Judy Musicant on sat 30 jan 99
Here is another black cone 6 glaze:
Shiny Black
Neph Sy ------------------------40
Flint (Silica)----------------------15
Ball Clay--------------------------10
Cryolite----------------------------10
Dolomite--------------------------10
Ger. Borate-----------------------10
Copper Carb.----------------------5
Barnard Clay---------------------20
This is a studio regular in my area. Very stable, doesn't run, looks GREAT
over Randy's Red. Brownish where too thin, but doesn't need to be too
thick, either.
I would certainly welcome a review on the durability of this glaze.
By the way, in the Randy's Red formula that I posted a while back, and that
Vheena recently reposted, the Red Iron Oxide is listed as "Special" because
that's the way it's described in the Ceramic Supply of NY and NJ catalogue
where I get it. It's distinguished in their catalogue from Spanish RIO.
They don't have just plain old RIO. Probably the same thing?
Judy Musicant
Ron Roy on mon 1 feb 99
Hi Judy,
My calculations indicate plenty of alumina with boron included with the
fluxes and even enough SiO2 but - the KNaO is oversupplied and most of that
is Na2O.
It's gonna craze on most cone 6 bodies I think - which gives any acid a
larger surface area to work on.
Combine that with all that copper carb and you probably have a similar
senario to that other black cone 6 glaze that John Hesselberth is going to
comment on soon.
Both copper and sodium are well know for their ability to make glazes
leach. It's the cryolite that adds so much sodium and alumina.
It's not the kind of liner glaze I would recommend and I certainy would not
store food in it.
There is a fair bit of Manganese in Barnard clay (Blackbird) - the analysis
I have says 3.3% and while I don't think that is much of a problem if
ingested - the dust and fumes indicate yet another case for proper house
keeping and good ventilation while firing.
FORMULA & ANALYSIS
------------------
*CaO........ .27 5.45%
MnO2....... .03 .82%
*MgO........ .18 2.61%
*K2O........ .08 2.77%
*Na2O....... .35 7.76%
Fe2O3...... .08 4.34%
TIO2....... .01 .30%
*B2O3....... .11 2.84%
AL2O3...... .44 15.91%
SiO2....... 2.66 57.17%
RATIO 6.11
EXPAN 617.15
WEIGHT 279.62
When I look at it with the Boron out of unity it looks even worse - much
oversupply of KNaO and oversupplied with alumina.
RR
>----------------------------Original message----------------------------
>Here is another black cone 6 glaze:
>
>Shiny Black
>
>Neph Sy ------------------------40
>Flint (Silica)----------------------15
>Ball Clay--------------------------10
>Cryolite----------------------------10
>Dolomite--------------------------10
>Ger. Borate-----------------------10
>Copper Carb.----------------------5
>
>Barnard Clay---------------------20
>
>This is a studio regular in my area. Very stable, doesn't run, looks GREAT
>over Randy's Red. Brownish where too thin, but doesn't need to be too
>thick, either.
>I would certainly welcome a review on the durability of this glaze.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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