iandol on mon 5 aug 02
Dear Michael Cave,
I presume you intend getting a range of effects from your reduction such =
as blue or green celadon, copper reds, manganese violets and so on.
Without knowing the compositions of your glazes it is difficult to =
suggest a temperature to commence a general reduction. But it seems to =
be a rule of thumb to reduce early for a reasonable length of time =
before the glaze commences fusion, that is during the early stages of =
sintering. Once the glaze melts it seals in the colouring oxides and the =
atmosphere has difficulty diffusing in through the viscous molten glaze =
to effect further transmutations. Your initial reduction temperature =
will be determined by the types of melting fluxes you are using. If you =
incorporate any boron based frits or fluxes in your glaze recipes then =
choose a relatively at low heat down in the cone 012/08 range. If you =
are relying on some form of Feldspar to initiate melting then you may =
have to go up to cone 04 or 02 and reduce until the temperature =
indicates somewhere near cone 8 if you are firing to cone 10. It is not =
unusual to employ a clearing burn at the end of a firing without any =
reduction whatsoever, but since some people like to cool slowly while =
maintaining a reducing atmosphere there are no hard and fast rules.
You are going to have to do a lot of experimentation and reading. I know =
the old standards like Rhodes Kiln book may be dated but for recent =
viewpoints perhaps Vince Pitelka's book would be helpful as would be =
that of Nils Lou.
This is an area of practice where there are many variables. Intensity =
and duration of reduction are paramount but it also seems important to =
consider the thickness of your glazes and the body on which they are =
applied. So be sure to keep copious records of all the factors relating =
to your work as you progress onwards.
Best regards,
Ivor Lewis.
KLeSueur@AOL.COM on tue 6 aug 02
Records, records, records. I've been firing cone 10 reduction for 27 years. I still record everything I do to adjust the kiln.
Get a notebook and on each page record the number of the firing. The date. The weather. Record start time and the time you do every adjustment to burners, blowers, or damper. For myself, I control my burners by a main valve on a 1 1/2" line. the handle is parallel to the wall and numbers are written on the wall to record the position of the handle on the valve. The same with the blowers. I don't have a damper, but if you do, mark numbered lines on it with black slip. Record the position at every phase of the firing.
The look at the pots when they come out. Under reduced--close the damper one more mark on the next firing. Over reduced? Open it one mark.
Make small adjustments for each firing. Once you get a good firing, follow that schedule for the next one. If you get another good firing you're on your way to controling the kiln.
On my kiln I can control a cooler bottom or top by removing peep hole plugs during the firing. If the top is cool I remove a plug and this draws the heat up to the top. My kiln has burners mid high at the back and has no bag wall. At times I've placed posts on the middle shelf horizontally to defect heat.
Record everything. I mean everything you do.
Buy a CO2 analyzer from Bacarach. It's lots cheaper than a Digital fire and easy to use. If you buy one I can tell you where to get sampling tubes cheap.
Record everything.
kathi LeSueur
Ron Roy on wed 7 aug 02
It is important to get the body reduced - all the way through - before the
glazes seal over - if you fail to get the body reduced - or your reoxidize
the body after reducing - you will not get proper results.
The latest temperature I can reduce at is about cone 04 - after that I run
the risk of not getting the body properly reduced - I do not use boron in
my glazes but I would think that would require a lower - into reduction
temp because the glazes would seal over at a lower temperature.
All this and keeping in mind - not all parts of a kiln are at the same
temperature - especially on the way up and firing fast.
You can start reduction lower but make sure you don't try to do it below
the ignition point of the gas you are using. I make sure I'm at least over
800C but I'm not sure I would advise anyone to use a pyrometer to ascertain
what temp the kiln is at - unless the pyrometer is calibrated with cones.
