ACTSNYC@cs.com on wed 10 nov 99
> ---------- Forwarded message ----------
> Date: Tue, 9 Nov 1999 13:00:22 EST
> From: Michael Banks
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Hazards of encapsulated cadmium stains II
> Resent-Subject: Hazards of encapsulated cadmium stains II
>
> ----------------------------Original message----------------------------
> In answer to a couple of queries from Ray Aldridge:
> SNIP
> I tend to be more concerned that the zircon
> stain carrier can be significantly dissolved by some high alkaline
stoneware
> glazes.
> Michael Banks,
> Nelson,
> New Zealand
-----------------------------------------------
There were many good points in Michael Banks' post, but the one I'd like to
emphasis is marked above. It supports the point I am trying to make in my
other post.
Monona Rossol
ACTSNYC@cs.com on thu 11 nov 99
.
> ---------- Forwarded message ----------
> Date: Wed, 10 Nov 1999 12:06:10 EST
> From: Ray Aldridge
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Hazards of encapsulated cadmium stains II
> Resent-Subject: Re: Hazards of encapsulated cadmium stains II
> ----------------------------Original message----------------------------
> At 01:00 PM 11/9/99 EST, Michael wrote:
> >----------------------------Original message----------------------------
> Michael, thanks-- extremely helpful information. I hope I can draw on your
> knowledge a little more.
> > The Cd and the Se (another deadly poison BTW), will
> >condense in the kiln walls, flue, etc on cooler surfaces. Cadmium is
> >commercially produced from condensation of flue gases (from smelting zinc
> >ore, Cd having a lower boiling point (767oC) than zinc (907oC).
-----------
The range at which metals fume is not restricted to their *boiling points.*
Fuming begins at their *melting points* and increases steadily in the volume
emitted as temperature increases. To say that substances only fume at their
boiling points is like saying that water only evaporates when it boils.
For another more relevant example, we see lead fume emitted from solders well
below the boiling points of the metals. And emissions start even lower if
the metals in the solder are at a eutectic point. This is relevant because
glazes contain metal compounds called fluxes that lower melting points.
For a more visual example: chromium has a boiling point of 2672 o
Centigrade--4841 o Fahrenheit. Yet most of us have seen chromium from one
glaze fume over to an adjacent tin-containing glaze to flash it pink.
All kinds of interesting, wonderful, and unpredictable things occur in kilns
because of the complexity of the chemical mixtures we call glazes. You
cannot predict accurately when metals will begin fuming from glazes.
> This is interesting, because one of the cautions Ron Roy brought up was
> that using cadmium-bearing glazes could result in the contamination of the
> kiln and subsequent contamination of wares fired in the kiln, which in view
> of what you say here seems pretty plausible. <
Sure is. All the metals that fume will recondense into the brick. To reduce
the amount of lead/cadmium/whatever in the kiln the best strategy is to vent
the kiln's internal atmosphere at high temperatures, the higher the better.
That's when the most fuming activity is occurring.
> (snip)
>
> I tend to be more concerned that the zircon
> >stain carrier can be significantly dissolved by some high alkaline
> stoneware
> >glazes.
> >
>
> Michael, in your opinion, what would be the safest type of base glaze for
> these pigments? ,
Good question. I'd like Michael's opinion on this as well.
>
> Thanks again for your patience-- I appreciate it very much. I know some
> folks are tired of the discussion, but while I'd find these pigments
> extremely useful in my work, I want to be as sure as possible that I'm
> producing safe ware. Because of the techniques I use, it's really not
> feasible for me to test every possible glaze combination for leaching. I
> currently use six slips and six major glazes, layering these freely. Four
> of the slips are quite active and have significant effect on the overlying
> glazes, and some pots might have two layers of slip and three layers of
> glaze. And firing temps may vary by as much as 2 cones, depending on
> placement. Add to that the differences engendered by the order in which
> the slips and glazes are laid down, and the possibilities become an
> unmanageable number, at $30 a pop (testing for cadmium and selenium.)
> Because of this, I use nothing but the most innocuous ingredients in my
> glazes.
>
> A couple of posters have said that in the United States, manufacturers are
> required by law to test their products for leaching, and if that's true,
> then I might as well abandon the idea of using inclusion pigments. But no
> one has been able to point me toward the actual regulation, and I haven't
> been able to find it on my own.
As I said before, it is in 16 Code of Federal Regulations Part 109. If you
can't figure out how to reach FDA on the Internet, look in the Blue Pages of
your phone book under US Government offices. Try the Government Printing
Office and talk to them about how best to get a copy of the FDA regulations
that pertain to lead and cadmium leaching.
If you contact FDA directly, they usually are helpful and have some
additional compliance information. Some of this is free. I have a good
spiral bound book on compliance from them. They have several offices in the
Washington area, but I'd start with the one at 200 C St., S.E., W, DC, 20204.
I think their general number still is 800/532-4440.
I thought all you Internet people would know how to find a government agency.
If you want to try the business approach, there is the Society of Ceramic and
Glass Decorators, 1627 K St., N.W., Suite 800, W DC 20006. You'll have to
look up their number, but Sandra Spence there should be able to help.
Or since Cerdec has been mentioned, call them and ask where to get copies of
the regs. Believe me, they have them.
Monona Rossol
ACTS
181 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@compuserve.com
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