Karl P. Platt on wed 11 nov 98
So this automated note came to me yesterday or so telling me that it was
time to "confirm" my subscription to Clayart, and since I'd had it set
to "nomail" for quite a while now, as I've been busy in doing the
academic thing and otherwise, I resolved to peek in to see what the
state of things had become -- recalling that I'd been discouraged by a
precipitous drop in the level of conversation. There were some
interesting things, to be sure, but one did observe a number of axes
still being ground which must by now be something resembling miserable
little stubs.
Where to start?
> As my malmixed red devitrified over the course of a few days, the red color >d
First, divitrification is not something that can happen at room
temperature. What devitrification refers to is the crystallization of a
glassy material at elevated temperatures -- there are a lot of reasons
why this occurs, but we'll spare this for now and only note that this
behavior is key to the development of many types of matte glaze.
What actually happened in the offending glaze was corrosion by whatever
it was exposed to and then some subsequent form of recrystallization.
The glaze, whatever it was, had to have been seriously high in alkali
and/or boric oxide (B2O3) to show the behavior described. That and/or it
was exposed to an extreme solvent. No details were mentioned in the
quoted post.
The color changes may be attributed to the solvation of the coloring
ion(s) exposed to the solvent either within or extracted from the glaze.
> Has anyone ever tested their witch's brew
> for the dissolved presence of the suspected leachates?
Yes. Way more than once. I hate to be repetitive, as I've told this tale
here before and just got done bitching about stale content here, but one
of my early career tasks was to produce a cone 6-8 Bristol type glaze
(that incidentally bore no small amount of BaO) which was used on tile
for lining chemical vats in paper making and chemical processing
industries. These vats were used for substances far more agressive than
OJ or vinegar, and never showed color changes. They also didn't leach
perceptable amounts of Ba as was proved by routine testing (AA) done to
develop and maintain stable and durable glaze.
What does this say? It makes the point that it is entirely possible to
compound glazes which are extremely stable at the ranges of temperatures
which have come to be fashionable among Studio Ceramists over the past
decade -- including those glazes containing elements some would have us
believe are incapable of existing in any stable form. In this vein we
should also note that virtually all US produced tableware glazes were
predicated on lead frits for decades and there exist no documented cases
of anyone ever having been harmed by the use of these.
> I intend to have one of my glazes, which has barium in the
> recipe, tested for leachability at our local government testing laboritories,
Why were you surprised? I'll reckon it's because you only know what the
granola fascists financially vested in promulgating hysteria here and
elsewhere have told you. How does it feel to be made a fool of?
I'd submit that your government is quite reasonable. Why? No-one
anywhere has *ever* been ill affected by a potter's Ba bearing glaze,
certainly much less by any commercial maker's glaze. No-one anywhere can
bring forth a single studio ceramist stricken down by the use of barium.
Doesn't exist. I've asked way more than once for someone to produce
something, anything more than weird anecdotes or bureaucratic blither to
lend substance to the hysteria, but, alas, I remain unsatisfied. Show me
one and I'll shut-up and go away.
> I have heard of 2 cases of Parkinson like syndrome among unskilled
> workers making clays and glazes for a local pottery supplies store (Montreal)
This, for those who missed it, is an anecdote. Anecdotes, we need to
remember, are not peer-reviewed or the stuff scientific conclusions are
based on.
Let me toss a couple into the brew and see if they call any attention.
I'll recall, a glaze maker of 40 years who is very alive today at 80.
Leyland, not a Rhodes Scholar, worked as the guy who weighed and mixed
about 3 tons of glaze each day under pretty rustic conditions for most
of his career -- that amounts to about 30,000 tons of glaze. All of the
glazes were raw, some contained PbO (added as insoluble frit) and (yes)
they frequently employed BaCO3. Leyland never smoked, didn't stand
around huffing dust (what reasonable person would?) and washed his hands
before eating. Leyland is
a guy who took care of himself and practiced normal hygiene. But the
quoted postreferenced MnO2, used since deep antiquity to produce various
colors and effects in glazes -- browns, purples and with Fe metallic
effects. So we want to
note that as a routine part of Leyland's duties (during 40 years), in
addition to routinely adding whole bagsful of MnO2 to the ball mill(s)
he also
screened MnO2 several times a week to get out the fraction that fell
through 60 mesh, but stayed on 80 mesh -- this was to make the "specks"
frequently seen in wall tile glazes, which are great way to obscure
pinholes! We can fairly assert that this fellow handled more manganese
in a day than most potters will see in their careers and that he did so
for a very long time -- and under
conditions which would make a modern studio seem antiseptic. Leyland, we
again observe, is very hardy at 80.
