Garret D. Bonnema on wed 23 aug 00
In an effort to correct some recent bad firings in my MFT kiln I have been
searching the net for info on copper reds. (I also sent my oxy-probe for
repairs and have been told it was broken, so fixing it should help.) I found
the great article on copper reds by Karl Platt at the digitalfire web site.
In it he states.
"We should note again that oxygen analyzers cannot meter reduction- they are
sensitive to the presense, not the absense of oxygen. As such, other means,
like metering orifices, or even a decent pressure guage are preferred."
Could someone elaborate on this statement and its relevance for studio
potters?
I have been using the firing schedule of starting reduction at ^010 and
reducing all the way up to ^9 when I shut it down. I keep the probe at
.60-.65 and until recently the copper reds have come out fairly well, but
not always consistantly. I am assuming my recent failures have been because
of a malfunctioning oxy-probe, although I was getting readings that were in
the range I have gotten over the 2.5 years I have been firing with this kiln
and probe.
Garret Bonnema
Bethel, ME- where we are still hoping for summer to come for a while.
Jonathan Kaplan on wed 23 aug 00
>In an effort to correct some recent bad firings in my MFT kiln I have been
>searching the net for info on copper reds. (I also sent my oxy-probe for
>repairs and have been told it was broken, so fixing it should help.) I found
>the great article on copper reds by Karl Platt at the digitalfire web site.
>In it he states.
>"We should note again that oxygen analyzers cannot meter reduction- they are
>sensitive to the presense, not the absense of oxygen. As such, other means,
>like metering orifices, or even a decent pressure guage are preferred."
>
>Could someone elaborate on this statement and its relevance for studio
>potters?
Sure!
Garret:
The AIC probe or that with one can buy from Bailey or Axner is really not
an oxygen analyzer. An analyzer is a seriously expensive piece of
equipment.
The oxygen probe that potters us (AIC, Nils, Axner, Bailey) does not
analyze the combustion in the kiln. Rather, it senses the pressure in the
firing chamber at the tip of the probe which is a zirconium oxide based
sensor. It measures partial pressures of oxygen at the ends of the tip and
sends out a small EMF which then provides a numeric reading on your meter,
which then coresponds to a relative atmospheric condition such as excess
air, neutral, light reduction, moderate reduction, heavy reduction.(yes I
know this is a run on sentence!) Basically, the tip of the probe is
sensitive to the oxygen content in the atmosphere. The damper controls the
pressure in the kiln, and really controls the secondary air at the burner
ports, hence your reduction.
We use adjustable limiting orfices on our gas line and it does indeed meter
a precise amont of fuel. Our primary air is supplied by blowers having
North American manual butterfly valves to control the volume of air. Our
reduction is accomplished with the damper only. Precise numbers have been
consistant over 250 firings or so, many with copper reds. Our probe reads
.50 at cone 08 and as temperature increases over time and back pressue is
slightly adjusted in the kiln, .61 the the finish of the firing. We have a
50 cubic foot fiber car kiln.
>
>I have been using the firing schedule of starting reduction at ^010 and
>reducing all the way up to ^9 when I shut it down. I keep the probe at
>.60-.65 and until recently the copper reds have come out fairly well, but
>not always consistantly. I am assuming my recent failures have been because
>of a malfunctioning oxy-probe, although I was getting readings that were in
>the range I have gotten over the 2.5 years I have been firing with this kiln
>and probe.
I would submit that not only are copper reds dependant on early reduction
as you mention, but also upon the cooling of your kiln, how "tight" your
kiln is. Also, how much penetration your burners are able to produce. Also
placement of ware within the chamber and what we refer to as "thermoclines"
whcih are differences in atmosphere and temperature from shelf to shelf,
piece to piece, layer to layer, etc. Then there is also potter's intuition
that you may refer to as malfunctioning of the probe or failures of the
copper reds, eg consistence. Much has been written on copper reds that I am
sure you are well aware of by Pete Pinnell and David Hendley in CM. There
is also much mythology. And then there are sometings that work!
I will share with you and the list, what has worked quite effectively for
us is getting consistent copper reds. Susan Davy mentioned to us that she
brushs one copper red over another and the results are quite good. We took
it a step further and rather then brushing, we apply one copper red first
by dipping or pouring, and then using a second different copper red with a
much lower specific gravity, pour a thin wash over the first application.
