Michele D'Amico on thu 7 apr 05
I sometimes fire my pots in a group studio kiln that is fired (but not by
me) to ^10 in reduction. Lately I'm having a problem with groggy clays
that are high in iron shattering either in the kiln or the first time they
touch hot water. When they break the clay under the glaze is black.
What's causing this?
Michele
damicom@cruzio.com
John Britt on thu 7 apr 05
Too much reduction which is causing carbon coring.
Hope it helps,
John Britt
www.johnbrittpottery.com
Snail Scott on thu 7 apr 05
At 01:45 AM 4/7/2005 -0400, you wrote:
>...When they break the clay under the glaze is black.
>What's causing this?
Carbon-core is not primarily due to the
final firing, but to insufficient bisquing.
High-iron clays are especially vulnerable to
carbon-coring.
The bisque firing needs to be a clean, neutral/
oxidizing (not reducing) environment, and
needs to be for a sufficient period of time.
Either your clay is being bisqued too quickly,
or it's being done in a slightly reducing
atmosphere. Point out the problem to whoever
is doing the bisque firings, and see if they
could be extended, or (if they're done in a
fuel-burning kiln) whether they could be
bisqued in an electric kiln instead. If not,
suggest (courteously) that perhaps there is
some reduction going on during the bisque,
and (since they perhaps hadn't been aware of
it) they could avoid that in the future.
-Snail
Craig Clark on thu 7 apr 05
Michele, it is my guess that there is an overly agressive "body
reduciton" that is ocurring somewhere early in the firing. I'm thinking
this because you are seeing the carbon deposition in the clay body upon
inspection. It may be taking place at around bisque temp. If you watch
the firing and there is an abundance of black smoke puffing from the
kiln at this early stage or if you can really "smell" the reduction
there is a good chance that the body reduction of the firing is being
done for to long and period of time and with much more of a reduciton
atmoshpere than is necessary.
Another thing to look at is whether or not this is a systemic
problem or if the troubles are isolated to your work alone or that of a
few others. Are any of the other folks pots cracking? If not then the
trouble is with either your clay body/glaze combo or with your pots.
This could also be a severe mismatch between the glaze that you use and
the claybody itself and have little to do with the firing of the kiln.
Does it happen with all of the glazes in the studio? What type of clay
body are you using? Do you folks purchase it or mix it up yourselves? If
you mix it up do you have a communal slip bucket that is processed back
into each batch of mud? Are there a number of different clay bodies that
get dumped into the communal bucket as is often the case with
institutional settings? What I'm getting at here is that there may
several contributing factors. Do you know what the coefficient of
expansion/contraction of your clay body and glazes are? The answers to
these questions will help lead you to a solution to the problem.
Hope this helps
Craig Dunn CLark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Ron Roy on fri 8 apr 05
How can you have too much reduction John?
RR
>Too much reduction which is causing carbon coring.
>
>Hope it helps,
>
>John Britt
>www.johnbrittpottery.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Brant Palley NMCLAY.com on fri 8 apr 05
It is not carbon; it is the red iron oxide converting to black iron oxide.
A problem common to downdraft kilns (Giel) especially at high altitude.
Brant Palley
www.nmclay.com
Spring Sale April 11 to 16!
John Britt on fri 8 apr 05
Ron,
In my experience, if you begin reduction around cone 012 and it is very
heavy (oxiprobe .70 and above) with an iron clay body and you hold it for
several hours (or until the end of the firing) you will get black coring.
This is regardless of how you bisque.
Of course, black coring is a variable term and it may be a grey to a black
in the center of the piece or tile. A good way to check without cracking
your work is to use the same body in the cone pack and then you can crack
the cone pack.
Is that what you are after?
John Britt
www.johnbrittpottery.com
Snail Scott on sat 9 apr 05
At 02:07 AM 4/8/2005 -0400, you wrote:
>It is not carbon; it is the red iron oxide converting to black iron oxide.
>A problem common to downdraft kilns (Giel) especially at high altitude.
Excellent point. The conventional term is 'carbon
core', but that doesn't mean that it's an accurate
description. I tend to still call it that out of
old habit, but the term 'black core' seems to be
gaining in popularity, and that's a good thing.
