "food safe" or not without having it
professionally tested. In fact there is no universally accepted definition
of "food safe", but a professional test could tell you if it leached
lithium, or any other oxide. And even if testing did prove that your glaze
was leaching lithium, there's no standard for what would be "safe".
2. No one knows that lithium from either raw spodumene or leached from a
spodumene-containing glaze is harmful, even to people who are taking lithium
for manic-depressive disorder. It may be, and that may even be a logical
assumption, but I don't believe any definitive testing on that subject
exists. Certainly no one has ever tested whether lithium absorbed from
inhaling raw spodumene dust could affect a manic-depressive potter taking
lithium as a medication. There is too little interest and too few subjects
to test. It seems logical that lithium carbonate might be a danger in this
situation, but can the lithium oxide that's part of a spodumene molecule do
the same thing? No one knows.
Those who would not use lithium because of its possible danger to those few
susceptible people are making that decision on the maxim, "Why take
chances?", not on the basis of data. I don't say that decision is wrong or
silly, just that it's not supported by data.
Keep in mind also some facts about oxide leaching and about this glaze. For
an oxide to leach, it has to be subjected to a strong acid or alkaline
substance for an extended period of time. The at-home test that Ron and
John suggest is three days in vinegar, a pretty strong acid.
This means that the glaze in question has to be on the inside of the pot.
It makes no difference what you put on the outside; it won't be coming into
prolonged contact with food or with you.
And remember that this glaze is very matte and very light in color. It will
show marks from metal utensils very easily and they will make an unpleasant
sound on it. It is not a good choice for a liner glaze.
All this having been said, it's good that you care about your customers,
your glazes, and yourself, but keep this all in perspective. Remember that
the most dangerous substance in your studio (and this is supported by
testing) is clay dust.
Paul Lewing, Seattle
Hannah Brehmer on mon 21 apr 03
Thanks to Lily about the possible toxicity of a spodumene glaze, since =
it contains lithium. I looked on Google and scanned 11 pages of =
headings for spodumene. All seemed to be concentrating on the =
gemstone qualities of the mineral. I tried lithium, and those =
headings were about taking it as medication. (So okay, I didn't =
read every posting! I would still be there now if I did..) So what =
I'm hoping is that Ron or others might be willing to say whether they =
think the spodumene glaze is food safe or not. To recap: Custer: 30, =
EPK: 26, Dolomite: 22, Spodumene: 20, Whiting: 2. Tin Oxide 6%. =
=20
Much appreciation to the people on this wonderful list - you're the =
best!
Warmest wishes-
Hannah from Tahoe, where we have been having one snowstorm after =
another. Time to move down to the wine country. =20
Ron Roy on tue 22 apr 03
Hi Hannah,
As we explain in our book - food safe does not mean much unless you are
taking about lead and cadmium in unstable glazes.
We prefer to use the words stable and/or durable.
As we also note in our book - it is very difficult to find matte glazes
that are durable - because - as in this case - alumina mattes depend on a
shortage of silica - and as we explain - one of the rules applicable to
making stable/durable glazes in - have enough silica.
I calculated this glaze using the Australian Spodumene - and it certainly
is short of silica - if it's fired at cone 10 it is probably melted well
enough but if it's fired at cone 6 it will not be well melted and that
would make it worse.
Would it be safe next to food is the question and I don't think anyone can
say for sure that it is not - will it leach some lithium into food - I
would say yes - testing will be the only way to find out. Will there be
enough Lithium to cause anyone any harm - I don't know. If acid food is
cooked in a casserole - stored for a day - reheated - stored again - all
that will increase the extraction of whatever is in that glaze for sure.
It is our opinion that matte glazes are best not used inside food
containers - not only because of the tainted food question but they are not
as serviceable as gloss glazes. They are hard to keep clean and stain free,
they often mark from cutlery and they sound horrible when they come in
contact with spoons.
