Tom Wirt on tue 28 sep 99
>>From: David Hendley
>>Subject: The search for the perfect clay and those mean, nasty clay
suppliers
> ----------------------------Original message----------------------------
>I get tired of people complaining about
> their clay and the company that makes it.
> And searching for that holy grail of perfect clay.
Hi David....don't know if this was aimed at me, but I guess I'm taking it as
such since my post apparently triggered it. First off, I wasn't complaining
about clay companies without also accepting the responsibility that "he who
complains should fix". It is obvious that poor performance on the part of
clay companies is fairly common as are poorly formulated clays. The concept
of clay companies providing clays is not exactly new. I believe, at least
in Japan, certain families supplied clay for the potters in their towns. I
would suspect that if the clay wasn't to the potters liking, there were
discussions about how to fix it. That is exactly what I did. Started
talking with my supplier about how to fix it. And when no information or
help was forthcoming, I proceeded to learn how to fix it myself, just as you
suggested.
> First of all, everyone has different expectations and
> desires for their clay.
> In other words, the perfect clay does not exist.
> Second, things change. Every batch of clay will be
> different than the one before.
No one disputes this....and I haven't heard anyone suggesting
otherwise....it is inherent in a product that is mined out of the ground by
bulldozers and draglines. But I would suggest that when you get a pug of
clay that is too wet to throw on one end and too dry to wedge on the other,
someone's not doing their job....the job for which I am paying them.
>
> So, if you want to use prepared ready-to-use clay,
> you have the responsibility to test the clay, extensively
> the first time you get it, and every you receive a
> new shipment. You need to order a new batch soon
> enough to test it before you use it for your work.
> If you want quality control, it's right there for you to test.
>
> As for clay companies handing out their recipes, well,
> there really are not any great secrets.
> If you consider yourself part of an 'industry' and you have
> no idea what is in your primary ingredient, educate yourself!
> Read books, experiment.
> The next time you're at your clay supplier's place, have a look
> around. What are there dozens of pallets of in the warehouse?
> What clays are offered for sale in dry bags? If you know
> anything about clay formulation, you now have a good idea
> as to what's in your claybody.
This is exactly what I did. A few well placed questions to innocent people
started to get me a general idea of what was in the body. And a little more
studying turned up that the primary fireclay used, wasn't even recommended
for use in pottery clays.
> There's no reason for you to feel 'trapped' or 'locked in'
> to one clay. Know your stuff and test other options, and
> you'll be ready to switch at a moment's notice.
I'd submit that for a production potter, supplying regular customers with
oven ware type products, it's not as easy to switch from one body to another
as you imply. Better to find or develop your own proper body, and have
backup suppliers who will mix it for you. That or have alternate formulas
substituting other clays for the ones in your primary body. My understanding
is you generally make one-off work for sale to individuals. That may make
some difference in your flexibility as to bodies..
>
> Years ago, I voted against this whole system with my
> feet and my money.
Not everyone has this opportunity. Many/most of us are in the position of
relying on someone to supply clay. For Betsy and I, the investment to be
able to mix 16 tons of clay a year, would be significant. Is it worth it?
maybe, but our current situation prohibits it.....and we already handle that
16 tons maybe 15 or 20 times during our process. If I don't have to handle
it another 4 or 5 times, I'm a happier camper.
> Just as I wouldn't blindly buy a pre-made glaze and base
> my livelihood on it, I am even more careful with my clay.
> It's way too important to me to let someone else take
> care of it and just deliver me the ready-to-go product.
> Sure, it's more work to develop your own claybody. Yes,
> it takes away from so-called 'creative time' (I would contend
> that it is the first part of the creative process).
> So, if you want a database that lists commercial claybodies,
> along with successes, handling characteristics, etc., it can't
> hurt anything, and might prove helpful. Let's start it now,
> on Clayart - any volunteers?
So this is exactly what I proposed. I have done a lot of studying. I'm
willing to share the information that I've learned. Maybe you'd share some
of what you've learned about formulating bodies also. There are no clear,
simple texts that I was able to find that give a concise way to go about
formulating bodies. You are right, it's not actually that difficult....but
no one's written it down in one place. . I'd suggest this kind of
information should also be posted for those who want it.
And there's no one place to go to get things like chemical and physical
properties of the various clays. Seems like the internets a natural for
this kind of information
> There's no substitute for the effort of thoughtfully and thoroughly
> taking control of the most important material in your work.
So that's exactly;y what we're trying to do here. It'll take awhile to get
there, but Bob Wilt's responded that it might be able to become part of the
ClayArt glaze database. We'll see/ Anyone who wants to help, labor or
information, please let me know.
