Stuart Altmann on sat 4 may 96
Several days ago, a message on Clayart about Cornwall stone indicated that
there are four varieties of it: purple stone, hard white, df
(defluorinated), and cornish stone H&G. Well, not quite. Hammill &
Gillespie is the primary importer of Cornwall stone into the USA. A call to
their office in Livingston NY yielded the following information. First,
Cornwall stone is no longer being deflourinated. The last of this df
version was produced in 1973-74, and by about 1975 the stock was gone. The
material that is not deflourinated is distinguished by a vegetable dye that
burns off in the kiln without a trace; the color is not due to flourspar.
The color is various shades of blue, perhaps indicating different batches
from the mine. I didn't ask about "hard white" Cornwall. As for Cornish
stone H&G, that's just a catalogue entry for the stuff that Hamil &
Gillespie distribute in the U.S.A.--which is virtually all of it here.
Several people have suspected Cornwall stone as being responsible for
pitting of their glazes. That seems unlikely, since the loss on ignition
(read, outgassing) in a typical analysis of Cornwall stone (sent to me by
H&G) is 1.5%, i.e., one of the lowest L.O.I. values among common glaze
ingredients.
Ron Roy on sat 4 may 96
Cornwall Stone - my information is from the book "Out of the Earth Into the
Fire" published by American Ceramic Society - 1996. Not to say all the
information in the book is undisputable but I was impressed on how up to
date most of the information was.
There are other factors we must consider here. The person who complained of
the pin holes said it was a new supply purchased from Baily's and it did
have a blue colour. I guess the next question is where did Baily's supply
come from.
I suppose the other point which may be a factor is what grade was the old
Cornwall Stone that worked well and how does the new supply differ. Could
the new supply have less flux than the old?
The other point raised is the LOI being low in Cornwall stone. If the LOI
of common feldspars is compared to Cornwall Stone we find 1.5 high. I do
not believe that is a factor because it is gone by the end of the firing.
More significant is the fact that P2O5 and F are listed in the analysis
separate from LOI.
Perhaps someone would care to get the current analysis from H&G and Baily's
so we can see what we are dealing with - that is if we are using current
supplies.
Ron Roy, Toronto, Canada
Kollin Baker on sat 14 mar 98
Is there a substitute for Cornwall Stone?My local supplier in Austin Tx
doesnt have a substitute. If any one knows please let me know.
Pi Pottery and Design
512.323.8274
Andrew Lubow on mon 16 mar 98
Equivalent Chemicals
Alkaline leadless frit = Ferro 3110 = Frit 386 (Standard Ceramic Supply)
= Pemco P-991=Potterycrafts Ltd P2962
Ball Clay = Kentucky Ball Clay= OM#4
Standard Borax Frit = Ferro 3134 = Frit 550 (Standard Ceramic Supply)
= Pemco P-926= Hommel 14=Potterycrafts Ltd P2957
Calcium Borate Frit = Colmanite = Gerstley Borate
=Potterycrafts Ltd P2954
Calcium Carbonate = Whiting
China Clay = EPK = Florida = Georgia China Clay
Cornish Stone = Cornwall Stone = Carolina Stone = Kona A-3 = Pyrophylite
Fremington Clay=Albany Slip
Kona A-3 = equal mix of F4 Kona and Custer
Potash Feldspar = Bell =Buckingham G-200 = Kingman = K-200 = Custer
= Clinchfield # 202
Soda Feldspar = Spruce Pine 4 = Kona F- 4
Lead Bisilicate = Ferro 3498 = Hommel 14 = Frit 28 ( Standard Ceramic
Supply )
=Pemco Pb -700
Zirconium Silicate = Opax = Superpax = Zircopax
Converting Parts to %
(ingredient / total of ingredients) X 100 = %
Substitutions
100 of Barium Carbonate = 75 of Strontium Carbonate
-----Original Message-----
From: Kollin Baker
To: Multiple recipients of list CLAYART
Date: Sunday, March 15, 1998 6:17 AM
Subject: Cornwall Stone
----------------------------Original message----------------------------
Is there a substitute for Cornwall Stone?My local supplier in Austin Tx
doesnt have a substitute. If any one knows please let me know.
