daniel on tue 27 apr 04
Hi Joe,
Do you mean cornwall stone, also called I think china stone ? I know
precious little about to be honest, but found one thing of interest last
week when we were mixing a raku glaze with it. We found it had lumped a bit,
a thing it seems to do. I guess it draws in water. Anyhow, we were looking
for a substitute and found mention in Parmalee (Ceramic Glazes) of a thing
called Carolina stone. Can't find anything about Carolina stone but you
asked for quirky info, so I guess this qualifies. Oh, hang on, actually it
is listed on ceramicmaterials.info also. Listed as a pegmatite similiar to
cornwall stone. So not that quirky really, sorry :)
Tony Hansen's site (digitalfire) also has an article describing how to
manufacture a substitute material for a naturally ocurring one, using
cornwall stone as an example. URL
http://www.digitalfire.ab.ca/cermat/education/194.html
Wayne, on the blue colour thing, I was sniffing around the archives and
this seems to be consistent with what I found there. Colour can vary in this
range it seems. Can I find the reference now ? Oh no !! Oh well, it turns
out there's quite a bit in the archives on it.
> The last time i bought Cornwall Stone, I got two bags.
> One is the standard greyish white color one would
> normally associate with powdered rock.
> The other has a decided blue tinge to it.
> What's up with that??!
>
Thanx
D
Belmont, California, USA
(ex terra australis)
Joseph Coniglio on tue 27 apr 04
CORNWALL
----
Ya'll for some reason, this is request for info is getting dropped and
not making April Week 4 list. This is try #3 for the...
...lovely, innocuous, legendary; sold in 50 and 100lb bags of
CORNWALL...
I've heard some very interesting things about it. A great British Isles
terra Cotta, greyish, full of silica and minerals---great for plants...
...superb as a fine clay ingredient in some glaze ingredients.
Anyone want to expand of this or offer some interesting or quirky info
about it...like it's mined in only one place on the planet...etc???
Please post.
Joe at Garnet 'darnet!!
wayneinkeywest on tue 27 apr 04
The last time i bought Cornwall Stone, I got two bags.
One is the standard greyish white color one would
normally associate with powdered rock.
The other has a decided blue tinge to it.
What's up with that??!
I have half a mind (left) to go over to that place
where "the sun never sets", and complain
about their quality control.
Maybe the illustrious Ms Kaiser
(on whom the sun allegedly never sets) could shed
some light on the subject. At least she could offer me
a cuppa should I get that far, and not get run off by angry
kilt wearing locals bearing torches, flinging haggisses
(preferably cooked, but cooled) at me.
(Yes, I know I've mixed in attributes from three countries :>)
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Joseph Coniglio"
> CORNWALL
> ----
> Ya'll for some reason, this is request for info is getting dropped
and
> not making April Week 4 list. This is try #3 for the...
>
>
> ...lovely, innocuous, legendary; sold in 50 and 100lb bags of
> CORNWALL...
>
> I've heard some very interesting things about it. A great British
Isles
> terra Cotta, greyish, full of silica and minerals---great for
plants...
>
> ...superb as a fine clay ingredient in some glaze ingredients.
>
> Anyone want to expand of this or offer some interesting or quirky
info
> about it...like it's mined in only one place on the
planet...etc???
>
> Please post.
>
> Joe at Garnet 'darnet!!
Ron Roy on wed 28 apr 04
Take a look at Mimi Obstler's "Out of the Earth into the Fire" - she has a
section on Cornwall Stone - 3 different analysis for four different types.
An excellent book to have if you are interested in materials and how they
fundction in clays and glazes. Published by The America Ceramic Society.
Purple Stone
Hard White
D.F. Stone (deflourinated)
Cornish Stone.
Somebody explained this to me - different mines and different processing -
I seem to remember - there are fewer mines now.
If there are names on the bags - or batch numbers you may be able to to get
specific analysis for what you have.
Email hamgilinc@aol.com
The analysis for the Purple Stone in her book is:
SiO2 - 72.80
Al2O3 - 15.80
Fe2O3 - 0.18
CaO - 1.90
MgO - 0.12
K2O - 3.70
Na2O - 3.60
TiO2 - 0.07
F - 0.90 (fluorine)
P2O5 - 0.38
LOI - 1.25
RR
>The last time i bought Cornwall Stone, I got two bags.