-Snail
Ron Roy on mon 11 apr 05
Thanks John,
>Ron,
>
>I did not see this on clayart.
>
>John
>> Hi John,
>>
>> I don't think you can over reduce - once the Fe2O3 is reduced to FeO you
>> cannot reduce any further.
>>
>> Black coring which happens in a glaze firing is the result of a body being
>> properly reduced - then - because the kiln atmosphere returns to oxidation
>> - the outer clay is somewhat reoxidized and turns a different colour than
>> the inside clay - which is darker - hence the name black coring.
>>
>> If it happens in the bisque firing it is because the organics don't have
>> enough oxygen to burn out properly. There is an illustrated example in the
>> Hamer Dictionary by the way - page 26 in the 4th edition.
>>
>> See also bloating on the next page.
>>
>> We have also to remember that if a body has a lot of iron to start with -
>> it can be over fired with proper reduction. The cure in that case would be
>> to reformulate and make the body more refractory. In other words - if you
>> have a clay body that is bloating because of reduction - it needs
>> changing.
>>
>> RR
>>
>>
>>
>>>In my experience, if you begin reduction around cone 012 and it is very
>>>heavy (oxiprobe .70 and above) with an iron clay body and you hold it for
>>>several hours (or until the end of the firing) you will get black coring.
>>>This is regardless of how you bisque.
>>>
>>>Of course, black coring is a variable term and it may be a grey to a black
>>>in the center of the piece or tile. A good way to check without cracking
>>>your work is to use the same body in the cone pack and then you can crack
>>>the cone pack.
>>>
>>>Is that what you are after?
>>>
>>>John Britt
>>>www.johnbrittpottery.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Britt on mon 11 apr 05
Ron,
I am in the unusual position of disagreeing with you, but I think the
problem here is semantics.
The colloquial expression =93over reduced=94 is not a technical term, but
rather used to indicate that a clay body has been fired in such heavy
reduction that the strength of the body is compromised. (Black cored)
While it may not be "technically" precise, it is a common term in many
studios across the country and is often used in a comparative manner.
It is like Goldie Locks and the porridge, but in this case if you have
three clay bodies in a firing, porcelain, light stoneware and dark
stoneware, and you fired in heavy reduction the dark stoneware would be
said to be over reduced, the stoneware would be ok and the porcelain would
be just right.
I think that the difference here is you want to change/reformulate the
clay body while I want to change the firing cycle. As many other potters,
I rarely make my own clay but rather purchase clay bodies and put them
into different firing atmospheres and compare them, hence the comparative
term, =93over reduced=94.
A dark clay body used in a heavy celadon cycle would be =93over reduced=94
while the same body in an oxidation cycle would be perfect.
Hope that clarifies my position,
John Britt
www.johnbrittpottery.com
Ron Roy on tue 12 apr 05
Hi John,
I understand your position.
You are saying that some clay bodies - which have not been formulated
correctly need to be under reduced - is that correct?
I also understand that most potters have to put up with less than ideal
clays because they buy them.
What I am railing against are terms that lead to misunderstanding.
My hope in the long run is - the people who make clay for potters will
learn how to make clay that - in this case - does not need under reduced to
work properly.
The more we understand as potters - and the more demanding we are - the
faster the changes will take place.
Thanks for your explanation and for giving me a chance to better explain mys=
elf.
RR
>I am in the unusual position of disagreeing with you, but I think the
>problem here is semantics.
>
>The colloquial expression =93over reduced=94 is not a technical term, but
>rather used to indicate that a clay body has been fired in such heavy
>reduction that the strength of the body is compromised. (Black cored)
>While it may not be "technically" precise, it is a common term in many
>studios across the country and is often used in a comparative manner.
>
>It is like Goldie Locks and the porridge, but in this case if you have
>three clay bodies in a firing, porcelain, light stoneware and dark
>stoneware, and you fired in heavy reduction the dark stoneware would be
>said to be over reduced, the stoneware would be ok and the porcelain would
>be just right.
