Lesley Alexander on fri 25 may 01
The recipe for Black Waxy, indeed handsome in the picture at
http://www.frogpondpottery.com/glazestability/glaze0125.html, contains
2.5% oxide and 2.5% manganese oxide, and leaches .06 mg/l cobalt and
13 mg/l manganese. If we use parameters given out by our water company
(and Santa Barbara water is not the tastiest) based on 'aesthetic
standards' for the California Department of Health, the limit for
manganese is .05. There is no date given for 'safe' amounts of cobalt.
We are back to the question of what is safe. Some have argued here
that drinking water standards are too stringent. But even if one mixed
up that glaze and got equally 'good' results in a test, would we really
want to give such a pot to a family with young children? Who might store
food in it.....??? Perhaps this is an unanswerable question at this
point in our knowledge. Lesley
John Hesselberth on fri 25 may 01
on 5/25/01 7:04 PM, Lesley Alexander at celadon@SILCOM.COM wrote:
> We are back to the question of what is safe. Some have argued here
> that drinking water standards are too stringent. But even if one mixed
> up that glaze and got equally 'good' results in a test, would we really
> want to give such a pot to a family with young children? Who might store
> food in it.....??? Perhaps this is an unanswerable question at this
> point in our knowledge.
Hi Leslie,
You are right it is unanswerable. But be aware of a couple things. The
federal standard for manganese of 0.05 mg/l is a SECONDARY standard.
Secondary standards are for things like color or taste or smell, not for
health issues. Also remember that the FDA and California standards for
release of lead and cadmium (two materials that accumulate in the body) from
ceramic surfaces are from 7 to 200 times higher than the water standards for
lead and cadmium. This is presumably because the acid leaching test is a
very rigorous test. At the very least it causes one to wonder what the
relevance of water standards are when used to compare to an acetic acid
leaching test.
In short, while water standards are a useful reference point, in my opinion
they are no more than that. To try to apply them--particularly secondary
standards which have no health implications-- to the ceramic leaching tests
is certainly an extremely conservative thing to do, but probably way beyond
what is appropriate.
What I do know for a fact is that this glaze is way toward the stable end of
the glaze spectrum and far more "safe" than lots of manganese-containing
glazes that are being sold today that have never been tested by anyone. I'd
rather be eating off it than most of the other manganese containing glazes
I've tested.
On the other hand if you want to follow secondary water standards for an
acetic acid leach test that is your choice and right to do so.
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.
scott lykens on fri 25 may 01
believe it or not it exhists somewhere, i am quite positive the stuff that
make pink tums pink is cobalt, and i know for a fact it is other food dyes.
aparently the FDA has an amount that is considard safe for human consumtion,
comparitively, i have also been told there is a food safe level of rodent
fesis in canned food. Tuna for instance, although it is gross, and i think
hard information to get a hold of without actually running a company that
make s these kinds of products, i have a relative that produces edible food
dyes. These dyes are used from everything to coloring candy to writing the
words on pills. All i have been told is its low enough to be safe, yet high
enough to provide reproducable color value in dyes. The Dyes were required
to pass FDA testing standards and hte FDA and OSHA visited frequently before
his operation was even allowed to open for business. no product made pre
federal approval of the lab was legally saleable.
I was at one time told that if a glaze contained less than 11% barium it was
considered food safe, has anyone ever heard of this??
it was in some journals a roomate had from the library and because he needed
a term paper and lived with a student potter he decided to write on food
safety requirments for packaging and serving.
I believe commercial resteraunts are a generally a bit more stringent than
required as it generally doesnt take failing a health board test too many
times before business disappears.
>
Hope this adds to some discussion and i certainely mean no harm by exposing
things others have told me who worry about this stuff for a living. I
would imagine that most large reseach universities would have periodicals
that contain this kind of info. I noticed the Alfred libraries have a
exchange program with public libraries and a researchable data base, all of
which i found through the ACERS web site. I have not yet reserved any books,
but i did call alfred libraries and inquire about out of NY access, they
said up to your local library, and perhaps the local charges shipping but
they were OK with multi state lending.
OK enough for me for now.
bye, sct
>The recipe for Black Waxy, indeed handsome in the picture at
>http://www.frogpondpottery.com/glazestability/glaze0125.html, contains
>2.5% oxide and 2.5% manganese oxide, and leaches .06 mg/l cobalt and
>.13 mg/l manganese. If we use parameters given out by our water company
>(and Santa Barbara water is not the tastiest) based on 'aesthetic
>standards' for the California Department of Health, the limit for
>manganese is .05. There is no date given for 'safe' amounts of cobalt.
