Craig Clark on mon 7 mar 05
Patricia, I have been aware of the fading problem, especially with
lusters and copper matts, in the Raku glazes for quite some time. Have
read a number of articles and posts about it and have finally started to
test a few suggested solutions offered up by Tom Buck. He gives the best
explantion of the degradation of raku glazes that I have read. In the
article "First You See It, Then You Don't" he really explains what
occurs and why it happens. Just follow the link if you are
interested...http://ceramic-materials.com/cermat/education/113.html
I'll be running the glaze alternatives that Tom suggests and putting
them to the same test that I have my other Raku glazes, all of which
have failed miserably with the exception of the white and yellow
crackles. I leave them out in my backyard here in Houston for about a
year. They are subjected to a host of known carcinogens, unknown
carcinogens, humidity, ocassional freezing temps, many days over 100 F,
moonsoon type rains, fall-out from the pecan trees, and guano from a
wide variety of birds and the errant bat. I'll be posting the results of
the tests over the next many months.
I don't know that the use of Bismuth Subnitrate will have any affect
on the longevity of your lusters. Unless it somehow provides alumina for
the melt to make a stronger, more durable glass matrix. This would help
to prevent the continuing oxidation of the oxides. Have you done any
tests to confirm your hypothesis?
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Patrcia Dailey on tue 8 mar 05
Hi,
I'm not sure how or if it slows degradation, but I am sure that the colors are brighter. The only
explanation I have is that since the colors are brighter to begin with, they may last longer. I have
pieces with bismuth subnitrate in the glaze that I did several years ago, and they are still attractive
and bright. (Perhaps not quite as bright). Those pots I have done without the bismuth seem duller
both to begin with and overall even more so now. These are basically the same glazes, except I
add the bismuth subnitrate. My pots don't sit outside, but they are in my office, which is bright
and sunny. They all seem to have kept their shine, and color. I'd be really interested in your
glaze testing results.
Hope this helps,
Patricia
Mike Flaherty on tue 8 mar 05
could bismuth oxide (Bi2O3) have amphoteric properties like alumina (Al2O3)?
just a guess, but maybe that's why they seem to retain color for longer
than other glazes.
mike
On Tue, 8 Mar 2005 01:08:51 -0500, Patrcia Dailey wrote:
>Hi,
>I'm not sure how or if it slows degradation, but I am sure that the colors
are brighter. The only
>explanation I have is that since the colors are brighter to begin with,
they may last longer. I have
>pieces with bismuth subnitrate in the glaze that I did several years ago,
and they are still attractive
>and bright. (Perhaps not quite as bright). Those pots I have done without
the bismuth seem duller
>both to begin with and overall even more so now. These are basically the
same glazes, except I
>add the bismuth subnitrate. My pots don't sit outside, but they are in my
office, which is bright
>and sunny. They all seem to have kept their shine, and color. I'd be
really interested in your
>glaze testing results.
>Hope this helps,
>Patricia
>
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