Laurie Kneppel on wed 31 mar 04
Just for fun I was browsing through the archives on my lunch hour and
reading past discussions about oribe glazes. I noted that most of the
recipes people shared had a fair amount of copper in them. I didn't get
to read all 250+ messages, but I wondered if anyone ever did find a
food-safe oribe? Is there such an animal? I did note that various
people suggested using a liner glaze on the inside and the oribe on the
outside just to be sure.
Laurie
Sacramento, CA
Ivor and Olive Lewis on thu 1 apr 04
Dear Laurie,
Listening to the chatter and reading the commentaries about using
Copper oxide or carbonate in any glaze seems to confirm the idea that
there are no chemical reactions between Copper compounds and any of
the other chemicals we put into our glaze recipes. This seems to be
the case with proportions even as small as one percent.
In "Handbook for Australian Potters" the authors tell us that Copper
red is caused not by the colour of the reduced oxide or the metal but
because the metal is in a colloidal state, which means it is still a
discrete element as Atoms, not Ions. The hue we see is due to the
optical effects of those colloidal particles interfering with light.
Now, I have repeatedly said before that until we can get into the
deeper chemistry of Copper and the compounds we wish it to associate
with we will not solve this problem of the instability of copper
bearing glazes.Perhaps such finishes should not be used pottery where
there will be domestic use.
I prefer liner glazes to be glossy transparent and for the liner to
overlap the lip or rim.
Best regards,
Ivor Lewis. Redhill, South Australia
.
Ron Roy on fri 2 apr 04
Hi Laurie,
I did a lot of testing on a typical oribe - just to see if I could make one
more durable. We should say durable or stable - food safe is too loose a
term.
No way - they are short of silica and when I tried to increase the silica
the glaze changed - when I tried to reduce the copper the colour changed -
in both cased to a very muddy dark - sort of red.
The copper must be over supplied and come out of solution as the glaze
cools to get the effect.
RR
>Just for fun I was browsing through the archives on my lunch hour and
>reading past discussions about oribe glazes. I noted that most of the
>recipes people shared had a fair amount of copper in them. I didn't get
>to read all 250+ messages, but I wondered if anyone ever did find a
>food-safe oribe? Is there such an animal? I did note that various
>people suggested using a liner glaze on the inside and the oribe on the
>outside just to be sure.
>
>Laurie
>Sacramento, CA
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Laurie on fri 2 apr 04
Hi Ron and Ivor,
Thank you for the information about oribe glazes. And oops, yes I meant
durable rather than food-safe! I think I will play it safe and use a
"safe" liner glaze on anything that might become functional (to
somebody, sometime) and save any oribe for the outside only. I used
some oribe on the outside of some mugs I glazed at the community
college and put a white liner on the inside and let it spill over the
rim slightly. They were not fired in the last glaze kiln so i will have
to wait and see how the glazes work together.
It's funny - the things I make at home I am less likely to experiment
with, while the pieces I make in this class I will try all sorts of odd
(to me) glaze combinations just to see what they do. I had an
interesting mug come out of the last firing. The outside was glazed
with a rutile green and the inside with a semi-matte white and rimmed
with the white. Where the two glazes meet on the outside they have a
pinkish hue and the rutile green got some nice crystal formation. I
thought they were bubbles but they are crystals. Maybe not the most
functional mug, but fun to look at. One I didn't care for was oribe on
the outside and chun blue on the inside and rim. Someone might like it,
but not a great color combo to me. One of these days i will try to get
photos up on my website - which is in bad need of updating, I think it
still says Happy New Year! LOL!
Laurie
Sacramento, CA
On Apr 2, 2004, at 7:26 AM, Ron Roy wrote:
> Hi Laurie,
>
> I did a lot of testing on a typical oribe - just to see if I could
> make one
> more durable.
Lee Love on sat 3 apr 04
Ron Roy wrote:
>No way - they are short of silica and when I tried to increase the silica
>the glaze changed - when I tried to reduce the copper the colour changed -
>in both cased to a very muddy dark - sort of red.
>
>
Sometimes a little knowledge about how glazes were traditionally
used goes a long way. ;-)
Oribe is fired in oxidation. You get green with it in
oxidation. You can get some very interesting colors in a neutral
atmosphere, all the ranges between red, purple, green and blue.
Oribe can also be used to get red on chun by splashing some on top of
the Chun application, which is fired in reduction.
If you want a glaze with more silica in it that works
similarly to oribe, but tends not to be as deep a green, Nuka Sage
works. The main ingredient in Nuka is rice hull ash, which is mostly
organically processed silica, very fine silica.
Oribe food safe? They seem to think so here in Japan.
Leaching depends on the food you put in it. Don't use it with
orange juice or as a lemon platter. (No brainer) Sushi is okay.
It is great on the outside of anything. I am also guessing that
the traditional preparation of the surfaces of oribe removes oxides from
the surface.
Lee In Mashiko, Japan
http://mashiko.org
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