>
>I think that the difference here is you want to change/reformulate the
>clay body while I want to change the firing cycle. As many other potters,
>I rarely make my own clay but rather purchase clay bodies and put them
>into different firing atmospheres and compare them, hence the comparative
>term, =93over reduced=94.
>
>A dark clay body used in a heavy celadon cycle would be =93over reduced=94
>while the same body in an oxidation cycle would be perfect.
>
>Hope that clarifies my position,
>
>John Britt
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Ron Roy on sat 16 apr 05
I have no comments about reduction weakening a clay body aside from the
fact that overfired (glassified) stoneware clay is brittle.
Carbon cored ware suffers from the fact that if the body is unevenly
reduced you have differences of expansion within the body. That cannot be
beneficial.
You are right to pin point cristobalite as a possible contributor to glaze
dunting in high iron type bodies fired in reduction.
If you have a glaze that is crazed that kind of dunting will not happen -
so it is possible to avoid cristobalite dunting by raising the
expansion/contraction of the glaze.
It is the combination of a high expansion body and a too low expanding
glaze that produces the problem.
High iron bodies need to be designed with enough spar to melt any
cristobalite as it is formed. Harder to do with high iron bodies because
they are being fluxed with the reduced iron. It means you need more
refractory clays and the proper amount of spar - like 10%.
See Peter Sohngens article in Studio Potter - vol 28 #1. Any one who
designs cone 10 stoneware bodies should know that article by heart.
RR
>Scraping the bottom of my memory barrel, I remember having thermal
>shock problems(mugs cracked when hot water was poured in) with the
>early pots fired in my first reduction gas firings. I was told by
>friends that my clay was high in iron and silica and that the reduction
>had produced a problem with that combo of materials. Does this make
>sense when thinking of carbon coring producing weaker pots? Does it
>have anything to do with crystabolite?
>
>Jennifer, bowing under her ignorance....
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sat 16 apr 05
Hi Jon,
I am assuming that reduction means fully reduced - as most potters would
understand. Certainly not partially reduced or half reduced - or somewhat
reduced - or reduced and partially reoxidized.
It simply follows that clay bodies should be formulated to work properly
under fully reduced conditions.
That would the the standard - I would expect all other bodies - that needed
a different kind of heat treatment would have instructions - like only
light reduction needed or do not fully reduce.
Do you think I am being unreasonable?
RR
>Greetings All--- Hi John and Ron ---you wrote---=93You are saying that some
>clay bodies - which have not been formulated correctly need to be under
>reduced - is that correct?
>
>My hope in the long run is - the people who make clay for potters will
>learn how to make clay that - in this case - does not need under reduced to
>work properly.=94
>
>
>Excuse me--- but how did you come to decide what=92s an ideal clay and what=
an
>ideal reduction firing cycle consists of. Are you referring to some ideal
>parameters that you have developed and feel should apply to a very narrow
>category of pottery like functional tableware?
>
>I can understand how a particular clay can be applied to a particular
>technique and a particular firing cycle applied to get specific results, bu=
t
>I don=92t see how there can be universally ideal clays and firing cycles.
>
>Some clays are most certainly designed to be lightly reduced or even
>oxidation fired, I=92m not sure I would call that incorrectly formulated.
>
>Also---how does firing clay in neutral/oxidation conditions some how make i=
t
>=93under reduced and less than ideal=94? Potters who fire in gas
>neutral/oxidation atmospheres or in electric kilns might take exception to
>that.
>
>Best regards
>Jon Pacini
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
John Britt on sat 16 apr 05
Ron,
I did not address this as I was only trying to get clear about the
semantics in the last post, but since Jon bought it up.....I have never
heard of a clay body that came with instructions - "Use only in fully
reducing conditions", or "Use under only light reduction conditions only".
Actually, I have never seen a box of clay come with any instructions. Nor
have I ever seen a clay recipe come with instructions about atmosphere,
except maybe =93good in salt=94.
