BVCuma on sat 15 jun 02
>>I do have a problem with "pulling" handles etc.
So plasticity is not at its optimum..
The clay does have a tendancy to crack.<<
>>I plan on trading off equal amounts of ball clay
for the fireclay till this bad habit is broken.<<
________________________
I would like to clarify these contradictory statements.
The body I am using cracks on forming or pulling/bending handles...
Not on drying... creation of S-cracks etc
So a reduction of a course fireclay
and an increase in plastic ballclay
would reduce the shortness ie. cracking in forming
and not increase "a tendancy to crack" in drying
ie. high shrinkage...as it does not exist.
Actually a body that is of any use to me must
be able to withstand vigourous even careless drying method.
I dislike a body that needs to be pampered for two weeks etc.
Dry in 2-3 days if desired is good...
even a flash dry in the sun on simpler forms is a must.
With respect to fireclay, Ivor did mention high silica as
one of the problems, I am assuming there are more??
This can be dealt with as at present as I add a good measure of flint
and the amount overall can be adjusted.
I never read anywhere about fireclay being lousy =
etc.(non-plastic..maybe)
It offers refractability and tooth with course and varied particle size.
These are important qualities and therefore are part of my =
composition...
Actually fireclay is the major component at present..
Any inputs regarding these "poor qualities" of fireclay is appreciated.
Thanx in advance
Bruce
Paul Herman on sat 15 jun 02
Bruce,
When you use the term "fireclay" you are covering a very wide range of
refractory clays. Some are high in silica and some are not. Some have
lots of iron and other impurities and some burn white. Some are fine
grained and some are coarse, some lousy etc. The answer, as always, is
test, test, test.
Good luck,
Hardway Herman
Bruce asks:
> I never read anywhere about fireclay being lousy etc.(non-plastic..maybe)
> It offers refractability and tooth with course and varied particle size.
> These are important qualities and therefore are part of my composition...
> Actually fireclay is the major component at present..
>
> Any inputs regarding these "poor qualities" of fireclay is appreciated.
>
> Thanx in advance
> Bruce
Tony Ferguson on sat 15 jun 02
Cuma,
Try 2 parts fire clay 1 part ball clay + grog (20%) + feldspar (10-15%).
Can dry overnight. Add 1/2 of 1% epsom salts = quicker plasticity.
Thank you.
Tony Ferguson
Stoneware, Porcelain, Raku
www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "BVCuma"
To:
Sent: Friday, June 14, 2002 9:30 PM
Subject: Fire clay (is it really so bad)
>>I do have a problem with "pulling" handles etc.
So plasticity is not at its optimum..
The clay does have a tendancy to crack.<<
>>I plan on trading off equal amounts of ball clay
for the fireclay till this bad habit is broken.<<
________________________
I would like to clarify these contradictory statements.
The body I am using cracks on forming or pulling/bending handles...
Not on drying... creation of S-cracks etc
So a reduction of a course fireclay
and an increase in plastic ballclay
would reduce the shortness ie. cracking in forming
and not increase "a tendancy to crack" in drying
ie. high shrinkage...as it does not exist.
Actually a body that is of any use to me must
be able to withstand vigourous even careless drying method.
I dislike a body that needs to be pampered for two weeks etc.
Dry in 2-3 days if desired is good...
even a flash dry in the sun on simpler forms is a must.
With respect to fireclay, Ivor did mention high silica as
one of the problems, I am assuming there are more??
This can be dealt with as at present as I add a good measure of flint
and the amount overall can be adjusted.
I never read anywhere about fireclay being lousy etc.(non-plastic..maybe)
It offers refractability and tooth with course and varied particle size.
These are important qualities and therefore are part of my composition...
Actually fireclay is the major component at present..
Any inputs regarding these "poor qualities" of fireclay is appreciated.
Thanx in advance
Bruce
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OWLPOTTER@AOL.COM on sat 15 jun 02
As a potter who mixes their own clay bodies, I wold sure like to see a
listing of all of the fireclays (mined in the U.S.) that are available to
potters. Does anyone know if such a list exists? Where would I start to
compile such a list?
Thanks in advance.
-Carolynn Palmer, Somerset Center, Michigan
Matt MacIntire on sat 15 jun 02
How about starting with your local ceramic supplier...
Campbell's Ceramic supply lists only two...