Pi Pottery and Design
512.323.8274
Louis on fri 20 mar 98
Kollin,
I don't know what is available in your area, but Godfrey spar and
Carolina Stone are recomended by James Chappell. Also recommended was :
Feldspar 67
Silica 22
kaolin 11
The formula for Cornwall Stone is:
SiO2 71.1
Al2O3 16.82
Fe2O3 0.16
CaO 1.6
MgO 0.05
K2O 6.57
Na2O 2.29
CaF2 0.5
Refrence Page 225 Advanced Ceramic Manual by John W. Conrad
Good luck Louis
Kollin Baker wrote:
> ----------------------------Original
> message----------------------------
> Is there a substitute for Cornwall Stone?My local supplier in Austin
> Tx
> doesnt have a substitute. If any one knows please let me know.
>
> Pi Pottery and Design
> 512.323.8274
Gary Navarre on tue 19 oct 04
From: "Bonnie Staffel"
Date: Tue, October 19, 2004 9:59 am
Dear Gary,
Did we have some communication about a Cornwall Stone recipe of mine? My
memory recalls that there were two interested. I found the one in an
email, but then remembered that you acquired a batch of the old Cornwall
on your trip south. If it was you, I did find the recipe if you are
interested in it.
Regards,
Bonnie
Bonnie,
Ya, I think I wrote something like that. I don't think I'll need to
order any more materials for now though. If my "business plan"
materializes, as it seems to be doing, I would like to go back downstate
somewhere round Thanksgiving to get some other materials from the stash.
By then I hope to have a couple hundred wreaths made and take some down
to sell in Kalamazoo, unless I find somewhere here to wholesale.
Who'da thunk it, adding Christmas wreaths to my product line. I got my
wreath machine table built last week and made about a dozen practice
wreaths. Some have a few pine cones I collected. They are kinda neat to
make. I plan to just use natural stuff, no "Cheesy flock, glitter, or
fake ice" or all the other plastic schlock. The cool thing is I can take
the scrap and burn it in my Koie Ash Cooker and make a good quantity of
Balsam stem ash for glaze. Any sticks will be saved for one of the
secondary stoke holes in the kiln. Might as well do the grunt work now
while I can.
You know what I'm thinkin, if my plan comes together I could bring you
enough Cornwall Stone so you could make a batch of one of your old
favorites. Would a 5 lb. coffee can do? I don't have a scale anymore, my
stepsons cousins stole it just before I closed the last studio. It
depends on how much you need to make a decent batch. Let me know.
G. in Da U.P.
Bonnie Staffel on thu 21 oct 04
Gary, you would make my dreams come true, to make at least one more batch of
the old CS and get that beautiful waxy matte white glaze again. I would be
happy to give you my stash of the "green stuff," ugh!!! Sounds like a good
project for this winter. On top of that I would also get to meet you as
well. Better get my floor files cleaned up!!
Warm regards,
Bonnie Staffel of Charlevoix, MI.
http://webpages.charter.net/bstaffel
http://www.vasefinder.com/
Potters Council member
Lou Roess on fri 22 oct 04
> get that beautiful waxy matte white glaze again.
Bonnie, I have checked the archives and don't find much in the way of
recipes for Cornwall Stone. Our studio has some that no one seems to
use and I'd like to try it . Would you (or anyone else who has some)
consider posting your recipes with Cornwall as an ingredient?
TIA
Lou in Colorado
John Britt on fri 22 oct 04
Here is a nice glaze:
HAYSTACK ORANGE-- cone 10 Ox or Reduction
Custer Feldspar 42.31
Cornish Stone 18.84
Whiting 18.84
EPK Kaolin 6.66
OM-#4 9.95
Zinc Oxide 3.38
Rutile 4.44
Red Iron Oxide 6.67
Of course there are many otherslike:
MOTTLED PURPLE
cone 10 reduction
Cornish Stone 40.23
F-4 Feldspar 3.75
Whiting 6.54
Silica 17.80
Neph. Sye. 2.02
Magnesium Carb 3.17
Gerstley Borate 2.59
Zinc Oxide 3.75
Barium Carbonate 1.25
Wood Ash 18.86
Black Copper Oxide 1.90
Tin Oxide 3.20
I also have a several nice celadons with cornwall stone,
Enjoy,
John Britt
www.johnbrittpottery.com
ASHPOTS@AOL.COM on sat 23 oct 04
In the Cushing Handbook there are a bunch of Cornwall Stone recipes.. Ive
tested a few and i want to use a few of them , i always remember that after the
kiln is loaded and firing..