>One is the standard greyish white color one would
>normally associate with powdered rock.
>The other has a decided blue tinge to it.
>What's up with that??!
>
>I have half a mind (left) to go over to that place
>where "the sun never sets", and complain
>about their quality control.
>
>Maybe the illustrious Ms Kaiser
>(on whom the sun allegedly never sets) could shed
>some light on the subject. At least she could offer me
>a cuppa should I get that far, and not get run off by angry
>kilt wearing locals bearing torches, flinging haggisses
>(preferably cooked, but cooled) at me.
>(Yes, I know I've mixed in attributes from three countries :>)
>
>Wayne Seidl
>Key West, Florida, USA
>North America, Terra
>Latitude 81.8, Longitude 24.4
>Elevation 3.1 feet (1m)
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on wed 28 apr 04
Dear Wayne,
It is probable that the Blue tinge comes form one of the minerals
which constitute the rock, My guess would be Fluorite, Calcium
Fluoride which is often coloured deep purple.
Best regards,
Ivor.
.
wayneinkeywest on wed 28 apr 04
Thanks Ivor. I actually like the blue tinge.
Let's me stay "certain" when I grab for a bag
looking only out of the corner of my eye.
I've thought for some time of introducing
food colorings into some of the other compounds
and ingredients I use frequently, to make it
easier to grab what I need, such as oranges for
tenmoku, green for greens/ teals/ turquoise, etc.
Similarly, colo(u)ring the chemicals that get mixed together
as a recipe would also make it easy to grab
ingredients off the shelf. "Ok, tenmoku...grab all the oranges"
Funny no one has suggested this in the past.
Best Regards,
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Ivor and Olive Lewis"
> Dear Wayne,
> It is probable that the Blue tinge comes form one of the minerals
> which constitute the rock, My guess would be Fluorite, Calcium
> Fluoride which is often coloured deep purple.
> Best regards,
> Ivor.
Liz Willoughby on wed 28 apr 04
Wayne,
from Hamer's Dictionary
"Cornwall Stone. D.F. stone. Carolina Stone. A feldspathoid which is
used as a flux in bodies and as a major constituent in glazes. It
contains feldspar, quartz, kaolinite, mica and a small percentage of
fluorspar...........
Cornish stone is not a single mineral like potash feldspar or whiting
and thus it cannot be a chemical formula. It is a crushed igneous
rock with similar properties to those of feldspar but varying greatly
in actual composition. Hence its many names, some which are linked
with a single quarry source.......
It is almost free from iron and thus is nearly white. The purple
variety of cornish stone is colored by fluorspar but this burns to
white (colorless) also."
There is a lot more written about it. God, I love my Hamers.
Meticky Liz from Grafton, Ontario, Canada, where the sun is shining.
P.S. story, ...30 years ago I needed some Cornwall Stone to make up
a glaze. Went into Ron's "Rodaco Clay" business, and asked for it.
Ron says, sure, I have a bag here, you want to buy it? I was just
wet behind the ears in clay, thinking it would be a "small bag". I
think that bag weighed 200 lbs. But it was the old real stuff with a
purple tinge from Cornwall. I still have some left. Thanks Ron,
glad I bought it.
>
>>week when we were mixing a raku glaze The last time i bought
>>Cornwall Stone, I got two bags.
>>One is the standard greyish white color one would
>>normally associate with powdered rock.
>>The other has a decided blue tinge to it.
>>What's up with that??!
>>
Ivor and Olive Lewis on thu 29 apr 04
Wayne,
You might like to check the knowledge base. I have a nudging feeling
that the violet colour is due to traces of Manganese but I cannot
recall the reference. Might have been something I picked up when I was
in Castleton.
Keep it simple friend. Colour coding may be a good idea for the big
boys who employ people who behave as idiots when mixing hundred ton
batches.
Thing of the confusion if one tub had a rainbow of coloured bands
because it went in six differing styles of glazes.
Best regards,
Ivor Lewis. Redhill, South Australia
Bonnie Staffel on thu 29 apr 04
The present day Cornwall Stone is dyed I have heard, to differentiate it
from the original CS that is no longer mined. The new one is made up to
resemble the chemistry of the old CS but when I used it in my recipe, it did
not come out the same. So I substituted other feldspars to make the glaze
work. However, as nice as it came out, it just wasn't the same.
