Jean Todd on wed 12 apr 00
I gave my daughter a bowl which has been in use for at least 10 years.
During that time it has been washed in a dishwasher but that should not have
done what has happened over the years.
It is glazed in an iron glaze with a Chun over the top. Where the chun is
there are lots and lots of tiny even holes, resembling coral. What has
happened and why?
Chun used.
Feldspar Potash 50
Silica 23
Calcite 13
Zinc Oxide 11
Bone Ash 3
Iron Oxide .5
I am not sure which iron glaze I used as a base glaze.
Jean
"Lang may your lum reek"
E-mail mallyree@ix.net.au
Ben and Emmy on fri 14 apr 00
Jean,
If my memory of a small book by some university researchers (MIT, I think-
not sure) on a few specific types of Chinese glazes serves me, the effect
that this glaze pursues is the result of minute cavitations within the
glaze. The refraction of light through the cavity/glaze interface results in
the depth of color and unusual surface quality found in these type of
glazes. (The generation of these cavities may be related to the bone ash
(and phosphorus volatility at melt temperatures--->just a guess). The
cavities closer to the surface may have been ruptured by normal use, leaving
this pattern. Eliminating bone ash or reducing melt viscosity should help
this issue- but will probably destroy the effect you want. Ready to be
informed of just how wrong I am---- just in case.
Ben Holtz
I gave my daughter a bowl which has been in use for at least 10 years.
During that time it has been washed in a dishwasher but that should not have
done what has happened over the years.
It is glazed in an iron glaze with a Chun over the top. Where the chun is
there are lots and lots of tiny even holes, resembling coral. What has
happened and why?
Chun used.
Feldspar Potash 50
Silica 23
Calcite 13
Zinc Oxide 11
Bone Ash 3
Iron Oxide .5
I am not sure which iron glaze I used as a base glaze.
Jean
"Lang may your lum reek"
E-mail mallyree@ix.net.au
John Hesselberth on sat 15 apr 00
Jean Todd wrote:
>----------------------------Original message----------------------------
>I gave my daughter a bowl which has been in use for at least 10 years.
>During that time it has been washed in a dishwasher but that should not have
>done what has happened over the years.
>It is glazed in an iron glaze with a Chun over the top. Where the chun is
>there are lots and lots of tiny even holes, resembling coral. What has
>happened and why?
>
>Chun used.
>
>Feldspar Potash 50
>Silica 23
>Calcite 13
>Zinc Oxide 11
>Bone Ash 3
>Iron Oxide .5
>
>I am not sure which iron glaze I used as a base glaze.
>Jean
>"Lang may your lum reek"
>E-mail mallyree@ix.net.au
Hi Jean,
You already put your finger on it--the dishwasher. This glaze is on the
low side with respect to alumina content (0.225). It is also on the low
side for silica (2.53). Low alumina is known to give poor resistance to
alkaline materials like dishwasher soap.
It would appear to be a borderline stable glaze which will hold up for a
while, but not a lifetime.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
The only things in life that are certain are death and taxes; however
only taxes come once a year. Anonymous
Ron Roy on sat 15 apr 00
Hi Jean,
You don't say what temp it was fired to - there is a lot of zinc and not a
lot of alumina or silica - even for a cone 6 glaze. I don't see any clay in
the recipe - is that right? I think so because it totals 100.
RR
>----------------------------Original message----------------------------
>I gave my daughter a bowl which has been in use for at least 10 years.
>During that time it has been washed in a dishwasher but that should not have
>done what has happened over the years.
>It is glazed in an iron glaze with a Chun over the top. Where the chun is
>there are lots and lots of tiny even holes, resembling coral. What has
>happened and why?
>
>Chun used.
>
>Feldspar Potash 50
>Silica 23
>Calcite 13
>Zinc Oxide 11
>Bone Ash 3
>Iron Oxide .5
>
>I am not sure which iron glaze I used as a base glaze.
>Jean
>"Lang may your lum reek"
>E-mail mallyree@ix.net.au
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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