Kris Baum on thu 27 mar 97
I've been lurking on this thread, but my anxiety forces me to jump in.
As a nascent potter, I'm still experimenting with various glazes and
colorations to find some that I like. I get my glaze formulas from CM and
published books, mostly. In my log book, I carefully wrote in big letters
"Toxic in fired form: barium, cadmium, lead" and I have been careful to
keep those out of my studio. (Although my business is mostly tiles, I
do make some functional ware and I prefer to use only food-safe glazes,
to prevent mishaps.) Now it appears that manganese, lithium, and who
knows what else may be unsafe glaze components. If anything can migrate
out of the glaze matrix then surely many glaze components are potentially
toxic in the fired form.
I'm a former scientist (research biologist) so I understand and accept
the reality that, with science, there are not always simple answers or
rules. However, I would like to make functional ware and I would prefer
not to poison my family or anyone else. I am also concerned about
potential liability. And I don't have the financial resources to do
leach testing on every glaze nor to carry liability insurance (at least,
until I start making a profit.)
If a published recipe says that it is food-safe, can that be relied upon?
And if one tinkers with the glaze a little (e.g., like upping the lithium
carb from 1 to 1.5%, or substituting whiting for strontium carbonate),
does that invalidate the presumption of non-toxicity?
How are others handling this issue? Are we only free from litigation if
we limit our glazes to commercial glazes that are rated food-safe? To say
nothing of being able to sleep at night...
--
===============================================
Kris Baum, Shubunkin Pottery,
mailto:shubunki@erols.com
===============================================
Ric Swenson on fri 28 mar 97
>----------------------------Original message----------------------------
>I've been lurking on this thread, but my anxiety forces me to jump in.
>As a nascent potter, I'm still experimenting with various glazes and
>colorations to find some that I like. I get my glaze formulas from CM and
>published books, mostly. In my log book, I carefully wrote in big letters
>"Toxic in fired form: barium, cadmium, lead" and I have been careful to
>keep those out of my studio. (Although my business is mostly tiles, I
>do make some functional ware and I prefer to use only food-safe glazes,
>to prevent mishaps.) Now it appears that manganese, lithium, and who
>knows what else may be unsafe glaze components. If anything can migrate
>out of the glaze matrix then surely many glaze components are potentially
>toxic in the fired form.
>
>I'm a former scientist (research biologist) so I understand and accept
>the reality that, with science, there are not always simple answers or
>rules. However, I would like to make functional ware and I would prefer
>not to poison my family or anyone else. I am also concerned about
>potential liability. And I don't have the financial resources to do
>leach testing on every glaze nor to carry liability insurance (at least,
>until I start making a profit.)
>
>If a published recipe says that it is food-safe, can that be relied upon?
>And if one tinkers with the glaze a little (e.g., like upping the lithium
>carb from 1 to 1.5%, or substituting whiting for strontium carbonate),
>does that invalidate the presumption of non-toxicity?
>
>How are others handling this issue? Are we only free from litigation if
>we limit our glazes to commercial glazes that are rated food-safe? To say
>nothing of being able to sleep at night...
>--
>===============================================
>Kris Baum, Shubunkin Pottery,
>mailto:shubunki@erols.com
>===============================================
------reply------
IMHO
Good points, These are concerns that I, too, have had. I want to believe
that I have enough experience and common sense to formulate my glazes using
materials that won't harm me or my family, and that I form and fire wares
safely and that my customers will enjoy my wares and be confident that they
are free from harmful leachates like lead, cadmium and so on. A
responsible person has to think in those terms.
The threads that have come up since I started lurking on the net a few
months ago (toxicity, Barium, Salt glazing, manganese, et al.) have made me
wonder if it may be time for Alfred and Ohio State and some of the larger
ceramic engineeering / ceramic art schools have students do their master's
thesis in real, practical, useful issues that can shed some light on the
"great mysteries" of toxicity.
They really are not great mysteries, are they? ... just un -tested
theories and speculation drawn from suppositions? I would encourage some
of our ceramics school that have chemistry departments to sponsor research.
The Society of Glass and Ceramic Decorators and the American Ceramic
Society, surely have done much work in studying dinnerware and release of
potentially harmful "stuff"...and if a student could be interested in
developing a reliable test for toxicity for potters glazes and bodies, or
some light could be shone into this great deep black hole.... that could be
a great service to us all. They wouldn't have to feel like they were
"re-inventing the wheel" ...so to speak because I have the feeling there
are people in manufacturing and idustry that know a lot about these
subjects. As restriction get tighter on the ppm releases, we will all have
to think seriously about safe potting.
