Ray Aldridge on sun 18 jun 00
At 03:36 PM 6/18/00 -0700, you wrote:
>Mel,
>
> A friend with a Ph.D. in Chemistry as well as an MFA in clay said that
he takes
>issue with the science of the guy who wrote that article. His concern was
that
>the author did not take into account the salt in the kiln from the previous
>firings. I believe that it was stated that this was negligible. I have been
>around salt kilns that you really did not need to add salt to because that
there
>was so much salt in it from previous firings. Also I would not consider
CM to be
>any kind of Scientific journal were there would be any peer review.
Because of
>that I would not be so quick to jump on the No pollution from a slat kiln
band
>wagon.
Maybe I'm misremembering the article, but I seem to recall that he was
measuring actual emissions at the stack. Unless you think he was lying,
this would seem to be dispositive evidence.
>
>I have seen what the stuff coming out of the stack has done to metal
everywhere
>near and would not want anything that I cared about nearby.
Hot salt water corrodes metal. No great mystery here. I think the issue's
been settled, unless someone comes along and demonstrates that the guy who
did the emissions measurements was lying.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
rickmahaffey on sun 18 jun 00
Mel,
A friend with a Ph.D. in Chemistry as well as an MFA in clay said that he takes
issue with the science of the guy who wrote that article. His concern was that
the author did not take into account the salt in the kiln from the previous
firings. I believe that it was stated that this was negligible. I have been
around salt kilns that you really did not need to add salt to because that there
was so much salt in it from previous firings. Also I would not consider CM to be
any kind of Scientific journal were there would be any peer review. Because of
that I would not be so quick to jump on the No pollution from a slat kiln band
wagon.
I have seen what the stuff coming out of the stack has done to metal everywhere
near and would not want anything that I cared about nearby. Of course that is
just one person's opinion. Also we found that slat ware did not sell well.
Rick Mahaffey
mel jacobson wrote:
> many have written a year ago, nils others, that what comes
> out of the stack of a salt kiln is salt.
>
> a year ago a fellow wrote a very scientific paper for cm
> with the same conclusion.
>
> all of the data is in, proven, but will people listen?
> probably not. emotional evidence seems to rule over
> science. `my brother in laws friend told me at a party
> that chlorine gas comes from the stack and it will kill you. don't
> ever get near a salt kiln.` BS
>
> mel
>
> FROM MINNETONKA, MINNESOTA, USA
> http://www.pclink.com/melpots (website)
>
> ______________________________________________________________________________
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ferenc jakab on mon 19 jun 00
>
> A friend with a Ph.D. in Chemistry as well as an MFA in clay said that
he takes
> issue with the science of the guy who wrote that article. His concern was
that
> the author did not take into account the salt in the kiln from the
previous
> firings. I believe that it was stated that this was negligible. I have
been
> around salt kilns that you really did not need to add salt to because that
there
> was so much salt in it from previous firings. Also I would not consider
CM to be
> any kind of Scientific journal were there would be any peer review.
Because of
> that I would not be so quick to jump on the No pollution from a slat kiln
band
> wagon.
I don't know anything about scientific testing of emissions from salt kilns,
but I do know that when I was at Art School we were forced to evacuate the
sculpture studio several times when the clay-eaters fired up the
multichamber salt kiln. What was stinging out eyes and burning our throats
sure as hell smelt like chlorine. It was the same smell as when you open a
bottle of bleach and get an accidental smell. Very distinctive. Eventually
they were only allowed to insert salt at night when we were all safely at
home.
Additionally, was that test specifically for chlorine gas or just for salt?
Feri.
Gavin Stairs on mon 19 jun 00
At 06:36 PM 6/18/00, Rick Mahaffey wrote:
>... I have seen what the stuff coming out of the stack has done to metal
>everywhere
>near and would not want anything that I cared about nearby. Of course that is
>just one person's opinion. Also we found that slat ware did not sell well.
>
>Rick Mahaffey
>
>mel jacobson wrote:
>
> > many have written a year ago, nils others, that what comes
> > out of the stack of a salt kiln is salt.
....