Sincerely,
Bonnie Staffel
http://pws.chartermi.net/~bstaffel/default.html
http://www.vasefinder.com/
wayneinkeywest on thu 29 apr 04
Ivor:
Thank you for your response.
To the comment about the tub with the band of rainbow
colors because it is used in 6 different glazes, I can only smile...
and think to myself...
"...But is it art??!!"
I believe I've been reading this list too long
There are 4 large letters prominently posted on one of the beams
in the area where I throw. I can always see them from the
corner of my eye: KISS (keep it simple, stupid)
Thanks again.
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Thursday, April 29, 2004 2:23 AM
Subject: Re: `Cornwall ---the clay---the glaze component
> Wayne,
> You might like to check the knowledge base. I have a nudging
feeling
> that the violet colour is due to traces of Manganese but I cannot
> recall the reference. Might have been something I picked up when I
was
> in Castleton.
> Keep it simple friend. Colour coding may be a good idea for the
big
> boys who employ people who behave as idiots when mixing hundred
ton
> batches.
> Thing of the confusion if one tub had a rainbow of coloured bands
> because it went in six differing styles of glazes.
> Best regards,
> Ivor Lewis. Redhill, South Australia
>
>
____________________________________________________________________
__________
> 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.
>
Carol Tripp on thu 29 apr 04
Hi Wayne,
I like the blue tinge of Cornwall Stone too but I think the idea of coloring
the other white powders is more trouble than it is worth. When you are
making glazes, you are just going to have to PAY ATTENTION! But there
is a use for food coloring in the pottery. I put it in my wax so I can see
it on white bisque. And Greg Daly, of GLAZES AND GLAZING TECHNIQUES, puts
it in some of his glazes so he can see them well when he paints, splashes,
sprays them on in his multiply layering technique.
Ooh, this is getting fun - food coloring, frosting roses and balloons. And
Earl K says there is a Vitamin S that is in cake. I don't think I'm getting
enough of that;-)
Best regards,
Carol
Dubai, UAE
Sea level or perhaps under water.
Wayne wrote:
>Thanks Ivor. I actually like the blue tinge.
>Let's me stay "certain" when I grab for a bag
>looking only out of the corner of my eye.
>I've thought for some time of introducing
>food colorings into some of the other compounds
>and ingredients I use frequently, to make it
>easier to grab what I need, such as oranges for
>tenmoku, green for greens/ teals/ turquoise, etc.
>
>Similarly, colo(u)ring the chemicals that get mixed together
>as a recipe would also make it easy to grab
>ingredients off the shelf. "Ok, tenmoku...grab all the oranges"
>
>Funny no one has suggested this in the past.
>
_________________________________________________________________
MSN 8 helps eliminate e-mail viruses. Get 2 months FREE*.
http://join.msn.com/?page=features/virus
Stephen on thu 29 apr 04
If you recall a past post about chichen grit from Mt. Airy, N. C.I may not
havre mentioned that I ball milled some ( it is a type of granite). Its
breakdown is very similar to cornwall stone with a trace more iron. It
worked very well as a substitute in a celedon that called for cornwall
stone.
Stephen
mailtoandrew@FSMAIL.NET on fri 30 apr 04
Opps, I ve just noticed I post a message to a wandering thread of this
subject. So if you can indulge me ....
Some myths and misinformation have surrounded China stone. Hopefully the
following will clarify:
What is it?
A feldspar
It is the only flux that currently is commercially extracted in the UK,
and is found in the county of Cornwall in the SW of the country.
More specifically it is a medium grained, feldspar-rich partially
decomposed granite. In composition it is a heterogeneous mix of quartz,
feldspar and mica, with minor traces of kaolin and fluorspar, and a low
content of iron-bearing minerals
Traditionally China stone was sold as a variety of grades dependent on the
fluorine content and extent of kaolinisation, which was evident by both
colour and texture of the parent rock, These characteristics were
reflected in their names: Hard purple, Mild purple and Hard White. However
the appearance of the processed materials were identical.
Other names
Include China stone and Cornwall stone, and historically Moorstone or
Growan.