First of all, I would doubt that a clay body is ever "fully" reduced. Is
this possible? That every molecule of Fe203 is changed to Fe0. I don't
think you ever get that kind of precision under any circumstances let
alone with potters working in gas kilns with unpredictable winds, corroded
burners, old leaky uneven kilns etc. And that is not to mention then being
able to hold that reducing atmosphere to the end of the firing and also
not allowing it to oxidize on the cooling cycle. I think it is impossible
and unreasonable to expect. There is simply never that kind of precision
in pottery. (Unless I am the sloppy odd ball here?)
Secondly, what is =93light reduction=94? How much, for how long?
What I have seen is potters trying store bought clay bodies in their
typical cycle and then determining if they are acceptable. If a particular
clay body is black cored then we say =93that clay body is over-reduced=94 an=
d
use it in a different cycle or quit using it. If they use a clay body and
like the look in their cycle then they will try using it a bit more and
after a longer time period of watching and learning the characteristics of
the clay body with their glazes then they finally adopt the clay body into
their =93line=94.
Just my thoughts,
John Britt
www.johnbrittpottery.com
Lee Love on sun 17 apr 05
One way to have rich iron under a glaze and not have to worry
about over reducing an iron body, is to do what Hamada did: Use a low
iron body(Mashiko Nami tsuchi) and just put an iron slip (ocher in
Hamada's case) over the body before you bisque.
This is especially important with glazes that have solubles
in them that seal the glaze surface early. Shinos traditionally were
put on low iron clay. If iron was desired, an iron slip was put on the
light body.
I have been testing different iron colored blends, but
find the light colored Mashiko clay with ocher slip over it less
problematic, so I am going back to it. The Nukas look best over
ocher. Otherwise, they are too stark white.
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
"We can make our minds
so like still water
that beings gather about us
that they may see,...
....their own images, and so live for a moment with a clearer,
perhaps even with a fiercer life
because of our quiet." -- W. B. Yeats
Jon Pacini on fri 22 apr 05
Greetings All-Hi Ron--- It's not a case of being unreasonable, I think
you're making an assumption that the vast majority of clay users are
reducing their clay a specific "common" amount and then you're saying,
'generally, clays should be made to fit that criteria'.
I'm not at all certain that you are making a correct assumption about the
techniques employed by potters. And I'm not certain that anyone can assume
anything specific about how a clay is going to be used once it leaves the
warehouse.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Hi Jon,
I am assuming that reduction means fully reduced - as most potters would
understand. Certainly not partially reduced or half reduced - or somewhat
reduced - or reduced and partially reoxidized.
It simply follows that clay bodies should be formulated to work properly
under fully reduced conditions.
That would the the standard - I would expect all other bodies - that needed
a different kind of heat treatment would have instructions - like only
light reduction needed or do not fully reduce.
Do you think I am being unreasonable?
RR
>Greetings All--- Hi John and Ron ---you wrote---"You are saying that some
>clay bodies - which have not been formulated correctly need to be under
>reduced - is that correct?
>
>My hope in the long run is - the people who make clay for potters will
>learn how to make clay that - in this case - does not need under reduced to
>work properly."
>
>
>Excuse me--- but how did you come to decide what's an ideal clay and what
an
>ideal reduction firing cycle consists of. Are you referring to some ideal
>parameters that you have developed and feel should apply to a very narrow
>category of pottery like functional tableware?
>
>I can understand how a particular clay can be applied to a particular
>technique and a particular firing cycle applied to get specific results,
but
>I don't see how there can be universally ideal clays and firing cycles.
>
>Some clays are most certainly designed to be lightly reduced or even
>oxidation fired, I'm not sure I would call that incorrectly formulated.
>
>Also---how does firing clay in neutral/oxidation conditions some how make
it
>"under reduced and less than ideal"? Potters who fire in gas
>neutral/oxidation atmospheres or in electric kilns might take exception to
>that.
>
>Best regards
>Jon Pacini
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sat 30 apr 05
Hi Jon,
I prefer to think of myself as idealistic rather than unrealistic - and
being realistic is some times the thin edge of the wedge on the road to
shoddy work.
Tuckers sells a whole line of cone 10 reduction clays - I fire them in
reduction to cone 10 and the lab fires them to cone 10 oxidation - so i can
see clearly just how much the difference is.
The Newman red body is black in reduction and light brown in oxidation for
instance - it has the most iron.
