iandol on thu 3 apr 03
Dear Terry,
Now I understand.
Not really a chemical thing at all.
By having a smoky atmosphere there will be a soot deposit all over the
pot by the time the Sodium Carbonate starts to melt at 800+ deg
Celsius. This will wick outwards into the layer of soot, and as you
say, in that state it will be protected from oxidation.
No great mystery. Just needs the artistic touch to exploit it.
Best regards,
Ivor
----- Original Message -----
From: "Terry M. Sullivan"
To:
Sent: Thursday, 3 April 2003 1:25
Subject: Re: Carbon rappers: Fuel
> Ivor,
>
> Did I post a "comprehensive chemistry lesson about getting the
carbon
> into the fabric of an imature glaze" ? Gosh, I must have had one,
or
> two, more beers that night cause I don't recall it. Uh Oh ! ; - )
>
> Anyhow; I as I understand the way Malcolm Davis does it, and we did
it
> at Nottingham; is that the shino glaze has a high concentration of
> sodium ( like almost 17% in one of Malcolms glazes). Malcolm
stresses
> that it is the drying time that is criticle in allowing the soluable
> sodium to migrate to the surface. Not so much application or
thickness
> but the drying.
> Around cone 012-010 the sodium begins to melt and eventually form a
> liquid layer on the pot. So the thing is to get lots of elemental
Carbon
> into the kiln atmosphere at that time. Not CO or CO2, but just
Carbon.
> Like soot ! This stuff gets into the surface underneath the sodium
and
> is then sealed off from oxidation by the melting sodium layer. Then
> keeping the atmosphere in fairly high reduction on up until the
Shino
> glaze melts with the Carbon imbeded in it one gets lots of Carbon
> trapped in the higher fire glaze. I have little idea what happens
to
> the sodium. Maybe some of it burns off and some incorporates with
the
> Shino ingrediants at the higher temp melt.
>
> Malcolm discovered the much higher concentration of sodium in the
shino
> glaze by accident ( mixed sodium carbonate instead of another
material
> ), but it worked and he got spectacular results. Those wonderful
orange
> brush stokes Malcolm gets are by using a wax resist. It inhibits the
> migration of the sodium and results in a rich orange shino blush on
the
> grolleg porcelain.
>
> The guy who seems to have a good handle on the Elemental Carbon
thing is
> Dave Finklnburg.
>
> I'm not in any way that knowledgable on the chemistry or the firing
> technique.I'm positive you are far more knowledgable on all this
shino
> and carbon trap stuff than me. Just did it and saw the results. It
was
> tricky for sure and we did have one "vanila" shino firing from
missing
> the crucial carbon trap times, temp, and atmosphere. A bit to much
> tequilla with the crew that night. During the day, and sober, one
can
> more clearly see if the leval of carbonization is adequate for
Malcolms
> method. ; - )
>
> Yours, Terry Sullivan
> Nottingham Arts
> www.nottinghamarts.org
>
>
>
>
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