It is not
A pegmatite
A feldspathoid
Petunse, which is a relatively similar material, used historically by the
Chinese.
Colour
The misnomer regarding the colour of the dried milled material has
sometimes been repeated in print. It has been claimed that the slight
green or blue colour that can be detected is evidence of mineralogy or
even the fluorine content. However the colour is simply and identification
stain added during processing. This practice is common during ball milling
to help identify the different materials produced, without which all the
nonplastics look identical white suspensions. Although used for
identification when in aqueous suspension a faded hint can remain when the
material is subsequently dried. The dyes are vegetable based, used at less
than 0.5 litre per tonne, and burn out without effect.
Consistency
China stone has suffered from the undeserved reputation of being variable
in composition. The source of the perception is likely that from its first
use over 250 years ago until quite recently there were a number of
companies worked separate deposits that were all being marketed by similar
names. Therefore whilst material from one supplier may have remained
consistent it would not necessarily have been identical to that produced
by another.
For some years only the grade known as 80:20 has been sold. Production
controls, including regular analysis, result in a product that has been
consistent for many years. Typical compositions of this are.
Chemically
SiO2 72.8
Al2O3 15.5
Fe2O3 0.14
TiO2 0.05
CaO 1.5
MgO 0.10
K2O 4.3
Na2O 3.1
F 1.0
LOI 1.7
Mineralogically
Quartz 29
Orthoclase 11
Albite 27
Muscovite 22
Kaolinite 2
Fluorite 2
It is perhaps worth noting that all commercial feldspars contain other
minerals. Although treatment processes are often used to enrich the
feldspar content it is erroneous to think of commercial grades as being
pure. The most common ancillary mineral is quartz and can represent
between 5 and 35% of most of the feldspar raw material used in ceramics.
Fluorine
To alleviate the problem associated with the fluorine emissions froth
flotation treatment was introduced in the 1960s. Marked in as DF Stone, or
Defluorinated Stone, it had a substantially reduced fluorine content. Due
to the reduced market demand production of DF stone ceased in the late
1990s.
Sustainability
China stone is now mined by a single company, it continues to be processed
and sold for ceramic applications. As geological reserves are large it is
economics that govern its life and whilst demand is sufficient it will
most likely continue. However the biggest users are UK industrial
manufacturers have largely moved to feldspars or Nepheline syenite from
Scandinavia.
Hope that helps,
Andrew
Wood Jeanne on fri 30 apr 04
Andrew, Thanks for the information, very interesting.
Do you have any information on how early it was used?
Medieval pottery being an interest of mine.
Thanks,
Jeanne W.
--- mailtoandrew@FSMAIL.NET wrote:
>
>
> What is it?
> A feldspar
> It is the only flux that currently is commercially
> extracted in the UK,
> and is found in the county of Cornwall in the SW of
> the country.
>
__________________________________
Do you Yahoo!?
Win a $20,000 Career Makeover at Yahoo! HotJobs
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daniel on fri 30 apr 04
Hi Andrew, All,
First an apology. I made the statement that cornish stone is a pegmatite in
my post based largely on a less than accurate reading of Parmelee. I then
failed to quote with rigour.
The quote that drove that part of my post was this (p32 1973 ed):
"Corwall Stone
Conrwall stone is also called Cornish stone, stone, or China stone. It is
an altered pegmatite of granite rock whose constituent minerals are pale or
smokey brown quartz, white feldspar frequently more or less decomposed,
usually other minerals, lepidolite (a lithia mica) and tourmaline (a
silicate containing alumina, lime, magnesia, alkalies, and sometimes
fluoride and boron in small quantities)."
I quoted the above two sentences completely but am really only concerned
with the "...altered pegmatite ...". Andrew, given that I (as stated in my
post earlier) know little about this substance, I'd be very interested in
your comments on this quote in light of your remarks that cornwall stone is
not a pegmatite.
I'd also be interested in your opinion on the distinction between a true
feldspar and a feldspathoid.
> It is not
> A pegmatite
> A feldspathoid
> Petunse, which is a relatively similar material, used historically by the
> Chinese.
