Jim Murphy on wed 4 jun 03
Hi Ivor,
I'm trying to understand the application of theory here. I won't dare make
reference to "eutectic" mixtures.
Let's say we're searching for a suitable combination of two materials -
let's call them a Primary Melter and Auxiliary - to serve as the basis for
the Flux component of a new Cone 6 glaze. Let's also say we're pretty sure
the Primary Melter is a non-crystalline material with glasslike melting
behavior (kinda like Volcanic Ash). Also, the Auxiliary material is a
material with high "CaO" (kinda like Wollastonite).
I'm guessing this would be where a fuse button line-blend test would have
some value. In other words, mix-up different ratios of Primary Melter to
Auxiliary, form them into cone- or button-shapes, then fire to Cone 6 for
evaluation. Hmmm, let's make that three sets of tests, fired to Cone 5, 6
and 7, respectively.
The plan would be to take the "best" fired test button combo of Primary
Melter and Auxiliary and use it as the Flux combo for a Cone 6 Glaze "Grid
Test", whereby Alumina and Kaolin are varied.
Now, my question is - how does one determine which fired test button may be
most suitable for the grid test ?
Is it simply a matter of looking at the fired test results for the button
that visually looks like it melted/fused the best, or are there supplemental
tests one may use to select the best candidate for the grid test ?
I'd appreciate your thoughts here.
Best wishes,
Jim Murphy
Jim Murphy on wed 4 jun 03
Ivor,
Ooops ! I've corrected (below) my last post - it's Alumina and "Silica" that
are varied in the grid test.
Jim Murphy
Hi Ivor,
I'm trying to understand the application of theory here. I won't dare make
reference to "eutectic" mixtures.
Let's say we're searching for a suitable combination of two materials -
let's call them a Primary Melter and Auxiliary - to serve as the basis for
the Flux component of a new Cone 6 glaze. Let's also say we're pretty sure
the Primary Melter is a non-crystalline material with glasslike melting
behavior (kinda like Volcanic Ash). Also, the Auxiliary material is a
material with high "CaO" (kinda like Wollastonite).
I'm guessing this would be where a fuse button line-blend test would have
some value. In other words, mix-up different ratios of Primary Melter to
Auxiliary, form them into cone- or button-shapes, then fire to Cone 6 for
evaluation. Hmmm, let's make that three sets of tests, fired to Cone 5, 6
and 7, respectively.
The plan would be to take the "best" fired test button combo of Primary
Melter and Auxiliary and use it as the Flux combo for a Cone 6 Glaze "Grid
Test", whereby Alumina and Silica are varied.
Now, my question is - how does one determine which fired test button may be
most suitable for the grid test ?
Is it simply a matter of looking at the fired test results for the button
that visually looks like it melted/fused the best, or are there supplemental
tests one may use to select the best candidate for the grid test ?
I'd appreciate your thoughts here.
Best wishes,
Jim Murphy
on 6/3/03 1:59 AM, iandol at iandol@TELL.NET.AU wrote:
> Dear Jim Murphy,
>
> My Friend, I think you are picking up the vibes. Your summation seems in tune
> with my thinking.
>
> The notion of a cone 6 with Calcium oxide as a sole representative of the R2O
> group would not work even if you hit on the right mixture of prime
> ingredients. The melting range is too narrow and overfiring might increase the
> fluidity to the extent where it all ran from the pot onto the shelf. Remember,
> Most glazes are compromises combining a selection of complementary,
> contrasting and even opposing qualities.
>
> The Calcium Felspar, Anorthite, has a listed melting point of 1550 or
> thereabouts and does not contain Sodium or Potassium. If it did it would be a
> different material, some sort of Rock, like Nepheline Syenite. I suggested it
> as the third entity in the triumvirate which encompasses the 1170 Eutectic
> Point.
>
> IF Calcium oxide is not dissolved into the melt it will be available for
> attack by water or acids. If it is in solution in a glass it will not be open
> to attack at the same rate. If it reacts on cooling to precipitate
> Wollastonite or Anorthite (depending on the original chemistry" it will be
> insoluble to water and, I suspect, many acids.
>
> Lime, AKA CaO, does not promote Fusibility. But it has a major effect on
> Viscosity. It also affects that other quality of importance, Surface Tension.
> Perhaps the commentators you speak of confuse an exceptional degree of
> Fluidity with Fusibility. It is well known that Felspars can "Fuse" and be
> taken to very high temperatures without becoming "Fluid"(see Singer and
> Singer)
>
> Care should be taken when considering the qualities of some materials.
> Volcanics by mature and definition are fast cooled materials. I believe both
> Ash and Pumice are Glassy by nature. I would treat them as being Prime Melting
> Agents, as Natural Frits. This would confirm your opinion that they might be
> useful agents in Cone Six Glazes.
>
> Best Regards,
>
> Ivor Lewis.
>
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