Martin Rice on wed 6 mar 02
----- Original Message -----
From: "Mark Mondloch"
To:
Sent: Wednesday, March 06, 2002 4:38 PM
Subject: Re: [CLAYART] my perfect hiding place
Mark wrote:
. When I left night classes , I took
> along their very basic ^6 clay recipe that used locally available
materials.
> Over the past 20 yrs I continually changed that recipe until it morphed
into
> my present ^10 body. Now I have my basic recipe mixed for me, but mix
> variations at home for specific projects at hand.
When I wrote in asking about how to go about making my own clay, Lois
Richter was kind enough to send me a recipe that she thought might be ideal
for the materials I believed I could get here. She called it a ^04 though
what she sent me was labeled ^08-^04. Mark talks above about taking a basic
^6 clay recipe and eventually evolving it into a ^10 body.
My naive questions are: what is it that makes a body a ^04 or a ^10 or what
have you? Does this refer to at what cone number certain glazes will work on
a given claybody -- for example the title of the book about "^6 glazes?"
At this point in my early efforts I'm confused. The guy at the supply house
I bought things at today to make my first clay told me that it would bisque
at ^06 but it would be stronger at ^04. Does that mean that this claybody
will be a ^06-^04 claybody and have nothing to do with what cone I'll have
to use for my glazes, that cone number being a reflection of the type of
glaze I use? And, last question for now: if I use a claybody that bisques at
^04, does that imply limitations at to what cone I can glaze at?
Thanks so much,
Martin
Lagunas de Barú, Costa Rica
www.rice-family.org
Snail Scott on thu 7 mar 02
At 06:39 PM 3/6/02 -0600, you wrote:
>My naive questions are: what is it that makes a body a ^04 or a ^10 or what
>have you? Does this refer to at what cone number certain glazes will work on
>a given claybody -- for example the title of the book about "^6 glazes?"
Martin-
When a clay body is described as firing to a certain cone,
that refers to the highest temperature that particular
clay may be fired to without slumping, bloating, or
showing other detrimental signs of overfiring. Low-fire
clays will generally be less vitrified at their maximum
temperature than high-fire clays; that's their nature.
They may get more vitrified if fired higher, but will
show effects of overfiring as mentioned above. Clays
which are described as having a firing 'range', such as
^6-^10 of some such, are only optimally vitrified at the
top temperature listed; the lower temperature may be OK
for many purposes, but the clay will be less fully
vitrified at that temperature, and be weaker and more
porous. Simply speaking, low-fire glazes (and clays)
have more fluxes in them than their high-fire kindred,
allowing them to melt at lower temperatures.
Like clays, glazes have optimum firing temperatures,
and like clays, some may tolerate a fairly wide range
of temperatures and function adequately, while others
require a more precise temperature for best results.
(Fully melted but not dripping off the clay would be a
typical desired result.) Like clays, glazes may be
formulated for optimum result at any of a wide choice
of temperatures.
Generally, glazes should be chosen which fire at the
same temperature as the clay underneath. Glazes which
melt at tmeperatures higher than the vitrification
point of the clay underneath would be useless, since
the clay would be slumped, melted, bloated, or maybe
just over-brittle by the time the glaze had fully
melted. On the other hand, it is possible to use
glazes which melt at a lower temperature than the
optimum firing temperature of the clay beneath. This
can court difficulties with glaze fit, such as crazing
due to incompatible coefficients of expansion, but this
is not inevitable. Note, however, that if a glaze is
chosen which fires much lower than the clay, the clay
must first be fired to its maturation temperature
(which makes it hard to apply a good glaze coat), or
else the clay must be left underfired, leaving it
weaker than it would be if designed to vitrify at
that temperature.
Often, people bisque earthenware to a temperature higher
than the final glaze firing, for several reasons. One
is to burn all the organic materials out of the clay,
as they can cause the colors of some low-fire glazes to
burn out, or cause blistering of the glaze surface as
the gasses try to escape. Firing higher before the glaze
firing means that anything which might outgas at the
glaze temperature has already done so. (That's why most
commercial low-fire glazes recommend a ^04 bisque and a
^06 glaze firing.) And, a lower-firing glaze will save
on the cost of that final firing, even if the clay must
first be fired higher for durability. Low-fired glazes
also offer a different color palette than those
available at higher temperatures, so a ceramist may
choose to use stoneware (high-fire) clay, and fire it to
its appropriate cone, and then apply a low-fire glaze
for aesthetic reasons.
>...And, last question for now: if I use a claybody that bisques at
>^04, does that imply limitations at to what cone I can glaze at?
