Cynthia Bracker on thu 19 aug 04
I have been looking into the problems that Mark Strayer has been having
with his spectrum glazes at Cone 6. Something recently struck me and I
wanted some other opinions. I had noticed a while back that the
standard computer programs on Skutt and L&L kilns (others as well, I'm
sure) will DECREASE the rate of climb for the last hour or two of a
firing. I am told this is to achieve better glaze success. Typically
in a Kiln Sitter kiln, the switches are all on high and the elements are
on at full power for the last part of the firing, and controlling the
rate of temperature climb is not really possible. So my questions are:
1. Could the reduced temperature at the end of the firing help solve
problems like Mark described (Severe blistering not likely the result of
improper bisque firing, application etc.) as well as problems like
pinholing, crazing etc. that also seem to have no apparent cause (or at
least no typical cause)
2. If so, could one try to achieve this same speed reduction in a manual
kiln by turning the switches down to medium at say 2000deg Farenheit. or
through some other method?
Thanks
Cindy Bracker
Snail Scott on thu 19 aug 04
At 02:09 PM 8/19/2004 -0500, you wrote:
>...the
>standard computer programs on Skutt and L&L kilns (others as well, I'm
>sure) will DECREASE the rate of climb for the last hour or two of a
>firing...Typically
>in a Kiln Sitter kiln, the switches...are
>on at full power for the last part of the firing, and controlling the
>rate...not really possible...
>1. Could the reduced temperature at the end of the firing help solve
>problems like Mark described...>2. If so, could one try to achieve this
same speed reduction in a manual
>kiln by turning the switches down to medium at say 2000deg Farenheit. or
>through some other method?
The rate of climb on a non-computerized kiln will
slow down as the temperature rises, anyway, due
to the inefficienty of the equipment; more so on
older elements. You can certainly slow it down
manually, though. I generally do it by turning
just the middle element to 'med'. This is enough
to totally stall out a mid-range stoneware firing.
As to whether it will solve Mark's problem, I
don't know. Maybe. Probably worth a try.
-Snail Scott
John Hesselberth on thu 19 aug 04
On Thursday, August 19, 2004, at 03:09 PM, Cynthia Bracker wrote:
> 1. Could the reduced temperature at the end of the firing help solve
> problems like Mark described (Severe blistering not likely the result
> of
> improper bisque firing, application etc.) as well as problems like
> pinholing, crazing etc. that also seem to have no apparent cause (or at
> least no typical cause)
> 2. If so, could one try to achieve this same speed reduction in a
> manual
> kiln by turning the switches down to medium at say 2000deg Farenheit.
> or
> through some other method?
Hi Cindy/ Mark,
Most kilns--automatic or manual--slow down significantly as they
approach cone 6--regardless or how they are set/programmed-- just
because they are incapable of raising the temperature very rapidly when
they are that hot. I don't think a manual kiln will reach cone 6 if it
is set to medium at 2000. It will be doing well to hold 2000. So I
doubt that would help blistering.
Blistering is probably caused by rapid evolution of gases at the wrong
time--I doubt that it is boiling. Rather it is probably a carbonate
releasing oxygen or some other gas-evolving chemical reaction. I don't
think we can always figure out what causes it, but I will advance one
theory. I have seen glazes which contain a large amount of iron oxide
blister on occasion and I think it may be due to thermal reduction of
the Fe2O3. That is reported to happen more like cone 8 or 9 and is
thought to be important in forming oil spot glazes. But I speculate it
can start earlier than that under some circumstances. One of the glazes
in our book--Waxwing-- will blister if fired a little too hot or put on
a little too thick. Why it does and Waterfall brown doesn't, I haven't
a clue. They are obviously different compositions, but both contain a
large amount of iron oxide. I can only speculate that in Waxwing there
is a catalytic effect that triggers the thermal reduction at a little
lower temperature--but that is speculation.
But that is why, in an earlier post, I suggested that going to Spectrum
is the only hope of getting a definitive answer. They are the only ones
that know the composition of this glaze and who have enough experience
with it to have figured out how to solve it. But if the glaze in
question happens to be dark brown, I would try firing it a half or full
cone less and maybe putting it on thinner and see if that helps.
Jacob's thought of firing to cone 6 and soaking for a bit a 5 might be
another way to give time for the glaze to settle down.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
John Hesselberth on thu 19 aug 04
On Thursday, August 19, 2004, at 07:15 PM, John Hesselberth wrote:
> carbonate releasing oxygen
Ooops, yes I know better. Sorry about that--should be CO2
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Mark Strayer on fri 20 aug 04
All this help is fantastic and so welcome! I plan on going to Braker's to=
mmorow
with some examples of bubbling and get some first hand feedback. I will
make a list of the Spectrum glazes I have seen this problem with and post=
.
