David Hendley on fri 17 may 02
I beg to differ.
Rain can have a lot to do with good reduction, especially if you are
firing a woodburning kiln.
There are examples of old kilns (17th century) that actually
incorporated ponds of water into the designs to ensure good reduction.
Nisse Holmstrom presented a paper called 'Project Aquagama'
at the '99 Woodfire Conference that details many studies that
show the effects of water and/or steam on firing.
Owen Rye in Australia has been experimenting with introducing
water into kilns for 10 years. To quote him, 'Water has a reducing
effect, even when the oxygen probe registers that the kiln is in
oxidation.'
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Rod"
To:
Sent: Friday, May 17, 2002 10:35 AM
Subject: Re: A good pee and reduction
> Tony,
> As I'm sure you know already whether or not it is raining or not
really
> has nothing do do with good reduction. Or put another way running a
> sprinkler would not make any difference. I remember when I first got into
> pots that there was this old tale about potters got better reduction on
> overcast\rainy days. In a sense this is true but not really.
>
> When it is overcast there is more atmospheric pressure and less oxygen
> in the air. This is why the old tale seems to still persist. The reality
of
> the matter is simpy one will find that they set their dampers, primary air
> differently on a rainy\overcast day as opposed to a clear day. The
cheapest
> method (and the one I used before I got my Oxy probe) was to use a
barometer
> and to put barometric readings with your regular kiln logs. That way you
can
> tell what level fiddleing you may need to do on any given day of firing.
> With my Oxyprobe I of course get perfect and dependable firings regardless
> of the weather.
>
> Cheers,
> Rod
>
> --------------------------------------------
> RedIron Studios
> www.redironstudios.ca
> rod@redironstudios.ca
> Vancouver, B.C. Canada
> --------------------------------------------
Rod on fri 17 may 02
Tony,
As I'm sure you know already whether or not it is raining or not really
has nothing do do with good reduction. Or put another way running a
sprinkler would not make any difference. I remember when I first got into
pots that there was this old tale about potters got better reduction on
overcast\rainy days. In a sense this is true but not really.
When it is overcast there is more atmospheric pressure and less oxygen
in the air. This is why the old tale seems to still persist. The reality of
the matter is simpy one will find that they set their dampers, primary air
differently on a rainy\overcast day as opposed to a clear day. The cheapest
method (and the one I used before I got my Oxy probe) was to use a barometer
and to put barometric readings with your regular kiln logs. That way you can
tell what level fiddleing you may need to do on any given day of firing.
With my Oxyprobe I of course get perfect and dependable firings regardless
of the weather.
Cheers,
Rod
--------------------------------------------
RedIron Studios
www.redironstudios.ca
rod@redironstudios.ca
Vancouver, B.C. Canada
--------------------------------------------
----- Original Message -----
From: "clennell"
To:
Sent: Friday, May 17, 2002 3:59 AM
Subject: A good pee
> Sour Cherry Pottery
>
> > Question:
> > In a cone 9-10 kiln, if reduction has been adequate up to the point of
the
> > soak, but is very light during the soak, what if anything is directly
> > affected? Is melting and oxide involvement pretty much completed by
then,
> > or are there still late bloomers (glaze elements) being affected?
> > (Soak takes place at top temperature, probably averages 40 minutes in
length.)
>
> Here I thought that Malcolm Davis would be giving you the definitive on
> carbon trapping in the next Studio Potter mag. In my contribution I gave
all
> I knew. Now I just had my best carbon trap firing in over 85 firings. I
log
> each firing carefully and the two best I've ever had there was one thing
in
> common- it was pissing down rain. this was not just a sprinkle but teaming
> down- both times. If you pass by our pottery and see a massive sprinkler
> system on the roof it's not fire protection but lust for the soot.
> Maybe my buddy west coast Les will let me build next to him on rainy
> Vancouver Island. Here I was thinking about retiring in Texas- two stikes
> against it- no rain and Red Stripe.
> Cheers,
> Tony
>
>
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>
iandol on sat 18 may 02
Dear Rod,
You say <less oxygen in the air.>>
Please explain why there is less oxygen in the air when the pressure is =
high. And what happens when the pressure is high but it is not overcast? =
or it is overcast during a Depression?
