ivor & olive lewis on thu 10 sep 09
Dear Paul Borian,
I would imagine that the answer to your question resides in the batch
recipe.
One thing I would suggest to speed up your research process is to do a line
blend and set your test tiles at an angle on a good bed of alumina or kaoli=
n
to record any variations in viscosity.
Zirconium Orthosilicate, ZrSiO4 is noted as decomposing at 1540 deg C (2894
F). The phase diagram Al2O3-SiO2-ZrO2 shows a melting point of 1775 for
ZnSiO4.
Best regards,
Ivor Lewis,
Redhill,
South Australia
Eleanora Eden on thu 10 sep 09
Hi Roy,
Thanks for your comments. This all makes me wonder if I should go back
to using tin ox and zircopax together. I was always doing it then I was sh=
opping
for more tin and decided to go exclusively with zircopax. Used 5% tin and =
10%
zircopax, something like that.
I could have sworn I saw a comment in Hamer that tin has an elastic quality=
that
helps glazes fit. Now I can't find it.
When I was working at ^10 I had this glaze that Pete Voulkos helped me opac=
ify.
Unfortunately, I changed this glaze to volume in the distant past and have =
no record
of the original by weight:
4 feldspar
1 bone ash
2 talc
2 china clay
1/2 tin
I changed the tin straight across for zircopax and it worked great.
Thanks,
Eleanora
>Hi Eleanora,
>Our cone 6 majolica glaze in our book has 16% - I have a zorcopax white fo=
r
>cone 10 that has 20%.
>I does slow down melting - you are adding a refractory and you may have to
>add more flux in some cases.
>
>How zirconium silicates work (and Tin) - they simply do not melt and stay =
as
>crystals in a glaze - like snow flakes in air - get enough of them and you
>have opacity.
>
>The general rule was 5% tin or twice as much pax - if that is not enough a=
dd
>more.
>
>It is helpful to have some idea of expansion as they both lower expansion =
-
>and as John Hesselberth found - pax has a negative effect on stability.
>
>RR
>
>On Wed, Sep 9, 2009 at 8:14 AM, Eleanora Eden wrote:
>
>> Hi Paul,
>>
>> To opacify a glaze 10% or 12% is not uncommon. I have even gone
>> up to 15%, but have been nervous as it seems so much.
>>
>> I also am interested to know if anybody is using 15% or more in a glaze.
>>
>> Eleanora
>>
>>
>> >i know there is not an exact answer for this one but i am presently
>> >experimenting with various amounts of zirconium silicate (zircopax) in =
one
>> >of my glazes and was just wondering what would be the maximum amount i
>> >should even try testing. i don't really understand how this material wo=
rks
>> >- does it actually make glazes more opaque without raising the melting
>> temp?
>> >in my case i have a glaze that needs to be very fluid because it
>> runs/drips
>> >but it also needs to have some opacity to get the depth of color.
>> Otherwise
>> >it just looks like a semi-clear blue glaze. Adding silica makes it more
>> >opaque but also stiffer so it doesn't run as well, that's why it seems
>> like
>> >zircopax is the thing to use.
>> >So far i am testing with 5% and will try 10% in the next firing. Are th=
ere
>> >glazes that use even more than that?
>> >any comments on this material would be of interest to me. In particular=
, i
>> >would like to know if it can lead to various glaze flaws when used in
>> >higher amounts.
>> >
>> >thanks,
>> >Paul
>>
>>
>> --
>> Bellows Falls Vermont
>> www.eleanoraeden.com
>>
>
>
>
>--
>Ron Roy
>15084 Little Lake Road
>Brighton, Ontario, Canada
>K0K 1H0
--
Bellows Falls Vermont
www.eleanoraeden.com
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