Ron Collins on tue 3 sep 02
Hello Ron......hope things are fine with you. On the birk's celadon, in
your educated opinion, do you think that reducing the zinc from 5 % to 1.75%
would still be acceptable flux amount? I remember reading a long time ago
in CM that 2 percent zinc makes a flux, but oddly, over 2 percent reacts in
the opposite way. I know that I can test it, and will with the lower zinc
amount, and all other things being equal....but what do you think? and yes,
I did buy the necessary ingredients to try all your glazes and use your
recommended frits, etc...for developing some of my own glazes from
suggestions in the book, because, after all, I have the book, and wanted to
do what everyone else was haviing fun with too. But I am having such a time
getting materials for clay now...the toilet factory quit selling the nice
ball clay and kaolin that I depended on, and trust me, there are no other
sources. You can understand, I am sure, that using non-imports in good old
reliable glazes has to be a part of living in the third world. So, bottom
line, do you think that the zinc matters anyway? It does pinhole some, with
the 5 percent, and it is irritating. By the way, the xavier's revised base
glaze makes me the most beautiful faux blue celadon with no defects of any
kind....it is just wonderful, and I thank you and john for giving me access
to that base.....when I tried it as xavier's jade green, since I have to use
my weird feldspatho,, it was just a pretty ugly yellow green, although the
glaze is great, I couldn't get good color .....so thanks for a great base
for a pretty Bruce Chotrane (wrong spelling) looking blue celadon......I am
going to order from Axner some om4 and epk, enough to do me, and if I don't
start making some real money, I guess I'll stick jewelry on an umbrella and
walk around the street........my best, see you in san diego....Melinda
iandol on wed 4 sep 02
Dear Melinda,
Although your post is addressed to Ron Roy perhaps you will accept my =
response.
I think there is some confusion about the meaning of the term "Flux". As =
I read both literature and posts on clayart I get the feeling that =
people are talking about making things melt. I do not think this is the =
case with Zinc Oxide.
My own idea is that this chemical has a limited solubility in any =
silicate melt, otherwise it is a refractory material which imparts =
opacity because of a suspension which remains undissolved as discrete =
particles of Zinc oxide.
However, the small proportion which does dissolve alters the character =
of a glaze by changing surface tension and viscosity. This is consonant =
with the definition of "Flux". These changes give the bright effect of =
the lead glazes, which Bristol glazes were used to replace.
There are many unresolved issues in Glaze Chemistry. The behaviour of =
refractory oxides is just one.
Sorry that you can no longer get some of the necessary raw materials =
from a local source. I am sure you will find a way round any impasse.
Best regards,
Ivor Lewis
John Weber on fri 6 sep 02
I would like to ask a follow up question about Zinc. I know this thread is
about "reducing" the amount of Zinc but my question has to do with firing in
a reducing atmosphere. In Hammer's book it states that if Zinc is used in a
reduction atmosphere the Zinc is lost. Does this mean that the addition of
Zinc would have no effect on a glaze if fired to a Cone 10 Reduction because
it is all lost or is there still some residual effect, such as it still
functioning as a flux?
Ron Roy on fri 6 sep 02
Hi Melinda,
Good to hear from you - and yes - see you in San Diego.
Zinc is a mid temperature flux - even in amounts over 5% - the Bristol
glaze relies heavily on zinc as a replacement for lead.
The recommended trouble free amount is 2% so your idea is OK. You can also
get around using higher amounts but you must make sure you have no reducing
atmosphere during both bisque firing and glaze firing - it means good
ventilation (extra oxygen) and time to burn up any carbon coming from clay,
glazes and wax.
Removing that much Zinc may result in a glaze that is not melted enough -
if that becomes the problem send it to me and I will make some adjustments.
Zinc has a rather low expansion so if crazing becomes the problem it can be
dealt with in a number of ways.
