Paul Lewing on mon 15 dec 03
on 12/14/03 10:37 PM, Ron Roy at ronroy@TOTAL.NET wrote:
> It is interesting that many potters still think - if the glaze is made with
> a lead frit - it will be safe - nothing could be further from the truth.
Hi, Ron. I have heard this opinion that you just stated before, from you
and others. And I've heard the opposite opinion that you referred to. What
I'd like to ask anyone who holds either opinion is this: Have you ever made
the identical molecular formula with raw lead and a lead frit, fired them
both in the same firing, and had the resulting glazes tested professionally
by the same lab at the same time? It would seem to me that until someone
does that, neither side can claim to know absolutely.
Paul Lewing, Seattle
Ron Roy on sat 20 dec 03
Hi Paul,
Frits are suppose to be safer for the potter - because the lead is tied up
more or less - with alumina and silica - so it is not as toxic.
The durability of the glaze is a function of how durable the glass is. The
durability (from attack by acids and alkalines) is not dependant on where
the lead comes from - raw or fritted.
If the glaze does not have enough alumina and silica or is over loaded with
colouring oxides - or is not melted properly - it will release lead when in
contact with liquid foods.
We explain this in our book.
It would be the same with any oxide - Barium for instance - it is the
chemistry of the melted glaze that influences stability - whether the
barium comes from Carbonate or frit.
If I did as you said - made a glaze with frit and raw lead - the same
molecular formula - they would both have the same lead release. Not hard to
do - but not in my kiln.
RR
>> It is interesting that many potters still think - if the glaze is made with
>> a lead frit - it will be safe - nothing could be further from the truth.
>
>Hi, Ron. I have heard this opinion that you just stated before, from you
>and others. And I've heard the opposite opinion that you referred to. What
>I'd like to ask anyone who holds either opinion is this: Have you ever made
>the identical molecular formula with raw lead and a lead frit, fired them
>both in the same firing, and had the resulting glazes tested professionally
>by the same lab at the same time? It would seem to me that until someone
>does that, neither side can claim to know absolutely.
>
>Paul Lewing, Seattle
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Paul Lewing on sat 20 dec 03
on 12/20/03 2:56 PM, Ron Roy at ronroy@TOTAL.NET wrote:
> Frits are suppose to be safer for the potter - because the lead is tied up
> more or less - with alumina and silica - so it is not as toxic.
> If I did as you said - made a glaze with frit and raw lead - the same
> molecular formula - they would both have the same lead release. Not hard to
> do - but not in my kiln.
Ah, so you have not done the test. I still wonder if anyone ever has. I
completely understand your reluctance to do that test in your kiln, though.
I would if I had any raw lead, but I don't feel like going out and actually
buying some lead oxide to do it.
Anyone out there ever really done it?
Paul Lewing, Seattle
Ron Roy on sun 21 dec 03
Just a small addition that I thought of last night.
If a glaze was unstable because it needed a bit more melt - and a frit were
introduced (think of a frit as pre melted material) - to take the place of
unmelted material - you would certainly get faster melting of that glaze -
so durability could be increased that way.
On the other hand - depending on how much lead is in a glaze - lead oxide
is such a powerful melter - I'm not at all sure that would work in a low
fire glaze.
From some of the comversations I have had with John - he says there is lots
of info on lead glaze issues around - see what you can find on the net.
RR
>> Frits are suppose to be safer for the potter - because the lead is tied up
>> more or less - with alumina and silica - so it is not as toxic.
>> If I did as you said - made a glaze with frit and raw lead - the same
>> molecular formula - they would both have the same lead release. Not hard to
>> do - but not in my kiln.
>
>Ah, so you have not done the test. I still wonder if anyone ever has. I
>completely understand your reluctance to do that test in your kiln, though.
>I would if I had any raw lead, but I don't feel like going out and actually
>buying some lead oxide to do it.
>Anyone out there ever really done it?
>Paul Lewing, Seattle
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
ASHPOTS@AOL.COM on sun 21 dec 03
Paul, i have white lead and red lead,, id ship it to you but its probably
treated like a toxic material ,, come and get it. Cheryl Sculley would make you
dinner , for sure,
Ive had it for years,, It came from a person in Miami. I was invited to her
home after she had moved to greener pastures. She died of Alzimers , bad
spelling. Any way it was probably all the bad stuff she was using in her pottery.. I
still have the stuff but have never used or opened them..
Happy Hollidays
Mark
www.lookoutmountainpottery.com
John Hesselberth on sun 21 dec 03
On Saturday, December 20, 2003, at 07:44 PM, Paul Lewing wrote:
> I still wonder if anyone ever has. I
> completely understand your reluctance to do that test in your kiln,
> though.
> I would if I had any raw lead, but I don't feel like going out and
> actually
> buying some lead oxide to do it.
> Anyone out there ever really done it?
