Pat Wehrman on wed 5 jun 96
A great problem-
white smoke emitting from our electric kiln at bisque temps (1500-1800F)
The shelves have recently been washed with 1 part flint, 1 part kaolin
and 1.5 parts alumina hydrate. This is the second "event" and unless a new Pope
has been elected, I don't know why this happens.
Both times have been a heavy bisque load and glazes have acted weird on
the "smoked" bisque. The smoke is not steam, but looks like it. It will coat a
mirror with a fine white powder and the skin of the kiln outside open peeps also
has the powder.
I suspect we are using too much alumina and it is oxidizing. Any ideas,
theories or tests to conduct would be greatly appreciated.
TIA,
Pat wehrman@goldrush.com
Bob Kavanagh on wed 5 jun 96
Although the term water smoking usually refers to what happens when
chemical water is driven off from the clay, we should remember that
it combines with organic burnoff, the evaporation of salts and other
similar volatile compounds. I would suspect them and materials like
sulpher before I would think of alumina. IS there any odour?
Have you tasted this powder (literally)?
Ken Stevens on thu 6 jun 96
If there is alumina on the mirror, it is being carried out in steam or some
other product of high temp. reactions. Alumina in ceramics is often used to
describe both aluminum oxide or the hydrate; in either case, alumina is as
oxidized as it gets. It is one of the more refractory of the common ceramic
materials, and it is certainly not decomposing. Reacting? I suppose that
depends on what gases are forming in the kiln, but it would not be the most
likely suspect - if its purity is high.
Ken Stevens
Univ. of Puget Sound
Tacoma, WA
wehrman@goldrush.com on fri 7 jun 96
Bob-
Thank you for your reply.
I took your advice and tasted the powder, it was not salty.
After spending a few days stewing about this problem, I finally
considered that maybe I didn't screw up. I called my clay supplier and guess
what- it was the clay. He had only three other complaints, but I suspect there
would be more if potters weren't so reluctant to blame the material.
We still don't know what is causing the problem, he has contacted his
raw materials suppliers, but there has been no progress beyond that. He has
offered to work with me, which I appreciate.
Thanks for considering this problem.
Best regards,
Pat wehrman@goldrush.com
C Pike on sat 22 jun 96
In 1974 I had a 10 cu. ft. electric kiln which I fired daily in my studio.
I was doing bisque firing for my production stoneware. The studio was
fairly large and old with lots of natural ventilation. The kiln wasn't
vented.Who knew? One evening as I was preparing to leave and was waiting
for the kiln to shut down, I pulled the peep hole plug to check the cone
and to my amazement was greeted with a 10 inch long blue flame. This was
at cone 07. You would imagine all the organic stuff would be long gone .
No one was ever able to tell me what was burning off at such a high
temperature. Within weeks I was diagnosed as having carbon monoxide
poisoning (from inadequate ventilation) even though I always had windows
open.It was quite serious and I took nearly a year off to recuperate.
After starting up potting again I was a lot more careful about the bisque
kiln as I was now sensitized to the smell and would get quite ill if I got
a wiff. I set the kiln up in a small closet like room with heavy clear
plastic walls that were absolutely air tight. I could turn the kiln up by
opening a small door(approx. 8" by 10") near the controls and reaching
inside. This kiln room had two ventilation pipes going through the wall to
the outside. One was three inches in diameter, was just above floor level
and was for allowing cool air to enter the room.. The other pipe was 4
inches in diameter with a squirrel cage fan attached and set up to blow the
hot gasses out of the room. The 4 inch hole through the wall and the fan
were also mounted near floor level with a pipe extension running up the
wall to remove the hottest gasses. This system if installed properly will
exhaust 100% of the kiln gasses. When the fan is running you can see the
walls of the kiln room sucking in. Even when you adjust the controls
through the small 8" by 10" door, the room still holds negative pressure.
This set up can be an advantage in the basement of a house as it does not
create any kind of pressure differential in the basement and therefore will
not pull flu gasses down the house chimney when the furnace is running. Due
to the size of this kiln room, the kiln only had approx 18" clearance from
the walls therefore I protected them with 1" fibreglass insulation with a
reflective foil facing. The insulation was mounted 1" out from the walls
with spacers .
The reason I started writing this was about the toxic nature of the
kiln fumes. After using this system for awhile I noticed a white powder
covering all the walls and a build up on the vanes of the fan. I had a
friend at a university analyze this for me and it was found to contain
cadmium and selenium. REALLY BAD STUFF. It wasn't just how bad this stuff
is but how much of it there was on the walls in this room. After approx.
one year the fan blades were caked with this.
If you can smell ANY smoke from your kilns your playing with your
life. I can no longer work as a potter . I've been diagnosed as having
environmental illness and the mould in clay makes me quite ill along with
many other things our wonderful world throws at us. I now make tiles with
a dual shaft extruder I built myself, but I wear a breathing apparatus
that brings me clean air while I'm in the part of our studio where we have
any wet or drying clay. It's not fun anymore.
Even though our industry has smartened up a lot, I still see
pictures of studios with kilns in the middle of them and no ventillation, I
know of potters who have house basement studios who use electric kilns with
hood type kiln vents that don't let TOO much "stuff" get into the
house.(Meanwhile the kids are rolling around and eating everything off the
floor they can get their hands on).How about potters who Raku and don't
breath TOO many fumes. If you're one of those people who think there is no
risk or it won't happen to me---------------I wish you luck, you may need
it. If you're like most indestructible human beings (self included) that
need to learn things first hand before you can learn anything, I can say
from experience by the time you learn it will be much to late.You only get
one chance with this stuff and it's BEFORE you have problems.
Bob Pike
----------------------
Bob & Connie Pike pikec@cadvision.com
1303 10th Ave SE High River,Alberta T1V 1L4 Canada (403-652-5255)
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Leslie Ihde on sun 23 jun 96
Connie ,
Your message was very informative. I wonder what you think of my set
up-
(I can guess). I have my kiln in the basement which I must walk outside
to get to- the basement has an old cellar type door. I fire with the
basement door open, and I dnot smell fumes in the house. It's an electric
kiln. I don't do anything else.
Regarding raku sickness- I have sometimes accidently inhaled fumes which
made me feel ill for a few days after wards. I sometimes feel stuffy when
I fire the kiln- but have assumed it was allergy related. After all these
posts, maybe not.
As a self-taught potter, I only figured out that kiln fumes could be a
problem in later years. It's amazing how few beginning pottery books
address the safety issue and how few potters seem concerned. Maybe it
just seems impossible to people that such earthy things as pots and clay
and glazes could be toxic.
Any way, thanks to everyone for the cautioning remarks.
Leslie at Turning Point in Vestal, NY
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