Jesse Hull at Wiseman Ceramics on sat 9 feb 08
After reviewing the posts on "k-23 insulators", I wanted to add an option
that's probably not new to some here, but shouldn't be overlooked:
K-25 IFB.
After firing many electric kilns made from the industry standard for
hobby/studio kilns (K-23), and building gas reduction kilns using a
combination of K-23 and K-26, I've since found K-25 beneficial on three poin=
ts:
1)...in it's ability to provide the needed insulation value. The K-25 may
need SLIGHTLY more energy to heat at the lower temps, but makes up for it
above 2000F (when the kiln is working the hardest). At 2000=B0F, k-25 has a
Thermal Conductivity rating of around 1.7 --as a reference, K-23 rates at
around 1.8
2)...in it's ability to release heat at the higher temperatures that I'm
currently firing to (^11-12), outperforming in this regard a kiln of the
same size and wall thickness comprised of K-23 brick.
3)...in that K-25's are more structurally sound. Because the brick is less
fragile than K-23's, I feel comfortable using 2-1/2 inch thick bricks.
Obviously, this increased my kiln's ability to cool from peak.
Why would I want to cool fast? Because I prefer establishing/ maintaining
the heatwork to achieve the precise cone value needed, and then drop out of
that range before residual heatwork trips me up. Understand that I'm
referring specifically to the higher temp's (2270-2370=B0F). The brick
provides a slow natural drop through quartz inversion, etc, comparable to
what those using K-23's are used to.
For the entire post covering my views toward "Selecting a High-fire Electric=
Kiln", refer to that page of my website at:
http://jessehull.com/2008/02/06/selecting-or-designing-an-electric-high-fire=
-kiln/
The extra cost to have my kiln made from k25 was negligible.
Even if you're not firing as high as I do, consider leaving the K-23 for
what it was designed for... ^8 and below.
Last note: I understand that my choices in kiln materials and methods may
not seem very "green-friendly". If so, consider another post I've listed
here before, dealing with the actual power consumption/cost of firing an
electric kiln:
http://jessehull.com/2008/02/03/electric-kiln-actual-energy-consumption/
~jesse.
mark Cortright on sun 10 feb 08
I think a few other points should be made on the K2300 as well as k25. The 23 insulate better but
will in the long run at cone 10 will turn to c--p especially in any fire box area as well as flue and
burner ports. I know this to be true due to several kilns I made where that happened in my youth.
If you fire only once in a blue moon fine-but 30-40 cone 10-11 glaze fires a year will eat up those
k23 like low fire at cone 10. They can be used but only in the cooler areas upper walls back walls
etc. You really need k26 and k28 in the firebox area and if you want long life use some hard brick
on all spans and burner areas. My Arch has some k23's that went south after 5 years of heavy use-
The whole thing is k26 with some k28s now and has many hundreds of cone 11 fires on it now
looking great.
The k25 are a good choice with the largest drawback the price as they are not used as much -they
seem to higher in price that the standards used including k26's. Besides price should not be the
decieding factor - long term holding up should play an important role as well as how well they
insulate. K 23 for me at cone 11 are not a great choice- I fire way to much and rebuilding before
you have to is better left to those who need to learn this one the hard way.
Mark Cortright
arcata ca.
www.liscomhillpottery.com
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