Eric Suchman on tue 29 jun 04
I know, I know....Lead is highly toxic. My question, however is, at what
temperature lead ceases to give off toxic vapours, (most importantly!) and
at what temperature lead is burned out, (second most important). I have a
small quantity of lead carbonate and an amount of litharge, for oil painting
purposes, and am wondering about their low fire attributes, either as an
onglaze or what-ever. (we're talking oxidation here unless there are some
raku exceptions)
Thanks,
Eric in Oceanside
Paul Lewing on wed 30 jun 04
on 6/29/04 7:20 PM, Eric Suchman at esuch@EARTHLINK.NET wrote:
> My question, however is, at what
> temperature lead ceases to give off toxic vapours, (most importantly!) and
> at what temperature lead is burned out, (second most important). I have a
> small quantity of lead carbonate and an amount of litharge, for oil painting
> purposes, and am wondering about their low fire attributes, either as an
> onglaze or what-ever.
Eric, you probably need Edouard Bastarache to answer this question in great
detail, but I'll quote you some lines from an article he sent me this week
in response to some questions I had for him about lead.
Lead carbonate (white lead) when heated it decomposes at 400 degrees Celsius
and emits lead monoxide, carbon monoxide and carbon dioxide.
Red lead oxide (minium) when heated to more than 500C there is release of
oxygen and toxic lead fumes.
Yellow lead oxide (litharge) when heated to between 3000C and 400C it is
converted to lead tetraoxide.
Lead silicate emits toxic lead fumes when heated to decomposition. (No
temperature given)
Lead frits, such as lead bisilicate, lead sesquisilicate, and lead
boro-silicate, no information in he relevant literature about breakdown
products.
Hamer & Hamer say that lead frits do not breakdown until about cone 3.
I know this doesn't answer your question, if what you meant is at what
temperature is all the lead gone. I doubt that all of it ever leaves. It
doesn't seem to me that it could all be gone ever, otherwise you'd be left
with only alumina and silica in many lead glazes, and that wouldn't really
be a glaze.
Paul Lewing, Seattle
Ilene Mahler on wed 30 jun 04
eric can you e-mail me I need info on a Calif
galery..ilene...imahler@comcast.net...Thanks
----- Original Message -----
From: "Eric Suchman"
To:
Sent: Tuesday, June 29, 2004 11:20 PM
Subject: lead and fumes
> I know, I know....Lead is highly toxic. My question, however is, at what
> temperature lead ceases to give off toxic vapours, (most importantly!)
and
> at what temperature lead is burned out, (second most important). I have a
> small quantity of lead carbonate and an amount of litharge, for oil
painting
> purposes, and am wondering about their low fire attributes, either as an
> onglaze or what-ever. (we're talking oxidation here unless there are some
> raku exceptions)
> Thanks,
> Eric in Oceanside
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
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melpots@pclink.com.
Jon Pacini on wed 30 jun 04
Greetings All----- Hi Eric---you wrote---I know, I know....Lead is highly
toxic. My question, however is, at what
temperature lead ceases to give off toxic vapours, (most importantly!) and
at what temperature lead is burned out, (second most important).
If you don t already have this book you should get a copy---Frank and Janet
Hamer, The Potters Dictionary of Materials and Techniques . Start there,
page 197.
Hamer has 2 = pages devoted to lead and it s various incarnations. You ll
get the reasons why it was used extensively in the past, some basics on how
to use it in glazes, some precautions on the handling of the raw material
and warnings regarding the ramifications of it s solubility after firing.
I ve never tested for fuming so my experience is decidedly limited. I can
say that most of the raw lead glazes that I have used, appear to fume. Low
fire (as low as 012) or high fire (^6). They will leave a halo on your
shelving. Colors will migrate and affect the pots positioned next to them.
Lead frits and silicates are more stable. Above ^6 raw lead will pretty much
totally volatilize, though I ve heard of lead silicate being used in higher
temp glazes. Not good to be around a kiln with lead in it unless you are in
a well-ventilated area. And try to keep your neighbors in mind if you use
such volatile materials.
I ve got a bizarre lead story I d like to share, an example of gross
negligence in the handling of a toxic substance, please don t try this.
A few years back while vacationing down Mexico way, I visited a roof tile
operation, common red roof tile made from local clay. The kilns were crude
clay walls with shards piled on top of the rows of stacked tile. The Kilns
were coal fired to a red heat by sight---very scientific they were --- and
lead carb was shoveled into the firebox to provide color flashing from the
fumes. No masks, no gloves, just rip open the bags and shovel it in.
Not a practice I would care to see repeated under any condition.
I m not the Chicken Little type, I do encourage you to experiment with
various materials and techniques, but I strongly recommend that you research
and learn as much as possible about your materials when experimenting. And
please ---always use prescribed precautions when dealing with toxic
materials.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
Jon Pacini on thu 1 jul 04
Greetings All-----
Yet another sorid tale of lead and fumes ---this one related to me by Bill
Lisonbee, longtime potter and Ceramic Engineer.
Bill was consulting for a Dinnerware manufacturer converting their glazing
operation over from lead glazes to leadless. The company had been producing
leaded ware for 50 some years and it had been quite a project cleaning the
place up, changing over production methods. But all was looking good, the
testing had been done in their lab facilities and now they were starting on
a limited production run of ware. The glazing went well, the firing was
good, the ware came out it was beautiful. Off it goes to be certified
leadless non-toxic by an independent lab. A week later back comes the
verdict ---glaze has soluble lead.
