Stephani Stephenson on thu 7 may 09
couple of questions on claybody
as i 've mentioned before, i want to come up with a clay body I like
suitable for tile,sculpture/artchitectural ceramics
using handbuilding techniques vs. slipcasting, ram pressing, etc.
I 'll be firing in the cone 1-3 range
I don't want a high talc body.
but I am thinking of ways to lower the maturation point of the body
I'd love it if anyone has experience or ideas to share on the following:
1. Some claybodies have a percentage of feldspar.
What about substituting spodumene for some or all of the feldspar?
Spod is useful as a feldspar with a lower melting point in glazes?
would it hold true in clay body. known drawbacks?
2. I know this has been asked before, but how would Glaze calc be useful=
=3D
in this process,=3D20
in helping me understand the maturation range of a clay. Would I run it t=
=3D
hrough as a=3D20
glaze?.=3D20
would I look at limit formulas as a guide?, knowing that the addition of =
=3D
grog may change=3D20
the actual results of course...but can I use it as a relative comparison =
=3D
tool ? for=3D20
comparing one formula to the other in an attempt to get at least a more =
=3D
'fused' matrix in=3D20
a clay body containing grog?
3. I was talking to someone this morning was asking me about pumice. but=
=3D
what about=3D20
the use of pumice as a body flux?
some low fire bodies use frit. we have also discussed cullet. would pumic=
=3D
e act like cullet.=3D20
are there issues with soluble ingredients?
My friend said that he loved using pumice as a glaze ingredient, except t=
=3D
hat it has a=3D20
tendency to foam, in the batch, which makes mixing and applyig difficult.=
=3D
any advice on the foam problem? we talked about washing or calcining the =
=3D
pumice at a=3D20
low temp... but it got me to thinking about pumice in the clay body.
Also , pumice is cheaper than frit.
OK those are my questions. It's going to take me at least a 5-6 months to=
=3D
work through=3D20
all this. My first batch of clay was nice and workable, not finished test=
=3D
ing it completely,=3D20
though I believe I made a nice cream to buff stoneware body :)
probably too porous at my temp and not enough color, bit I'll see how it =
=3D
handles , then do=3D20
the final shrink/absorp tests.
Ok to answer on or off list. thought it would be a good discussion
Stephani Stephenson
Ron Roy on fri 8 may 09
Hi Stephani,
Ways to lower the absorbency of a low fire clay - some red earthenware's
will help - Neph Sy will help but you have to also add epsom salts to
counter the defocculation - perhaps the best would be a combination of NS
and frit so you have some wiggle room. I can't recommend spodumene because
the expansion may wind up too low and make it difficult to stop crazing in
most glazes.
If it turns out to be a dark clay you will probably need to add some barium
carbonate (try 0.2% to start) to prevent scumming.
How to use calculation software with clays - Lets say you have a clay that
is too open - you calculate the recipe just the way you do a glaze and note
how much alumina there is - silica is important as well but alumina is wher=
e
the clue is. As you add more flux you will see the alumina decrease - not
very complicated I know but it works. You need to remember that some of wha=
t
we call fluxes don't work well at cone 1 to 3 - your best melters are Sodiu=
m
and Potassium and Boron - frits are very useful here but keep in mind - the=
y
help melting so well they cut down the "range" of a clay - hence my disaste=
r
warning. Best to make clay up in advance and test it to make sure it works
properly.
I have worked at reducing the absorption of earthenware clays but - the
closer you get to an ideal absorption the closer you get to disaster - so
choosing materials becomes very important - choose materials that are the
most stable. Hard to do if you don't test raw materials over time but I can
help there.
You can also use % analysis (in most calc programs) reduce refractories and
add melters to lower maturing temperature.
I don't know about pumice - is it the same each time? Foaming sounds ominou=
s
- ever hear of anyone using it - what is the analysis? You will just have t=
o
try some and see if it lowers absorbency.
You should be doing all you testing with the grog included - no use
developing a body with no grog and then starting all over again. Small
amounts of grog can be added to a body and not affect maturity but over 5%
and there will be some effect.
Glad to help along the way - RR
On Thu, May 7, 2009 at 6:44 PM, Stephani Stephenson
wrote:
> couple of questions on claybody
> as i 've mentioned before, i want to come up with a clay body I like
> suitable for tile,sculpture/artchitectural ceramics
> using handbuilding techniques vs. slipcasting, ram pressing, etc.
>
> I 'll be firing in the cone 1-3 range
> I don't want a high talc body.
>
>
> but I am thinking of ways to lower the maturation point of the body
> I'd love it if anyone has experience or ideas to share on the following:
>
> 1. Some claybodies have a percentage of feldspar.
