Chris Schafale on tue 6 oct 98
Hey folks --
This is for anyone using an Envirovent or other electric kiln vent
which draws air in through holes in the lid. I have a vague memory
of a comment in the last few months about problems with glazes on
pieces placed immediately below the vent holes. Has anyone had this
experience? I just got a couple of cookie jars back from
firing at the community art center. On the lid of each is a
strange rough, underfired-looking spot with a lighter center about
1/4 inch in diameter and a surrounding area that gradually blends
into the rest of the glaze, which looks just fine. I wondered if
this might possibly be the result of a cool draft hitting that area
at close range if these pieces were loaded at the top of the kiln.
Unfortunately, when I asked the director about it, she insisted that
it must be something I did wrong when glazing the piece and was
completely resistant to even exploring the idea that it might have to
do with the firing. (Thank God I'm getting my own kiln soon -- then
I'll have only myself to blame, but at least I'll know what I did,
hopefully.)
Anyway, what I'm trying to figure out is, would it be worth
paying to refire these pieces, in the hopes of smoothing out the
rough areas? Also, when I do have my own kiln, do I need to beware
of putting pieces too close to the vent holes?
Thanks for any thoughts.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
Jonathan on wed 7 oct 98
Chris,
I've never had a problem with my envirovent and cool spots like you
describe at cone 6. When I fired to the lower cone 04, I did get better
glaze melt when I turned the vent off a few minutes before the cone
sitter tripped, but now I leave it on through out the soak and turn it
off when I turn the kiln off. I've never noticed spots like you got,
but maybe the kiln you use is bigger and thus the holes in the lids
bigger, letting in more air? Don't know.
Jonathan in DC
Erin Hayes on wed 7 oct 98
Chris,
This does indeed happen with the kilnvents. The only solution is to be
sure not to place glaze work under the holes. If you refire them in a
different spot they do fine.
Erin.
Potterman on wed 7 oct 98
-----Original Message-----
From: Chris Schafale
To: CLAYART@LSV.UKY.EDU
Date: Tuesday, October 06, 1998 5:55 AM
Subject: Envirovent and cool spots
----------------------------Original message----------------------------
Hey folks --
This is for anyone using an Envirovent or other electric kiln vent
which draws air in through holes in the lid. I have a vague memory
of a comment in the last few months about problems with glazes on
pieces placed immediately below the vent holes. Has anyone had this
experience? I just got a couple of cookie jars back from
firing at the community art center. On the lid of each is a
strange rough, underfired-looking spot with a lighter center about
1/4 inch in diameter and a surrounding area that gradually blends
into the rest of the glaze, which looks just fine. I wondered if
this might possibly be the result of a cool draft hitting that area
at close range if these pieces were loaded at the top of the kiln.
Unfortunately, when I asked the director about it, she insisted that
it must be something I did wrong when glazing the piece and was
completely resistant to even exploring the idea that it might have to
do with the firing. (Thank God I'm getting my own kiln soon -- then
I'll have only myself to blame, but at least I'll know what I did,
hopefully.)
Anyway, what I'm trying to figure out is, would it be worth
paying to refire these pieces, in the hopes of smoothing out the
rough areas? Also, when I do have my own kiln, do I need to beware
of putting pieces too close to the vent holes?
Thanks for any thoughts.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
<
is used or not, the piece should survive a second (or third or fifth)firing.
My experience is that some pots actually start to only attain a sense of
uniqueness after several high-fires.
Most underfiring blemishes work and smooth out when refired to proper
temperature at a reasonable firing schedule.
Karsten
Janet H Walker on thu 8 oct 98
...when I do have my own kiln, do I need to beware
of putting pieces too close to the vent holes?...
I'm sure you'll get some people who will argue with you but, my
experience is "yes". You have to worry about it. If the very
top shelf of ware is close to the top of the kiln, that's the
worst case. Because there is only one element trying to heat
those pots and the air is being pulled in the holes very close
to the pots. I have measured the top shelf being a full cone
lower than the next to the top shelf.
My solution to all this is to use a cap shelf. That is, I put
an empty shelf at the very top of the load. Yes, this does
decrease the capacity of the kiln but it also increases the
evenness of the firing as reported by the cones on the shelves.
If you have a better insulated kiln or one of the nifty controllers
that can run the top elements hotter than the bottom, then your
experience may differ.
Cheers,
Jan Walker
Cambridge MA USA
Dennis Davis on fri 9 oct 98
Chris Schafale wrote
> This is for anyone using an Envirovent or other electric kiln vent
> which draws air in through holes in the lid.
> Also, when I do have my own kiln, do I need to beware
> of putting pieces too close to the vent holes?
*** Chris,
When you have your own kiln, consider leaving room to post and put a shelf over
the top of what would normally be considered the "top" shelf stack. This will
prevent the air coming in the lid holes from passing directly over any pots.
Dennis in Stafford, VA
Caryl W. on fri 9 oct 98
>Date: Wed, 7 Oct 1998 09:00:13 EDT
>Reply-To: Ceramic Arts Discussion List
>From: Potterman
>Subject: Re: Envirovent and cool spots
>To: CLAYART@LSV.UKY.EDU
>
>----------------------------Original
message----------------------------
>
>-----Original Message-----
>From: Chris Schafale
>To: CLAYART@LSV.UKY.EDU
>Date: Tuesday, October 06, 1998 5:55 AM
>Subject: Envirovent and cool spots
>
>
>----------------------------Original
message----------------------------
>Hey folks --
>
>This is for anyone using an Envirovent or other electric kiln vent
>which draws air in through holes in the lid. I have a vague memory
>of a comment in the last few months about problems with glazes on
>pieces placed immediately below the vent holes. Has anyone had this
>experience? I just got a couple of cookie jars back from
>firing at the community art center. On the lid of each is a
>strange rough, underfired-looking spot with a lighter center about
>1/4 inch in diameter and a surrounding area that gradually blends
>into the rest of the glaze, which looks just fine.
I may be way off base with this, but what you describe sounds like the
spot that can appear from the dipping tongs when you dip the pot into
the glaze bucket. I've found on a few glazes that I use, that even if I
smooth this area out really well before firing, it still appears in the
fired glaze.I have an Envirovent but I've never made the connection
between it and the spots you've described.Just a thought.
Caryl
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paul on tue 13 oct 98
I would suggest (to those who have cool spots in their kiln as a result
of using the envirovent) that the holes in the top of your kiln are too big
for the heat generating ability of your kiln. Cover up some of the intake
air with a kiln shelf piece or a small tile. I built my own vent and had to
figure out how big to make this hole - naturally I made it too big and was
cooling the kiln too much. I also had a type of passive damper in the box
under the kiln and that gave some relief but not enough.
This situation is like many for kiln building - make it a little big
and then block it off if necessary. It is easier to block off than to make
it bigger once it has already been built.
-Paul Wilmoth
----------------------------Original message----------------------------
...when I do have my own kiln, do I need to beware
of putting pieces too close to the vent holes?...
I'm sure you'll get some people who will argue with you but, my
experience is "yes". You have to worry about it.
My solution to all this is to use a cap shelf.
Cheers,
Jan Walker
Cambridge MA USA
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