The questions are, no doubt, so variable that maxims will not cover EVERY
glaze formulation, if you change just one thing, are you releasing
something harmful?
Good question.
Barium, manganese, Lead Cadmium and the whole host of materials that can
cause harm to humans ought to be understood better and controlled so that
we can all sleep better.
Just my thoughts on a sunny Vermont afternoon.
Ric Swenson, Bennington
Ron Roy on fri 28 mar 97
Kris Baum asked how others handle the toxic glaze issue?
>If a published recipe says that it is food-safe, can that be relied upon?
>And if one tinkers with the glaze a little (e.g., like upping the lithium
>carb from 1 to 1.5%, or substituting whiting for strontium carbonate),
>does that invalidate the presumption of non-toxicity?
First of all I don't believe all glazes labeled "food Safe" are. There
seems to be any number of attitudes. They range from "use it till you find
a body" or "it must be safe or it would be banned." I just know the glaze
makers concerns are other than completely altruistic.
>How are others handling this issue? Are we only free from litigation if
>we limit our glazes to commercial glazes that are rated food-safe? To say
>nothing of being able to sleep at night...
So to turn to a positive approach...
I know what materials are innocuous and when making a liner glaze I use them.
I'll start a list of materials that I know are safe to use in a relatively
balanced glaze. I wish I could say any glaze but there are certain oxides I
think can be a problem like Boron and Zinc. I have no objection to being
corrected. I know Boron is a "soft" material so you need some skill to use
it or it could come out of glazes. If you are low firing you have to use it
- even at cone 6 it is a very useful flux (oops - I promised myself not to
get into that one.)
All clays except Barnard (Black Bird) which has a fair bit of MnO2.
Bentonite.
All feldspars including Cornwall Stone and Neph Sy.
Silica
Whiting
Tin oxide
Zinc Oxide?
Frits 3110, 3124, 3134, 3195, 3278, 3269. (there are many more but these
are the ones I use - all have some boron.)
Iron oxide, Rutile and Titanium Dioxide
Dolomite
Gerstely Borate
Talc
Wolastonite
Zircopax
Strontium Carb (has a small amount of Barium 1to2%)
Magnesium Carb
Bone Ash
Soda Ash (soluble)
Encapsulated stains?
I think small amounts of Cobalt (under 0.5 %) and (Copper 2% or less) are
OK but there are some glazes that would give them up I am sure.
If you can't make a decent liner glaze from the above it's your ability to
make glazes that needs improvement. Get smarter or hire someone to do it
for you.
I don't believe in "simple" glazes. I think the minimum number of materials
in a glaze - the very least - should be 4 and in that case it should
include at least 2 complex materials like feldspar, clay, frit, etc. The
more complex the glaze the better I say.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Kris Baum on sat 29 mar 97
Ron -
Thanks so much for the instructive reply on safe glaze ingredients. I've
printed it out for reference, and checked my glaze recipes (and got some
good news, some bad!).
Re: safe ingredients, I take it that lithium carbonate and spodumene are
verboten (they were not on your list)? I thought that lithium produces
more durable glazes than other alkaline fluxes, which led me to believe
that those glazes would be less likely to release colorants, etc. and be
better for food use? In James Chappell's book "The Potter's Complete
Book of Clay and Glazes", 1991, he gives a ^6 ovenware glaze recipe
containing lithium carbonate and spodumene. (As an aside, couldn't a
little bit of lithium be beneficial in making us all less manic? :-))
Re: colorants, how does one know if a stain is encapsulated? (E.g., if
I'm using a Mason stain and it doesn't say anything about encapsulation,
should I presume it isn't?) And where does one get encapsulated stains?
Re: getting smarter, that's what we all aspire to, isn't it? I know
that postings from you and the other Clayarters who are kind enough to
respond to queries are enabling me, and perhaps a few others, to get
smarter. Thanks!
===============================================
Kris Baum, Shubunkin Pottery,
mailto:shubunki@erols.com
===============================================
Ron Roy on sun 30 mar 97
Kris wrote:
>Thanks so much for the instructive reply on safe glaze ingredients. I've
>printed it out for reference, and checked my glaze recipes (and got some
>good news, some bad!).