The calculated expansion of matte glazes is not reliable - it is important
to test these types of glazes to make sure the expansion is not to low for
the clay they are on - which can lead to shivering - the last thing you
want is razor sharp slivers of glaze in food.
Hope this helps but I'm sure it is not the answer you wanted - sorry about that.
RR
>Thanks to Lily about the possible toxicity of a spodumene glaze, since
>it contains lithium. I looked on Google and scanned 11 pages of
>headings for spodumene. All seemed to be concentrating on the gemstone
>qualities of the mineral. I tried lithium, and those headings were
>about taking it as medication. (So okay, I didn't read every posting!
>I would still be there now if I did..) So what I'm hoping is that Ron
>or others might be willing to say whether they think the spodumene glaze
>is food safe or not. To recap: Custer: 30, EPK: 26, Dolomite: 22,
>Spodumene: 20, Whiting: 2. Tin Oxide 6%.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 25 apr 03
I am thinking that silica and clay may not be the most dangerous in the
studio - lead and cadmium would be more so as would manganese dust and
fumes.
It would be best to generally regard kiln fumes dangerous ads well - we owe
it to ourselves and those around us to be informed about the toxins we come
in contact with in pottery. The subject is not covered in nearly all the
books we commonly use - a puzzling omission.
RR
>All this having been said, it's good that you care about your customers,
>your glazes, and yourself, but keep this all in perspective. Remember that
>the most dangerous substance in your studio (and this is supported by
>testing) is clay dust.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Paul Lewing on fri 25 apr 03
on 4/25/03 11:39 AM, Ron Roy at ronroy@TOTAL.NET wrote:
> I am thinking that silica and clay may not be the most dangerous in the
> studio - lead and cadmium would be more so as would manganese dust and
> fumes.
Remember that
>> the most dangerous substance in your studio (and this is supported by
>> testing) is clay dust.
Ron, you are right, as usual. Lead, cadmium, and manganese are indeed more
dangerous, gram for gram. I guess I should have stated it that silica and
clay are the biggest potential hazard in the studio, because there is so
much more of them than of any other dangerous substance.
And my other real point would be that, while we should all be as careful as
we can, there can be no such thing as "zero tolerance" for hazardous
substances in a pottery studio. There is just no way to completely avoid
some clay and glaze dust.
Paul Lewing, Seattle
J. B. Clauson on fri 25 apr 03
Many moons ago at an NCECA convention held in San Diego, California, USA,
(not this last one but one some years ago) there was a woman who gave a
lecture on pottery safety. I bought her book which is a very comprehensive
compendium of the do's and don'ts of studio safety. However, when I left
Shards, etc... (a pottery), the book stayed with the pottery. I can't
remember the woman's name or the title of the book.
Anyone out there remember? Or does anyone know of another source for
pottery safety?
We could all use some resources on this subject. I see a lot of running
scared without enough knowledge as well as the devil-may-care attitude that
my hobby can't hurt me. Both of these are dangerous in my book.
Jan C.
Ababi on sat 26 apr 03
Yes Jan
I remember her name though I was not at the time in San Diego.
Monona Rossol and the book: The Artist's Complete Health and Safety Guide, I am
not opening the book every day only when I have a new material.
By the way: Kerosine is dangerous and chrome is dangerous. A banana peel too! You
need the proper precaution to each material. ( Writing the last sentence I am not
underestimate our classic poisons)!
Ababi
---------- Original Message ----------
>Many moons ago at an NCECA convention held in San Diego, California, USA,
>(not this last one but one some years ago) there was a woman who gave a
>lecture on pottery safety. I bought her book which is a very comprehensive
>compendium of the do's and don'ts of studio safety. However, when I left
>Shards, etc... (a pottery), the book stayed with the pottery. I can't
>remember the woman's name or the title of the book.
>Anyone out there remember? Or does anyone know of another source for
>pottery safety?
>We could all use some resources on this subject. I see a lot of running
>scared without enough knowledge as well as the devil-may-care attitude that
>my hobby can't hurt me. Both of these are dangerous in my book.
>Jan C.
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