Best regards - RR
>Hello Ron......hope things are fine with you. On the birk's celadon, in
>your educated opinion, do you think that reducing the zinc from 5 % to 1.75%
>would still be acceptable flux amount? I remember reading a long time ago
>in CM that 2 percent zinc makes a flux, but oddly, over 2 percent reacts in
>the opposite way. I know that I can test it, and will with the lower zinc
>amount, and all other things being equal....but what do you think? and yes,
>I did buy the necessary ingredients to try all your glazes and use your
>recommended frits, etc...for developing some of my own glazes from
>suggestions in the book, because, after all, I have the book, and wanted to
>do what everyone else was haviing fun with too. But I am having such a time
>getting materials for clay now...the toilet factory quit selling the nice
>ball clay and kaolin that I depended on, and trust me, there are no other
>sources. You can understand, I am sure, that using non-imports in good old
>reliable glazes has to be a part of living in the third world. So, bottom
>line, do you think that the zinc matters anyway? It does pinhole some, with
>the 5 percent, and it is irritating. By the way, the xavier's revised base
>glaze makes me the most beautiful faux blue celadon with no defects of any
>kind....it is just wonderful, and I thank you and john for giving me access
>to that base.....when I tried it as xavier's jade green, since I have to use
>my weird feldspatho,, it was just a pretty ugly yellow green, although the
>glaze is great, I couldn't get good color .....so thanks for a great base
>for a pretty Bruce Chotrane (wrong spelling) looking blue celadon......I am
>going to order from Axner some om4 and epk, enough to do me, and if I don't
>start making some real money, I guess I'll stick jewelry on an umbrella and
>walk around the street........my best, see you in san diego....Melinda
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sat 7 sep 02
Hi John,
Apparently some times yes and sometimes no - I must have to do with when
the glaze seals over before reduction.
This is a complicated issue and there have been no definitive trials as far
as I know. We still don't know why - if it does have a melting effect after
reduction - it does help melting.
What is needed is for someone to test some glazes - in reduction - with and
without zinc. We can then try to see why some glazes benefit and other do
not.
Anyone want to do some testing?
RR
>I would like to ask a follow up question about Zinc. I know this thread is
>about "reducing" the amount of Zinc but my question has to do with firing in
>a reducing atmosphere. In Hammer's book it states that if Zinc is used in a
>reduction atmosphere the Zinc is lost. Does this mean that the addition of
>Zinc would have no effect on a glaze if fired to a Cone 10 Reduction because
>it is all lost or is there still some residual effect, such as it still
>functioning as a flux?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Weber on sun 8 sep 02
Sure Ron, I would be willing to run some tests on copper red glazes with and
without zinc. I assume we would want to pull draw trails at various cones,
but then what? A bit of guidance to help me set up the test to get the most
out of the results would be appreciated.
David Hendley on sun 8 sep 02
I've already done the testing. Remember, Ron, I showed you the results
at the Denver NCECA.
I tested 8 glazes that all called for at least 3% zinc oxide, and mixed
batches with and without the zinc.
They were fired at cone 10 reduction.
In 4 or 5 cases, we could tell no difference in the glazes with
and without the zinc. In a couple of cases, there seemed to
be slight differences. And in one case, there was a very noticeable
difference in the test tiles with and without the zinc.
I think, as Tom Buck suggested a few weeks ago, that zinc oxide
can serve a purpose in a reduction glaze by starting the melting
earlier in the firing, before it is vaporized.
I have no ideas as to why the zinc apparently has an effect in some
glazes, but not in others.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message ----- >
> This is a complicated issue and there have been no definitive trials as
far
> as I know. We still don't know why - if it does have a melting effect
after
> reduction - it does help melting.
>
> What is needed is for someone to test some glazes - in reduction - with
and
> without zinc. We can then try to see why some glazes benefit and other do
> not.
>
> Anyone want to do some testing?
>
> RR
>
>
> >I would like to ask a follow up question about Zinc. I know this thread
is
> >about "reducing" the amount of Zinc but my question has to do with firing
in
> >a reducing atmosphere. In Hammer's book it states that if Zinc is used in
a
> >reduction atmosphere the Zinc is lost. Does this mean that the addition
of
> >Zinc would have no effect on a glaze if fired to a Cone 10 Reduction
because
> >it is all lost or is there still some residual effect, such as it still
> >functioning as a flux?
>
@pclink.com.
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