I have records going back to 1997 and it is clear that the body is
serviceable in both situations - tighter in reduction but still a
servicable clay.
It happens to be the stoneware clay I use as well.
So I am having trouble understanding the comment that you can't have it
both ways and everything inbetween - it seems quite clear to me that proper
formulation is the key.
Of course I would not be writing this if Tuckers customers were complaining
about any of those bodies - and I assume they are all firing at least a
little differently. So what is different between there and here?
RR
>The fact of the matter is that you just never know how a box of clay is
>going to be used when it's purchased off the shelf. And as a potter, to
>purchase an unknown quantity and assume it's going to work to your
>expectations is a bit unrealistic. Granted, clays should work within the
>parameters laid down by the manufacturer, but under any given firing
>conditions it may come out lighter or darker or more vitreous or less. After
>all firing conditions vary from potter to potter.
>As I said previously I don't think you're being unreasonable, but rather a
>bit unrealistic. Everyone doesn't produce ware using the same techniques.
>You can't expect a clay to perform in exactly the same manner no matter how
>it's used.
>Best regards
>Jon Pacini
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jon Pacini on mon 2 may 05
Greetings All ---Hi Ron, Yes we often see ourselves quite differently than
others do. I consider myself quite conservative actually. Must mean
something different here than there.
Not sure why there are such differences with potters in our two locations,
though I pretty much work with potters nationwide. I guess many of the
potters that deal with Laguna are not as conservative in their techniques as
those that deal with Tuckers. I get calls from people trying to do all kinds
of wild things with clay. I’m not sure where they get this type of training
from, maybe they just like experimenting around and pushing the limits. I
must admit, I do encourage them to a certain extent, it sure makes for it an
exciting clay scene---seems quite wide spread too.
But still-- I just can’t imagine a clay that would work satisfactorily no
matter how you fired it. I’d think even your Newman Red based clay must have
some limitations. Oh---I’m sure you’ll explain that it doesn’t as long as it
is properly fired---but then we get back to that “who considers what
‘properly fired’ means” discussion.
Good luck with trying to impose standards on potters.
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co.
Ron Roy on thu 5 may 05
Hi Jon,
The Newman body works well as long as it's fired to cone 10 - no reduction,
some reduction, or full reduction.
I know there are many that find this unbelievable - it's what this
conversation is all about - properly formulated clay bodies - to do what
they are supposed to do when fired to the right temperature.
There are lots of potters who would welcome some standards on the part of
suppliers - not a question of imposing standards - the market place will
decide that - all in good time.
RR
>But still-- I just can=92t imagine a clay that would work satisfactorily no
>matter how you fired it. I=92d think even your Newman Red based clay must h=
ave
>some limitations. Oh---I=92m sure you=92ll explain that it doesn=92t as=
long as it
>is properly fired---but then we get back to that =93who considers what
>=91properly fired=92 means=94 discussion.
>
>Good luck with trying to impose standards on potters.
>
>Best regards,
>Jon Pacini
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Ceramic Design Group on thu 5 may 05
Ron:
I have followed this discourse for quite sometime and being somewhat (I =20=
guess) knowledgeable in clays and such, I wonder about this whole idea =20=
of standards.
I don't know how we can have standards with materials that are formed =20=
in the earth and then processed for industry. They are not beneficiated =20=
by any clay manufacturing company I know of. The extent of =20
beneficiation that I have seen is screening coarse fireclays, and it =20
still leaves problems. I only know of a few potters that wet mix to a =20=
slurry, Sweco the mix, filter press it and then pug mill it. Then and =20=
only then can there even be some degree of standards. Heck, clay body =20=
mfgs have different penetrometers with different scales so you can't =20
use any numbers to base moisture content from supplier to supplier.I =20
think to have standards for clay bodies is an effort wrought with =20
problems because it is impossible to have a standard from which to have =20=
a baseline. Provide a baseline and I might think differently. But what =20=
baseline and how do you quantify it?
I also question what is full reduction, some or no reduction? The only =20=
way to quantify this is with proper stochiometric combustion equipment =20=
and an oxygen probe. Most potters I know still fire by the seat of =20
their pants, at best.
