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question about naked raku

updated wed 14 feb 07


Vince Pitelka on tue 13 feb 07

I don't do any naked raku (well, at least not the kind with the refractory
glaze coating that cracks and then gets removed), and a woman named Terri
Gray emailed me a questions regarding a problem she is having with the
surface color yellowing just an hour or so after she finishes the firing. I
thought the problem might be due to soluble fluxes left in the clay, and
suggested that she soak the pots in water after the firing. She said that
she already does soak the pots in water to help loosen and remove the naked
raku glaze, and now I am thinking that this might be the problem - soluble
salts leaching to the surface as the water evaporates. At any rate, if you
are familiar with naked raku, please read Terri's message below and either
respond to the list, and I will forward to her, or else respond directly to
Thanks -
- Vince
From: Terri Gray []
Sent: Monday, February 12, 2007 1:37 PM
To: Vince Pitelka
Subject: Yellowing terra-sigillata!!!

Hello Vince,
I have been working on a yellowing problem for a year! This yellowing seems
to leach through after the piece has been fired cleaned and been sitting
over night. My initial recipe used titanium dioxide to give the sig an
oyster color. I read that titanium can have rutile impurities and can react
with sunlight (called phototrophy!). I immediately stopped using the
titanium. Then, I was told by respectable members of a raku forum that the
yellowing was the fault of the underlying clay body (I was using soldate 60
from laguna). So I promptly changed clays to Highwater Raku clay from North
Carolina. But that wasn't my answer either! I then consisered the OM4 clay
body that I was using in my terra-sigillata (some told me this was not a
pure white clay body), and I started using EPK as the clay ingredient. But
to no avail, still leaching yellow!
I am using the naked raku process using a intermediate slip, then and
overlying glaze that pops off after reduction. The intermediate slip
consists of EPK and 325 mesh silica, and the glaze that pops off consists of
3269 Ferro Frit and EPK. I don't think any of these materials could cause
difficulties over the terra-sig, or not? I am at a loss and can't seem to
get a break. Any suggestions? Thank-You for your time and brain power,
Terri Gray
p.s. My terra-sigillata recipe is clay, water (even tried purified water!),
and several drops of sodium silicate.
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111,