> We are back to the question of what is safe. Some have argued here
>that drinking water standards are too stringent. But even if one mixed
>up that glaze and got equally 'good' results in a test, would we really
>want to give such a pot to a family with young children? Who might store
>food in it.....??? Perhaps this is an unanswerable question at this
>point in our knowledge. Lesley
>
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will edwards on sat 26 may 01
Hello,
John makes a good point. recently I have spoke to FSIS officials and have=
been
back and forth with the USFDA on the issues of standards listed.
The Food Service Industry and Food, Drug Administration both have informa=
tion
available on web sites about lead and cadmium with lead being a zero tole=
rance
in water standards. So with that zero is zero in any amount on any item t=
hat
food or beverage is to be served from IMO. Cadmium has an mg/L of 0.005. =
(Go
ahead, Tell me how many ceramics glazes are sold with lead in them).
When I spoke with Brian who does my testing (Licensed USFDA/FSIS lab) we
talked about available materials (Bioavailable). Water test standards are=
for
those who want to go to the limits so to speak and use that as a stringen=
t
guide for either further services or to find keys that relate which mater=
ials
might pose a threat when an acidic solution or other-wise are prone to
degrading the glaze while in use.
BTW - The lab I use works for food service industries and is adept in tes=
ting
for materials known to create problems where food can be contaminated. Th=
ey
sit right in the middle of several processing centers for food-stuff! (Th=
ey do
bacterial testing for many packagers) However they also do work for chemi=
cal
companies that produce in-house solutions for cleaning in food service ar=
eas
and hospitals as well as other institutions. Any good lab will have the p=
roper
equipment and know how on testing for these materials if they are geared =
for
such in the first place. E.mail me and I will send you the procedures for=
testing if you need them. (Methods, etc)
If I can pull 9 mg/L of copper in a water test for such how much is too m=
uch
while in service as a food bearing item? We will slowly get some copper f=
rom
acidics that are capable of leaching out the copper over a period of time=
=2E =
Immediate available amterials compared to time reactive materials have
differing values. Would I eat off anything that had a 9 mg/L of copper in=
it?
Yes, I would.. I would know that the food I eat off it would be a non-aci=
dic
type food and one which I might consume in a hurry and not store items in=
=2E On
the other hand I would not store tomatoe soup in it and expect to eat it
latter in the week.
That is the reason for testing. No one knows this without it and not all
people are aware of the damages certain materials can do to a food bearin=
g
surface which in turn will create leaching potential. Manganese is rather=
heavy in many places in ground water especially in florida where I used t=
o
live. In combination with iron we all (floridians/deep South) know what i=
t
does and smells like. Making coffee with it was like making sludge!
The same test on one of the pieces I over-saturated with oxides also prod=
uced
less than <.04 chromium. I mixed several of these oxides beyond 4.00% and=
others were tested with single oxides. 4% copper - 4% cobalt Ox, etc... I=
am
currently readying another set for testing with the same procedures as th=
e
first to include some mattes this round. WHY? It is the only factual way =
of
knowing which material interact/react upon one another for the research I=
am
doing. My food service glazes have been tested, approved, used for a long=
time. But stability issues are ever changing and don't assume we are gett=
ing
exact materials everytime we order. I just proved that by ordering 55 pou=
nds
of material which in physical tests showed me a problem. I forced the iss=
ue
and found that the material analysis was NOT the same I had been using. T=
his
is for raw material and it was a coloring oxide. (The material was not a
threatening item but more of an time sucking problem since time is NOT wh=
at I
have right now) Each company will have some varients. That is another arg=
ument
why I choose frits and feldspars from large business. (They are normally =
held
to standards) Also I might add it is another reason I reduce the amount o=
f
materials in a glaze when possible. Stability and repeatability plays hea=
vy
when I am working out a solutionIn low Al203 glazes where chromium is 0.4=
0+
how many of you would consider eating off that? Thats one of those issues=
I am
talking about here. It takes lab work to find that out. I would eat off i=
t
once more! This one in particular if it was one I wrote for my own use!! =
But
thats not for everyone. When I shop and I look at ceramics in the BIG sto=
res I
always wonder how much of these are getting real serious testing prior to=
importing. They have safe-guards in place but we still hear how often re-=
calls
are done! Too much materials are getting thrown in at one time while too
little testing is being done over the long haul. Even our standards group=
s
have issues keeping up.
Note: I don't advocate any of my glazes for anything other than just glaz=
es
for use based on the persons tastes. (No pun intended) They in turn need =
to
always have their own tests done. I would appreciate it when they have th=
ese
tests done so we can compare some apples to apples. If you are putting in=
to
service any glaze, do so with background leachate testing that meets
regulatory criteria. (Mmmm)?
William Edwards
It is too early in the a.m. so hit me softly with questions that might ma=
ke
for a rude awakening!
____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=3D=
1
Ron Roy on mon 28 may 01
The danger is to the maker - don't breath Manganses dust and avoid the
fumes from manganese during firing.
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
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