Bob Johnson on sun 3 oct 10
I'm considering experimenting with some of the bright commercial glazes as
small accents on stoneware. But I'm wondering about the possibility that
some of the colorants (e.g., chrome and cadmium) might volatilize at firing
temperatures, even though they are frits. I don't want to breathe these. As
I understand it, frits make these toxic nasties safe for the consumer-but
what about for the potter?
I know that kilns should be well ventilated, and mine is a gas kiln located
outside. Still, I do light reduction-which means pressure inside the kiln
could conceivably push toxic gases out into the atmosphere near the kiln,
rather than out the flue. So, here's my real question: Do frits absolutely
bind toxic metals and keep them from volatilizing at temperatures in the
^6-^10 range?
Bob Johnson
Roseburg, Oregon
Bob Johnson on wed 6 oct 10
A few days ago, I inquired on the list about the possibility of volatile
toxic metals that might be released from frits or commercial glazes during
firing. A couple of people suggested that I contact the manufacturer
directly--which I did. FYI, here's the reply I received from Coloramics:
Bob,
The majority of the Stroke and Coat colors do not contain the metals you
sight (Ni, Cd, Mn, Cr). Cadmium and chromium may be present depending on
color selection. Any emission is expected to be low considering the use of
encapsulated pigments and/or high temperature calcined pigments.
In our consultation with OHSA and in their professional opinion, it would
be difficult/impossible to exceed PEL (OHSA) limits for any volatile
constituent created during a typical firing in our enclosed manufacturing
facility.
Given that the the placement of your kiln is outdoors, you would have
negligible risk of exposure to hazardous levels of metal vapors or carbon
monoxide.
Please contact me if you have any additional questions.
Steve Kutney
Coloramics, LLC
Dir of Technical Services
ph 614-675-2012
Neon-Cat on wed 6 oct 10
These elements top the list of what will most often evaporate or
volatilize (in oxidation or reduction) from glaze melts.
In alphabetical order:
antimony - Sb
boron - B (B2O3 concentrations above 2.5 weight %)
cadmium - Cd
chlorine - Cl
fluorine - F
lead - Pb
potassium - K
selenium - Se
sodium - Na
sulfur - S
Bob, if you can find the MSDS for a glaze, the information you sought
is often given. Calling a supplier or manufacturer is good, too =3D96 I=3D9=
2m
glad you found your answer and shared it with us!
Marian
neoncat
Lee Love on wed 6 oct 10
Thanks for the info Bob. I have a good cone 3 amber working and want
to color slip for slip trailing decoration. I have been leaning
toward mason stains rather than oxides for the coloring (for example,
the black and also the manganese brown color slips under amber.
On Wed, Oct 6, 2010 at 12:38 PM, Bob Johnson wrote:
> Bob,
>
> The majority of the Stroke and Coat colors do not contain the metals you
> sight (Ni, Cd, Mn, Cr). =3DA0 Cadmium and chromium may be present dependi=
ng=3D
on
> color selection. =3DA0Any emission is expected to be low considering the =
us=3D
e of
> encapsulated pigments and/or high temperature calcined pigments.
>
> In our consultation with OHSA and in their professional opinion, =3DA0it =
wo=3D
uld
> be difficult/impossible to exceed PEL (OHSA) limits for any volatile
> constituent created during a typical firing in our enclosed manufacturing
> facility.
>
> Given that the the placement of your kiln is outdoors, you would have
> negligible risk of exposure to hazardous levels of metal vapors or carbon
> monoxide.
>
> Please contact me if you have any additional questions.
>
> Steve Kutney
> Coloramics, LLC
> Dir of Technical Services
> ph 614-675-2012
>
--=3D20
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Neon-Cat on fri 8 oct 10
Hi Kathleen! Hi all!
You asked some very interesting questions!
In gas systems, the effusion rate is inversely proportional to the
square root of molar mass, but we don't get into effusion during glaze
or clay body processes. There are no great generalities for our
systems. It is not necessarily the lighter elements that volatilize --
there are many variables that influence what stays and goes. Many
elements, like zinc, readily combine with other things in our systems
so seldom escape. Much is written about crystal structure and
coordination numbers, vapor transport, diffusion and its various
mechanisms, partial pressures, kiln atmospheres, kinetics, etc. as
they affect volatilization. It's all fascinating. Stains give an added
twist.
Oh, so many reasons -- so little time.
I=3D92m going to have to pass this time =3D96 with the end to home remodeli=
ng
here I=3D92ve spent the last few days getting out of =3D91science-mind=3D92=
so I
can relax into clay work. Your questions are quite a hook back into
thinking though. All my more recent work has been with natural color
or oxides and while there are some corollaries to stains and synthetic
colorants, I just don=3D92t know that much about them, especially as they
are used in a clay body. These would be good questions for others to
answer or for you to explore or to ask of industry folks, like Mason
(http://www.masoncolor.com/Home.htm).
Maybe I=3D92ll have some time the next time around with this topic.
Meanwhile, you have fun and report back...
I=3D92m still intrigued by the challenge to write explanations in one
paragraph using monosyllable words =3D96 that=3D92s been a real head-shaker=
to
think on and kind of fun to play with (but that doesn't get anything
made here either)!
Have a pleasant, safe & sane weekend, everyone!
Marian
neoncat
On Wed, Oct 6, 2010 at 11:20 PM, wrote:
>
> Hi Marian,
> Your list looks like the lighter elements volatilize? ( Don't have a peri=
=3D
odic table in front of me) Just out of curiousity(sp?) What about metals in=
=3D
body stains?Do they behave the same way?
> And how exactly do they encapsulate cadmium and selenium?
> I'm not worried about toxicity-i treat everything as if it was to curb my=
=3D
casual tendencies.
> Thanks
> Kathleen
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