John Weber on tue 19 feb 02
Although I use Ash glazes over a high calcium glaze and get some good
results, lately I have been looking for more "rivuleting" of the glaze.
That great look of ash when it flows in streams that separate and come back
together again. I have obtained this effect successfully when applied on
raw clay but not over my base glaze. I wondered if anyone of our glaze folks
could help point me in the right direction. What element is it that favors
this effect. If CaO I can add some whiting and run a line blend but I think
it is more complicated than that. Any help would be appreciated. Firing is
to cone 10 in reduction. I use Oak Wood Ash that I guess has a composition
of: % 15.3 SiO2 .13 AlO3 2.4 Fe2O3 30.2 CaO 12.2 MgO 14.0 K2O 9.12 Na2O .1
MnO 13.8 P3O5 2.75 LOI. I use a base glaze which is a matt cone 10 with
the following analysis:
Na2O 0.07 Al2O3 0.49 SiO2 2.44
K2O 0.15 P2O5 0.00
MgO 0.34 TiO2 0.10
CaO 0.44 Fe2O3 0.03
ZrO2 0.15
Alumina:Silica ratio is 1.00:4.96
Neutral:Acid ratio is 1.00:5.54
Alk:Neut:Acid ratio is 1.00:0.49:2.73
Expansion: 78.0 x 10e-7 per degree C
John Weber
Manakin-Sabot, VA
ASHPOTS@AOL.COM on tue 19 feb 02
Hi Ya,,, i do ash glazes also... i use the ash glaze on Wonder White from
HighWater
I spray all my ash glaze..I let it be thinner at the bottom ,, ,,, I use 50%
ash 50% red clay...
I also use 50% Plastic Vitrox 50% ash and 3% cobalt Carb for a blue,,,,its
real blue
I also dig some red clay out of a cave near me ,,in the Valley..it works also
but has sand that still is grainy after a firing...i use a 40% mesh then a
80%mesh to screen before i spray....
I also use the sprayers from Harbour Frieght I LOVE THEM
In a big about Ash galzes ,,, i think it was the Rogers book ,,, it was
called threading
Capt Mark on Lookout Mountain
Rising Fawn Ga Noble Ga is near me,,,its been in the news lately
Richard Aerni on tue 19 feb 02
John,
I am sure others will weigh in on this one. My advice is not really of the
technical nature you seek, rather it is in the nature of a push along a
path, some of which you will have to blaze for yourself.
You are asking questions which one can answer partially, but I sense you are
looking for _the_ answer, and I must say, that is one you will have to find
for yourself. I can say that it has been my experience that high levels of
calcium in a high temperature glaze does cause rivuleting. I believe it is
due to the high surface tension that high calcium glazes have. As to why
the ash behaves differently on your matte glaze than on clay, I would gently
suggest that you examine what the differences are between your clay body and
the base glaze. Think on it, then test, then keep testing. You have
probably reached a point in your work, in your quest for a "look," where it
is incumbent on you to start breaking your own ground. Glaze and technical
gurus can give you all kinds of advice, most of it theoretical, but in the
work of each of us are implanted so many variables that theory becomes
muddied, and results become more variable. In the end, it all becomes
empirical. You must develop your own hunches, give them a try, and over
time, by pushing the envelope, develop a look that is your own. I don't
mean this in any unkind way. It just seems like it is time to take that big
step into the unknown.
Have you read Tichane's _Ash Glazes_? If not, I would suggest you obtain a
copy and give it a good read. See how his work squares with your own
experiences.
Hoping you stay in it for the long run.
Best,
Richard Aerni
Bloomfield, NY
----- Original Message -----
> Although I use Ash glazes over a high calcium glaze and get some good
> results, lately I have been looking for more "rivuleting" of the glaze.
> That great look of ash when it flows in streams that separate and come
back
> together again. I have obtained this effect successfully when applied on
> raw clay but not over my base glaze. I wondered if anyone of our glaze
folks
> could help point me in the right direction. What element is it that favors
> this effect. If CaO I can add some whiting and run a line blend but I
think
> it is more complicated than that. Any help would be appreciated. Firing
is
> to cone 10 in reduction. I use Oak Wood Ash that I guess has a
composition
> of: % 15.3 SiO2 .13 AlO3 2.4 Fe2O3 30.2 CaO 12.2 MgO 14.0 K2O 9.12 Na2O .1
> MnO 13.8 P3O5 2.75 LOI. I use a base glaze which is a matt cone 10 with
> the following analysis:
> Na2O 0.07 Al2O3 0.49 SiO2 2.44
> K2O 0.15 P2O5 0.00
> MgO 0.34 TiO2 0.10
> CaO 0.44 Fe2O3 0.03
> ZrO2 0.15
>
> Alumina:Silica ratio is 1.00:4.96
> Neutral:Acid ratio is 1.00:5.54
> Alk:Neut:Acid ratio is 1.00:0.49:2.73
>
> Expansion: 78.0 x 10e-7 per degree C
>
> John Weber
> Manakin-Sabot, VA
Craig Martell on tue 19 feb 02
Hello John:
The problem you are having in getting the stringing effect over your base
glaze is basically the base glaze. There's some diffusion going on that's
changing the ash glaze enough to alter the effects you want.
The stringing effect is seen in glazes that are predominantly lime with
regard to fluxes. The experiments that I've done tell me that glazes need
to have at least 0.8 Ca in the Seger Formula and be lower in alumina and
silica. Ash glazes of this type are high flux glazes and sadly, durability
goes in the toilet. My most reactive ash glaze has a Ca value of 0.88 in
the formula. Also, you can't rely on "ideal" analyses for any ash. They
always vary enough to be useless as guides to what you are actually working
with. You can send 100 mesh samples to a certified lab and have an XRF
analysis done. You can then plug this into your glaze calc program and get
a much more accurate idea of what you are working with. If you take all
the ash that you have and blend it into one larger supply that's going to
last a while, the economics of doing an analysis are much better. You can
also work this all out empirically with line, triax, and quad blends. I
usually rely on soda spars for the glaze cores in my ash glazes. Potash
works ok but the soda spars are more active and the glazes run more and the
color is a bit zingyer. Is that a word?
regards, Craig Martell in Oregon
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