I have used Newman Red in casting bodies and found that after sieving =20=
it to get all the junk out it is a pretty good material to add to a =20
clay. I don't know about all the different atmostpheres though, and I =20=
would posit that it does have a very low iron content. I don't have my =20=
data sheet as I am traveling, but I would think that it is pretty low =20=
so it might impart little actual iron thus not acting to provide any =20
fluxing action (As Redart does) but just enough color the body. Just my =20=
opinion.
Respectfully,
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
Plant location for commercial deliveries excluding USPS
1280 13th Street Suite K
Steamboat Springs CO 80487
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
On May 5, 2005, at 4:23 PM, Ron Roy wrote:
> Hi Jon,
>
> The Newman body works well as long as it's fired to cone 10 - no =20
> reduction,
> some reduction, or full reduction.
>
> I know there are many that find this unbelievable - it's what this
> conversation is all about - properly formulated clay bodies - to do =20=
> what
> they are supposed to do when fired to the right temperature.
>
> There are lots of potters who would welcome some standards on the part =
=20
> of
> suppliers - not a question of imposing standards - the market place =20=
> will
> decide that - all in good time.
>
>
>
> RR
>
>
>> But still-- I just can=92t imagine a clay that would work =20
>> satisfactorily no
>> matter how you fired it. I=92d think even your Newman Red based clay =20=
>> must have
>> some limitations. Oh---I=92m sure you=92ll explain that it doesn=92t =
as =20
>> long as it
>> is properly fired---but then we get back to that =93who considers =
what
>> =91properly fired=92 means=94 discussion.
>>
>> Good luck with trying to impose standards on potters.
>>
>> Best regards,
>> Jon Pacini
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> =
_______________________________________________________________________=20=
> _______
> 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 =20
> melpots@pclink.com.
>
>
Louis Katz on fri 6 may 05
This is what I have on Newman
I am not sure but believe it came from a report sent to me by laguna =20
this year. I don't know the date of the report.
Newman Red Clay
P.C.E. 19-20
Silica/Alumina ratio: 4.7:1
Equivalent Molecular Weight: 465.096
Molecular Formula of Newman Red Clay:
K20 0.044 Al2O3 1.000 SiO2 4.676
Na2O 0.017 Fe2O3 0.229 TiO2 0.058
CaO 0.004 LOI 1.922
MgO 0.026 =09
Percentage Analysis
60.38 % SiO2
21.92 % Al2O3
0.88 % K2O
0.22 % Na2O
0.23 % MgO
0.05 % CaO
7.87 % Fe2O3
1.00 % TiO2
7.45 % L.O.I.
______________
100.00 % TOTAL
On May 5, 2005, at 8:01 PM, Ceramic Design Group wrote:
> Ron:
>
> I have followed this discourse for quite sometime and being somewhat =20=
> (I guess) knowledgeable in clays and such, I wonder about this whole =20=
> idea of standards.
>
> I don't know how we can have standards with materials that are formed =20=
> in the earth and then processed for industry. They are not =20
> beneficiated by any clay manufacturing company I know of. The extent =
=20
> of beneficiation that I have seen is screening coarse fireclays, and =20=
> it still leaves problems. I only know of a few potters that wet mix to =
=20
> a slurry, Sweco the mix, filter press it and then pug mill it. Then =20=
> and only then can there even be some degree of standards. Heck, clay =20=
> body mfgs have different penetrometers with different scales so you =20=
> can't use any numbers to base moisture content from supplier to =20
> supplier.I think to have standards for clay bodies is an effort =20
> wrought with problems because it is impossible to have a standard from =
=20
> which to have a baseline. Provide a baseline and I might think =20
> differently. But what baseline and how do you quantify it?
>
> I also question what is full reduction, some or no reduction? The only =
=20
> way to quantify this is with proper stochiometric combustion equipment =
=20
> and an oxygen probe. Most potters I know still fire by the seat of =20
> their pants, at best.
