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cone 6 ash glaze question

updated mon 26 sep 05


Allyson May on fri 23 sep 05

I have recently been testing some ^6 (oxidation) ash glazes. I have had =
some very good result thus far but I am still testing a few recipes. I =
found a recipe scribbled in pencil in one of my sketchbooks and have no =
idea where it came from. It is titled ^6 Wood Ash from a Clear Base.

Gerstley borate 50
Silica 32
Kaolin 16
Whiting 2

Bentonite 2
Wood ash (unwashed) 20-30

I have not seen an ash glaze where the ash was not in the base recipe =
(be kind. I have limited experience). To all those who are ash experts, =
does this glaze seem o.k.? I don't have access to glaze calculation =
software so I'm not sure what the expected out come of this recipe might =
be? Any ideas or help would be great! The recipes I really like so far =
are Val Cushing's ^6 Wood Ash (unwashed ash) , and one from the archives =
with washed ash. I will be testing Lili Krakowski's Hannah's Cider and =
one of Mark Issenberg's next. Thanks for any help in advance.
Allyson May
Stoney Creek Pottery
Bloomington, IN

Lili Krakowski on sun 25 sep 05

Hi, Allyson:

Because it is pouring rain and I can't work outdoors, I am being a semi-good
person this afternoon. So I fed your recipe[s] to GlazeMaster

Your recipe GB 50, silica 32, kaolin 16, whiting 2, translates into:
Na2O .110, K2O .003, MgO .003, CaO .884, Al2O3 .439, B2O3 .865, SiO2 3.896,
and a coefficient of expansion of 57.53 which sounds scary in relation to

With the addition of 20 ash the recipe goes:
GB 41.7, silica 26.7, kaolin 13.3, whiting 1.7 ash 16.7. (I used the
"unwashed oak ash" in GlazeMaster list.)

And this translates into:

Na20 .069, K20 160, MgO .593, Al203 .208, B203 .412, Si02 1.861, and a
coefficient of expansion of 76.33

From likelihood of dunting to likelihood of crazing in one fell swoop!

It all is very curious .....

The original glaze is a boral calcate glaze of which there are lots. I
wonder why anyone added that 2 whiting....and the silica seems high....but
as long as the glaze works....if it does.

With the woodash, the picture changes, as you see. It is more alkaline, it
has more magnesium, and less alumina and silica....A glaze heading for your
shelves, I would guess, and not a pretty picture.

I have no idea what inspired the notation in your notebook UNLESS you
wanted to experiment with my favorite tool, the straight line blend. What I
would expect is that you would get a more broken up or mottled surface with
the addition of the wood ash....and a runnier glaze....

By the way; I have toyed with white glazes that looked too "bathroomy" and
replaced whiting with some bone ash.

That is the best I can do right now. I think the notation was from a work
in progress, an idea in progress.....AND NOTE: I am and remain firmly
OPPOSED TO USING unwashed ash, as dangerous; and the batch of ash you have
probably is quite different from the oak ash in Glaze Master. Ash varies a

Good luck

Lili Krakowski

Be of good courage