Michael Wendt on wed 11 jun 08
Paul,
I got a quote a few years ago from their plant at High
Hill MO
so if that is the source, it is calcined
quite hot to eliminate any further fired shrinkage.
I reckon they call it flint clay because it is not a
high
alumina clay like the fire clays or kaolins but a
rather sandy clay. Ask for a chemical analysis
of the fired grog if you do order.
As to my own experience with sand, I used Lane
Mountain 125 mesh foundry sand for years and
it worked fine except larger pieces were touchy
through red heat so I moved away from that body
to the Alfred Porcelain Recipe.
The old body recipe was:
Body Formula for cone 10 white stoneware we call 38
special
Helmer 30 mesh 100
Custer Feldspar 75
Nepheline Syenite 25
125 mesh sand 35
200 mesh silica 25
see:
http://www.wendtpottery.com/helmer.htm
for more data
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
Paul Borian on wed 11 jun 08
Thanks to the replies I got about using sand I decided to hold off on it
for now so I am still looking for a better grog than mullite. It serves
the purpose but creates a lot of extra work because it always leaves
sharps on some pots no matter how hard I try to prevent it.
So now I am looking at a product called "Christy fine flint clay" grog
(as called by Columbus clay) and "Missouri 35F" (as called by Laguna)
and I think they are the same thing. I called both of those suppliers as
well as Christy Minerals and no one could tell me 100% that they were
the same but everyone seemed to think so. Actually, everyone I spoke
with today was a bit confused at times on the subject of grog (I
actually called 4 suppliers), and in some cases I called the same
supplier twice and spoke to different people each time and got
conflicting views on this subject. In some cases I was the one clearing
up confusion, like by explaining that flint clay grog and mullite are
not the same thing - and I did this more than once today.
=20
Anyway, I have it narrowed down to "flint clay grog" even though I still
don't know (and could not get anyone to explain to me) what it actually
is other than "clay" (even though one supplier told me it was calcined
silica but the company than produces it told me it was "clay" from
Missouri (but they could not tell me why it is called flint clay).
=20
So does anyone know if the stuff Laguna sells as Missouri 35F is Christy
fine flint clay? If I could confirm this it would help me compare prices
and find the best deal. Either way it looks like I am going to have to
do some driving to get it so I want to shop around.
=20
Thanks,
Paul
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