Peter Powning on sat 23 nov 96
Can anyone tell me about so-called "encapsulated cadmium" as a glaze
colourant? A glaze company that I deal with ensures me that cadmium in this
form is essentially inert, both before and after firing, and that it is food
safe in an 06 glaze and safe to handle as a glaze, dry or wet. I'm impressed
but sceptical. Anyone with an authoritative answer?
Peter Powning
http://www.discribe.ca/powning
John L Worner on mon 25 nov 96
Hi Peter,
I think you are referring to the inclusion pigments made by Cerdec. I recently
attended a workshop by Sandy Simon. She demonstrated the use of these pigments.
I have also been told that they are non-toxic because of the way the chemicals
are "encapsulated (contained within another chemical that prevents their
release)".... They are stable to 2300F!! Sandy used P25 frit with hers (60
grams stain, 40 grams frit and water). However, P25 is a low-fire frit and her
pieces were fired to cone 7. We did however try with the P25 frit just to see
what would happen. (What the heck - we can make more!)The pieces haven't come
out of the glaze firing yet, so I don't know how they have turned out (we fired
to cone 8). The stains were applied to the wet pot after throwing.
Cerdec's address is Cerdec Corporation, West Wylie Avenue, P.O.Box 519,
Washington, Pennsylvania 15301:
Fax 412-228-3170. http://www.cerdec.com or e.mail cerdec @telerama.com. Good
luck :)
Anne
Lili Krakowski on sun 5 feb 06
Encapsulated Cadmium Stains were mentioned the other day.
Question: When those little guys first came on the market, it was =
bruited they could be dissolved in some glazes, the encapsulation =
disintegrating (it that is the right word) and cadmium being released =
into the glaze, therefore making the glaze potentially hazardous, and in =
need of testing if used for food related ware.
(Gee, that was a long sentence. Must catch my breath.)
OK. Was this true? If so, is it still true?
Lili Krakowski
Be of good courage
Bobbruch1@AOL.COM on tue 7 feb 06
David Hendley writes:
<<Extra careful hygiene needs to be practiced
when working with cadmium encapsulated stains.>>>>
David: What are the issues for a potter?
Can cadmiun in the encapsulated stains
be absorbed through the skin? Are the
kiln fumes a source of potential contamination?
Bob Bruch
David Hendley on tue 7 feb 06
Again, the short answer: who knows?
To me, the only reasonable course of action for a studio potter
without a industrial hygienist on staff, and with no regular testing
of kiln emissions and the environment around the kiln, is to treat
these stains as potentially hazardous.
This would be my attitude regardless of what any literature
from the manufacturer might state - healthy skepticism.
I do, by the way, (carefully) use cadmium inclusion stains, so
I personally think the risk is manageable.
Some would argue, as Monona Rossol did on Clayart years
ago, that these stains should not be used by studio potters
at all, except with regular monitoring and testing of the potter,
the pots, the kiln, and the studio.
David Hendley
Old Farmhouse Pottery
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> David Hendley writes:
> <<> Extra careful hygiene needs to be practiced
> when working with cadmium encapsulated stains.>>>>
>
> David: What are the issues for a potter?
> Can cadmiun in the encapsulated stains
> be absorbed through the skin? Are the
> kiln fumes a source of potential contamination?
Ron Roy on tue 7 feb 06
Hi Bob,
I'm not sure about absorption through the skin but it can affect eyes, nose
and respiratory tract.
Kiln fumes and dust (systemic entry) are the worst.
RR
>David Hendley writes:
><<>Extra careful hygiene needs to be practiced
>when working with cadmium encapsulated stains.>>>>
>
>David: What are the issues for a potter?
>Can cadmiun in the encapsulated stains
>be absorbed through the skin? Are the
>kiln fumes a source of potential contamination?
>
>Bob Bruch
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on tue 7 feb 06
Hi Lili,
I find myself in agreement with David Hendley - be very careful and also
have any ware tested once in a while to make sure you are under the lawful
limit - if you must use it at all. I would not use it inside functional
ware
I do not think the crystals break down in a glaze - but - I have seen a
microphotograph of the product - you can see the cadmium encased in the
crystals - they used that photo in their advertising - but! - You can also
see that all the crystals are not complete and there is some cadmium not
encapsulated.
I have also heard you can smell the cadmium when you open a container of
encapsulated cadmium - a sure sign there is some not locked away.
On the other hand - much better than using the unencapsulated form.
Cadmium is about 10 times more toxic than lead by the way - consider it a
highly toxic material.
RR
> Encapsulated Cadmium Stains were mentioned the other day.
>
>Question: When those little guys first came on the market, it was bruited
>they could be dissolved in some glazes, the encapsulation disintegrating
>(it that is the right word) and cadmium being released into the glaze,
>therefore making the glaze potentially hazardous, and in need of testing
>if used for food related ware.
>
>(Gee, that was a long sentence. Must catch my breath.)
>
>OK. Was this true? If so, is it still true?
>
>Lili Krakowski
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Tom Buck on wed 15 feb 06
Lili, others:
inclusion stains or encapsulated stains are colourant particles of
metallic oxides surrounded by high-purity zircon (aka "natural" zirconium
orthosilicate). This compound melts at 2550 degrees Celsius.
recall that one of our chief opacifying agents is zircon
(Zirconium Silicate sold under a few trade-names), and that the best
whitening effect occurs when the particle size is ultra small (500 - 1000
mesh)
now also note that it is a misnomer using the term "dissolve" to
describe what happens to zircon when it is included in a glaze and the
glaze melts to form a liquid ("Liquidus"). the zircon particles remain
intact and "disperse", that is, become suspended, throughout the Liquidus.
and even with aggressive flux oxides present (for example, K2O, Na2O and
CaO), the zircon particles show little interest in melting and forming
glass by themselves, instead they remain intact.
encapsulating technolgy has advanced greatly in the past 20 years,
and it used widely. yet, it undoubtedly is stretching the technology to
get some ZrSiO4 molecules in a form that will surround colourant oxides.
if the encapsulated product does indeed have a few molecular layers of
ZrSiO4 enclosing an individual particle of colourant, then there is little
danger that the ZrSiO4 sheath will breakdown at lowfire and midfire
temperatures.
but the producers of such stains do demand that they not be fired
to highfire cones (ie, above Cone 6). Still, there are some encapsulated
stains designed for Cone 10 service, and generally are quite costly.
inclusion stains should be considered safe if the stain is
properly handled (for example, do not ball-mill the glaze), and if
mistreating the stain is avoided -- ie, avoid physical actions (no
abrasion etc.) and chemical contacts (avoid aggressive acids, aggressive
gases, eg, fluorine, and very heavy reduction producing lots of carbon
monoxide).
recall too that these inclusion stains are made for industrial users, not
studio potters, and the makers would soon be out of business if their
products caused damage or injury.
later shalom Tom.
Tom Buck ) --
primary address. "alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
| |
|