I thought the consensus was that at higher temperatures, say over 1000 =
Celsius, when there was high humidity in the atmosphere that with excess =
carbon, created by deliberate reduction, water vapour entering into the =
kiln was reduced to hydrogen and carbon monoxide, both of these gases =
enhancing the reduction effect as well as increasing thermal efficiency =
due to their higher flame temperatures.
As far as I can see, your oxygen sensing device tells you only about the =
presence or absence of one element and nothing about the rest of the =
kiln atmosphere.
Interesting thoughts.
Best regards,
Ivor Lewis
clennell on sun 19 may 02
Sour Cherry Pottery
>
>> Tony,
>> As I'm sure you know already whether or not it is raining or not
> really
>> has nothing do do with good reduction. Or put another way running a
>> sprinkler would not make any difference. I remember when I first got into
>> pots that there was this old tale about potters got better reduction on
>> overcast\rainy days. In a sense this is true but not really.
>>
>> When it is overcast there is more atmospheric pressure and less oxygen
>> in the air. This is why the old tale seems to still persist. The reality
> of
>> the matter is simpy one will find that they set their dampers, primary
air
>> differently on a rainy\overcast day as opposed to a clear day. The
> cheapest
>> method (and the one I used before I got my Oxy probe) was to use a
> barometer
>> and to put barometric readings with your regular kiln logs. That way you
> can
>> tell what level fiddleing you may need to do on any given day of firing.
>> With my Oxyprobe I of course get perfect and dependable firings
regardless
>> of the weather.
>>
>> Cheers,
>> Rod
Rod: Weather sure does effect reduction and firing time. A rain storm has
stalled my wood firings for several hours. When I should have been
celebrating with a nice Merlot, I was still stoking.
Perfect firings for me are always the next firing I'm about to do. I get
dependable results, but my log has shown the days it's pissin down I get
more racers per load than on high pressure days.
By the way the spinkler on the studio roof was a joke.
Cheers,
tony
John Christie on sat 25 may 02
On Sat, 18 May 2002 16:43:25 +0930, iandol wrote:
>I thought the consensus was that at higher temperatures, say over 1000
Celsius, when there was high humidity in the atmosphere that with excess
carbon, created by deliberate reduction, water vapour entering into the
kiln was reduced to hydrogen and carbon monoxide, both of these gases
enhancing the reduction effect as well as increasing thermal efficiency due
to their higher flame temperatures.
>Ivor Lewis
Dear Ivor,
I am afraid that I am having some difficulty with this!
What do you reduce to "create" the "excess carbon"?
What do you use as a reducing agent?
How does the water-gas reaction (water+carbon+heat=hydrogen+carbon monoxide
and/or methane) increase thermal efficiency?
Surely the "extra" heat energy produced by the "higher flame temperature"
of the burning hydrogen has precisely the same value as the energy required
to reduce the water to hydrogen in the first place.
Moreover, in the water-gas reaction, energy is "wasted" in heating the
water to the temperature of the flue gases and, if some or all of the water
is introduced to the kiln in liquid form, latent heat is used
(and "wasted") in its vapourisation.
John
iandol on sun 26 may 02
Dear John Christie,
You are correct about the heat equation for the Watergas reaction.
It is an Endothermic reaction, that is, it requires heat to sustain it. =
But if sufficient air is admitted to maintain the breakdown of the fuel =
yet ensure that some of the carbon which is freed remains unburnt yet =
hot enough, the water gas reaction will proceed.=20
What you have to get, either with gas, oil or wood, is a smoky flame. So =
you pump in extra fuel or reduce the intake of air to make that happen. =
That's "Reduction". If the temperature is above about 1050 (the higher =
the better) free carbon in the kiln atmosphere will react with water =
vapour to give hydrogen and Carbon Monoxide. This assists in reducing =
the glaze. If you want to exploit the fuel value of Water Gas and the =
higher flame temperatures, additional air has to be admitted. Which =
might explain why some kilns are built with "Mouse Holes". Thanks for =
the prompt to include these in my current kiln rebuild.
Best regards,
Ivor Lewis.
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