Cedar Heights Fireclay
Hawthorne Bond (a.k.a. Missouri Fireclay)
Axner also carries
A.P. Green Fireclay
Newman Red
Plainsman is working on a substitute for A.P. Green Fireclay, but it is
not available yet.
There used to be a lot more fireclays, but I don't ever see them for
sale anywhere. Does anyone know of any others that are still
available?
Matt
-----Original Message-----
From: OWLPOTTER@AOL.COM [mailto:OWLPOTTER@AOL.COM]=20
Sent: Saturday, June 15, 2002 2:28 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Fire clay (is it really so bad)
As a potter who mixes their own clay bodies, I wold sure like to see a
listing of all of the fireclays (mined in the U.S.) that are available
to potters. Does anyone know if such a list exists? Where would I
start to compile such a list? Thanks in advance. -Carolynn Palmer,
Somerset Center, Michigan
Jim Kasper on sat 15 jun 02
Hi Carolynn,
I have just started to explore this area myself. The link I list below has a link to a database, but it was dead tonight. Hopefully it will come back.
http://pubs.usgs.gov/info-handout/clays/
Regards,
Jim Kasper
http://zafka.com
> From: OWLPOTTER@AOL.COM [mailto:OWLPOTTER@AOL.COM]
> As a potter who mixes their own clay bodies, I wold sure like to see a
> listing of all of the fireclays (mined in the U.S.) that are available
> to potters. Does anyone know if such a list exists? Where would I
> start to compile such a list? Thanks in advance. -Carolynn Palmer,
> Somerset Center, Michigan
>
> ______________________________________________________________________________
> 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.
>
BVCuma on sun 16 jun 02
Well having motivated myself to "know my materials"
Here is what I was able to dig up from pottery "papers"
or is it "capers"=20
; )
Anyway..
Fireclay is found in close association with deposits=20
of coal as it was the undersoil of forest vegetation=20
that grew over 280 million yrs ago.
Therefore it is found directly under coal seams today.
Two basic types are distinguished...
compressed rock fireclays and underclays.
Rock type are both solid rock and shales,
which must be mined and milled and take
upto thirty years to "weather" into a plastic condition.
The underclay form is more akin to tradition clays
and is quarried and prepared as such.
Both forms contain organic impurities upto 3% carbonaceous material.
Other impurities upon heating produce sulfur and carbon dioxide gases.
Which when trapped can lead to "black coring" and "bloating" at high =
temp.
Bound water is released more slowly than with other clays.
Therefore careful ramping of temp and venting should be practiced.
Fireclays contain contain between 10% and 40% alumina,
and between 40% and 80% silica...
compared to China clay which contains=20
38% alumina and 46% silica.
Siliceous clays often take glazes better than aluminous ones
because they integrate well in the early stages of firing.
The best clays for salt glazing are fireclays. (Hamers)
Rich glaze quality and color in caladons and other reduced iron glazes
is reputed to derive from the use of fireclay in bodies.
The iron pyrite impurity (source of sulfur gas) =20
is said to add visual interest in the glaze surface manifesting=20
as dark slightly ashy spots.
This has been referred to as yielding a "sweated color".
Though if larger pyrite nodules are present
they can be unsightly in their effect (so Fournier says)
Finally in Hamers (from which most of the info is sourced)
Slum...=20
Fireclay containing a large amount of fine coal=20
which makes it necessary to fire the clay slowly
although the coal does help the firing=20
if sufficient oxygen can be introduced.
Funny....Slum is a term used here to describe
a poorly maintained unsanitized densely populated living environment.
In contrast to the brickmakers who condition their clay body
with a coal grog that assists in a complete burning of the=20
intricately stacked bricks which are laid down
in such a fashion as to create huge in-situ kilns.=20
In summery I would agree that fireclay maybe=20
alot like my all time favorite movie,
The Good, the Bad and the Ugly... but potentially Beautiful.
AIAIEYA YAYAYA
AIAIEYA YAYAYA !!!
; )
Bruce
ps. "fireclay" is what I asked for
"fireclay" is what they sent me...
what it really is...I don't know
but we call it "fireclay"..
and I like it.
why?... because it's decent.
=20
=20
OWLPOTTER@AOL.COM on mon 17 jun 02
Thank you to Jonathan and RR for your informational posts.
I am so thankful to hear from other potters who mix their own clay bodies.
It seems that we are few and far between "out there" and information is
scarce.
-Carolynn Palmer, Somerset Center, Michigan
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