Hi all,
I agree with Rick that the science in CM is not unimpeachable, and the
articles that I have seen tend to be on the light side of science. Mel and
Rick may have been referring to the article by Gil Stengel, for which I
provided a calculation of the effluent composition of an example firing of
one of Gil's salt kilns. Gil presented the same material at 1997
NCECA. The main conclusion to be drawn is that whatever happens to the
Chlorine from the salt, it is relatively dwarfed by the other quantities of
material flowing through the kiln. In particular, the oxygen and fuel
which combine to produce tons of CO2, H2O and some CO as well. Wil
Shynkaruk of Utah State University also wrote an article on salt kilns, and
presented at the same NCECA. He did some experiments, but I wasn't able to
use his results to improve my model of what is going on. However, I
believe that Mel is close to being correct with respect to the salt. With
a couple of caveats.
I have not yet seen any authoritative report on the amount of Chlorine (as
chloride, Cl-) contained in salt glazes. I would dearly love to do some
work on this, and maybe I will one day. Or someone else will. But, in the
absence of any evidence either way, I presume, on the basis of the
diffusion of volatile or fugitive species in a semiliquid like a glaze
melt, that some of the chloride in a glaze melt is released in favor of
oxygen. There is evidence, in the re-emission of salt from a second firing
of a salted kiln, that much of the chloride is retained. So I would not go
so far as to say that all of the chloride escapes. However, whatever does
escape will emerge from the kiln either as chloride, most probably
associated with water as HCl, hydrochloric acid, or as Chlorine, Cl2, the
elemental gas. The latter reaction is favored only at relatively low
temperatures, so a high temperature salting is not expected to release much
Chlorine, and at least one set of measurements has been done which supports
this. The same measurement found slight indications of HCl, which supports
my earlier hypothesis. This work was done in England some years bag, using
sampling tubes, so the data were scant, and rather coarse in resolution.
So the best statement so far is that salting releases only very slight
traces of Chlorine gas, if any, but may release measurable HCl. The vast
remainder of the salt escapes unaltered, as salt. Score one for Mel.
The observations of corrosion in exposed metalwork around a salt kiln may
be attributed to the salt. Salt is a well known catalyst of steel and
other metal corrosion. People who drive cars where salt is used on roads
as a de-icer are well aware of this. So there is no need to invoke HCl as
a corrosive agent for this.
All of that does not mean that the salt fume from the kiln is good to
breathe. There are no doubt many trace elements in the vapor which might
not be good to breathe. Whatever you put into a kiln is going to come out
this way to some extent. Whether it is significant depends on many
circumstances. I wouldn't hazard it with such glaze ingredients as lead,
cadmium, zinc, manganese, vanadium, barium, uranium, etc. Fortunately,
these are not commonly used in salt firing, or at least I hope not. But
even if these elements are not present, there are potentially some nasty
hydrocarbons there, like furans, dioxins, aromatics of other sorts,
organo-halides and the like, and also traces of nitrogen oxides, and
abundant carbon oxides. I do not mean to set off all the alarm bells by
mentioning those materials: I have no reason to believe that they are
present in anything more than trace levels, except of course the CO and
CO2. However, all other combustion systems produce these noxious products
in traces, so I don't expect that kilns are exempt. By other systems I
mean furnaces, industrial kilns and burners of all sorts, and internal
combustion engines (cars and trucks). So I don't think it is a good idea
to breathe the effluent of any kiln, much less a salt kiln. The traces
from a salt kiln might be somewhat worse, owing to the mobilizing effect of
the salt.
I would also mention that soda, as a replacement for salt, merely replaces
the effluent salt, NaCl, with effluent soda, NaOH. soda is probably a more
vicious immediate pollutant, although it must quickly be reacted with local
carbolic and humic acids and the like to become relatively innocuous. I
would say that the relative environmental arguments are so slight that the
esthetics should prevail. If your preferred glaze depends on salt, then
salt. If you like the soda, or a mix, go for it.
The bottom line is that kilns are net producers of pollution, and salt
kilns are slightly worse than an ordinary reduction kiln, in that they
produce some salt as well. All kilns, even electrics, produce some of
these byproducts, and fuel fired kilns produce copious quantities of CO2,
which is a primary greenhouse gas, and not innocuous. Does this mean that
kilns are bad? No, not much more than any other industrial activity. But
no fuel using activity is blameless. As has been pointed out on this list
before, if you want to make a difference, stop using your car, or just
plain stop. The fundamental problem is not that one activity is worse than
another: it is that we are too many for the Earth to carry. Think on that
for a while, wake up, and construct a life which is less burdensome in both
the short term and the long term. I think you will find that it has little
to do with whether you salt your kiln.
Gavin
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