jim or karen on fri 13 aug 04
I was looking for a recipe for Matt Turquoise and found one in the =
archives from 1996. The proportions seem odd to me (I thought it should =
add up to 100) and I was wondering if someone out there could help me =
out. I tried sending an email to the person who submitted this glaze =
recipe but it came back as "undeliverable." The recipe is as follows:
Strontium 120
Neph sye 280
EPK 18
Flint 32
Lithium Carb 8
Copper carb 20
Bentonite 8
Thanks from Salt Spring Island, BC
Karen Nakakihara
Edouard Bastarache Inc. on sat 14 aug 04
Here goes,
Strontium carbonate 120.00 25.1%
Nepheline syenite 280.00 58.6%
EPK 18.00 3.8%
Flint 32.00 6.7%
Lithium carbonate 8.00 1.7%
Copper carbonate 20.00 4.2%
-------- ------
478.00 100.0%
Later,
"Ils sont fous ces quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
John Hesselberth on sat 14 aug 04
On Friday, August 13, 2004, at 07:04 PM, jim or karen wrote:
> I was looking for a recipe for Matt Turquoise and found one in the
> archives from 1996. The proportions seem odd to me (I thought it
> should add up to 100) and I was wondering if someone out there could
> help me out. I tried sending an email to the person who submitted
> this glaze recipe but it came back as "undeliverable." The recipe is
> as follows:
>
> Strontium 120
> Neph sye 280
> EPK 18
> Flint 32
> Lithium Carb 8
> Copper carb 20
> Bentonite 8
>
Hi Karen,
This is an alkaline glaze with lots of strontium thrown in to boot. It
probably will give a turquoise color. Its Si/Al ratio is low enough for
it to be a matte glaze; however, its silica level is too low and its
copper level too high for it to be a durable glaze. If you are using it
for purely decorative work it is probably OK. I would not put it on
functional work without testing it very thoroughly. I would guess you
can draw the color right out of it with a slice of lemon or after a
couple days in vinegar. It also has an extremely high calculated
coefficient of expansion. While these calculations are not very
accurate for matte glazes, don't be surprised if it crazes.
Making a matte turquoise glaze that is durable and fits most clay
bodies is a real challenge. There may be a tiny window where it can be
done, but it will be very small--at least using copper as the colorant.
You would have a better chance using a turquoise stain or, perhaps, a
combination of cobalt and chrome with a base glaze of more normal
composition.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ivor and Olive Lewis on sun 15 aug 04
Dear John,
You say <slice of lemon or after a couple days in vinegar. >>
I have no doubt your supposition would be confirmed with a test. What
I would like to know from people who do this test would be, is there
any effervescence, any bubbling
from glazes which incorporate Strontium carbonate.
I think a test with 10% Sulphuric acid could tell us if there is any
unconverted Strontium Carbonate remaining in a matt glaze whose recipe
included that ingredient.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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