Well---where s the lead coming from?? They decide to use new glaze buckets
and mixer, new hoses and spray guns and try it again.
The ware comes back ----soluble lead.
To make a long story a bit shorter, the lead was coming from the 50 year old
kiln. The bricks and furniture were saturated with fumed lead. They relined
the kiln, replaced the furniture---next firing, the ware passed the test.
For those of you who use salt, soda or any other Vapor method of glazing
this comes as no surprise. Any material that vaporizes is going to linger in
your kiln. Is it a reason not to use that material???
That depends on many things. The most important thing is that you are aware
of it. The only thing you get from being ignorant of the properties of the
materials you use is that it insures you will make mistakes.
Even someone who is as laissez faire about ceramics as I am can t stress
this enough---- You can choose to avoid the hazards involved in ceramics,
but to do so, you had better be aware of them. Be knowledgeable!!! Act
responsibly!!!
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Mike Gordon on thu 1 jul 04
Paul ,
Is this correct 3000C to 400C? Also has anybody fired a lead glaze to
C/10 to see if what you say about the left overs could really be a
glaze?? Mike Gordon
(Yellow lead oxide (litharge) when heated to between 3000C and 400C it
is
converted to lead tetraoxide.)
On Jun 30, 2004, at 10:12 PM, Paul Lewing wrote:
> on 6/29/04 7:20 PM, Eric Suchman at esuch@EARTHLINK.NET wrote:
>
>> My question, however is, at what
>> temperature lead ceases to give off toxic vapours,
> _______________________________________________________________________
> _______
> 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.
>
Paul Lewing on thu 1 jul 04
on 7/1/04 11:26 AM, Mike Gordon at clayart@EARTHLINK.NET wrote:
> Paul ,
> Is this correct 3000C to 400C? Also has anybody fired a lead glaze to
> C/10 to see if what you say about the left overs could really be a
> glaze?? Mike Gordon
>
> (Yellow lead oxide (litharge) when heated to between 3000C and 400C it
> is
> converted to lead tetraoxide.)
Good eye, Mike! I did indeed hit the 0 key one too many times. It should
have read "between 300C and 400C".
Sorry.
Paul Lewing, Seattle
Logan Oplinger on fri 2 jul 04
On Tue, 29 Jun 2004 20:20:13 -0700, Eric Suchman
wrote:
>I know, I know....Lead is highly toxic. My question, however is, at what
>temperature lead ceases to give off toxic vapours, (most importantly!) and
>at what temperature lead is burned out, (second most important). I have a
>small quantity of lead carbonate and an amount of litharge, for oil
painting
>purposes, and am wondering about their low fire attributes, either as an
>onglaze or what-ever. (we're talking oxidation here unless there are some
>raku exceptions)
>Thanks,
>Eric in Oceanside
Hello Eric,
In addition to what Jon has just said, a quick search of the clayart
archives found this previous communication:
http://www.potters.org/subject51954.htm
In part, it says:
***********
Edouard Bastarache on wed 3 apr 02 (edouardb@SOREL-TRACY.QC.CA)
Hello Ivor,
Basic lead carbonate (C2H2O8Pb3) is unstable under the following conditions
: if heated it decomposes at 400 C and emits lead monoxide, carbon monoxide
and carbon dioxide.
Red lead (Pb3O4)) is unstable under the following conditions : if heated to
decomposition (over 500 C), there is release of oxygen and emission of
toxic
fumes of lead.
Yellow lead ((Pb) is unstable under the following conditions: if heated at
300-400 C
it transforms into lead tetraoxide.
Later,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
**************
There is a part to your inquiry that concerns me, where you ask "what
temperature lead ceases to give off toxic vapours, (most importantly!) and
at what temperature lead is burned out, (second most important)."
I am not sure if lead carbonate and litharge BEGIN to decompose at
temperatures below those cited above, giving off fumes containing lead
products. Suffice it to say that once vaporization begins, as the
temperature increases, vaporization will continue at an increasing rate.
When will it stop? That depends on the initial amount of lead compound
present, and the cumulative heat work done on the lead compound (time +
temperature). Also, it is probably not good to phrase your question to ask
at what temperature lead is "burned out". The lead will not "burn out"
like organic compounds. In a kiln, carbon compounds will react with excess
oxygen in the air to form carbon dioxide which remains a gas after it is
driven out of the kiln. Lead compounds & fumes on the other hand (I'm
being general here) will react to some extent with the various materials in
the kiln. Lead in glazes can give off fumes. Paints that contain lead
will probably react with glaze materials if used in combination with
glazes, but will also decompose to give off fumes at temperatures that most
low-fire glazes are fired to. Some of the fumes formed within the kiln
will find their way out, becoming available for anyone around the kiln to
breath in if the fumes are not properly vented away.
There has also been considerable discussion on clayart about what to do
with lead contaminated kilns that have been used to fire ceramics with lead
glazes. Since this topic is not part of your inquiry, I will leave it to
you to review what others have said. I bring this up here only to
emphasize that once lead compounds are fired within a kiln, a kiln can
become contamninated with lead.
If I have been unclear about anything I have said, please say so. If I
have misrepresented any of the issues concerned with the hazards of lead, I
will stand corrected.
Logan Oplinger
Another Tropical Island, where this past week
16 inches of rain in one day, wettest June day on record.
37+ inches of rain for June, wettest June on record.
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