Oddly, the optimum bisque temperature for most high-fire
and low-fire clays is similar. It is above the temperature
at which the clay has had all its molecularly-bonded
moisture driven off so it will no longer turn back into
mud when wetted. This is a principal reason why bisque
firing is performed - so the pots won't collapse when
glazed. This (in theory) allows for a bisque temperature
anywhere between ^012 or so, and ^02 or so, unless it's
a very low-fire clay. Another factor narrows the choice,
however. The higher the temperature goes, the more of the
silica in the clay will begin to melt, strengthening the
clay. This reduces the chance of acccidental breakage
during glazing. (There are other factors, as the chemical
process is actually fairly complex, but let's keep it
simple for now.) Further, there is no real reason to
bisque too high, as it wastes fuel. It also reduces the
absorbency of the clay, making it harder to get a glaze
coating of adequate thickness. It may even push the limits
of very low-fire clays. Most people therefore favor ^06-
^04 for bisque no matter what the cone rating of their
clay is, but not everyone does, as every type of work had
its own requirements, and every ceramist has their own
preferences. The factors mentioned here apply to almost
all clays, and earthenware has the added factors
mentioned in the previous paragraph.
Bisque firing is not a requirement, however. Though
glazing unfired clay may take a little practice, and not
all glazes work well on raw clay, it can be an efficient
way of reducing firing cost and production time, and
eliminates the need to store bisqueware before glazing.
It's not appropriate for all work, but it's a good option
for some.
In a nutshell: Clay is usually best fired at the highest
temperature it is designed for. Glaze usually works best
if formulated for the same temperature as the clay.
There are a zillion exceptions to this 'rule' but it's
not a bad starting point.
(I hope I've answered your questions and not confused the
issue too horribly!)
-Snail
Khaimraj Seepersad on thu 7 mar 02
Hello to All ,
Martin ,
take the clay body and fire it up cone 6.
See if it disrupts , bloats or melts.
[ please do this in a high fire saucer -
porcelain or stoneware , if it melts it
will ruin your shelf ]
It helps to have a test kiln.
See if Anne Possoz is still on the list ,
I believe she was building a page to
show how to make a Test Kiln.They are
not difficult to put together.
If the body withstands cone 6 , try cone 8
, if it melts or bloats go lower.
Determine the maturing temperature by
cone.
Then you will automatically know what
temperature to look for in a glaze.
As to getting the glaze to fit . Well without a
chemical analysis of the body ,we will have
to use glazes with known expansions.
We will find a low expansion , a medium
expansion and high expansion glaze.
Or you can ask someone to do the analysis.
Cement making companies can do this .
It would be helpful if you could list , just what
you were able to obtain.
Until you respond.
Khaimraj
-----Original Message-----
From: Martin Rice
To: CLAYART@LSV.CERAMICS.ORG
Date: 06 March 2002 20:55
Subject: Claybodies and cones
>When I wrote in asking about how to go about making my own clay, Lois
>Richter was kind enough to send me a recipe that she thought might be ideal
>for the materials I believed I could get here. She called it a ^04 though
>what she sent me was labeled ^08-^04. Mark talks above about taking a basic
>^6 clay recipe and eventually evolving it into a ^10 body.
>
>My naive questions are: what is it that makes a body a ^04 or a ^10 or what
>have you? Does this refer to at what cone number certain glazes will work
on
>a given claybody -- for example the title of the book about "^6 glazes?"
>
>At this point in my early efforts I'm confused. The guy at the supply house
>I bought things at today to make my first clay told me that it would bisque
>at ^06 but it would be stronger at ^04. Does that mean that this claybody
>will be a ^06-^04 claybody and have nothing to do with what cone I'll have
>to use for my glazes, that cone number being a reflection of the type of
>glaze I use? And, last question for now: if I use a claybody that bisques
at
>^04, does that imply limitations at to what cone I can glaze at?
>
>Thanks so much,
>Martin
>Lagunas de Barú, Costa Rica
>www.rice-family.org
Bill Arnold on thu 7 mar 02
Take a small amount of clay and make a bar that will fit into a Dawson ki=
ln
sitter. Install in the kiln sitter and put a full range ot cones in kiln.
Fire kiln. Inspect cones. Do not fire clay above cone that is bent.
Bill
----- Original Message -----
From: "Khaimraj Seepersad"
To:
Sent: Thursday, March 07, 2002 10:24 AM
Subject: Re: Claybodies and cones
> Hello to All ,
>
> Martin ,
>
> take the clay body and fire it up cone 6.
> See if it disrupts , bloats or melts.
> [ please do this in a high fire saucer -
> porcelain or stoneware , if it melts it
> will ruin your shelf ]
>
> It helps to have a test kiln.
> See if Anne Possoz is still on the list ,
> I believe she was building a page to
> show how to make a Test Kiln.They are
> not difficult to put together.
>
> If the body withstands cone 6 , try cone 8
> , if it melts or bloats go lower.
> Determine the maturing temperature by
> cone.
>
> Then you will automatically know what
> temperature to look for in a glaze.
>
> As to getting the glaze to fit . Well without a
> chemical analysis of the body ,we will have
> to use glazes with known expansions.
> We will find a low expansion , a medium
> expansion and high expansion glaze.
>
> Or you can ask someone to do the analysis.
> Cement making companies can do this .
>
> It would be helpful if you could list , just what
> you were able to obtain.
> Until you respond.
