Earl Brunner on mon 17 jul 00
I wouldn't go much over 20% but it shouldn't affect the
firing range of lower temperature clays. Its very
refractory. I have a pot from Nepal, that my son's in-laws
sent me that has a lot of mica in the clay. Its full of
little sparkly specks.
Shelley Corwin wrote:
>
> I'm going to mix in some powdered commercial mica from Laguna with native and
> low fire clays. Anyone out there have a clue as to proportion and/or fluxing
> temperature? i figure about 30-50% by volume, and haven't a clue about the
> cone. Same question for chunky vermiculite. Thanks. shelley
>
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Earl Brunner
http://coyote.accessnv.com/bruec
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Shelley Corwin on mon 17 jul 00
I'm going to mix in some powdered commercial mica from Laguna with native and
low fire clays. Anyone out there have a clue as to proportion and/or fluxing
temperature? i figure about 30-50% by volume, and haven't a clue about the
cone. Same question for chunky vermiculite. Thanks. shelley
iandol on tue 18 jul 00
Shelley,
Look in recent archives. We had a thread runnung on mica.
I believe I said it started to decompose about 1000deg Celsius forming a =
liquid and Mullite. It will depend upon the mineral from which your =
sample is made. Ask your supplier about this.
As for proportions, the best thing to do is run some line blend tests =
over the range 5% to 50%. If you have a good potash mica you will not =
need a lot. Remember, a clay body is not expected to fuse like a glaze, =
just sinter and vitrify.
Good luck with your trials,
Ivor Lewis
Michael Banks on tue 18 jul 00
Depends on the chemistry of the mica Shelley and where Laguna got it from.
White mica (muscovite, sericite) usually fuses between Orton cone 6 to 10,
but this is highly dependant on it's potash, lithium and fluorine content.
This mica usually has about 10% potash, 0.6% fluorine and less than 0.55
lithia, but the latter two fluxes can vary greatly. Higher fluorine in
particular (can rise to several % in some), causes a dramatic drop in
melting point. On the other hand, mica derived from a sedimentary deposit
(such as some commercial sericites) can be deficient in the normal alkalis
(caused by partial weathering to hydromica, illite) and be quite refractory.
The most flux-rich mica, lepidolite (lithium mica) containing ~6% lithia,
~7% fluorine and 9% potash melts as low as 800oC, but even muscovite can
contain up to 3.5% lithia and a lot of fluorine, which makes melting point
prediction hard. Just stick some on a tile and test fire it. Laguna may be
able to provide an analysis for their product and will give you some idea of
the amounts of fluxes present.
Michael Banks,
Nelson,
NZ
----- Original Message -----
Shelley Corwin wrote (clip):
> I'm going to mix in some powdered commercial mica from Laguna with native
and
> low fire clays. Anyone out there have a clue as to proportion and/or
fluxing
> temperature? i figure about 30-50% by volume, and haven't a clue about
the
> cone. Same question for chunky vermiculite. Thanks. shelley
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