I spent $24 for his book.. All of us should have this book, its a good read
I dont have his address or email , but maybe someone from NY will jump in
with info.. My friend David F is there in Alfred , maybe he will see this note....
spend $24 and have all kinds of good info and recipes
Mark on my way to Hotlanta to visit Mudfire and eat Pho
lela martens on sat 23 oct 04
Hi Lou,
Here is one recipe. I have only done a small test tile with it so far, and
that came out very nice. I will be testing further in my next firing. I also
don`t know about it`s stability, or even where it came from, an old recipe
hanging around our guild room.
Note the lithium.
Tenmoku Gold cone 5 - 6
cornwall stone----------61.0
whiting-------------------8.0
gerstley borate--------3.0
lithium carb-------------5.5
dolomite-----------------7.0
flint------------------------5.5
add red iron oxide----10.0
Lela
Ron Roy on mon 25 oct 04
Note the amount of Lithium Carb - this can lead to shivering problems on
some clays - and crazing and shivering on other clay bodies.
RR
>Hi Lou,
>
>Here is one recipe. I have only done a small test tile with it so far, and
>that came out very nice. I will be testing further in my next firing. I also
>don`t know about it`s stability, or even where it came from, an old recipe
>hanging around our guild room.
>Note the lithium.
>
>Tenmoku Gold cone 5 - 6
>
>cornwall stone----------61.0
>whiting-------------------8.0
>gerstley borate--------3.0
>lithium carb-------------5.5
>dolomite-----------------7.0
>flint------------------------5.5
>add red iron oxide----10.0
>
>Lela
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Bonnie Staffel on tue 26 oct 04
Dear Andrew,
I am a little confused here. I know that CS is produced but it is dyed
green to differentiate it from the original. The new stuff just doesn't do
the same thing, the melting isn't as good. It has been a while since I
tried the green stuff and I have about 75 pounds of it just sitting here. I
was told that the original mine was shut down for some reason quite a few
years ago. Will you please clarify this for me?
Thanks,
Bonnie Staffel
http://webpages.charter.net/bstaffel
http://www.vasefinder.com/
Potters Council member
mailtoandrew@FSMAIL.NET on wed 27 oct 04
Hello Bonnie,
Firstly I must admit to some interest with CS due to having worked with it
for years and being puzzled by the myths that have been associated with it.
Whilst I obviously can not pass comment on the material you have a little
background information may be of interest:
CS is found in same area of county of Cornwall in the UK as the famous
china clays.
Probably for historic reasons the material is known by several names:
Cornish stone, Cornwall stone, China stone, Stone, and in very old
references Moorstone or Growan. It is not however, as it is sometimes
classed, petunse.
Traditionally CS was produced in a number of grades depending on
mineralogical content. Names of these included Hard purple, Mild purple
and Hard White. Since at least the mid 1970s a single company have
operated a single pit. For some years after only two grades were sold;
both were similar blends of Soft white and Hard purple. The difference
between the two was one was treated to remove a small amount of a fluorine
bearing mineral whilst the other was not. Sometime during the mid 1990s
the treated grade, called DF stone, was withdrawn. The other grade
continues to be produced.
As you note the unfired colour is not white due to the presence of a very
small amount of stain, added during processing to differentiate from other
materials, without which it would be white. The colour in no way reflects
the mineral content. The dye does not effect properties and fires out.
Other misnomers with CS include what it actually is: its a feldspar. And
that its inconsistent: test data shows otherwise.
Rather than boring other ClayArters I hope you will not mind if I email
you further information.
Kind regards,
Andrew
Ron Roy on wed 27 oct 04
Hi Bonnie,
Not hard to adjust the melting to make it melt more.
RR
>Dear Andrew,
>
>I am a little confused here. I know that CS is produced but it is dyed
>green to differentiate it from the original. The new stuff just doesn't do
>the same thing, the melting isn't as good. It has been a while since I
>tried the green stuff and I have about 75 pounds of it just sitting here. I
>was told that the original mine was shut down for some reason quite a few
>years ago. Will you please clarify this for me?
>
>Thanks,
>
>Bonnie Staffel
>http://webpages.charter.net/bstaffel
>http://www.vasefinder.com/
>Potters Council member
>
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>
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>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
dianamp@COMCAST.NET on thu 30 dec 10
Hi Clayart:
I inherited buckets of a material (at the U.) labelled DF Stone.
Presume it is a substitute for Cornwall Stone but never used it.
Anyone have experience with DF Stone. Is it a good sub??
Thanks,
Diana Pancioli
EMU
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