>
> I have used Newman Red in casting bodies and found that after sieving =20=
> it to get all the junk out it is a pretty good material to add to a =20=
> clay. I don't know about all the different atmostpheres though, and I =20=
> would posit that it does have a very low iron content. I don't have =20=
> my data sheet as I am traveling, but I would think that it is pretty =20=
> low so it might impart little actual iron thus not acting to provide =20=
> any fluxing action (As Redart does) but just enough color the body. =20=
> Just my opinion.
>
> Respectfully,
>
> Jonathan
>
> Jonathan Kaplan
> Ceramic Design Group
> PO Box 775112
> Steamboat Springs CO 80477
> (970) 879-9139
>
> Plant location for commercial deliveries excluding USPS
> 1280 13th Street Suite K
> Steamboat Springs CO 80487
>
> info@ceramicdesigngroup.net
> www.ceramicdesigngroup.net
>
>
>
>
>
>
>
> On May 5, 2005, at 4:23 PM, Ron Roy wrote:
>
>> Hi Jon,
>>
>> The Newman body works well as long as it's fired to cone 10 - no =20
>> reduction,
>> some reduction, or full reduction.
>>
>> I know there are many that find this unbelievable - it's what this
>> conversation is all about - properly formulated clay bodies - to do =20=
>> what
>> they are supposed to do when fired to the right temperature.
>>
>> There are lots of potters who would welcome some standards on the =20
>> part of
>> suppliers - not a question of imposing standards - the market place =20=
>> will
>> decide that - all in good time.
>>
>>
>>
>> RR
>>
>>
>>> But still-- I just can=92t imagine a clay that would work =20
>>> satisfactorily no
>>> matter how you fired it. I=92d think even your Newman Red based clay =
=20
>>> must have
>>> some limitations. Oh---I=92m sure you=92ll explain that it doesn=92t =
as =20
>>> long as it
>>> is properly fired---but then we get back to that =93who considers =
what
>>> =91properly fired=92 means=94 discussion.
>>>
>>> Good luck with trying to impose standards on potters.
>>>
>>> Best regards,
>>> Jon Pacini
>>
>> Ron Roy
>> RR#4
>> 15084 Little Lake Road
>> Brighton, Ontario
>> Canada
>> K0K 1H0
>> Phone: 613-475-9544
>> Fax: 613-475-3513
>>
>> =
______________________________________________________________________=20=
>> ________
>> 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 =20
>> melpots@pclink.com.
>>
>>
>
> =
_______________________________________________________________________=20=
> _______
> 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 =20
> melpots@pclink.com.
>
Jon Pacini on fri 6 may 05
Greetings All---Hi Jonathan------You know, you could make a clay body from
reagent grade minerals that come with a “certified analysis”. This type of
analysis is light years beyond the typical ones we get for ceramic grade
minerals.
Perhaps this clay could then be used for such a baseline as you have
suggested and standards drawn from that. And since these are certified
minerals, computations with glaze programs would definately then be of
greater value.
Here’s a small sampling of what the certified minerals cost from Fisher
Scientific.
Kaolin (acid washed) 500gr---$28.00
Ferric oxide (red, anhydrous) 500gr---$20.00
Silica (floated, about 240 mesh) 3kg---$28.75
Calcium Carbonate (powder) 500gr---$88.00
Cobalt Oxide (black) 500gr---$429.70
Potassium Carbonate (anhydrous powder) 500gr---$39.40
A ton of clay or a hundred pounds of glaze might get a bit expensive---but
hey!!--- I’m sure every potter will appreciate the stability of these
materials.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co.
Ron Roy on sun 8 may 05
Hi Jonathan,
I was not suggesting that the mines provide standard clays - of course
there will always be differences - The Feldspar Corporation used to send an
analysis with each shipment. That could be a standard - and if we had some
clout with the mines we could insist.
I was talking about taking responsibility for what we make particularly
with functional pots - apply some standards - pots that don't leak - clay
that does not leak when fired to the advertised temperature - glazes that
don't deteriorate with use.
We would all be better off if those standards were more common.
I simply stated that we test every batch of the Newman Red at cone 10 - in
oxidation and reduction - and it works under both conditions - some one
said a high iron body could not be serviceable in both oxidation and
reduction - I am simply saying - it depends on the formulation - and it can
be done.