> What about substituting spodumene for some or all of the feldspar?
>
> Spod is useful as a feldspar with a lower melting point in glazes?
> would it hold true in clay body. known drawbacks?
>
> 2. I know this has been asked before, but how would Glaze calc be useful
> in this process,
> in helping me understand the maturation range of a clay. Would I run it
> through as a
> glaze?.
> would I look at limit formulas as a guide?, knowing that the addition of
> grog may change
> the actual results of course...but can I use it as a relative comparison
> tool ? for
> comparing one formula to the other in an attempt to get at least a more
> 'fused' matrix in
> a clay body containing grog?
>
> 3. I was talking to someone this morning was asking me about pumice. but
> what about
> the use of pumice as a body flux?
>
> some low fire bodies use frit. we have also discussed cullet. would pumic=
e
> act like cullet.
> are there issues with soluble ingredients?
> My friend said that he loved using pumice as a glaze ingredient, except
> that it has a
> tendency to foam, in the batch, which makes mixing and applyig difficult.
> any advice on the foam problem? we talked about washing or calcining the
> pumice at a
> low temp... but it got me to thinking about pumice in the clay body.
> Also , pumice is cheaper than frit.
>
> OK those are my questions. It's going to take me at least a 5-6 months to
> work through
> all this. My first batch of clay was nice and workable, not finished
> testing it completely,
> though I believe I made a nice cream to buff stoneware body :)
> probably too porous at my temp and not enough color, bit I'll see how it
> handles , then do
> the final shrink/absorp tests.
> Ok to answer on or off list. thought it would be a good discussion
>
> Stephani Stephenson
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
Craig Martell on fri 8 may 09
Hello Stephanie:
If you decide to use a calculation program with the claybody work it's a
good thing to use R2O3 unity instead of flux unity. What that means is the
alumina (R2O3) will be the value that is expressed by 1.0 instead of the
fluxes being at 1.0. This makes the numbers more sensible.
I hope this will make some sense.
regards, Craig Martell Hopewell, Oregon
Snail Scott on fri 8 may 09
On May 7, 2009, at 5:44 PM, Stephani Stephenson wrote:
> I 'll be firing in the cone 1-3 range
> I don't want a high talc body.
> but I am thinking of ways to lower the maturation point of the body...
I had a chat with John Gill at NCECA on a similar subject,
namely, reducing the temperature of my body without
reducing plasticity (as adding feldspar is likely to do).
He suggested replacing the grog with a feldspathic
sand. I haven't looked into this yet, but...
-Snail
Neon-Cat on fri 8 may 09
Ron and others, some of you know that I=3DE2=3D80=3D99ve been working with =
calcar=3D
eous local clays (rich in calcium carbonate from our local limestone). For =
=3D
comparison, if I wanted to fire (as they are) two clay samples from another=
=3D
region, according to your calculation software programs I shouldn=3DE2=3D8=
0=3D99=3D
t waste my time trying to work with these two clays (below)? I never though=
=3D
t to consider the alumina and flux ratios -- that would be easy. So these p=
=3D
robably won=3DE2=3D80=3D99t get off the ground without major adjustments or=
addit=3D
ions even if I fire to cone 10 (2350 F, oxidation)? I do want my local clay=
=3D
-made vessels to be durable and my clay seemed similar in many ways to the =
=3D
two clays of the samples. Perhaps an investment in software is the way to g=
=3D
o...=3D20
Chemical analysis by element (% wt) as provided to me.
The high calcium clay:=3D20
calcite: CaCO3
SiO2 25.70=3D20
Al2O3 9.39=3D20
TiO2 0.49=3D20
Fe2O3 5.41=3D20
MgO 1.81=3D20
MnO 0.05=3D20
CaO 27.60=3D20
Na2O 0.06=3D20
K2O 2.11=3D20
P2O5 0.11=3D20
L.O.I. 26.10=3D20
Total 98.80=3D20
The high dolomite clay
dolomite: CaMg(CO3)2
SiO2 23.80
Al2O3 9.33
TiO2 0.38
Fe2O3 3.97
MgO 11.90
MnO 0.11
CaO 17.70
Na2O 0.23
K2O 3.93
P2O5 0.11
L.O.I. 27.80
Total 99.30
Thanks!
Marian
Neon-Cat
--- On Fri, 5/8/09, Ron Roy wrote:
> From: Ron Roy
> Subject: Re: questions on making a claybody :spod pumice, etc.
