Carolyn Sleeper on tue 30 oct 01
I found a cone 10 recipe for a glaze that contains 60% granite. Is there
an equivalent, or what has anyone used in granite's place? What exactly is
granite in a glaze?
Dannon Rhudy on tue 30 oct 01
At 12:44 PM 10/30/01 -0500, you wrote:
>I found a cone 10 recipe for a glaze that contains 60% granite. Is there
>an equivalent, or what has anyone used in granite's place? What exactly is
>granite in a glaze?
It's powdered granite. I expect you can buy it, but
I get mine from the local headstone-makers. They've a
big pile of it out back, which they are glad to give
away. It has some other stone in it, small amounts of
marble for instance. I don't know the breakdown, but
it works well in glazes calling for granite. In my case,
these are mostly ash glazes.
regards
Dannon Rhudy
Russ Fish on tue 30 oct 01
An over-simplified answer is that it is a high alkali (usually over 12 %
combined sodium and potassium) flux material. It is still sold commercially
out of Georgia and Arkansas. I don't see it sold much in the US in
non-commercial applications. The refined and beneficiated granite that is.
Most all the granite in the US (ceramic grade) is now utilized to produce
roofing granulates. I have had good success substituting Nepheline Syenite,
but using the A-400 grind (not using the more common A-270). The higher
surface area helps compensate for the deficient amount of potassium in the
Nepheline Syenite versus the granite. You might still need to adjust the
alumina/silica ratio slightly to maintain the glaze compression.
Good luck,
Russ
----- Original Message -----
From: "Carolyn Sleeper"
To:
Sent: Tuesday, October 30, 2001 11:44 AM
Subject: Granite in glaze?
> I found a cone 10 recipe for a glaze that contains 60% granite. Is there
> an equivalent, or what has anyone used in granite's place? What exactly is
> granite in a glaze?
>
>
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> Send postings to clayart@lsv.ceramics.org
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>
Martin Howard on wed 31 oct 01
Carolyn
That granite may well be mostly limestone and marble (again mostly
limestone) CaCO3.
But with it may also be lots of real granite material such as feldspars,
syenites and almost anything else.
Visit the yard of a Monumental Mason and you find him or her calling
virtually every stone, granite. The slop of washed out fine cuttings from
the cutting tables there make wonderful glaze material for a clear glaze at
cone 2 for me, but probably goes much higher. My local yard uses 6 different
"granites" from around the world.
Yours probably uses the same.
Get a good lot at one go. It's all waste to them. Have it analysed at CERAM
or your equivalent, Alfred. Just looks like white powder, so taking it there
is better than posting at this time.
There must be so many excellent RMs that are just waste and space hogs to
others which we potters could use.
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
This web-site is being updated NOW!
Martin Howard on wed 31 oct 01
A real problem here is language!
The term granite is used loosely for many rocks that are nowhere near the
geologist definition. That is wide enough in itself.
So, whatever your source of "granite", get an analysis first and then start
to test it and use it. Fournier is helpful, but it is very much an average
in a wide spectrum.
My "granite" slop from the monumental mason's yard analyses as:-
SEGER % WT.
K2O 0.007 0.822
Na2O 0.006 0.465
CaO 0.942 65.872
MgO 0.041 2.048
ZnO 0.004 0.405
1.000 69.61
Al2O3 0.037 4.713
Fe2O3 0.023 4.595
0.060 9.31
SiO2 0.274 20.529
TiO2 0.004 0.400
ZrO2 0.001 0.154
0.279 21.08
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
This web-site is being updated NOW!
Ababi on wed 31 oct 01
I don't know how deep you want to dig in the rocks, There is an
interesting E-book at http://digitalfire.com .
Ababi
---------- Original Message ----------
>I found a cone 10 recipe for a glaze that contains 60% granite. Is
>there
>an equivalent, or what has anyone used in granite's place? What exactly
>is
>granite in a glaze?
>________________________________________________________________________
>______
>Send postings to clayart@lsv.ceramics.org
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
Wade Blocker on wed 31 oct 01
An analysis of typical granite shows some 70% of silica,14.5%of
alumina;various percentages from 4.5 potash to 0.05 baria. In decomposition
granite contains felspar, flint etc and at one remove clay. Robert
Fournier. Mia in ABQ
John Baymore on wed 31 oct 01
Is there an equivalent, or what has anyone used in granite's place? What
exactly is
granite in a glaze?
Carolyn,
Hi.
I use some local materials in glazes and clay bodies.
Here is the typical analysis for the granite that I use that comes from a=
quarry about 5 miles from my studio. As they say... your milage may vary=
. Each granite formation is different........ so take the below
information with a "grain of salt".
Mineralogical =
Quartz 36%
Feldspar 53%
Mica 9%
Typical Chemical Analysis =
SiO2 74%
Al2O3 13%
Na2O 2%
K2O 4%
CaO 2%
MgO 1%
Fe2O3 2%
LOI 2%
So in a sort of "flip" answer...... granite is sort of like "heavily
quartz-y potash feldspar" . So in a real "quick and dirty"
approach...... you could sub a blend of about 60% potash feldspar and 40=
%
flint for the granite content of the glaze you have ....and adjust from
there. Maybe add a "pinch" of red iron oxide. And pepper to taste .
Or for more accuracy, if you are comfy with molecular calculation.... mak=
e
it up from that approach. =
But if you don't know the analysis of the granite that the glaze's
originator used....... you are kinda' shooting in the dark anyway.
Hope this gives you a bit of a "picture" as to what granite is doing in a=
glaze (or clay). It's coming to you from "The Granite State" .
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop 2002 Dates TBA"=
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