As for telling if a body is reduced or not and all the variables in between
- you can get a pretty good idea by looking at the fired clay - especially
when there is iron present. It is an excellent way to help diagnose
problems.
Newman is a refractory high iron bearing clay - it has more iron in it than
Red Art for instance.
If you are going to use it you must sieve it - it is one of our more
interesting unrefined clays -.
RR
>I don't know how we can have standards with materials that are formed
>in the earth and then processed for industry. They are not beneficiated
> by any clay manufacturing company I know of. The extent of
>beneficiation that I have seen is screening coarse fireclays, and it
>still leaves problems. I only know of a few potters that wet mix to a
>slurry, Sweco the mix, filter press it and then pug mill it. Then and
>only then can there even be some degree of standards. Heck, clay body
>mfgs have different penetrometers with different scales so you can't
>use any numbers to base moisture content from supplier to supplier.I
>think to have standards for clay bodies is an effort wrought with
>problems because it is impossible to have a standard from which to have
>a baseline. Provide a baseline and I might think differently. But what
>baseline and how do you quantify it?
>
>I also question what is full reduction, some or no reduction? The only
>way to quantify this is with proper stochiometric combustion equipment
>and an oxygen probe. Most potters I know still fire by the seat of
>their pants, at best.
>
>I have used Newman Red in casting bodies and found that after sieving
>it to get all the junk out it is a pretty good material to add to a
>clay. I don't know about all the different atmostpheres though, and I
>would posit that it does have a very low iron content. I don't have my
> data sheet as I am traveling, but I would think that it is pretty low
>so it might impart little actual iron thus not acting to provide any
>fluxing action (As Redart does) but just enough color the body. Just my
>opinion.
>Jonathan
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on tue 10 may 05
Hi Jon,
No need to go that route - just institute a program of testing bodies and
raw materials - you can then compensate for variable raw materials.
Not rocket science - but it does take a particular point of view to start wi=
th.
Not a bad idea to test glazes for stability either - then potters would
know which are appropriate for liner glazes.
RR
>A ton of clay or a hundred pounds of glaze might get a bit expensive---but
>hey!!--- I=92m sure every potter will appreciate the stability of these
>materials.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Jonathan Kaplan on fri 13 may 05
Ron:
I forgot to add this to my earlier lengthy post to you and list...
Glaze fit problems, for me, are easier to solve by adjusting the glaze,
not the clay. And like yourself, I use Insight. I have also worked with
Matrix and Glazemaster but have always used Insight as my glaze
calculation program of choice.
I have always used HyperGlaze as my data base and it creates the
worksheets for out mixing. The new OSX version that Richard just put
out is really nice.
Respectfully,
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
(please use this address for all USPS deliveries)
Plant Location:
1280 13th Street Suite K
Steamboat Springs CO 80487
(please use this address for all UPS, courier, and common carrier
deliveries only!!)
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
Ron Roy on sun 15 may 05
I as well - yes - easier to change the glaze - but in some cases - with
some types of glazes it will be an advantage to also adjust the clay.
If for instance all your glazes were crazing - making some adjustment to
the body makes sense.
I feel that - it there is a way to stop crazing for the soda ash shinos -
the answer will partially be in using a high expansion body.
RR
>Glaze fit problems, for me, are easier to solve by adjusting the glaze,
>not the clay. And like yourself, I use Insight. I have also worked with
>Matrix and Glazemaster but have always used Insight as my glaze
>calculation program of choice.
>
>I have always used HyperGlaze as my data base and it creates the
>worksheets for out mixing. The new OSX version that Richard just put
>out is really nice.
>
>Respectfully,
>
>Jonathan
>
>Jonathan Kaplan
>Ceramic Design Group
>PO Box 775112
>Steamboat Springs CO 80477
>(970) 879-9139
>(please use this address for all USPS deliveries)
>
>
>Plant Location:
>1280 13th Street Suite K
>Steamboat Springs CO 80487
>(please use this address for all UPS, courier, and common carrier
>deliveries only!!)
>
>info@ceramicdesigngroup.net
>www.ceramicdesigngroup.net
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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