> To: Clayart@LSV.CERAMICS.ORG
> Date: Friday, May 8, 2009, 11:11 AM
>=3D20
> How to use calculation software with clays - Lets say you
> have a clay that
> is too open - you calculate the recipe just the way you do
> a glaze and note
> how much alumina there is - silica is important as well but
> alumina is where
> the clue is. As you add more flux you will see the alumina
> decrease - not
> very complicated I know but it works. You need to remember
> that some of what
> we call fluxes don't work well at cone 1 to 3 - your
> best melters are Sodium
> and Potassium and Boron - frits are very useful here but
> keep in mind - they
> help melting so well they cut down the "range" of
> a clay - hence my disaster
> warning. Best to make clay up in advance and test it to
> make sure it works
> properly.
>=3D20
> I have worked at reducing the absorption of earthenware
> clays but - the
> closer you get to an ideal absorption the closer you get to
> disaster - so
> choosing materials becomes very important - choose
> materials that are the
> most stable. Hard to do if you don't test raw materials
> over time but I can
> help there.
>=3D20
> You can also use % analysis (in most calc programs) reduce
> refractories and
> add melters to lower maturing temperature.
>=3D20
=3D20
> Glad to help along the way - RR
Neon-Cat on sat 9 may 09
Hi all,
I hope you will read the article at the link provided.=3D20
=3DE2=3D80=3D9CMineralogical transformations of calcareous rich clays with =
firing=3D
: A comparative study between calcite and dolomite rich clays from Algarve,=
=3D
Portugal=3DE2=3D80=3D9D,
M.J. Trindade, M.I. Dias, J. Coroado, F. Rocha;
Applied Clay Science 42 (2009) 345=3DE2=3D80=3D93355=3D20
http://dspace.estt.ipt.pt/dspace_estt/bitstream/1234/41/1/Trindade%20et%20a=
=3D
l%202009_Applied%20Caly%20Science.pdf
It details two low fire clay bodies fluxed with carbonates (Mg and Ca). Ron=
=3D
panned my samples (taken from this article) as way out of line. Much of th=
=3D
e world for thousands of years has depended on and enjoyed ceramic products=
=3D
made with their local calcareous clays. While many of you love computer-ge=
=3D
nerated analysis they just fall so far short sometimes and have tended to m=
=3D
islead the studio pottery field and take us away from basic fundamentals re=
=3D
garding our materials and proper ceramic concepts, like fluxing, a chemical=
=3D
reaction. Some would have you believe that statistics on an oxide like CaO=
=3D
can tell you something about how carbonates actually work in a real clay b=
=3D
ody (or glaze) system. To me, a poor kitchen cook, this is analogous to me =
=3D
equating the temperature at which a cake should bake to how much heat is re=
=3D
quired for me to totally crisp-fry an egg to a cinder in a stovetop skillet=
=3D
.=3D20
The article may help. I hope. It is lonely out here with no clay science bu=
=3D
ds to play with. Really.=3D20
Check the aluminum at the end of firing. Much of it is just kind of along f=
=3D
or the ride so I can=3DE2=3D80=3D99t buy Ron=3DE2=3D80=3D99s Al-ratio stuff=
either as a=3D
n important consideration in clay body formulation.=3D20
For your quick reference these are the formulas for the minerals created in=
=3D
the clay body at the end of Ca-firing:=3D20
Gehlenite: Ca2Al(AlSi)O7
Wollastonite: CaSiO3
Larnite: Ca2SiO4
Note the low temperatures and the short firing schedules. Basically =3DE2=
=3D80=3D
=3D98done=3DE2=3D80=3D99 at 800 C (1472 F, cone 015), vitrified and as =3DE=
2=3D80=3D98don=3D
e=3DE2=3D80=3D99 as they=3DE2=3D80=3D99re gonna get at 1100 C (2012 F, cone=
03). This s=3D
tuff is durable, too. Humble potters made everything out of it, from coarse=
=3D
ware to fine ware, storage jars and tableware, flat and fluted tiles, bric=
=3D
ks, etc. You can see some of the pottery created with similar clay of that =
=3D
region (as fired in the Trindade et al article) many years ago and the kiln=
=3D
s it was fired in by going to the virtual museum here:
http://www.mnarqueologia-ipmuseus.pt/documentos/rouxinol/main.html
Roman kilns in the Tagus estuary
(http://www.mnarqueologia-ipmuseus.pt/?a=3D3D2&x=3D3D2)
Try clicking here and there in the exhibit to get more photos or close-ups.
