search  current discussion  categories  glazes - cone 8-10 

cone 10 ox glaze tests

updated thu 2 nov 00


Wesley C. Rolley on wed 1 nov 00

I was inspired by Cindy Strand's Cone 10 Ox glaze tests and decided to
repeat the tests in my own environment. It was something interesting to
do while waiting for Ina Currie's new book to arrive, (just to note that
this was not a highly scientific approach.)

Since there are significant differences between my environment and
Cindy's, I should clarify them.

1. I used Cinnamon, a general purpose red stoneware clay from the
Claymaker in San Jose. It has 33.8% Newman's Red in the body. I use it
because I like the warmth of the clay when fired.

2. I always single-fire, so raw glaze the pots. I've never bisqued a pot
in my life.

3. Because I single-fire, I use a ramp/hold profile on my Skutt that is
much slower than Cindy's firings. My firings take nearly 20 hours. to
temp. I generally fire on the way down, but, to be a little like Cindy, I
shut it down, buttoned it up and let it cool naturally.

4. I mixed a half-kilo batch of each glaze and carefully applied each to
three pieces: a small sakezuke, a slightly larger tea vessle (yunoumi) and
a larger yunoumi that was nearly cup sized. I have a real collection of
"glaze test sakezuke." Luckily I like sake on a cool evening.

As Cindy noted, these glazes came from Zakin's book on electric kiln

Finally, I will provide some URL's for the jpg images of these glazes on my
clay. The images are not great but should illustrate some aspects of the
glaze. The background is only the carpet on my family room floor.

My notes are interspresed with Cindy's and you may need to reference her
notes from her original post to get all of her background info. In my next
firing, I will test a couple more of the glazes and will also report on that.

I should also note that all of these glazes are outside of the limits for
^10 glazes as described in Insight. They also contain a small amount of
Lithium from the Spodumene. I am currently doing a vinegar test on the
Harpersfield (last in the list). Any use of these glazes for food
surfaces should be thoroughly tested.

Wes Rolley

>Woodbourne Base 92
>Zakin ^9
>Custer Spar 44
>Redart 20
>Ball Clay 8
>Dolomite 28
>Si:Al 6.07
>SiB:Al 6.07
>Expansion 7.71

I probably applied this too thinly and will try it again. I had a glassy
pooling of the glaze in the bottom with a "flower" of an off-white matte

>Pilgrim Vitreous Engobe 92 ^9

I did not use this glaze as the expansion is much too low for my body. In
general, I try to use glazes that have expansions over 6.8. I have had
troubles with shivering with some glazes.

>Deerpark Base ^9
>Silica 10
>Spodumene 8
>Ball Clay 30
>Redart 18
>Dolomite 34
>Si:Al 5.01
>SiB:Al 5.01
>Expansion 6.18
>Amber, mix of glossy surface and frosty matte with flow-stone like
downward movement of >color. Bison good. NVF.
>Applied to ^10 oxidation/reduction stoneware body--white to blond color in
>oxidation. Fired to ^10 in 9.09 hours (medium speed), cooled naturally with
>all vents closed. ***This applies to all the glazes***
>Pretty amber-colored glossy glaze which shows immediate crazing. Bison good.

On my body, it was a darker color. Some roughness from the sand/grog as I
had not smoothed or slipped the outside. The inside vertical surfaces were
very thin with the frosty matte characteristic that you noticed moving into
a pool in the bottom.

>Shan 92 ^9
>Spodumene 10
>Ball Clay 18
>Redart 36
>Dolomite 24
>Gerstley 12
>Si:Al 4.88
>SiB:Al 5.25
>Expansion 6.72
>Red-brown which shades to a pleasing greenish shade at the base, where
thick. Some dripping, not much. Didn't reach the shelf (I had a one inch
thickness of unglazed area at the base, though, so treat this one with care.)
>Satin to glossy surface with beautiful movement of color. Many pinholes.
Bison fair.

In my case, more brown/green in color. Nice movement where thick and the
glaze did not run below the line of my dip. I also noticed the pinholing,
but that does not bother me on some items. On the inside, I had very dry
vertical wals with some glassy pooling at the bottom. This might look
better if backed off to ^8 or 9. The color differences are obviously from
the increased iron picked up from the body.

>Harpersfield R 92 ^9
>Spodumene 10
>Ball Clay 16
>Red Iron Oxide 8
>Redart 44
>Dolomite 30
>Si:Al 5.07
>SiB:Al 5.07
>Expansion 7.05

>Dark red brown, frosty satin with an almost micaceous shine in the
sunlight. Slight downward movement of black color, some slight dripping
where thick. This is a gorgeous glaze. Bison fair.

Cindy was absolutely right on this one. It is the one glaze that looks the
same on my pieces as she described. I guess that 8% rio overpowers any

In a final bit of playfulness, I dipped the top and bottom of a vase in the
Harpersfield, leaving a bare area between them. Then, I dipped the top
and the bare area in the Woodbourne (first in Cindy's list). The result
was similar to the Harpersfield, but glossier and with a bit more melt.


Wes Rolley

"Happiness is to be fully engaged in the activity that you believe in and,
if you are very good at it, well that's a bonus." -- Henry Moore