> Khaimraj
>
>
>
> -----Original Message-----
> From: Martin Rice
> To: CLAYART@LSV.CERAMICS.ORG
> Date: 06 March 2002 20:55
> Subject: Claybodies and cones
>
>
>
> >When I wrote in asking about how to go about making my own clay, Lois
> >Richter was kind enough to send me a recipe that she thought might be
ideal
> >for the materials I believed I could get here. She called it a ^04 tho=
ugh
> >what she sent me was labeled ^08-^04. Mark talks above about taking a
basic
> >^6 clay recipe and eventually evolving it into a ^10 body.
> >
> >My naive questions are: what is it that makes a body a ^04 or a ^10 or
what
> >have you? Does this refer to at what cone number certain glazes will w=
ork
> on
> >a given claybody -- for example the title of the book about "^6 glazes=
?"
> >
> >At this point in my early efforts I'm confused. The guy at the supply
house
> >I bought things at today to make my first clay told me that it would
bisque
> >at ^06 but it would be stronger at ^04. Does that mean that this clayb=
ody
> >will be a ^06-^04 claybody and have nothing to do with what cone I'll
have
> >to use for my glazes, that cone number being a reflection of the type =
of
> >glaze I use? And, last question for now: if I use a claybody that bisq=
ues
> at
> >^04, does that imply limitations at to what cone I can glaze at?
> >
> >Thanks so much,
> >Martin
> >Lagunas de Bar=FA, Costa Rica
> >www.rice-family.org
>
>
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Martin Rice on thu 7 mar 02
Khaimraj wrote:
>
> It would be helpful if you could list , just what
> you were able to obtain.
> Until you respond.
> Khaimraj
>
Here's what I got as a package to make 100 lbs of clay:
50 lbs of Ball Clay - CAS #132-58-7 (from the Kentucky-Tennessee Clay Co. --
right here in little ol' Costa Rica, and me having lived 28 years in
Tennessee)
50 lbs of Talc (from the RT Vanderbilt Co, Norwalk, CT)
2.2 lbs of what they called carbonato (it's just a little plastic bag that
they bag up). Don't know what it is, but I'm assuming that it's probably
carbonato de calcio - whiting
Less than 100 grams of what they called "soda" but I don't know what kind.
Perhaps soda feldspar?
And a little jar of liquid that they called silicato - silicate. Don't know
what kind. Hope it's something like sodium silicate and not lead!
Supposed to mix it with 5 1/2 gallons of water and let stand a minimum of
eight hours. The folks said that it would bisque at ^06 but better at ^04.
I'll mix it up tomorrow!
Regards,
Martin
Lagunas de Barú, Costa Rica
www.rice-family.org
Ron Roy on fri 8 mar 02
Just a few clarifications,
Low fire clays cannot be taken to vitrification - you need an insoluble
melter (read frit) that works down there - and if you add enough of it the
firing range becomes so small you will have all kinds of trouble
maintaining a proper level of melting - it's just too unreliable for the
kind of technology potters use.
Some companies give a range of cones for their clays - it does not follow
that the top cone will give proper vitrification - nor does it mean the
clay will not be over fired at that same temperature.
This is one of the questions our clay testing program is designed to do -
find out what the true range is of the clays we buy.
There is no such thing as a clay that has a range of cone 6 to cone 10 - it
will be under fired -(read leak) at cone 6 - if it is vitrified enough not
to leak at 6 then it will be over fired at 10 - if there is iron present
and the clay is fired at cone 10 reduction and cone 6 oxidation then the
situation gets worse.
The way you find out what cone your clay should be fired to is to test it -
and measure the absorbency at the cone you want fire at.
All the clays (except for the earthenware) I work on have a firing range of
one cone - a little less or a little more and I am nor responsible anymore.
I find it difficult enough - keeping the vitrification at the right level
for one cone - our raw materials are variable - some more than others - the
trick is to choose materials carefully and have many different clays in a
body - to make sure no one clay can - if it goes downhill - affect the body
too much.
RR
>>My naive questions are: what is it that makes a body a ^04 or a ^10 or what
>>have you? Does this refer to at what cone number certain glazes will work on
>>a given claybody -- for example the title of the book about "^6 glazes?"
>Martin-
>When a clay body is described as firing to a certain cone,
>that refers to the highest temperature that particular
>clay may be fired to without slumping, bloating, or
>showing other detrimental signs of overfiring. Low-fire
>clays will generally be less vitrified at their maximum
>temperature than high-fire clays; that's their nature.
>They may get more vitrified if fired higher, but will
>show effects of overfiring as mentioned above. Clays
>which are described as having a firing 'range', such as
>^6-^10 of some such, are only optimally vitrified at the
>top temperature listed; the lower temperature may be OK
>for many purposes, but the clay will be less fully
>vitrified at that temperature, and be weaker and more
>porous. Simply speaking, low-fire glazes (and clays)
>have more fluxes in them than their high-fire kindred,
>allowing them to melt at lower temperatures.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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