=3D20
The authors, especially Trindade, are top dogs in ceramic archeology, have =
=3D
mega-buck funding (because they=3DE2=3D80=3D99re good), and work to help us=
under=3D
stand those who went before. Their obvious care and exquisite methodology i=
=3D
s beyond reproach. There are hundreds of studies on carbonate fluxes, at bo=
=3D
th low and high kiln temperatures, in ceramic archeology journals as well a=
=3D
s other scientific journals from varied research fields the world over. Low=
=3D
temperature carbonate fluxing has been done for thousands of years and is =
=3D
done today. So are a lot of other things studio potters have been lead to b=
=3D
elieve are =3DE2=3D80=3D9Cnot possible=3DE2=3D80=3D9D or =3DE2=3D80=3D9Cwro=
ng=3DE2=3D80=3D9D. Our t=3D
exts repeat the same basic info over and over with no one bothering to chec=
=3D
k current research. With open minds, let=3DE2=3D80=3D99s begin to explore c=
oncept=3D
s and materials, each enhancing the knowledge and growth of one another. OK=
=3D
? Keep and use your calculation software, it=3DE2=3D80=3D99s just not for m=
e howe=3D
ver much it might excite you.=3D20
I have photos to upload and put up this weekend of my calcareous clays and =
=3D
I am well pleased with how these clays performed fired. It=3DE2=3D80=3D99s =
been a=3D
very educational last month or so for me, too, clay-science-wise. I have a=
=3D
native clay body with 29% volcanic ash (dry weight %) now waiting to becom=
=3D
e something =3DE2=3D80=3D93 should be interesting and it should work well a=
t a mo=3D
derate temperature. My volcanic ash is kind of like airborne pumice only le=
=3D
ss scratchy since my local stuff has weathered millions of years. Kind of l=
=3D
ike working with recycled glass fluxing, too.=3D20
If someone can=3DE2=3D80=3D99t access the article I can email it to you as =
a 12 p=3D
age pdf file. Just ask. I am on mid-wife kitty duty, listening to some fine=
=3D
trance tunes, and will be around.
Ya=3DE2=3D80=3D99 all have fun,
Marian
Neon-Cat
Michael Wendt on sat 9 may 09
Marian,
Read :
The Arcanum
a book about porcelain development in Europe.
The first attempts used calcium based fluxes and they worked
fine at higher temperatures. They do require very tight
firing control due to a shorter firing range.
When I worked for the Idaho Research Foundation (part of
the University of Idaho at Moscow) in the early seventies
doing local materials location and development,
clays and related minerals were the main area of interest to
us so I developed a method that allowed me to generate
numerous samples of large enough scale to test throwing and
firing properties at the desired cone. I also added a
thermal gradient box to the side of my kiln to allow tests
to determine where a clay body was at its peak firing range
in one firing session.
If there is any interest in these methods, I could assemble
a video instruction set and burn it to DVD so it would cost
very little to distribute ( I figure about $20/ copy). As
anyone who got the plate making DVD, it would consist of
relatively crude snap shot style video with very little
editing. I am currently working to improve the plate and
platter video using Roxio Creator 2009. It allows me to
refine the clips, re-order them and do things like
voiceovers for narration if I can find the time to do it.
Post to clayart if anyone is interested the rapid clay body
development method.
Regards,
Michael Wendt
mwendt at wendtpottery dot com
Marian wrote:
Ron and others, some of you know that I=E2EUR(tm)ve been working with
calcareous local clays (rich in calcium carbonate from our
local limestone). For comparison, if I wanted to fire (as
they are) two clay samples from another region, according to
your calculation software programs I shouldn=E2EUR(tm)t waste my time
trying to work with these two clays (below)? I never thought
to consider the alumina and flux ratios -- that would be
easy. So these probably won=E2EUR(tm)t get off the ground without
major adjustments or additions even if I fire to cone 10
(2350 F, oxidation)? I do want my local clay-made vessels to
be durable and my clay seemed similar in many ways to the
two clays of the samples. Perhaps an investment in software
is the way to go...
Chemical analysis by element (% wt) as provided to me.
The high calcium clay:
calcite: CaCO3
Stephani Stephenson on sat 9 may 09
Thanks for many responses to my question...
here's some thanks and also a few more questions ideas for hopefully fur=
=3D
ther discussion
Ron, thank you for the suggestions on red earthenware and neph sy with ep=
=3D
som=3D20
salts..etc.
i could see where use of spod could be problematic...lithium may serve as=
=3D
an auxilliary=3D20
flux, but the lower COE also a factor..... maybe the % of spod in relati=
=3D
on to other=3D20
ingredients would determine its usefulness, or not. also the Aussie spod =
=3D
is kind of grainy.=3D20
wonder how that would play out in the 'hand' of the clay.
i definitely will be including some iron bearing clay. I see, too that cl=
=3D
ays like Redart are a=3D20
bit higher in silica ratio then others..
