Dave Finkelnburg on sun 21 sep 03
To those interested in the economics and environmental effects of firing,
Firing time versus energy consumption is so obvious it's easy to
overlook.
I've always made a habit of recording the gas usage with every firing of
my gas kilns. Lately I've had reason to fire a small Olympic updraft
frequently. This is not an energy-efficient kiln, but it turns out fine
cone 10 reduction-fired ware. Here are some observations I've made.
I fire from candling temperature of 200 F (~100 degrees C) to cone 10, ~
2,350 F (~1,300 C). I am firing biscuit-glazed, relatively thin ware
typically less than 1/4-inch (~less than 1/2-cm) thick.
I can use a moderate firing schedule and reach cone 10 in about 10
hours.
I can fire the same ware, loaded the same, over the same temperature
range, in 7 hours, and reduce the fuel consumption by 33%.
I can do the same in 6 hours and reduce fuel consumed by 38% over the
10-hour schedule.
I cannot observe any difference in appearance or function of the faster
versus slower-fired ware.
I would expect this time:energy used correlation is very similar in any
similarly-insulated kiln, even electric, because the energy lost goes to the
air. As a side benefit, of course, the faster firing produces less
pollution.
Lest someone (horrors!) leap to any conclusions here, I do always decide
on a firing schedule by the glazes and look I want. Oxidation firings go
faster than body reduction, carbon trapping really slows down the firing and
increases the fuel burned.
Still, this has reminded me to fire as long as necessary to achieve the
desired artistic and functional effects, but not longer.
Good firing!
Dave Finkelnburg, on a fine, sunny morning with the window here
open wide so I can listen to the gold finches and house finches as they
twitter-feed through the sunflower heads only a few feet away
www.idahopots.com
Ron Roy on mon 22 sep 03
Thanks for this information Dave.
We also have to remember that slower firings have a benefical effect on
even heating - a factor with most kilns. It only takes a few - sometimes
only one - unsalable pots to wipe out any fuel savings.
Slow firing from 1100C up with many cone 10 bodies increases cristobalite
production with many stoneware bodies - a distinct disadvantage.
Understanding process is the best way to make decisions about how long to
fire - keeping in mind - every pot acceptable from each load in the end is
the ideal.
RR
>To those interested in the economics and environmental effects of firing,
> Firing time versus energy consumption is so obvious it's easy to
>overlook.
> I've always made a habit of recording the gas usage with every firing of
>my gas kilns. Lately I've had reason to fire a small Olympic updraft
>frequently. This is not an energy-efficient kiln, but it turns out fine
>cone 10 reduction-fired ware. Here are some observations I've made.
> I fire from candling temperature of 200 F (~100 degrees C) to cone 10, ~
>2,350 F (~1,300 C). I am firing biscuit-glazed, relatively thin ware
>typically less than 1/4-inch (~less than 1/2-cm) thick.
> I can use a moderate firing schedule and reach cone 10 in about 10
>hours.
> I can fire the same ware, loaded the same, over the same temperature
>range, in 7 hours, and reduce the fuel consumption by 33%.
> I can do the same in 6 hours and reduce fuel consumed by 38% over the
>10-hour schedule.
> I cannot observe any difference in appearance or function of the faster
>versus slower-fired ware.
> I would expect this time:energy used correlation is very similar in any
>similarly-insulated kiln, even electric, because the energy lost goes to the
>air. As a side benefit, of course, the faster firing produces less
>pollution.
> Lest someone (horrors!) leap to any conclusions here, I do always decide
>on a firing schedule by the glazes and look I want. Oxidation firings go
>faster than body reduction, carbon trapping really slows down the firing and
>increases the fuel burned.
> Still, this has reminded me to fire as long as necessary to achieve the
>desired artistic and functional effects, but not longer.
> Good firing!
> Dave Finkelnburg, on a fine, sunny morning with the window here
>open wide so I can listen to the gold finches and house finches as they
>twitter-feed through the sunflower heads only a few feet away
> www.idahopots.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Susan Setley on mon 22 sep 03
In a message dated 9/22/03 3:07:16 PM, ronroy@TOTAL.NET writes:
<<
Slow firing from 1100C up with many cone 10 bodies increases cristobalite
production with many stoneware bodies - a distinct disadvantage.
>>
I did not know that. Thank you! Now -- can you translate 1100C into Farenheit
for the numerically challenged (I'm captain of that team - smile) who can
never remember the conversion formula? I have a friend who takes the Raku kiln
slowly all the way to Cone 06. What I was taught was to take it slowly to 500
(F), a little faster to 1000, and then blast it and get it up to 1870 as fast as
you can.
Roly Beevor on tue 23 sep 03
Ron Roy wrote
>
> Slow firing from 1100C up with many cone 10 bodies increases cristobalite
> production with many stoneware bodies - a distinct disadvantage.
Roy
Will time at high temperature not also increase mullite, thereby making a
stronger body (assuming the pot survives the cristobalite shock)? Is it
possible to carefully control temperature to optimise these effects?
Roland
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