ivor and olive lewis on mon 14 may 12
Zinc oxide is considered to be a valuable glaze ingredient with one major
drawback. It is unstable in a reducing environment. So why is it regarded a=
s
a compound that promotes melting ?. Fusing in the region of 1900 deg C (345=
2
F) it might be better considered as a Refractory material that would not
fuse before ingredients such as Frits, Borates and Felspars.
General knowledge of Zinc oxide as a ceramic ingredient seems to be
inconsistent but experience of those who make Zinc Crystalline Ware know
that high quantities of Zinc oxide reduce the viscous nature of Silicate
melts and promote high fluidity, This may be true of batches containing muc=
h
lower volumes of ZnO but to a lesser degree, though sufficient to mimic Lea=
d
glazes with smooth, bright, highly reflective surfaces by decreasing
Viscosity and Surface Tension.
Note that some zinc compounds have low melting points. Consider Zinc
Borates. ZnO.B2O3 has an MP in the 1000 deg C range (1832 F). 3Zn.O.2B2O3
mp 980 deg C (1796 F). Zinc Orthophosphate seems interesting, 3ZnO.P2O5, mp
900 deg C (1652 F). If these are stable in a reducing atmosphere they would
be a useful addition on the Glaze Lab shelves.
Regards,
Ivor Lewis,
REDHILL,
South Australia
Robert Harris on mon 14 may 12
Ivor - I'm slightly confused as to why you are mentioning melting
points when talking about the fluxing activity of zinc. Our most
commonly used flux, Calcium Oxide (as whiting/Calcium carbonate
becomes at 1517F/825C), has a melting temperature of 2572C/4662F. Yet
obviously it is a very active flux well below this temperature, or
indeed well below the temperature of ANY of the ingredients of (for
example) the classic Leach 40-30-20-10 recipe.
Robert
On Mon, May 14, 2012 at 2:09 AM, ivor and olive lewis
wrote:
> Zinc oxide is considered to be a valuable glaze ingredient with one major
> drawback. It is unstable in a reducing environment. So why is it regarded=
=3D
as
> a compound that promotes melting ?. Fusing in the region of 1900 deg C (3=
=3D
452
> F) it might be better considered as a Refractory material that would not
> fuse before ingredients such as Frits, Borates and Felspars.
> General knowledge of Zinc oxide as a ceramic ingredient seems to be
> inconsistent but experience of those who make Zinc Crystalline Ware know
> that high quantities of Zinc oxide reduce the viscous nature of Silicate
> melts and promote high fluidity, This may be true of batches containing m=
=3D
uch
> lower volumes of ZnO but to a lesser degree, though sufficient to mimic L=
=3D
ead
> glazes with smooth, bright, highly reflective surfaces by decreasing
> Viscosity and Surface Tension.
> Note that some zinc compounds have low melting =3DA0points. Consider Zinc
> Borates. ZnO.B2O3 has an MP in the 1000 deg C range (1832 F). =3DA03Zn.O.=
2B=3D
2O3
> mp 980 deg C (1796 F). Zinc Orthophosphate seems interesting, 3ZnO.P2O5, =
=3D
mp
> 900 deg C (1652 F). If these are stable in a reducing atmosphere they wou=
=3D
ld
> be a useful addition on the Glaze Lab shelves.
> Regards,
> Ivor Lewis,
> REDHILL,
> South Australia
--=3D20
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