Ron wrote
" frits are very useful here but keep in mind - they
help melting so well they cut down the "range" of a clay - hence my disas=
=3D
ter
warning. "
yes i have had experience with that. had one clay which performed well fo=
=3D
r a very=3D20
specific purpose. a special commercial clay...am sure it had a lot of ad=
=3D
ditional frit...it=3D20
had an extremely narrow window between dry and chalky, and 'melted flopp=
=3D
y flapjack'.
I really had to nail the firings.
thanks for the advice, Ron and Craig, on watching the alumina , (R2O3)a=
=3D
s a prime=3D20
indicator in the glaze calc.. and thanks ,Snail, ah now, felspathic sand.=
=3D
.. there are i'm=3D20
sure a bazillion acres of it in the desert east of here, but need to find=
=3D
out more about=3D20
that.
and also with ingredients...i need to keep an eye on not only stability =
=3D
but how they=3D20
affect handling , glaze interaction, as well.
I am pretty excited about Tims new grog and fireclay as well.
Marian , In reading about brick clays, i saw reference more than once to =
=3D
the fact that the=3D20
naturally occurring calcium in the native brick clay..helped flux the bo=
=3D
dy, making for=3D20
denser,stronger brick at lower temps. I know there is a huge possible va=
=3D
riation in=3D20
quantity and particle size with naturally occuring sources of clay, but s=
=3D
ounds like you=3D20=3D20
could be onto something.
As anside, one CLAYART friend wrote to me offllist with the idea of addi=
=3D
ng whiting to=3D20
a claybody for a source of calcium as at least an auxilliary flux at mid=
=3D
range.
Any reason why this is not done? I have seen wollastonite used in bodies =
=3D
as a source of=3D20
silica and calcium. I am remembering that whiting has an increased LOI. s=
=3D
hould that=3D20
matter?
any one have experience with whiting in claybody and detrimental effects =
=3D
in handling or=3D20
firing?
posted a separate article on pumice specifically in brick clays... seems =
=3D
like it still may be=3D20
a useful ingredient in a sculpture/tile/architectural body.
no further feedback on foaming issue so far.
with regard to other natural materials i was talking about diatomaceous e=
=3D
arth with some=3D20
folks, (actually with regard to using it for sowbug control in the garde=
=3D
n!), and a Jesse, a=3D20
New York potter, wondered about it in glazes. so now i am wondering about=
=3D
it in clay.
i suppose diatomaceous earth is not as rigorously controlled for particle=
=3D
size, but might=3D20
be an interesting way to add silica, calcium , and other minerals .
Michael i would be interested in your testing dvd, especially if the met=
=3D
hods could be=3D20
utilized with equipment found in the typical studio.
Stephani Stephenson
=3D20
Ron Roy on sat 9 may 09
Hi Craig,
I have tried that but found using the unity on fluxes much better. The
problem with unity on alumina is - it stays at 1.0 - when using unity on
fluxes and you are comparing amount of alumina before and after adding flux
- and the alumina goes down.
Because I deal with so many clay bodies it is also useful to see the amount
of alumina in each clay and they can be compared when trying to estimate
maturing temperature of other clay bodies - using unity on alumina gives th=
e
same 0.1 for all bodies - making it much harder to compare.
Trying it both ways will illustrate what I'm trying to say here.
RR
On Fri, May 8, 2009 at 1:10 PM, Craig Martell wrote:
> Hello Stephanie:
>
> If you decide to use a calculation program with the claybody work it's a
> good thing to use R2O3 unity instead of flux unity. What that means is t=
he
> alumina (R2O3) will be the value that is expressed by 1.0 instead of the
> fluxes being at 1.0. This makes the numbers more sensible.
>
> I hope this will make some sense.
>
> regards, Craig Martell Hopewell, Oregon
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
Snail Scott on sun 10 may 09
On May 9, 2009, at 10:59 AM, Stephani Stephenson wrote:
> ...Snail, ah now, felspathic sand... there are i'm
> sure a bazillion acres of it in the desert east of here, but need to
> find out more about
> that....
My local supplier says Pacer (the Custer
feldspar folks) process their feldspar in
a wide range of grits, from the powder we
use in glaze all the way up through gravel
to outright rocks, and several sizes of sand
are part of their product line. I don't know
about acquiring small quantities to test,
though.
The concept is not dissimilar to the glass-
as-grog-for-earthenware idea from NCECA
that Chris C. mentioned previously.
-Snail
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