>
>Re: safe ingredients, I take it that lithium carbonate and spodumene are
>verboten (they were not on your list)? I thought that lithium produces
>more durable glazes than other alkaline fluxes, which led me to believe
>that those glazes would be less likely to release colorants, etc. and be
>better for food use? In James Chappell's book "The Potter's Complete
>Book of Clay and Glazes", 1991, he gives a ^6 ovenware glaze recipe
>containing lithium carbonate and spodumene. (As an aside, couldn't a
>little bit of lithium be beneficial in making us all less manic? :-))
Again, the formulation of a glaze determines release. I am sure there are
durable glazes with lithium in them but which ones are they? Lithium is in
the same family as Sodium and Potassium but with a lower expansion than
either if kept at less than 20% of the KNaO. They are all low temperature
fluxes. Lithium and MgO are very useful when making ware which has to take
sudden local heat - as in stove top ware - low expansion/contraction. How
much of it leaching is problem? I don't know. I do know it will vary from
person to person. I left it off the list because I was not sure of it's
problems.
>Re: colorants, how does one know if a stain is encapsulated? (E.g., if
>I'm using a Mason stain and it doesn't say anything about encapsulation,
>should I presume it isn't?) And where does one get encapsulated stains?
See Monona's comments about encapsulated stains. They are the expensive
ones for sure. Perhaps others can answer the question about how to identify
them ad where to get them.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
ronroy@astral.magic.ca
Lawrence Ewing on mon 31 mar 97
>Lithium is in the same family as Sodium and Potassium but with a lower
>expansion than either if kept at less than 20% of the KNaO.
Hi Ron,
Could you please expand on your statement as it relates to the expansion
of
Li2O.
Many thanks,
Lawrence Ewing
lewing@clear.net.nz
21 Slant St
Careys Bay
Dunedin
NEW ZEALAND
ph (03) 472 8801
Author of MATRIX Glaze Calculation Software for Macintosh
Ron Roy on mon 7 apr 97
>----------------------------Original message----------------------------
>>Lithium is in the same family as Sodium and Potassium but with a lower
>>expansion than either if kept at less than 20% of the KNaO.
>
>Hi Ron,
>
>Could you please expand on your statement as it relates to the expansion
>of
>Li2O.
>
>Many thanks,
>
>Lawrence Ewing
Hi Lawrence!
I can and I will but I would simply be quoting from my three favorite texts
so why not read them yourself. If there are still questions I'll be happy
to add what I think. I don't have much experience with the oxide. I do know
it is in in many Shino glazes and I believe it's there to try to correct
crazing.
The Potter's Dictionary by Frank and Janet Hamer.
Ceramic Glazes by Parmelee and Harman (reprinted version)
Ceramic Glaze Technology by Taylor and Bull.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
ronroy@astral.magic.ca
Amanda Brown on wed 7 jun 06
I am wondering if glazes that are not safe for food or drink ware would
also be unsafe to use on ear stretchers or items that will sit in a body
or ear piercing. What about if it is in constant contact with the skins
surface.
Thanks for your time, and the great resource. Unfortunately, I had two
questions that I couldnt find in past postings.
Kind Regards,
Mandy Brown
Ron Roy on sat 10 jun 06
Hi Mandy,
There are some of the oxides we use that should not be in constant contact
with skin - the ovious ones would be uranium and lead but there are others
that can produce skin problems like, vanadium, selenium, nickel, chrome,
and cadmium.
I think you are right to be concerned - especially if unstabkle glazes are
used - a glazes ability to resist breakdown from acid is certainly a
factor.
This is a question that is best answered by those who have studied the
subject. I certainly don't know which of the above would be rated the worst
but all will have some effect if in contact with skin.
The Artists Complete Health and Safety Guide - by Monona Rossol - this is
from the third edition - there may be a 4th.
Keep in mind that food safe - as defined by local laws - means mostly lead
and cadmium release - so in the larger sense - it covers only the very
worst situations.
RR
>I am wondering if glazes that are not safe for food or drink ware would
>also be unsafe to use on ear stretchers or items that will sit in a body
>or ear piercing. What about if it is in constant contact with the skins
>surface.
>
>Thanks for your time, and the great resource. Unfortunately, I had two
>questions that I couldnt find in past postings.
>
>Kind Regards,
>Mandy Brown
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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