Gerry Barbe on fri 29 nov 96
On Thu, 28 Nov 1996, Autumn Downey wrote:
> ----------------------------Original message----------------------------
> I haven't easily found any information on how zircopax and Superpax compare.
> Are there any major differences in opacity, or melting properties and
> chemical formulas? So far, we have only used zircopax, so I haven't had
> direct experience with superpax, but was wondering if it might be a bit
> smoother.
We used both zircopax and superpax. The superpax is just as nice but
cheaper.
Here's my problem. I've used the same off white glaze for years. We ran
out of superpax and used Ultrox. Oh dear. Instead of coming out creamy,
the glaze is clear and harsh, no depth to it. It also allows the speckle
to show through the glaze which is not great considering the type of
decorating I do. A regular customer of mine asked for pieces without the
oatmeal glaze! When I told her it was the same glaze only we used Ultrox
instead of superpax she couldn'd believe it.
I have a garbage pail full of this glaze. Can I just add the
superpax to it? Anyone else have this problem? Is there a solution.
Ach...two more shows to go and all my Christmas orders!!!
Thanks, Marilyn in snowy Ailsa Craig
______________________________________________________________________________
anglersnet@aol.com on mon 2 dec 96
I hope you find of help and interest regarding opacifiers.
Zirconium Silicate opacifiers Ultrox 500W Ultrox 1000W, Zircopax,
Zircopax Plus, Superpax, Superpax Plus, Excelopax, etc. all have almost
identical chemical compositions and similar qualities in glazes. Their
opacification is directly related to the size of the fairly inert ZrSi
particles. The smaller they are, the greater scattering of light, the
more opacification. Finer particle sized grades such as Ultrox1000W and
Superpax Plus will contribute greater opacification for a given percentage
in a composition than microscopically courser versions such as Zircopax
and Ultrox 500W.
Zirconium Silicate is quite refractory and for the most part
insoluable in most glazes. It is common for up to 1% to dissolve and
therefore have no opacifying effect. Additional percentages will to some
degree increase the melting point and viscosity of the molten glaze.
Substantial additions will also change the glaze surface texture.
Generally finer grades are used where only minor changes in melt and
surface are desired for the opacification required. Zirconium Silicate
will also have an effect on the expansion of the glaze, generally reducing
the expansion and move in the direction of reducing crazing in glazes with
that defect.
There is no problem in mixing different grades and "brands" of these
opacifiers and to increase their level in a compostion. For your problem
with an "Oatmeal" effect due to incomplete opacification, I would suggest
testing increasing levels finer grades such as Superpax Plus or Ultrox
1000W. My guess is that you used Ultrox 500W and not as fine a grade as
you have been accustomed to using.
Bob Jameson
| |
|