While I could cite a whole host of other examples of old timers I know,
I would also point to myself, whose age will remain a secret, and who
has also had the odd fortune to have spent part of his career making an
awful lot of glaze -- also probably way more in a day than most readers
here will make in their careers. This is by no means a boast, nor, for
my part, a good thing. It's only a fact and an activity that was frankly
dull after a while. I should also note that I certainly can't make art
pots and ardently admire those who do -- but I can make killer glaze.
For some years now I've given a lot of attention to going whole hog and
making glass (hey, why stop at cone 10?). Many of these glasses and
glazes (many of which Leyland made-up) bore MnO2 and were first
developed in the lab by me. In all of this I only wish to make the point
that I and my much older colleagues are quite hale despite having been
in intimate contact on a daily basis with large volumes of
substances discussed here as though they were derived of the devil's
urine.
Now we have two anecdotes relating to persons who have been exposed to
what on the Studio scale would be considered to be EXTREMELY large
amounts (thousands of tons) of materials, including BaO, PbO and MnO2.
Now if one follows the logic of the hysterics, by all rights we ought to
be shriveled rasins of humanity with enough cancer, brain-rot and
uncontrollable drooling for 20 people.
Yet we are not, and, on the contrary, are physically the best we can be
-- shall we go surfing this weekend?
Should this be taken to mean that there are absolutely no risks
associated with handling powdered materials of any sort? Of course not.
Should we now assume that exposure to MnO2 prolongs life? No
--remembering that we're not hysterics. Should the quoted instance be
taken to mean that making glaze is suicidal? Of course not.
The writer from Canada cites an instance of two people taking ill at a
ceramic supply shop 20+ years ago and probably can't cite anything
having occured since. The situation in the US is not dissimilar.
Moreover, the malady is by no means clearly linked to MnO2 as presented.
Even if it was, if these two individuals are considered among all
ceramic workers in Canada in this 20 year period, both creative and
industrial, what we're really looking at is a seriously microscopic
portion of the population --- something like 0.0008%. In the US this
fraction would be even more miniscule merely as a matter of scale. We
could snipe about precise numbers, but my point is regardless of what
they are, what we're looking at is something statistically
insignificant, representing a set of circumstances way way out of
normal, reasonable people's reality. Something highly unusual was
associated with the instance -- probably extraordinary sloppiness in
some fashion.
What it boils down to is that if you're not an idiot who stands about in
spooge for hours on end or some slob who smokes, eats or drinks in the
shop, and if you wash you hands before eating, smoking (if ya gotta do
that), etc., the probability that any glaze material you'll handle will
make you sick is about as large as that of making a glaze in which
Cobalt produces vivid orange. That is, extreeeeeeeemly small -- making
allowances for one's individual genetic shortcomings, of course. There
are those statistically miniscule instances, like the first anecdote
above indicates, but in essentially all cases of these outer limits one
finds that there were aggravating factors at play and that these usually
relate to being a slob. Call it a form of Darwinism, if you will, that
no twaddling bureaucracy nor its dependents can resolve.
> ...my quest for a "safe"
> glaze , it exists in Parmelee's book, page 548, no.5, low temp. you have to re
OK. I'm sitting here looking at the above reference. It would be useful
for us all if whoever made the above remark would explain their logical
leap -- in detail, please.
KPP -- set to "mail" ;)
Tom Wirt on thu 12 nov 98
.....snip...
>my part, a good thing. It's only a fact and an activity that was frankly
>dull after a while. I should also note that I certainly can't make art
>pots and ardently admire those who do -- but I can make killer glaze.
>For some years now I've given a lot of attention to going whole hog and
>making glass (hey, why stop at cone 10?). Many of these glasses and
>glazes (many of which Leyland made-up) bore MnO2 and were first
>developed in the lab by me. In all of this I only wish to make the point
>that I and my much older colleagues are quite hale despite having been
>in intimate contact on a daily basis with large volumes of
>substances discussed here as though they were derived of the devil's
>urine.
>
>Even if it was, if these two individuals are considered among all
>ceramic workers in Canada in this 20 year period, both creative and
>industrial, what we're really looking at is a seriously microscopic
>portion of the population --- something like 0.0008%. In the US this
>fraction would be even more miniscule merely as a matter of scale. We
>could snipe about precise numbers, but my point is regardless of
................
Karl,
Reminds me of 15 or 20 years ago when 2 teachers came down with a strange malady
in, I thnik it was, Montana. same town, same rare disease.
The only thing that the attending physician could trace that these 2 did in
common was teach art and use 3Mspray cement. So prompted by an article by the
physician, 3M had to pull ALL spray cements off the market for a time while
testing was done.
