Craig Clark on fri 4 feb 05
Ivor was polite with his response to this topic. I will not be so
nice. In this day and age it is just plain ignorant and inconsiderate to
use a lead based anything which will then reside on the surface of a
ceramic object. Why use the stuff when there are far less toxic
alterantives.
Give your employees, and any unwitting soul who may come in contact
with the stuff in the future a break. Drop the lead.
Miny Rant Over
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008 (where we are finally beginning to clean up our
enviromental act!)
(713)861-2083
mudman@hal-pc.org
Eva Gallagher on sat 5 feb 05
Well I agree with the no lead propnents - that's why I was so surprised to
find in the new book Making Marks by Robin Hopper - the cover page of his
book has this plate with a bright red centre. He statesthat it is a chrome
red glaze fired to cone 6. He does say that it is not for functional work -
however if a high profile potter like Hopper uses it then its no wonder that
others keep on questioning its use.
Eva Gallagher
Deep River Potters Guild
Oldest Potters Guild in Canada - est 1954
----- Original Message -----
From: "Craig Clark"
To:
Sent: Friday, February 04, 2005 9:33 PM
Subject: Re: Lead based enamels..use other alternatives....
> Ivor was polite with his response to this topic. I will not be so
> nice. In this day and age it is just plain ignorant and inconsiderate to
> use a lead based anything which will then reside on the surface of a
> ceramic object. ......
> Craig Dunn Clark
> 619 East 11 1/2 st
> Houston, Texas 77008 (where we are finally beginning to clean up our
> enviromental act!)
> (713)861-2083
> mudman@hal-pc.org
>
> ______________________________________________________________________________
> 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.
Ivor and Olive Lewis on sun 6 feb 05
Dear Craig Clark, Lili and others,
It was pleasing to see Paul Lewing back his concerns with tests.
Perhaps there are several facets to the discussion about the use of
toxic material. These fall under "Exposure of workers to raw
materials", "Release of noxious emanations during processing and the
contamination of working environments" and "Hazards to potential
users".
Those who have grave concerns might ask the Lead Manufacturers for
validation for some of the claims that are made about the physical and
chemical properties of lead bearing glaze and overglaze materials.
I think it is worth noting that "Glaze Chemistry" implies far more
than juggling numbers and substituting ingredients in recipes. Can
anyone tell us, using the conventions and principles of modern
Chemistry, why some materials volatilise or leach so readily whereas
others seem to be resistant to these effects.
Frank Hamer does not, nor do others who publish commentary on
technical aspects of the ceramic arts.
Even though metallic lead melts below 400 deg C it does not boil until
it is heated to over 1700 deg C. Lead oxide (PbO) melts at 888 deg C,
PbO2 decomposes at 290 deg C and Pb2O3 decomposes at 530 deg C. Both
of the Lead Silicates melt between 700 & 800 deg C. Since no values
are given for the boiling points of any of these compounds conclusions
which may be drawn about their behaviour boils down to pure guess
work.
So someone has to sit down with a slide rule and calculate the bond
dissociation energies of the molecules from which these compounds are
formed and then estimate the temperature at which the breakdown
happens.
I am sure those who realise that we know so little will exercise
caution and look for proven alternative safe solutions.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Eva Gallagher on mon 7 feb 05
Hi Ivor
No he does not give the recipe - just that it is a lead based chrome red.
The reason for using it he says is that it is impossible to get that colour
any other way. It is his south west series and it is on the cover of his new
book. Everyone will want that glaze - so no wonder the question of using
lead comes up over and over.
Eva
Deep River
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Monday, February 07, 2005 12:51 AM
Subject: Re: Lead based enamels..use other alternatives....
> Dear Eva Gallagher,
> Does Robin Hoper give the recipe for this glaze or say if it is based
> on Lead Silicate, Lead Bi-silicate, Lead Carbonate or Lead oxide.
> Furthermore, does he claim to have made the pot or is he using the
> work of another person to illustrate some point in his text.
> I have seen examples of the Chrome Red based on high lead frits and
> Led Bisilicate and though drawn to the colour, shied away because of
> the problems.
> I will admit that the first glaze I ever concocted was a raw lead
> type, Red Lead from the wholesale paint supply house with an equal
> weight of the clay I was throwing tinted with a hint of home made
> cobalt oxide. That was in 1958 but I have never used a lead fluxed
> glaze since then.
> Best regards,
> Ivor Lewis.
> Redhill,
> S. Australia.
>
> ______________________________________________________________________________
> 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.
Ivor and Olive Lewis on mon 7 feb 05
Dear Eva Gallagher,
Does Robin Hoper give the recipe for this glaze or say if it is based
on Lead Silicate, Lead Bi-silicate, Lead Carbonate or Lead oxide.
Furthermore, does he claim to have made the pot or is he using the
work of another person to illustrate some point in his text.
I have seen examples of the Chrome Red based on high lead frits and
Led Bisilicate and though drawn to the colour, shied away because of
the problems.
I will admit that the first glaze I ever concocted was a raw lead
type, Red Lead from the wholesale paint supply house with an equal
weight of the clay I was throwing tinted with a hint of home made
cobalt oxide. That was in 1958 but I have never used a lead fluxed
glaze since then.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Jon Pacini on wed 9 feb 05
Greetings All---Hi Ivor----------Dr Herbert Sanders book Glazes for Special
Effects has a number of formulae for chrome reds. They are for very low
fire, ^010 and lower as I recall, and are primarily composed of various lead
compounds and chrome.
They must be some of the most toxic glazes ever developed. I worked with
them extensively back in the 70 s and they can be spectacular. Many of them
develop magnificent crystals, much like frost patterns on glass.
Not to be used on food surfaces of course-----------
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Ivor and Olive Lewis on wed 9 feb 05
Dear Eva,
Does Robin Hopper give the recipe?
E. Cooper and D. Royle give the clues to creating Chrome Red glazes on
pp 108-9 of "Glazes for the Studio Potter". They include three
recipes, one of which is based on Lead Bisilicate, one on Lead Oxide
and one is lead free.. Suggestion is for 2% Chrome Oxide.
Recommendation is for firing in a none reducing atmosphere.
A few hours work weighing and mixing glaze tile grids would very
quickly find several recipes that would behave on the clays you are
using. Might only need one firing to get close to the mark.
Perhaps it is irresponsible to discuss glazes that contain Lead
compounds without the caveats. Do not use them on any ceramic that may
ever, even the most remote circumstance, be used in conjunction with
food. If you must use Lead compounds, always take precautions to
protect your health and your environment. Disclose the nature of your
work.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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