Craig Dunn Clark on tue 2 mar 04
unstable
I have a few thoughts on the nature of Raku. Being one of those who
happily practice the technique I feel free to talk some trash about it. They
are indeed "unstable concoctions," (the glazes not the folks using the
process though some us are probably a bit questionable as well.)I'm laughing
as I think about this especially when I consider the fact that I was one of
the idiots who used to eat off of raku plates which I thought looked "really
cool" back in the 80's. Perhaps that is part of the reason I am the way I am
today.
Raku glazes, at least many of those used are inherently unstable because
there simply is not enough alumina in the melt to make them stable. Couple
that with the unvitrified clay body and there is most definitely a problem.
The worst of the offenders are the copper matts. If you put one of these
babies outside in SouthEast Texas, or even in an unairconditioned studio for
a few months the change is readily apparant. One of the frequently used
remedies is to seal the pots. Folks use various products that include, but
are not limited to, grout sealer, clear acrylic and wax.
There is an individual, named Tom Buck, who has done extensive research
and testing on this very subject. He was a chemical engineer for most of his
professional life as well as a potter. He has gone so far as to come up with
a number of more stable raku glazes that are posted for all the world to use
as part of the digital fire web site
http://www.digitalfire.ab.ca/cermat/education/113.html.
I have said this before and will repeat it. The man knows a great many
things concerning the nature of glazes and raku glazes in particular. He has
offered up the information in the spirit of education and a gradual
improvement of the knowledge base of the greater potting community.
I have been "meanin-ta-git-ta" testing some of Toms glazes so that I
could then photo and JPG them for anyone interested in seeing. Coming clean
once again, I must say that I have not yet budgeted the time to do this. I
still don't have a web site and am still using my old unstable glazes, not
the copper matts though, and will get to this one as time permits. Hopefully
before the two year old enters grade school......but not before I've
replaced the remainder of the plumbing on the house.
For anyone interested in this problem and proposed solutions I suggest
linking to Toms article and reading it and trying out some of what he
suggests.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Monday, March 01, 2004 10:38 PM
Subject: Re: cleaning carbon off raku - a problem with Copper
> Dear Friends,
> Reading about the problems with Copper coloured Raku Glazes leads me
> to think that they are very unstable concoctions.
> Given that John and Ron used copper as a leaching indicator in their
> work on Cone 6 glazes I suspect that there is something inimical about
> this element which makes it difficult to get it to react with
> aluminosilicate glasses and also remain inert.
> Any thought on why?
> Best regards,
> Ivor Lewis. Redhill, South Australia
>
>
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Ivor and Olive Lewis on wed 3 mar 04
unstable
Dear Craig,
I was not having a go at the instability of raku glazes.
My concern is related to the behaviour of Copper compounds in a
general sense.
Even respectable glazes would seem to discharge copper when tested
except when it is buried deep, as in undergalze decoration,
or in very low concentrations.
Natural minerals which contain Copper are few and those that contain
Silicon as a silicate always seem to be associated with Water. It may
be that the coinage element group of Gold, Silver and Copper are all
affected in this way and the fact that all three metals are found as
native metals may provide a lead to discovery.
Best regards,
Ivor Lewis. Redhill, South Australia
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