Klyf Brown on wed 23 jan 02
Locally I have available Adobe clay and bentonite. The Adobe by
itself is too plastic. It is like throwing rubber bands. The addition of
grog or fine silica sand knocks down this effect and makes a nice
throwing body. Adobe on it's own cracks like crazy too, and grog
helps this problem as well.
Klyf Brown in NM
1/22/02 11:22:36 PM, iandol wrote:
>I imagine grog made from bisque is good for drying a sticky clay and
making it more tractable because it will adsorb excess water, but I
cannot imagine any form of grog increasing the plastic strength of a
clay body.
iandol on wed 23 jan 02
Has anyone ever found research results which indicate what really =
happens when grog is introduced into plastic clay.
I imagine grog made from bisque is good for drying a sticky clay and =
making it more tractable because it will adsorb excess water, but I =
cannot imagine any form of grog increasing the plastic strength of a =
clay body. This is simply because the strength of plastic clay comes =
form the interaction of clay and water and their intimate relationship.
Given that many clay bodies are formulated with close to 50% none =
plastic materials, further additions of unplastic grog could have a =
deleterious effect on working properties causing shortness, so be sure =
of your reasons for incorporating it into any commercial clay body.
Best regards, Ivor Lewis
Craig Clark on thu 24 jan 02
Ivor, as usual makes sense. In the first clay class that I was in we
used both a commercial clay body and made our own. I subsequently became
enamored with grog because of the "tooth" it gave the mix. Both to our
homemade version and when wedged into the commercial body. I liked the way
it felt, and, overtime decided that it's addition enabled me to pull taller
lighter pots. I can't say that there is any imperical evidence of this. It
probably had more to do with improved throwing skills and getting acustomed
to a particular clay body than anything else.
I do know that the commercial clays that I have wedged grog into have
become less plastic, not more. They just don't stretch as well and lose that
buttery feel. Though I've also decided that they will "stand up better" than
whay I indignantley used to refer to as "that candyassed buttery shit" that
came in a bag." I've since changed my tune.
Addition of grog does help with more even drying, is a good idiea in any
sculptural endeavor, and also helps with thermal shock resistence when using
stressful firing techniques such as raku.
In the specific case of a raku firing grog is not the only answer.
Laguna and BlackJack use other additives in place of grog to impart the
same, if not greater thermal shock handling capacity. I'm not sure but I
believe they use molcholite.
So, if to use or not to use....grog....is the question, just give it a
try for awhile and see if you like it and wether or not it is necessary for
your particular use of clay.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "iandol"
To:
Sent: Wednesday, January 23, 2002 12:22 AM
Subject: Re: What it grog
Has anyone ever found research results which indicate what really happens
when grog is introduced into plastic clay.
I imagine grog made from bisque is good for drying a sticky clay and making
it more tractable because it will adsorb excess water, but I cannot imagine
any form of grog increasing the plastic strength of a clay body. This is
simply because the strength of plastic clay comes form the interaction of
clay and water and their intimate relationship.
Given that many clay bodies are formulated with close to 50% none plastic
materials, further additions of unplastic grog could have a deleterious
effect on working properties causing shortness, so be sure of your reasons
for incorporating it into any commercial clay body.
Best regards, Ivor Lewis
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Snail Scott on thu 24 jan 02
At 08:57 AM 1/24/02 -0600, you wrote:
>Laguna and BlackJack use other additives in place of grog to impart the
>same, if not greater thermal shock handling capacity. I'm not sure but I
>believe they use molcholite.
I consider molochite to be just a fine-textured
species of grog, really. That's the role it plays,
as a calcined refractory material.
-Snail
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