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e: soda

updated sat 3 jan 04


Lee Love on fri 2 jan 04

----- Original Message -----
From: "iandol"

> Whether using the salt or the carbonate, the glaze is suspect
>and prone to widespread crazing. There is difference between
>confusion and disregarding the facts.

And then there is also only regarding convenient facts.
If you know what you are doing, there is no problem with crazing. That's
not to say that crazing is alway undesirable. Of course, it can be a
problem on on vitrified clay at low fire. But used properly, it can be an
esthetic choice. If you think of the properties of soda and salt vapor,
you can use them to your advantage. Look at Ruggles and Rankin's work for
an excellent example or John Anthony's work. Right at this moment, I am
drinking sake (make from a Mashiko farmer's new rice) from an exquisite John
Anthony yunomi (as good as any I've seen in Japan) that is a fine example of
salt vapor flashing. There is no evidence of crazing on this piece (I'll
put up a photo tomorrow, when I have sunlight.)

If we simply stop to think a moment, the amount of crazing is
dependent upon the surface the salt or soda comes in contact with, wether it
be a claybody, a slip or a glaze. The amount of vapor agent used is also
very important. I have always used the minimum, because I am not
interested in a pigskin surface or a glaze coating. Primarily, I want
flashing, often on a surface that is still mat after the vapor introduction.
I am also interested in variations in color on glazed surfaces. I was
first exposed to this type of spare use of soda at the UofMN from Mark
Pharis and his grad students. It is nothing like what you are talking
about. At the UofMN, when I fired the salt kiln, I added no salt in the
firing. For my purposes, the residual salt on the kiln walls was enough.

One of my favorite uses of soda is with a stontium matt glaze: it
gives variation to the surface both in color and degrees of mattness. My
copper strontium glaze in soda can vary in different varieties of red, green
and blue and all mixes inbetween.

>Dipping a pot in a solution is not a form of vapour glazing. Spraying a
>hot saturated solution is still the best way of distributing sodium
>carbonate into a kiln

Here, you manipulate your sentence to suit your argument. Shame on you
Ivor. ;^) We were talking about the best way to get soda on the pot. If
you experiment with the solution I described and compare it with soda
solution blown into a kiln, you will eyeball the difference yourself.

>If you are going to make statements about events which happen
>associated with your firings, such as carbonates being more corrosive
>than Bi-carbonates you must qualify your information with facts
>and circumstances for it to serve any purpose.

Yes, better than simply quoting from what we have read. My preference is
always for experience above theory.

I've described my _experiences_ with soda ash and baking soda
previously on ClayArt. It is in the archives. Donovan had to redo the
softbrick door the last time I used soda ash at the clay center. The ITC
didn't stand up to the soda ash being blown in with a hopper that used a
shop vac as a blower. Using the same injection system with Baking Soda
caused no damage to the ITC coating. After I found this out, I only used
Baking Soda. Arm & Hammer is harder to find in Japan, so I will probably
use Soda Ash again.

Where I am thinking of trying it is the front of the kiln, where there is a
hardbrick door. One way to go is to try different mixtures of salt and
soda in dishes. Any shinos I put in are in a more reduced part of the kiln,
so they would not be effected by the salt. I try not to reduce the entire
kiln, because I've found that the red flashing from the flames is stronger
in oxidation or a neutral atmosphere.

Lee In Mashiko, Japan
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