Hank Murrow on tue 9 jan 07
glazes
On Jan 9, 2007, at 5:02 AM, Kathy McDonald wrote:
>
> What are the qualities of G200 that make it the same as,/or
> different from
> the other spars commonly used ?
Dear Kathy;
G200 is a (largely) Potassium spar with a Silica mole content of 6.
This makes it melt slightly lower than Custer which has a mole content
of 7. My advice to you is to begin making fusion buttons of the spars
available to you to SEE what they do. If you don't have a small assay
cup available to you, just take a thimble and pack it full of the spar
and carefully turn it over onto a piece of bisque. Now you will have a
delicate thimble-shaped pile of spar which you may carefully place in
the kiln and fire to your normal temps. Once you have done this for the
spars available to you, you will have a visual record of how they
behave in your firings. Until Moose Creek Feldspar is available, G200
is your best choice, IMHO.
Cheers, Hank
www.murrow.biz/hank
claystevslat on wed 10 jan 07
glazes
Kathy --
Simple, but useless answer -- every glaze is best for something,
and not so good for something else. (Well, I said it was useless.)
The characteristics of the various feldspars and related materials
relates to the concentration of the different elements in them,
the condition in which it is sold to you (fineness and particle
size, etc.) and the consistency of the material.
G0200 is
Silica -- 66.3
Alumina 18.5
Na2O -- 3.0
K2O 10.75
CaO 0.81
plus a tiny bit of iron and magnesium.
Kingman is given as
Silica -- 66.17
Alumina 18.72
Na2O -- 2.8
K2O -- 12.01
CaO -- .1
Plus a tiny bit of iron.
It was my understanding that Kingman was no longer available;
but whether it is or not a quick check shows that the two materials
are extremely close.
The other commonly used feldspars and similar materials that I know
about are (in no particular order, and not pretending to be
comprehensive)
Soda spars, like Kona F-4 (much more sodium)
Cornwall stone (more silica, less alumina, slightly more sodium)
Nepheline Syenite (more sodium, more alumina, less silica)
A-3 (is this stuff still around? It had more silica)
Alberta Slip (less silica and alumina, more calcium and iron)
Custer Feldspar (more silica)
I have used G-200 and for most purposes find it serves admirably as
a one-for-one sub for recipes calling for Kingman. It also often
serves one-for-one for Custer most of the time (sometimes it drops
the silica down a little low). It does not sub well for a soda spar
or Nepheline Syenite.
Soooo ... being a very consistent material, G200 is a 'good'
spar for recipes that are formulated for it, or similar materials.
Best wishes -- Steve Slatin
--- In clayart@yahoogroups.com, Kathy McDonald wrote:
>
> I noticed a comment made by Ron Roy related to using G200
> as a spar instead of Kingman spar. I deleted the post
> before
> I could cut and paste the quote.
>
>
> I believe he said that using the G200 as a replacement for
> the
> Kingman would not alter the glaze significantly.
>
> What are the qualities of G200 that make it the same as,/or
> different from
> the other spars commonly used ? I've been doing some reading
> but it all gets
> very confusing so I thought I would ask here to see if
> anyone had
> a straightforward way of explaining what the differences
> might be and whether
> one spar is better to use in some glazes than others.
Ron Roy on thu 11 jan 07
glazes
Hi Kathy,
Sorry - I should have done it with Custer as well before I made that
comment - same comment for Custer.
All are potash spars - and in this case the amount of spar in the recipe
was only about 20% so as long as you use a spar that has a similar analysis
you would not notice a difference in most cases. If you were running a
glaze calc program with respectable analysis plugged in - you could make
some minor adjustments if necessary.
Let me say again - this particular glaze - with all that soda ash is not my
idea of a stable glaze - it will not wear well.
Let me know if you have any questions - RR.
>I noticed a comment made by Ron Roy related to using G200
>as a spar instead of Kingman spar. I deleted the post
>before
>I could cut and paste the quote.
>
>
>I believe he said that using the G200 as a replacement for
>the
>Kingman would not alter the glaze significantly.
>
>What are the qualities of G200 that make it the same as,/or
>different from
>the other spars commonly used ? I've been doing some reading
>but it all gets
>very confusing so I thought I would ask here to see if
>anyone had
>a straightforward way of explaining what the differences
>might be and whether
>one spar is better to use in some glazes than others.
>
>I use G200 in a glaze called Robin Hopper's white and I
>really like the way it
>behaves in that glaze...cone 6. This same glaze also fires
>to cone 10 without
>any problem.
>
>G200 is a bit more expensive so I was wondering what if
>anything can justify
>the added expense of using it . I usually mix 20,000 g
>batches of glaze at a time
>but would be quite happy to pay the added cost for the
>better outcome in firing.
>
>
>Kathy
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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