Earl Brunner on sun 26 nov 00
If you are new to the list then you may not know about the archives.
The archives are a great resource since they contain just about all
previous posts. If you go here:
http://www.potters.org/categories.htm
you can search by categories. Go to Materials, then misc. The materials
are listed in alphabetical order. There is some good info here on zinc.
One thing you didn't indicate was whether or not you were reducing
during your firing. Some suggest that zinc may be reduced completely
out of a cone ten reduction glaze for example.
Michael Tannock wrote:
> Hi all,
>
> I have only just subscribed to clayart: it's great, similar to being at art
> school where it was learning by immersion.
>
> My questions relate to replacing zinc oxide in a glaze. I have two reasons
> for doing this. Firstly I want to be able to exploit colours from chrome
> oxide and the zinc doesn't agree with the chrome. Also I suspect that the
> zinc volatolises at my firing temp of orton cone 8 and causes bubbles in
> the
> glaze which may then become pinholes and or dimples on the glaze surface.
>
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
David Hendley on mon 27 nov 00
I think you are on the right track when you say:
| I have a feeling that I may have more luck with the not so glamorous
fluxes,
| MgO, or perhaps CaO. However the glaze seems to have quite a bit of CaO
in
| it already.
Try substituting with the MgO, if that is agreeable with the
color you want (Magnesium can make cobalt blue go towards
purple). It also has a relatively low expansion.
The amount of zinc in the glaze is so small that I don't think
it will be missed, and it may well be that the glaze will be fine
if you simply leave out the Zinc oxide.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----- Original Message -----
From: Michael Tannock
To:
Sent: Sunday, November 26, 2000 4:03 PM
Subject: Zinc Oxide substitution
| Hi all,
|
| I have only just subscribed to clayart: it's great, similar to being at
art
| school where it was learning by immersion.
|
| My questions relate to replacing zinc oxide in a glaze. I have two
reasons
| for doing this. Firstly I want to be able to exploit colours from chrome
| oxide and the zinc doesn't agree with the chrome. Also I suspect that the
| zinc volatolises at my firing temp of orton cone 8 and causes bubbles in
the
| glaze which may then become pinholes and or dimples on the glaze surface.
|
| Here is the flux unity formula for the glaze:
| K2O 0.1191
| Na2O 0.1374
| CaO 0.6370
| ZnO 0.1065
| Al2O3 0.3328
| B2O3 0.1310
| SiO2 3.4137
| I fire it to cone 8 oxidation. I use this glaze on domesticware. It has
| quite a good surface, shiney and transparent. I think that it is
reasonably
| durable.
|
| What is the collective wisdom out there on zinc oxide? There doesn't seem
| to be that much info on it. It seems to be a desirable flux in small
| amounts at a high enough temp and it has middle of the road coef of expn
of
| the flux group oxides. Books etc mention that it improves surface texture
| and strength.
|
| I have Lawrence Ewing's Matrix glaze software and intend to do a series of
| line blends, blending each of the other fluxes into the glaze and then
work
| from there. I guess that I will have to retotal the flux group to one
after
| the addition of the fluxes to maintain the silica, alumina and boron at
the
| same ratio rather than just chucking in more of the fluxes that I choose.
| To give an overall idea of what each addition will do I guess I will
design
| the new flux end of the line blend so that it has about double the present
| proportion of 0.1065 which I will then retotal to equal one.
|
| I have already tried a direct substitution of lithium carb 2.5% for the
Zinc
| Oxide 2.5% in the base glaze. This caused the glaze to go mat and
actually
| craze, though the glaze with LiO2 supposedly had a lower coefficent of
| expansion. It did, however, make a glass with less bubbles and a
reasonable
| colour response from chrome.
|
| I have a feeling that I may have more luck with the not so glamerous
fluxes,
| MgO, or perhaps CaO. However the glaze seems to have quite a bit of CaO
in
| it already. I may need to have a small amount of the likes of lithium as
| well as one of the alkalai earths to match the fluxing power of the zinc
yet
| not disrupt the balance of the glaze.
|
| Any comments on my methodology or on zinc oxide and substitutions for it
| would be appreciated.
|
| Thanks
| Mike Tannock
| Dunedin
| New Zealand.
|
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Jonathan Kaplan on mon 27 nov 00
>Hi all,
>
>I have only just subscribed to clayart: it's great, similar to being at art
>school where it was learning by immersion.