Thanx
Daniel "feeling a might guilty over lack of rigour on this one" Semler
Belmont, California, USA
(ex terra australis)
mailtoandrew@FSMAIL.NET on fri 30 apr 04
Hi,
It is generally understood that the first use of China stone for ceramic
applications was by Willaim Cookworthy. Along with discovering the Cornish
china clay deposits he is credited with developing an early, and possibly
the earliest, English porcelain in around 1768.
He is accepted as being the founder of the extensive china clay industry
in England.
Sorry I don't think that as early as your field of interest.
Regards,
Andrew
mailtoandrew@FSMAIL.NET on tue 4 may 04
Hello Daniel,
Why is China stone not a pegmatite. This is based on the definitions
introduced by EUROFEL, The European Association of Feldspar Producers.
According to these
Pegmatite have an alkali content of greater than > 6% and an alumina
content of 8 to 14%
Feldspars have an alkali content of greater than 6% and an alumina content
of above 14%.
Feldspathoids are a group of alumino silicate minerals. Some authorities
have suggested that in the absence of fixed chemical or structural
constraints the use of the term is somewhat arbitrary. However three
distinct groups are generally taken to exist, with these being leucite,
nepheline-kalsilite and soda-cancrinite.
The most useful feldspathoid to whiteware ceramics is nepheline syenite
which is an igneous rock that in appearance resembles a medium grained
granite. The primary phases are the minerals nepheline, albite feldspar
and microcline feldspar together with small amounts of various accessory
minerals. It is noticeably deficient in quartz. Although deposits are
found widely across the globe although only three areas have long term
major scale extraction; Canada, Norway and parts of the former USSR
It has been suggested that the reason nepheline syenite is a strong flux
in whiteware bodies compared than feldspar is a consequence of its
genesis. As with all feldspathoids nepheline formed from solidifying
magmas that were short of sufficient silica to form feldspar. Therefore if
nepheline is envisaged to be silica deficient feldspar the elevated
temperatures experienced during firing it reacts with quartz and silicates
in the other body components to reached an equilibrium not achieved during
formation.
And if you can excuse me to continue rambling it may be worth stating
definitions of rocks and minerals.
Minerals. These are naturally and industrially occurring chemical
compounds with characteristic atomic structures and chemical compositions
which vary within limits. Examples relevant to ceramics are quartz,
kaolinite and feldspar. Raw materials very rarely comprise pure minerals.
Rocks. These are aggregates of minerals. Examples relevant to ceramics are
kaolin and feldspar. The feldspars used in bodies are glazes are
invariably are rocks as other minerals are also present.
Hope that is of interest,
Andrew
Ivor and Olive Lewis on wed 5 may 04
Dear Andrew,
Mineral emplacements are also defined by grain structure and size
distribution as well as mineral and chemical content.
Pegmatite, or perhaps Granite Pegmatite, is notable for having Large
Crystals. I have handled a Beryl crystal which was some 20 cm from
face to face and this was a fragment of a much longer specimen that
came from the Triple Chance Mine in Western New South Wales, Muscovite
Mica books from this deposit can be more that 12 inches across. A
Spodumene crystal more than 14 metres long was found in the Black
Hills of South Dakota. This happens when cooling is slow and there
chance for crystals to segregate and grow in the magma. Rhyolite is a
microcrystalline rock of similar chemistry to Granite and forms where
cooling is more rapid. Should the same sort of magma be quenched or
cool very rapidly then you might get Obsidian, a Volcanic Glass. A
variety of this mineral is invested with white radiating crystals and
is known as Snowflake Obsidian.
So much to learn, so much to experience.
Best regards,
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From:
To:
Sent: Wednesday, 5 May 2004 12:38
Subject: Re: `Cornwall ---the clay---the glaze component
> Hello Daniel,
>
> Why is China stone not a pegmatite. This is based on the definitions
> introduced by EUROFEL, The European Association of Feldspar
Producers.
> According to these
>
> Pegmatite have an alkali content of greater than > 6% and an alumina
> content of 8 to 14%
>
> Feldspars have an alkali content of greater than 6% and an alumina
content
> of above 14%.
>
> Feldspathoids are a group of alumino silicate minerals. Some
authorities
> have suggested that in the absence of fixed chemical or structural
> constraints the use of the term is somewhat arbitrary. However three
> distinct groups are generally taken to exist, with these being
leucite,
> nepheline-kalsilite and soda-cancrinite.