RR
>Without knowing the compositions of your glazes it is difficult to suggest
>a temperature to commence a general reduction. But it seems to be a rule
>of thumb to reduce early for a reasonable length of time before the glaze
>commences fusion, that is during the early stages of sintering. Once the
>glaze melts it seals in the colouring oxides and the atmosphere has
>difficulty diffusing in through the viscous molten glaze to effect further
>transmutations. Your initial reduction temperature will be determined by
>the types of melting fluxes you are using. If you incorporate any boron
>based frits or fluxes in your glaze recipes then choose a relatively at
>low heat down in the cone 012/08 range. If you are relying on some form of
>Feldspar to initiate melting then you may have to go up to cone 04 or 02
>and reduce until the temperature indicates somewhere near cone 8 if you
>are firing to cone 10. It is not unusual to employ a clearing burn at the
>end of a firing without any reduction whatsoever, but since some people
>like to cool slowly while maintaining a reducing atmosphere there are no
>hard and fast rules.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
michael Cave on wed 7 aug 02
Thanks! Can I ask you at what cones do you shut off
the oxygen at the burners to reduce, for how long--For
example I did 30 min of reduction around ^06 then
again 1 hour around ^9 or 10 the sealed off the kiln?
Is this a common protocol? Any help is appreciated.
Chad
--- KLeSueur@AOL.COM wrote:
> Records, records, records. I've been firing cone 10
> reduction for 27 years. I still record everything I
> do to adjust the kiln.
>
> Get a notebook and on each page record the number of
> the firing. The date. The weather. Record start time
> and the time you do every adjustment to burners,
> blowers, or damper. For myself, I control my burners
> by a main valve on a 1 1/2" line. the handle is
> parallel to the wall and numbers are written on the
> wall to record the position of the handle on the
> valve. The same with the blowers. I don't have a
> damper, but if you do, mark numbered lines on it
> with black slip. Record the position at every phase
> of the firing.
>
> The look at the pots when they come out. Under
> reduced--close the damper one more mark on the next
> firing. Over reduced? Open it one mark.
>
> Make small adjustments for each firing. Once you get
> a good firing, follow that schedule for the next
> one. If you get another good firing you're on your
> way to controling the kiln.
>
> On my kiln I can control a cooler bottom or top by
> removing peep hole plugs during the firing. If the
> top is cool I remove a plug and this draws the heat
> up to the top. My kiln has burners mid high at the
> back and has no bag wall. At times I've placed posts
> on the middle shelf horizontally to defect heat.
>
> Record everything. I mean everything you do.
>
> Buy a CO2 analyzer from Bacarach. It's lots cheaper
> than a Digital fire and easy to use. If you buy one
> I can tell you where to get sampling tubes cheap.
>
> Record everything.
>
> kathi LeSueur
>
>
______________________________________________________________________________
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>
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>
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> reached at melpots@pclink.com.
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Hank Murrow on wed 7 aug 02
>Thanks! Can I ask you at what cones do you shut off
>the oxygen at the burners to reduce, for how long--For
>example I did 30 min of reduction around ^06 then
>again 1 hour around ^9 or 10 the sealed off the kiln?
>Is this a common protocol? Any help is appreciated.
>
>Chad
Dear Chad;
Another approach for achieving reduction is to use the damper
to create some back pressure and reduce the air intake. This can lead
to more even reduction in the chamber (if that is your goal). The
point at which you reduce is dependent upon the glazes you are using.
For shinos, I reduce beginning at C012, because they sinter early,
others may require later reduction.
Best, Hank in Eugene
vince pitelka on wed 7 aug 02
> Another approach for achieving reduction is to use the damper
> to create some back pressure and reduce the air intake. This can lead
> to more even reduction in the chamber (if that is your goal). The
> point at which you reduce is dependent upon the glazes you are using.
> For shinos, I reduce beginning at C012, because they sinter early,
> others may require later reduction.
Chad -
This is excellent from Hank. In my experience it is rarely wise to cut back
the primary air excessively, because this can just produce a long lazy,
smoky flame which migrates its way to the flue, giving very uneven
reduction. You need the turbulence of a stronger flame to circulate the
reducing atmosphere throughout the kiln. Far better to close the damper a
bit, creating greater back pressure. You may still need to cut back your
primary air a bit, but use that as a backup measure in order to get adequate
reduction.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@worldnet.att.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Earl Brunner on wed 7 aug 02
I do it all with the damper, the burners are situated under the kiln and the risk
of burning myself on the metal down there when the kiln is hot is just too great.