Works like a charm! But there are many caveats, and we have been lucky to
have worked with to different copper red formulas on a project with Susan
Davey that give consistant beautiful results.
Good Luck!
Best,
Jonathan
>
>______________________________________________________________________________
>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.
Jonathan Kaplan
Ceramic Design Group LTd/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
KLeSueur@AOL.COM on wed 23 aug 00
The Oxyprobe, while a fine instrument, appears to be very prone to
malfunctioning if the messages posted here are typical. The low tech Fire
Right CO2 analyzer made by Bacarach would probably be a more reliable
instument for most people. All you need to do with it is keep the chemicals
in it fresh (and once in a while change the diaphragm), and it's very easy
to know when they need changing. If you can find Wettlauffer's ":Getting Into
Pots" at your library (now out of print) there is an excellent article and
using this useful tool.
Kathi LeSueur
Ann Arbor, MI
Paul Taylor on wed 23 aug 00
Dear Garret
Your Oxi probe is OK. I hope!
This is a list of consistency you need to produce copper reds.
A recipe that allows for crystal forming in sympathy with your regular
firing schedule. Near enough is the best you will do.
To set the nuclei of the crystals that form the color-
You need the particle sizes in the slop - Particularly of the nuclei
former( Tin I expect) - to be of the right size. They get smaller with time
In the bucket.
The right rate of temperature clime.
The right amount of reduction.
The right temperature.
To make the crystals for the glaze color you need
The right thickness of glaze
the right rate of cooling flashed and/or ramped.
If you can get all that together and consistent good luck to you. If you
change any one of those perimeters you will get a different quality red if
any.
It has taken me my whole potting life to learn these and I still can not
get it right in my big kiln.
-- Regards Paul Taylor.
Westport Pottery, Liscarney, County Mayo. Ireland.
http://www.anu.ie/westportpottery/
> From: "Garret D. Bonnema"
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 23 Aug 2000 08:29:57 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: reduction/oxy-probes
>
> In an effort to correct some recent bad firings in my MFT kiln I have been
> searching the net for info on copper reds. (I also sent my oxy-probe for
> repairs and have been told it was broken, so fixing it should help.) I found
> the great article on copper reds by Karl Platt at the digitalfire web site.
> In it he states.
> "We should note again that oxygen analyzers cannot meter reduction- they are
> sensitive to the presense, not the absense of oxygen. As such, other means,
> like metering orifices, or even a decent pressure guage are preferred."
>
> Could someone elaborate on this statement and its relevance for studio
> potters?
>
> I have been using the firing schedule of starting reduction at ^010 and
> reducing all the way up to ^9 when I shut it down. I keep the probe at
> .60-.65 and until recently the copper reds have come out fairly well, but
> not always consistantly. I am assuming my recent failures have been because
> of a malfunctioning oxy-probe, although I was getting readings that were in
> the range I have gotten over the 2.5 years I have been firing with this kiln
> and probe.
> Garret Bonnema
> Bethel, ME- where we are still hoping for summer to come for a while.
>
> ______________________________________________________________________________
> 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.
Jonathan Kaplan on thu 24 aug 00
>In an effort to correct some recent bad firings in my MFT kiln I have been
>searching the net for info on copper reds. (I also sent my oxy-probe for
>repairs and have been told it was broken, so fixing it should help.) I found
>the great article on copper reds by Karl Platt at the digitalfire web site.
>In it he states.
>"We should note again that oxygen analyzers cannot meter reduction- they are
>sensitive to the presense, not the absense of oxygen. As such, other means,
>like metering orifices, or even a decent pressure guage are preferred."
>
>Could someone elaborate on this statement and its relevance for studio
>potters?
Sure!
Garret:
The AIC probe or that with one can buy from Bailey or Axner is really not
an oxygen analyzer. An analyzer is a seriously expensive piece of
equipment.
The oxygen probe that potters us (AIC, Nils, Axner, Bailey) does not
"analyze" the combustion in the kiln. Rather, it senses the pressure in the
firing chamber at the tip of the probe which is a zirconium oxide based
sensor. It measures partial pressures of oxygen at the ends of the tip and
sends out a small EMF which then provides a numeric reading on your meter,
which then coresponds to a relative atmospheric condition such as excess
air, neutral, light reduction, moderate reduction, heavy reduction.(yes I
know this is a run on sentence!) Basically, the tip of the probe is
sensitive to the oxygen content in the atmosphere. The damper controls the
pressure in the kiln, and really controls the secondary air at the burner
ports, hence your reduction. I am sure you know this well.
