Autumn Downey on wed 9 jul 97
We are due to make a chemical order and I'm wondering:
At our Guild we currently stock a bin of Georgia kaolin and smaller
quantities of EPK. We've been using the Georgia in recipes that call for
"kaolin" (no adjectives). It it necessary to keep both kinds?
I gather that EPK is better quality even though a little more expensive. If
we switched entirely to EPK, are the differences likely to cause problems in
the glazes (Cone 6 electric) where we have been using the Georgia kaolin?
Thanks.
Autumn Downey
Tony Hansen on thu 10 jul 97
>At our Guild we currently stock a bin of Georgia kaolin and smaller
>quantities of EPK. It it necessary to keep both kinds?
I would use EPK.
It is cleaner and helps to gel the glaze to give better application
qualities (less running, more even coverage). The chemistry of the
two is so similar that there should be little impact of the fired
properties of glazes.
--
T o n y H a n s e n, I M C thansen@digitalfire.com
=========================================================
INSIGHT5/Magic of Fire II demos at http://digitalfire.com
Ric Swenson on thu 10 jul 97
>----------------------------Original message----------------------------
>We are due to make a chemical order and I'm wondering:
>
>At our Guild we currently stock a bin of Georgia kaolin and smaller
>quantities of EPK. We've been using the Georgia in recipes that call for
>"kaolin" (no adjectives). It it necessary to keep both kinds?
>
>I gather that EPK is better quality even though a little more expensive. If
>we switched entirely to EPK, are the differences likely to cause problems in
>the glazes (Cone 6 electric) where we have been using the Georgia kaolin?
>
>Thanks.
>
>Autumn Downey
------------------reply---------
Autumn,
Edgar's Plastic Kaolin (EPK) is a product of Feldspar Corporation, (a
Zemex Industrial Minerals Company (707) 392-8660 or we site :
http:''www.ceramics.com/feldspar/
" Georgia Kaolin" Company is now called Drybranch Kaolin Co., (912)
750-3500 fax 912 746-0217 . They have many types of kaolin products and
blends. ( Pioneer Kaolin is my favorite DBK product for use in clay bodies.)
Nothing beats EPK in glazes.
Hope this helps.
Happy Potting!
Ric
Ric Swenson, Bennington College, Route 67 -A, Bennington, Vermont 05201-6001
802 442-5401 x 262 vox x 237 fax or dedicated fax 802 442-6164
email: rswenson@bennington.edu
Ron Roy on mon 14 jul 97
Hi Autumn,
I think EPK is better - especially at cone 6. EPK is a more plastic (Edgar
Plastic Kaolin) and will help keep your glazes floated better. The surface
will also be less powdery with EPK.
I have looked at both kaolins the molecular way and find very little
difference so I don't expect any changes in your glazes.
An even better strategy is to use a ball clay if the increased iron is not
a problem. That way you can get more clay in the bucket (ball clays have
less alumina so you need more of it to get the same Al203 in your glaze) -
you should do the substitution using calculation however. The other benefit
of using ball clay in glazes - bentonite works better as a suspender with
ball clay.
>At our Guild we currently stock a bin of Georgia kaolin and smaller
>quantities of EPK. We've been using the Georgia in recipes that call for
>"kaolin" (no adjectives). It necessary to keep both kinds?
>
>I gather that EPK is better quality even though a little more expensive. If
>we switched entirely to EPK, are the differences likely to cause problems in
>the glazes (Cone 6 electric) where we have been using the Georgia kaolin?
>
>Thanks.
>
>Autumn Downey
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/ronroy.htm
June Perry on tue 15 jul 97
Dear Ron:
It is my understanding that epk is really not that plastic in relation to
other kaolins. I knows it says Edgar Plastic Kaolin; but I have heard tell
that that is a misnomer. Maybe someone else can give some input here.
Vivika Heino once told me that epk can give a cooler look to glazes than some
other kaolins. I haven't tested that one - just putting it out there in case
someone else has.
I use grolleg a lot when I am looking for bright colors. It is more expensive
but I notice that it does brighten up some glazes.
Warm regards,
June
Jeremy/Bonnie Hellman on thu 17 jul 97
June, I also use grolleg porcelain (^6) and find it is a whiter white
(really a cooler (bluer) white) compared to non grolleg ^6 porcelain
which fires to a warmer (more yellow) white. I also like the way it feels
when I work with it, and it is a pleasure to carve. Needless to say,
having no colorants in the clay (no iron, manganese, etc) glazes don't
have those ingredients interacting.
Actually, more expensive is relative. I pay only pennies a pound more,
and when you think that your ingredients in a pot are considerably
cheaper than the value of your time, we are really discussing what
economists call "decimal dust" in the total cost process.
Bonnie Hellman in Pittsburgh, PA
>Dear Ron:
>
>It is my understanding that epk is really not that plastic in relation to
>other kaolins. I knows it says Edgar Plastic Kaolin; but I have heard tell
>that that is a misnomer. Maybe someone else can give some input here.
>Vivika Heino once told me that epk can give a cooler look to glazes than some
>other kaolins. I haven't tested that one - just putting it out there in case
>someone else has.
>I use grolleg a lot when I am looking for bright colors. It is more expensive
>but I notice that it does brighten up some glazes.
>
>Warm regards,
>June
From University of California Professor Robert Silensky:
"We've all heard that a million monkeys banging on a million typewriters
will
eventually reproduce the entire works of Shakespeare. Now, thanks to the
Internet, we know this is not true."
June Perry on fri 18 jul 97
Dear Bonnie:
I agree about the expense. When you break it down you're only dealing in
pennies per pot and to me it's worth some extra expense to have the
workability and color response that I want.
Warm regards,
June
Ron Roy on fri 18 jul 97
I have done a little research - using the lab reports generated by Tuckers
- All clays are tested for shrinkage and absorbency. There are only three
Kaolins tested so this is less than definitive.
Plastic to dry shrinkage - averaged over several batches.
EPK - 7.1
Tile 6 - 6.5 (more variable than EPK)
Pioneer - 4.1
As you can see EPK is a better suspender if we can count particle size as a
factor. I am quite sure Grolleg will work well because it is a plastic
kaolin as is English Standard. The reason Grolleg is whiter may be the
reduced amount of titanium present - tile 6 has lots more and EPK somewhat
more.
>>It is my understanding that epk is really not that plastic in relation to
>>other kaolins. I knows it says Edgar Plastic Kaolin; but I have heard tell
>>that that is a misnomer. Maybe someone else can give some input here.
>>Vivika Heino once told me that epk can give a cooler look to glazes than some
>>other kaolins. I haven't tested that one - just putting it out there in case
>>someone else has.
>>I use grolleg a lot when I am looking for bright colors. It is more expensive
>>but I notice that it does brighten up some glazes.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
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