I have gotten a little feedback from Spectrum through Cythia...They told
me that they test their glazes at cone 5 and they "should hold up at cone=
6", which makes me suspect I will see much better results at cone 5. Wha=
t
are the advantages and disadvantages of cone 5 vs cone 6?
PS I am a new member of this chat group (was turned on to it by Flat Rock=
Studios) and I must say I am overwhelmed by your responsiveness. I work=
in my ceramic studio alone and find the comrodery here fun and needed...I=
have been missing something durning my studio time and that is the compan=
y
and ideas of other ceramic artists. Thank You all.
-M
>-- Original Message --
>Date: Thu, 19 Aug 2004 14:09:53 -0500
>Reply-To: Clayart
>From: Cynthia Bracker
>Subject: Cone 6 glazes computer controlled vs. kiln sitter kiln
>To: CLAYART@LSV.CERAMICS.ORG
>
>
>I have been looking into the problems that Mark Strayer has been having
>with his spectrum glazes at Cone 6. Something recently struck me and I
>wanted some other opinions. I had noticed a while back that the
>standard computer programs on Skutt and L&L kilns (others as well, I'm
>sure) will DECREASE the rate of climb for the last hour or two of a
>firing. I am told this is to achieve better glaze success. Typically
>in a Kiln Sitter kiln, the switches are all on high and the elements are=
>on at full power for the last part of the firing, and controlling the
>rate of temperature climb is not really possible. So my questions are:
>1. Could the reduced temperature at the end of the firing help solve
>problems like Mark described (Severe blistering not likely the result of=
>improper bisque firing, application etc.) as well as problems like
>pinholing, crazing etc. that also seem to have no apparent cause (or at
>least no typical cause)
>2. If so, could one try to achieve this same speed reduction in a manual=
>kiln by turning the switches down to medium at say 2000deg Farenheit. or=
>through some other method?
>Thanks
>Cindy Bracker
>
>________________________________________________________________________=
______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pcli=
nk.com.
Donna Nicosia on fri 20 aug 04
Hi, I'm new to clayart and really enjoy reading and learning. I've used
spectrum glazes at cone 6 and haven't had any problems with it. Turns
out like it should. I have an old used Evenheat kiln, computer kind, and
yes, the temp. rate does slow down the last couple of hours. I also have
an old used kiln sitter kiln, Evenheat also, and I get the same results
with the both of them so I don't know what the answer is. Maybe it has
something to do with different colors as I've only used a small
selection of colors. Sorry I can't be of help. Donna
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Cynthia
Bracker
Sent: Thursday, August 19, 2004 3:10 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Cone 6 glazes computer controlled vs. kiln sitter kiln
I have been looking into the problems that Mark Strayer has been having
with his spectrum glazes at Cone 6. Something recently struck me and I
wanted some other opinions. I had noticed a while back that the
standard computer programs on Skutt and L&L kilns (others as well, I'm
sure) will DECREASE the rate of climb for the last hour or two of a
firing. I am told this is to achieve better glaze success. Typically
in a Kiln Sitter kiln, the switches are all on high and the elements are
on at full power for the last part of the firing, and controlling the
rate of temperature climb is not really possible. So my questions are:
1. Could the reduced temperature at the end of the firing help solve
problems like Mark described (Severe blistering not likely the result of
improper bisque firing, application etc.) as well as problems like
pinholing, crazing etc. that also seem to have no apparent cause (or at
least no typical cause)
2. If so, could one try to achieve this same speed reduction in a manual
kiln by turning the switches down to medium at say 2000deg Farenheit. or
through some other method?
Thanks
Cindy Bracker
________________________________________________________________________
______
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Mark Strayer on sat 21 aug 04
I sat down last night and studied which of my spectrum glazes seem to hav=
e
this problem of bubbling @ cone 6. The list is shorter than I thought.
I am placing these in two groups (1)really bad bubbling (2)Minor Bubblin=
g
Bad:
Textured Oasis
Textured Kiwi
Textured Moonscape
Minor:
Textured Iron
Textured Cascade
Textured Bronze
***Not sure what it means, but they ALL are in this "Textured"catagory of=
glaze.
I also have noticed that Textured Cascade runs really bad on the interior=
of pieces at cone 6...pooling at the bottom.
I'm taking a few of my pieces up to Brackers this morning for some expert=
opions and I will let everyone know what I find out.