Net, net was that we as consumers paid millions for what was later clinically
proven as a non-issue in the disease these 2 contracted. It was pure
coincidence. But, if I remember right, at the time, the screaming was intense.
I agree with you we need to exercise due caution and normal hygiene. But I see
a MacKenzie or Ferguson or a multitude of long time potters who have handled
these materials in quantity offer the years and are almost as hale as you. (I
can't picture Warren surfing).
Tom
Barney Adams on fri 13 nov 98
The problem has to do with common sense. There are a great deal of people
who lack common sense. Besides learning to handle these materials with
common sense one needs to handle fear with common sense. We have become a
socity where individuals dont take repondsibility for their own actions.
Government regulation on materials, the enviornment, etc are'nt going to fix
any thing. Each individual has to raise themselves up to be knowledgeble
of materials, take care of the environment, etc.
I deal with this at work constantly. I tell everyone when there's a mess on the
floor let's not go off looking at the janitor when it's easier to just take
the broom and sweep it up.
Just my opinion,
Barney
>
> ----------------------------Original message----------------------------
> ....snip...
>
> >my part, a good thing. It's only a fact and an activity that was frankly
> >dull after a while. I should also note that I certainly can't make art
> >pots and ardently admire those who do -- but I can make killer glaze.
> >For some years now I've given a lot of attention to going whole hog and
> >making glass (hey, why stop at cone 10?). Many of these glasses and
> >glazes (many of which Leyland made-up) bore MnO2 and were first
> >developed in the lab by me. In all of this I only wish to make the point
> >that I and my much older colleagues are quite hale despite having been
> >in intimate contact on a daily basis with large volumes of
> >substances discussed here as though they were derived of the devil's
> >urine.
> >
> >Even if it was, if these two individuals are considered among all
> >ceramic workers in Canada in this 20 year period, both creative and
> >industrial, what we're really looking at is a seriously microscopic
> >portion of the population --- something like 0.0008%. In the US this
> >fraction would be even more miniscule merely as a matter of scale. We
> >could snipe about precise numbers, but my point is regardless of
> ...............
>
>
> Karl,
> Reminds me of 15 or 20 years ago when 2 teachers came down with a strange mala
> in, I thnik it was, Montana. same town, same rare disease.
>
> The only thing that the attending physician could trace that these 2 did in
> common was teach art and use 3Mspray cement. So prompted by an article by the
> physician, 3M had to pull ALL spray cements off the market for a time while
> testing was done.
>
> Net, net was that we as consumers paid millions for what was later clinically
> proven as a non-issue in the disease these 2 contracted. It was pure
> coincidence. But, if I remember right, at the time, the screaming was intense
>
> I agree with you we need to exercise due caution and normal hygiene. But I se
> a MacKenzie or Ferguson or a multitude of long time potters who have handled
> these materials in quantity offer the years and are almost as hale as you. (I
> can't picture Warren surfing).
>
> Tom
>
Ron Roy on fri 13 nov 98
Far be it from me to spoil Karl's fun here but: The fact is that most of
the glazes we find are made by people who had no idea of how to make a
durable glaze and were even less interested in having them tested. We have
been choosing our glazes by how they look - not for their integrity.
The net result is chaos - production potters coping with cracked pots and
discoloured glazes.
Why not show us how Karl and post a durable, bubble free cone 6 clear glaze
that will react well with chrome/tin.
Or how about the Bristol glaze with BaO in - I'll bear the expense of
having it tested.
RR
>----------------------------Original message----------------------------
>> Has anyone ever tested their witch's brew
>> for the dissolved presence of the suspected leachates?
>
>Yes. Way more than once. I hate to be repetitive, as I've told this tale
>here before and just got done bitching about stale content here, but one
>of my early career tasks was to produce a cone 6-8 Bristol type glaze
>(that incidentally bore no small amount of BaO) which was used on tile
>for lining chemical vats in paper making and chemical processing
>industries. These vats were used for substances far more agressive than
>OJ or vinegar, and never showed color changes. They also didn't leach
>perceptable amounts of Ba as was proved by routine testing (AA) done to
>develop and maintain stable and durable glaze.
>
>What does this say? It makes the point that it is entirely possible to
>compound glazes which are extremely stable at the ranges of temperatures
>which have come to be fashionable among Studio Ceramists over the past
>decade -- including those glazes containing elements some would have us
>believe are incapable of existing in any stable form. In this vein we
>should also note that virtually all US produced tableware glazes were
>predicated on lead frits for decades and there exist no documented cases
>of anyone ever having been harmed by the use of these.
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
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