>
> The most useful feldspathoid to whiteware ceramics is nepheline
syenite
> which is an igneous rock that in appearance resembles a medium
grained
> granite. The primary phases are the minerals nepheline, albite
feldspar
> and microcline feldspar together with small amounts of various
accessory
> minerals. It is noticeably deficient in quartz. Although deposits
are
> found widely across the globe although only three areas have long
term
> major scale extraction; Canada, Norway and parts of the former USSR
>
> It has been suggested that the reason nepheline syenite is a strong
flux
> in whiteware bodies compared than feldspar is a consequence of its
> genesis. As with all feldspathoids nepheline formed from solidifying
> magmas that were short of sufficient silica to form feldspar.
Therefore if
> nepheline is envisaged to be silica deficient feldspar the elevated
> temperatures experienced during firing it reacts with quartz and
silicates
> in the other body components to reached an equilibrium not achieved
during
> formation.
>
> And if you can excuse me to continue rambling it may be worth
stating
> definitions of rocks and minerals.
>
> Minerals. These are naturally and industrially occurring chemical
> compounds with characteristic atomic structures and chemical
compositions
> which vary within limits. Examples relevant to ceramics are quartz,
> kaolinite and feldspar. Raw materials very rarely comprise pure
minerals.
>
> Rocks. These are aggregates of minerals. Examples relevant to
ceramics are
> kaolin and feldspar. The feldspars used in bodies are glazes are
> invariably are rocks as other minerals are also present.
>
>
> Hope that is of interest,
>
>
> Andrew
>
>
______________________________________________________________________
________
> 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.
mailtoandrew@FSMAIL.NET on wed 5 may 04
Dear Ivor
I must confess to being a little puzzled by your statement ... mineral
emplacements are also defined by grain structure and size distribution as
well as mineral and chemical content ... Surely the first use of mineral
should be rock instead, otherwise you are suggesting that the
classification of a mineral is dependent on the mineral!
Anyway the categorisation of China stone
As the name is specific to the ceramics industry it seems reasonable to
use the criteria applied by an associated authority, such as EUROFEL.
That classic book Rutleys Elements of Mineralogy advises of two factors
that should be considered for the classification of igneous rocks
1) Amount and type of constituents
See the EUROFEL definitions.
2) Texture, which depends upon the cooling history of the magma.
Quoting from the website http://pegmatopia.ou.edu/ ... most geologists
would define pegmatites as exceedingly coarse grained igneous rocks of
granitic composition ...
Sadly the site does not quantify exceedingly coarse grained and whilst Im
sure that size bands have been agreed, I think by either the BGS or USGS,
I dont have these to hand. However the lump of China stone on my desk, a
very effective paperweight, has no crystals exceeding 2.5mm which
certainly could not be classed as large.
Both factors preclude China stone from being a pegmatite.
Additionally in the book A Global Geology, published by Industrial
Minerals in 1997, Harben and Kuzvart group four sources of feldspar, with
China stone included in the last
Granite pegmatite
Feldspar bearing intrusive rocks
Feldspar gravel and sand
Partly kaolinised intrusive rocks
Regards,
Andrew
Ivor and Olive Lewis on thu 6 may 04
Dear Andrew,
Perhaps we are talking at cross purposes.
Rocks are defined by several factors; their assembly of minerals,
their texture and I also understand there is a colour index .
In a commercial world dominated by beaurocracies there will always be
standards of conformation.
I use Dana. It is sufficient for my needs.
Best regards,
mailtoandrew@FSMAIL.NET on thu 6 may 04
Dear Ivor
Yes perhaps we are talking at cross purposes, misunderstandings can easily
occur as due to the formatof ClayArt fluid conversations are not possible.
The reason for my original post was to counter some of the long standing
misconceptions about China stone, such as the reason for its blue colour
and that it is inconsistent.
Anyway China stone is
A rock
A ceramic raw material
A feldspar
A body and glaze flux
Consistent
The same as Cornwall stone and Cornish stone
Dont get me started on the misconceptions regarding bone, silica compared
to flint! I know some might consider me petty ...
And if you can excuse me being flippant about your referencwe to Dana ..
wasnt she a winner of the Eurovision Song Contest? :-) Apologies to those
outside Europe who dont know that annual competetion, and how awful it is.
