search  current discussion  categories  kilns & firing - misc 

electric kiln choices/insulation

updated fri 5 dec 03


Judy Musicant on wed 3 dec 03

The discussion about electric kiln choices prompts me to post this about =
choices in insulation thickness. It seens that most folks who discuss =
this subject state that more insulation (i.e. slower cooling) is better. =
Well, here is my experience. =20

For many years I fired in a little Skutt 818 - speaking of workhorses, =
by the way, never had a problem with that kiln. It cooled in about 5 =
minutes. Anyway, my primary glazes are a Val Cushing glaze that I use =
with several colorants (see Mike Bailey's cone 6 glaze book). I also =
use a lot of floating blue, god bless it. Finally decided to get a =
larger kiln, and went with the Bailey (which was really a Cone Art, with =
Bailey's name on it. Now I believe they make their own kiln). I got it =
in large part because of the 3" insulation, and the element in the =
floor, for more even heating. I was appalled after the first firing. =
My glazes hated the slower cooling. One of the qualities l like so much =
in the Cushing glazes is it's propensity to combine matte and shiny =
areas, depending on the thickness of the glaze. Where I overlap some of =
the colors with a different glaze, I get a rainbow of green, turquois, =
amber and pink. (Don't knock it unless you've seen it.) Well, the slow =
cooling eliminated all that. The overlap I loved was a drab, matt pukey =
gray green. (My studio mate and I call it schwah ). The shiny areas in =
general were all but eliminated. The colors were somewhat dulled. =
Floating blue tended to a dull blue/green. I fiddled with that kiln til =
the cows came home - tried to cool it faster, fired it hotter to begin =
with. Nothing worked. Finally I decided I shouldn't be suffering like =
that, plus I didn't want to develop a whole new glaze palette, specially =
since the ones I use are so popular. I tried a kiln load in a friend's =
7 cubic foot Skutt - with 2 1/2 insulation. Hallelujah! My colors were =
back. Sold the Bailey to a good home (Hi Holly and Mert) - people who =
already had one and appreciated the extra insulation, and bought myself =
a new Skutt. I'm happy again.

My advice to anyone preparing to buy new and to get more insulation. =
Try a kiln load in the more insulated kiln and see how your glazes come =
out. More insulation isn't necessarily better per se - just may be =
better for the glazes you like to use.

Judy Musicant

John Hesselberth on thu 4 dec 03

On Wednesday, December 3, 2003, at 07:44 PM, Judy Musicant wrote:

> Try a kiln load in the more insulated kiln and see how your glazes
> come out. More insulation isn't necessarily better per se - just may
> be better for the glazes you like to use.

Hi Judy,

You advise is well-taken. Some glazes do better with rapid cooling vs
slow. However, a word of caution. Glazes that are matte after having
been cooled rapidly are almost certainly in the category of 'unmelted
mattes'. That is they are matte because they were not fully melted
during firing and get their 'matteness' from unmelted tiny particles.
In my testing these glazes are usually significantly less durable than
matte glazes that have been formulated to be fully melted during firing
and then cooled slowly, allowing crystallization to occur during

If you are a sculptural or decorative potter this may not matter much
to you. If you are a functional potter who cares about durability --
well let's just say these 'unmelted mattes' that are formulated to be
matte even with rapid cooling are where I find my best examples for my
lemon juice demonstrations. They can result in truly terrible
functional glazes.