Hi Paul,
I haven't and don't plan to, but I bet it was done and is in the
literature some place. In the first half of the 1900s there was a huge
amount of work done to try to learn how to make lead glazes safe (and
to develop lead-free glazes). Much of this work that was published in
the scientific literature (vs being buried in private corporate
literature) is abstracted in a fascinating book titled "Literature
Abstracts of Ceramic Glazes" by J. H. Koenig and W. H. Earhart. There
were editions published in 1942 and 1951. You can find the book
available used occasionally for a few bucks--it is not what you would
call a best seller. If you want the 1942 edition I'll send you mine,
but the 1951 edition is really the one to have. For anyone interested
in glaze technology history (Ivor are you listening?), I include this
in a must-have library. It is not indexed and is over 300 pages, but it
is just fun to peruse the abstracts and get a sense of what was going
on in the 'golden days of glaze research'.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
pdp1@EARTHLINK.NET on sun 21 dec 03
Hi Mark,
If someone wants these ingerdients, and you want them to
have them, please do not worry about shipping them in the
Mail, via fed-ex, or U.P.S or whatever.
They are not 'dangerous' in any way that matters in that
context.
Merely package them with the view in mind, that the package
will be jostled, the same as anything. Put thenm in a
plastic Bag...put that in a second plastic bag...put that in
a Box with some crumpled newspaper.
If you are obliged to say what they are, say they are Glaze
Ingredients.
Regards,
Phil
Las Vegas
----- Original Message -----
From:
> Paul, i have white lead and red lead,, id ship it to you
but its probably
> treated like a toxic material ,, come and get it. Cheryl
Sculley would make you
> dinner , for sure,
>
> Ive had it for years,, It came from a person in Miami. I
was invited to her
> home after she had moved to greener pastures. She died of
Alzimers , bad
> spelling. Any way it was probably all the bad stuff she
was using in her pottery.. I
> still have the stuff but have never used or opened them..
>
> Happy Hollidays
>
> Mark
> www.lookoutmountainpottery.com
>
>
____________________________________________________________
__________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached
at melpots@pclink.com.
iandol on mon 22 dec 03
Two other sources of references are "Ceramic Abstracts" which I believe =
is published by Cambridge University in the UK and the other is =
"Chemical Abstracts" which seems to found in most University Libraries =
where the is a science faculty.
There should be a wealth of information in the AcerS archives and in the =
annals of the British Ceramic Research Association.
We have no excuses to support our ignorance.
Best regards,
Ivor Lewis. Redhill, South Australia
Paul Lewing on mon 22 dec 03
on 12/21/03 8:46 PM, Ron Roy at ronroy@TOTAL.NET wrote:
> If a glaze was unstable because it needed a bit more melt - and a frit were
> introduced (think of a frit as pre melted material) - to take the place of
> unmelted material - you would certainly get faster melting of that glaze -
> so durability could be increased that way.
Now there's an interesting line of speculation.
When we were in school, my wife did an independent study project to
investigate this very question. She mixed two glazes, one with raw lead
oxide and one with a lead frit, fired them both and tested the results.
Both showed the presence of lead in the leaching solution.
HOWEVER, she did not do a molecular substitution. She merely did a
weight-for-weight substitution of lead frit for lead oxide, and she doesn't
remember which lead frit she used. So it may not have been, in fact, the
same glaze.
Also, she tested the two results on an atomic absorption unit, or it may
have been a spectrograph. At any rate, the machine she used only indicated
the presence or absence of any particular element.
So all her test told us was that both of the glazes she used, which may or
may not have been identical, leached lead in some amount, but we don't know
how much, or if one was worse than the other.
Not a conclusive test, wouldn't you agree?
Paul Lewing, Seattle
Ron Roy on tue 23 dec 03
Hi Paul,
I would think - if you wanted to see if using fritted lead or lead oxide -
did anything to improve the stability of a glaze you would need to get both
molecular formulas as close as possible - and use fairly accurate analysis
as well.
Getting a quantative analysis is also a must - when you subbed a frit for
the raw lead you certainly got a different glaze - and probably a lot more
silica because most frits have a lot. I would think the glaze with the
lead oxide would be releasing a lot more lead because of the way you did
it.
RR
>> If a glaze was unstable because it needed a bit more melt - and a frit were
>> introduced (think of a frit as pre melted material) - to take the place of
>> unmelted material - you would certainly get faster melting of that glaze -
>> so durability could be increased that way.
>
>Now there's an interesting line of speculation.
>When we were in school, my wife did an independent study project to
>investigate this very question. She mixed two glazes, one with raw lead
>oxide and one with a lead frit, fired them both and tested the results.
>Both showed the presence of lead in the leaching solution.
>HOWEVER, she did not do a molecular substitution. She merely did a
>weight-for-weight substitution of lead frit for lead oxide, and she doesn't
>remember which lead frit she used. So it may not have been, in fact, the
>same glaze.
>Also, she tested the two results on an atomic absorption unit, or it may
>have been a spectrograph. At any rate, the machine she used only indicated
>the presence or absence of any particular element.
>So all her test told us was that both of the glazes she used, which may or
>may not have been identical, leached lead in some amount, but we don't know
>how much, or if one was worse than the other.
>Not a conclusive test, wouldn't you agree?
>Paul Lewing, Seattle
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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