Regards,
Andrew
Ivor and Olive Lewis on sun 9 may 04
Dear Andrew,
My reference text is "Dana's Manual of Mineralogy" Ed Hurlbutt. 8th Ed
1971.
Yes, I have picked up one catwailing of the other on TV during the
promo's for the Contest. I'll accept that as a "Funny Ha! Ha!"
Are you sure "China Stone" is both a Felspar and a Rock ? Or do you
mean the former is a component of the latter?
> Anyway China stone is
> A rock
> A ceramic raw material
> A feldspar
> A body and glaze flux
> Consistent
> The same as Cornwall stone and Cornish stone
Best regards,
Ivor Lewis. Redhill, South Australia
mailtoandrew@FSMAIL.NET on mon 10 may 04
Hello Ivor,
Yes China Stone is both a feldspar and a rock.
Firstly two definitions are needed
Minerals are naturally and industrially formed chemical compounds with
characteristic atomic structures and chemical compositions which vary
within limits.
Rocks are aggregates of minerals.
Specifically CS
The major phases in CS are orthoclase, albite, muscovite, kaolinite and
fluorite. So being a mixture of minerals that occurs as an aggregate it is
a rock.
But a feldspar? Yes. The name is used for a family of minerals, those of
major interest to ceramics being orthoclase, microcline, albite and
anorthite. But it is also used for those ceramic raw materials that
contain significant amounts of feldspar minerals.
All the popular feldspars, be it Forshammar, Kona, Custer etc, are not
pure minerals. They are crushed and milled rocks, which may have been
subject to beneficiation processes, which whilst composed predominantly of
feldspar minerals also have ancillary minerals such as quartz. Dependent
on which feldspar raw material is considered the feldspar mineral content
of the bag bought from a ceramic material supplier is typically between 65
to 90%, which will be a mixture of various types.
The purest commercially produced feldspar I am aware of is from Germany
which has a total feldspar content of around 95%
Referring again to the EUROFEL scheme China stone is classified as a
feldspar.
Its a pity there is not an established term for the feldspar rock as the
dual use can cause confusion. For comparison consider the clarity from the
use of kaolin, a rock, and kaolinite, a mineral.
Hope that clarifies.
Regards,
Andrew
Ivor and Olive Lewis on tue 11 may 04
Dear Andrew,
Thank you for that exposition.
It sounds as though there has been movement of the Goal Posts for the
convenience of Commerce.
Rather like the Steel Industry. I recall an alloy containing less than
50% metallic Iron which was called "Steel"
Just a matter of "Conventions".
Best regards,
Ivor Lewis. Redhill, South Australia
mailtoandrew@FSMAIL.NET on wed 12 may 04
Hello Ivor,
Perhaps categorisation is dependent on who is being asked? Consider again
China stone
To a geologist it is a partially kaolinised intrusive granite
To a ceramicist it is a flux
To a construction worker it is simply road stone.
As an aside ... considering you are in Australia and Im in the UK my
interpretation of hot weather is probably considerably different to
yours! :-)
Regards,
Andrew
Ivor and Olive Lewis on thu 13 may 04
Dear Andrew,
Today in this bit of Oz it's about 16=BA C and damp after two
millimetres of rain as Winter drags itself in. Now, with the mercury
that high at "Lords" or the "Oval" spectators would have the shirts
off their backs to get a tan as the batsmen sweat it out in the centre
!!
I suppose in the end it all boils down to "context".
Somewhere in the back of my mind was an idea that Fluorine in
untreated raw rock gets there because of the nature of the
Kaolinisation. Is it in some way implicated through contact
metamorphism in the presence of water at high temperatures and
pressures which caused injection into the fractured Granite and
promote Kaolinisation ?
Best regards,
Ivor Lewis. Redhill, South Australia.
mailtoandrew@FSMAIL.NET on thu 13 may 04
Hello Ivor,
So its not as hot down there as I thought! And I ll not comment about the
cricket as you might support your fellow Antipodeans for next weeks test.
Anyway F in CS ... Fluorine would have been present in the original magma
which, after solidification formed the Cornubian batholith. However the
location of the fluorine within the crystal structure of some of the
minerals is believed to be as a result of action of metasomatic and
meteoric fluids that lead to kaolinisation.
Regards,
Andrew
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