-M
>-- Original Message --
>Date: Fri, 20 Aug 2004 20:15:27 -0400
>Reply-To: artist@donnanicosia.com
>From: Donna Nicosia
>Subject: Re: Cone 6 glazes computer controlled vs. kiln sitter kiln=
>To: CLAYART@LSV.CERAMICS.ORG
>
>
>Hi, I'm new to clayart and really enjoy reading and learning. I've used
>spectrum glazes at cone 6 and haven't had any problems with it. Turns
>out like it should. I have an old used Evenheat kiln, computer kind, and=
>yes, the temp. rate does slow down the last couple of hours. I also have=
>an old used kiln sitter kiln, Evenheat also, and I get the same results
>with the both of them so I don't know what the answer is. Maybe it has
>something to do with different colors as I've only used a small
>selection of colors. Sorry I can't be of help. Donna
>
>-----Original Message-----
>From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Cynthia
>Bracker
>Sent: Thursday, August 19, 2004 3:10 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Cone 6 glazes computer controlled vs. kiln sitter kiln
>
>I have been looking into the problems that Mark Strayer has been having
>with his spectrum glazes at Cone 6. Something recently struck me and I
>wanted some other opinions. I had noticed a while back that the
>standard computer programs on Skutt and L&L kilns (others as well, I'm
>sure) will DECREASE the rate of climb for the last hour or two of a
>firing. I am told this is to achieve better glaze success. Typically
>in a Kiln Sitter kiln, the switches are all on high and the elements are=
>on at full power for the last part of the firing, and controlling the
>rate of temperature climb is not really possible. So my questions are:
>1. Could the reduced temperature at the end of the firing help solve
>problems like Mark described (Severe blistering not likely the result of=
>improper bisque firing, application etc.) as well as problems like
>pinholing, crazing etc. that also seem to have no apparent cause (or at
>least no typical cause)
>2. If so, could one try to achieve this same speed reduction in a manual=
>kiln by turning the switches down to medium at say 2000deg Farenheit. or=
>through some other method?
>Thanks
>Cindy Bracker
>
>________________________________________________________________________=
>______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
>
>________________________________________________________________________=
______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pcli=
nk.com.
Gary Harvey on sat 21 aug 04
Bubbling can also be the clay that is reacting to the chemistry of the
glaze. I have never had a Spectrum glaze bubble but I have had some bubbles
when I was once firing with a glaze I purchased years ago and it was NOT a
spectrum glaze. I also fire at cone 6. In fact I have had less problems with
Spectrum than with other glazes including the ones I made up. Gary Harvey,
Palestine TX
----- Original Message -----
From: "Mark Strayer"
To:
Sent: Saturday, August 21, 2004 8:26 AM
Subject: Re: Cone 6 glazes computer controlled vs. kiln sitter kiln
I sat down last night and studied which of my spectrum glazes seem to have
this problem of bubbling @ cone 6. The list is shorter than I thought.
I am placing these in two groups (1)really bad bubbling (2)Minor Bubbling
Bad:
Textured Oasis
Textured Kiwi
Textured Moonscape
Minor:
Textured Iron
Textured Cascade
Textured Bronze
***Not sure what it means, but they ALL are in this "Textured"catagory of
glaze.
I also have noticed that Textured Cascade runs really bad on the interior
of pieces at cone 6...pooling at the bottom.
I'm taking a few of my pieces up to Brackers this morning for some expert
opions and I will let everyone know what I find out.
-M
>-- Original Message --
>Date: Fri, 20 Aug 2004 20:15:27 -0400
>Reply-To: artist@donnanicosia.com
>From: Donna Nicosia
>Subject: Re: Cone 6 glazes computer controlled vs. kiln sitter kiln
>To: CLAYART@LSV.CERAMICS.ORG
>
>
>Hi, I'm new to clayart and really enjoy reading and learning. I've used
>spectrum glazes at cone 6 and haven't had any problems with it. Turns
>out like it should. I have an old used Evenheat kiln, computer kind, and
>yes, the temp. rate does slow down the last couple of hours. I also have
>an old used kiln sitter kiln, Evenheat also, and I get the same results
>with the both of them so I don't know what the answer is. Maybe it has
>something to do with different colors as I've only used a small
>selection of colors. Sorry I can't be of help. Donna
>
>-----Original Message-----
>From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Cynthia
>Bracker
>Sent: Thursday, August 19, 2004 3:10 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Cone 6 glazes computer controlled vs. kiln sitter kiln
>
>I have been looking into the problems that Mark Strayer has been having
>with his spectrum glazes at Cone 6. Something recently struck me and I
>wanted some other opinions. I had noticed a while back that the
>standard computer programs on Skutt and L&L kilns (others as well, I'm
>sure) will DECREASE the rate of climb for the last hour or two of a
>firing. I am told this is to achieve better glaze success. Typically
>in a Kiln Sitter kiln, the switches are all on high and the elements are
>on at full power for the last part of the firing, and controlling the
>rate of temperature climb is not really possible. So my questions are:
>1. Could the reduced temperature at the end of the firing help solve
>problems like Mark described (Severe blistering not likely the result of
>improper bisque firing, application etc.) as well as problems like
>pinholing, crazing etc. that also seem to have no apparent cause (or at
>least no typical cause)
>2. If so, could one try to achieve this same speed reduction in a manual
>kiln by turning the switches down to medium at say 2000deg Farenheit. or
>through some other method?
>Thanks
>Cindy Bracker
>
>________________________________________________________________________
>______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
>
>___________________________________________________________________________
___
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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