I don't adjust those bells at all. Besides it would necessitate removing the
skirting every time I wanted to make an adjustment. (Geil Kiln)
vince pitelka wrote:
> > Another approach for achieving reduction is to use the damper
> > to create some back pressure and reduce the air intake. This can lead
> > to more even reduction in the chamber (if that is your goal). The
> > point at which you reduce is dependent upon the glazes you are using.
> > For shinos, I reduce beginning at C012, because they sinter early,
> > others may require later reduction.
>
> Chad -
> This is excellent from Hank. In my experience it is rarely wise to cut back
> the primary air excessively, because this can just produce a long lazy,
> smoky flame which migrates its way to the flue, giving very uneven
> reduction. You need the turbulence of a stronger flame to circulate the
> reducing atmosphere throughout the kiln. Far better to close the damper a
> bit, creating greater back pressure. You may still need to cut back your
> primary air a bit, but use that as a backup measure in order to get adequate
> reduction.
> Best wishes -
> - Vince
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Hank Murrow on wed 7 aug 02
> > Another approach for achieving reduction is to use the damper
>> to create some back pressure and reduce the air intake. This can lead
>> to more even reduction in the chamber (if that is your goal). The
>> point at which you reduce is dependent upon the glazes you are using.
>> For shinos, I reduce beginning at C012, because they sinter early,
>> others may require later reduction.
>
>Chad -
>This is excellent from Hank. In my experience it is rarely wise to cut back
>the primary air excessively, because this can just produce a long lazy,
>smoky flame which migrates its way to the flue, giving very uneven
>reduction. You need the turbulence of a stronger flame to circulate the
>reducing atmosphere throughout the kiln. Far better to close the damper a
>bit, creating greater back pressure. You may still need to cut back your
>primary air a bit, but use that as a backup measure in order to get adequate
>reduction.
>Best wishes -
>- Vince
Thanks Vince;
During the day here, I was musing on this question and
thought I'd mention the kiln construction's contribution to
'reduction'. If the kiln is leaky.....that is, it sends out big
flames at the top and smaller flames out the bottom, there will be
some difficulty in getting enough reduction at the bottom. If you
really damp it to get big flames out the bottom peep, you may stall
the kiln. A persuasive argument for a very tight kiln construction.
in a tight kiln, a very small movement of the damper will give strong
and even reduction.
Another thought, Hank in Eugene
vince pitelka on thu 8 aug 02
> A persuasive argument for a very tight kiln construction.
> in a tight kiln, a very small movement of the damper will give strong
> and even reduction.
Hank -
Another good point. I learned early that a loose kiln full of leaks is hard
to control, while a tight kiln is just a pleasure to use. As a studio
potter in Northern California in the 70s and early 80s, I built a 100 cu.ft.
car kiln, and paid considerable attention to the design of the door and car
in order to assure a tight seal. The burner ports were the standard 4.5"
wide by 5" tall, but I carved a softbrick insert to reduce the port to a
round hole. The burner tips were about 2" outside diameter, and I carved
the softbrick to give a hole tapering out from 3" at the outer surface, to
4" at the inside surface. One could easily do the same with castable
refractory, such as you use for modeling the floor and burner ports on your
kilns.
The burner tips were mounted/2" from the outer surface of the brick. The
vertical damper was in the horizontal flue just outside the kiln, and was a
snug fit, giving a tight seal. With the restricted secondary air
entrainment focused directly around the burner tip, with plenty of stack
height (this was a downdraft kiln with a five-foot horizontal flue to the
stack), and with the tight seal on the door, the car, and the damper, the
slightest adjustment of the damper appreciably changed the kiln's
performance. This kiln was so easy to control. I could get even reduction
throughout with only a small flame at the spyholes, and only the slightest
flicker of yellow flame visible in the burner ports.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@worldnet.att.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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