>
>My questions relate to replacing zinc oxide in a glaze. I have two reasons
>for doing this. Firstly I want to be able to exploit colours from chrome
>oxide and the zinc doesn't agree with the chrome. Also I suspect that the
>zinc volatolises at my firing temp of orton cone 8 and causes bubbles in the
>glaze which may then become pinholes and or dimples on the glaze surface.
>
>Here is the flux unity formula for the glaze:
>K2O 0.1191
>Na2O 0.1374
>CaO 0.6370
>ZnO 0.1065
>Al2O3 0.3328
>B2O3 0.1310
>SiO2 3.4137
Mike:
Leave out the zinc and recalculate the glaze. Zinc is indeed your culprit
for the bubbling you describe and you will have have much more favorable
reaction with the chrome once the zinc is removed. Also, your glaze base
will also be much more useable with commercial stains if you wish without
the zinc.
You really don't need the zinc. Run a simple test without recalculating the
glaze leaving the zinc out. I think you will be pleased with the results.
Then recalculate to adjust the expansion if necessary.
Best
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jonathan@csn,net
http://www.sni.net/ceramicdesigin
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, FEd
Ex, etc.)
Michael Tannock on mon 27 nov 00
Hi all,
I have only just subscribed to clayart: it's great, similar to being at art
school where it was learning by immersion.
My questions relate to replacing zinc oxide in a glaze. I have two reasons
for doing this. Firstly I want to be able to exploit colours from chrome
oxide and the zinc doesn't agree with the chrome. Also I suspect that the
zinc volatolises at my firing temp of orton cone 8 and causes bubbles in the
glaze which may then become pinholes and or dimples on the glaze surface.
Here is the flux unity formula for the glaze:
K2O 0.1191
Na2O 0.1374
CaO 0.6370
ZnO 0.1065
Al2O3 0.3328
B2O3 0.1310
SiO2 3.4137
I fire it to cone 8 oxidation. I use this glaze on domesticware. It has
quite a good surface, shiney and transparent. I think that it is reasonably
durable.
What is the collective wisdom out there on zinc oxide? There doesn't seem
to be that much info on it. It seems to be a desirable flux in small
amounts at a high enough temp and it has middle of the road coef of expn of
the flux group oxides. Books etc mention that it improves surface texture
and strength.
I have Lawrence Ewing's Matrix glaze software and intend to do a series of
line blends, blending each of the other fluxes into the glaze and then work
from there. I guess that I will have to retotal the flux group to one after
the addition of the fluxes to maintain the silica, alumina and boron at the
same ratio rather than just chucking in more of the fluxes that I choose.
To give an overall idea of what each addition will do I guess I will design
the new flux end of the line blend so that it has about double the present
proportion of 0.1065 which I will then retotal to equal one.
I have already tried a direct substitution of lithium carb 2.5% for the Zinc
Oxide 2.5% in the base glaze. This caused the glaze to go mat and actually
craze, though the glaze with LiO2 supposedly had a lower coefficent of
expansion. It did, however, make a glass with less bubbles and a reasonable
colour response from chrome.
I have a feeling that I may have more luck with the not so glamerous fluxes,
MgO, or perhaps CaO. However the glaze seems to have quite a bit of CaO in
it already. I may need to have a small amount of the likes of lithium as
well as one of the alkalai earths to match the fluxing power of the zinc yet
not disrupt the balance of the glaze.
Any comments on my methodology or on zinc oxide and substitutions for it
would be appreciated.
Thanks
Mike Tannock
Dunedin
New Zealand.
_____________________________________________________________________________________
Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com
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