We use adjustable limiting orfices on our gas line and it does indeed meter
a precise amont of fuel. Our primary air is supplied by blowers having
North American manual butterfly valves to control the volume of air. Our
reduction is accomplished with the damper only. Precise numbers have been
consistant over 250 firings or so, many with copper reds. Our probe reads
.50 at cone 08 and as temperature increases over time and back pressue is
slightly adjusted in the kiln, .61 the the finish of the firing. We have a
50 cubic foot fiber car kiln.
>
>I have been using the firing schedule of starting reduction at ^010 and
>reducing all the way up to ^9 when I shut it down. I keep the probe at
>.60-.65 and until recently the copper reds have come out fairly well, but
>not always consistantly. I am assuming my recent failures have been because
>of a malfunctioning oxy-probe, although I was getting readings that were in
>the range I have gotten over the 2.5 years I have been firing with this kiln
>and probe.
I would submit that not only are copper reds dependant on early reduction
as you mention, but also upon the cooling of your kiln, how "tight" your
kiln is. Also, how much penetration your burners are able to produce. Also
placement of ware within the chamber and what we refer to as "thermoclines"
which are differences in atmosphere and temperature from shelf to shelf,
piece to piece, layer to layer, etc. Then there is also potter's intuition
that you may refer to as malfunctioning of the probe or failures of the
copper reds, eg consistency. Much has been written on copper reds that I am
sure you are well aware of by Pete Pinnell and David Hendley in CM. There
is also much mythology. And then there are sometings that work!
I will share with you and the list, what has worked quite effectively for
us is getting consistent copper reds. Susan Davy mentioned to us that she
brushs one copper red over another and the results are quite good. We took
it a step further and rather then brushing, we apply one copper red first
by dipping or pouring, and then using a second different copper red with a
much lower specific gravity, pour a thin wash over the first application.
Works like a charm! But there are many caveats, and we have been lucky to
have worked with to different copper red formulas on a project with Susan
Davey that give consistant beautiful results.
Good Luck!
Best,
Jonathan
>
>______________________________________________________________________________
>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.
Jonathan Kaplan
Ceramic Design Group LTd/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
Jeff Lawrence on sat 26 aug 00
Hello Garret,
Jonathan Kaplan mentioned a number of useful items in his posting to this
thread, but I'd like to highlight one for you:
He wrote:
> We use adjustable limiting orfices on our gas line and it does indeed
meter
> a precise amont of fuel.
This was a pearl of great price for me when he passed it on to me a couple
of years ago. The valve was 70 or 80 US dollars (I rigged one valve upstream
of both burners) and paid for itself in half a dozen firings in fuel savings
alone. Without it, my reduction firings were a total grope in the dark. Now,
time after time, I am able to reliably reproduce the same pathetic results!
Also from Jon is info on an outfit that makes them:
North American Manufacturing Company, Ltd.
4455 East 71st Street
Cleveland, OH 44105-5600 USA
Telephone: 216-271-6000
Fax: 216-641-7852
Now I'll have to try his double glaze technique for copper reds...
Jeff Lawrence ph. 505-753-5913
Sun Dagger Design fx. 505-753-8074
18496 US HWY 285/84 jml@sundagger.com
Espanola, NM 87532 www.sundagger.com
Ingeborg Foco on wed 30 aug 00
In case you are interested: I found their web site at: www.namfg.com
Ingeborg
Jeff Lawrence said:
> Jonathan Kaplan mentioned a number of useful items in his posting to this
> thread, but I'd like to highlight one for you:
>
> He wrote:
> > We use adjustable limiting orfices on our gas line and it does indeed
> meter
> > a precise amont of fuel.
> This was a pearl of great price for me when he passed it on to me a couple
> of years ago. The valve was 70 or 80 US dollars (I rigged one valve
upstream
> of both burners) and paid for itself in half a dozen firings in fuel
savings
> alone. Without it, my reduction firings were a total grope in the dark.
Now,
> time after time, I am able to reliably reproduce the same pathetic
results!
>
> Also from Jon is info on an outfit that makes them:
>
> North American Manufacturing Company, Ltd.
> 4455 East 71st Street
> Cleveland, OH 44105-5600 USA
> Telephone: 216-271-6000
> Fax: 216-641-7852
>
>
>
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