Tom Wirt
claypot@hutchtel.net
elizabeth priddy on thu 30 sep 99
good grief...
people go on and on about tradition and then ignore it.
traditional (not american studio potteries, this little
plan is new and may not last for long) potteries
were made of groups of people working together. The
fire man did not throw, the glaze maker did not fire,
the maker did not glaze, and the clay preparer did not
throw. Point being, "Jack of all trades, master of
none...". Maybe you can master every aspect of pottery
by the time you are very very old, but until then,
delegate some of the work, especially the parts that
are extremely time consuming but require little skill.
Like mixing clay. Re-invent (the wheel) clay bodies if you must and design your
---
Elizabeth Priddy
--== Sent via Deja.com http://www.deja.com/ ==--
Share what you know. Learn what you don't.
Mark Mondloch on sat 2 oct 99
Thank you Jonathan for the specific information in this post.
It brings up questions ...
-Would you consider AP Green fireclay acceptable if it were screened as it goes
into the mixer?
-Is 50 mesh screening of suspect coarse materials what it takes to eliminate
lime pop-outs in cone 10 ware?
-When and why is pyrophyllite used as a substitute for feldspar and flint?
-Would you include grog/kyanite/sand as fillers in the 80/20 and 70/30 ratio
of plastics to fillers- especially in a coarse tile type body?
-Is there a general rule-of-thumb ratio of feldspar to flint in a stoneware
body to take all the flint into solution? or is this too dependent on the
amount of free silica in the clays?
I've learned much about glazes from this list as they seem to be discussed in
the most minute detail. I want to have the same amount of control over my clay
but I still feel like my clay body testing is often led by blind guessing as
most published information I've seen is vague generalizations and clay body
composition doesn't seem to generate as much interest. I've assumed that part
of this is that raw clays are available on a more regional basis then glaze
materials, but the comparison of specific clays by Jonathan is very helpful.
Thank you.
Sylvia
Jonathan Kaplan wrote:
> ----------------------------Original message----------------------------
> So here's an addendum to my pervious clay body posting......
>
> We need to acknowledge that if indeed there is no perfect caly body for
> each and everyone of us and that each batch will vary from load to load
> within certain parameters (thanks David Hendley) and that we all have
> different expectations, hows about a small primer on what goes into your
> claybody? These are some general parameters, brief as they may be:
>
> Low temperature whiteware cone 06-04
>
> Basically variations on 50 parts ball clay 50 parts talc, with some PV
> clay. There are formulas that may have some Neph Sy as an auxiliary flux or
> even some frit. Not a whole lot of useable fluxes at this temperature. Body
> doesn't enter a glass phase and is very punky and full of organics from the
> ball clay. Very tight firing range. Some bisque at 04 to burn out the
> organics and glaze at 06.
> Glazes prone to pinhole if bisque is not high enough. Body subject ot
> delayed moisture crazing. This us why most potters working at this
> temperature glaze their wares completely stilt them in the glaze kiln.
>
> Low temperature red clay (terra cotta) cone 04-06
>
> Can have some fireclay, some kaolin, talc or neph sy for a flux, (although
> talc is the major flux at this temperature range) ball clay, maybe
> pyrophyllite, perhaps frit for a flux, and of course a red clay (Red Art,
> etc.) I have seen some bodies with flint. Same firing parameters as above
> as above. Again, unless there is frit present as a flux, the body is very
> punky and unvitrified. There are solubility problems with frits in clay
> bodies and again, a tight firing range. Also, terra cotta bodies need some
> Barium Carbonate in them to eliminate the scumming on the surface. Again,
> glazes are prone to pin holing if bisque is not high enough to burn off
> organics. Delayed moisture crazing can be a potential problem due to poor
> clay/glaze interface and lact of body vitrificaton
>
> Mid Temperature clay bodies cone 3-6
>
> At this range, we can use feldspars, flint, and a host of other materials
> that are not effective in the lower earthenware range. Stoneware bodies in
> this range can use fireclays, "stoneware" clays, ball clays, kaolins such
> as Macnamee, EPK, Tile 6, etc. Fireclays can also be used. Stay away from
> the coarser fireclays such as AP Green. Greenstripe or Sutter are finer
> grinds. Pyrophyllite can be used as a partial substitute for flint and
> spar. The feldspar/flint combinations need to be greater than for those at
> a higher temperature range. Good vitirfication is possible with a balanced
> flint and feldspar content. Porcelain bodies at this range are also
> possible, but need a higher feldspar content to bring the body into a
> vitrified state due to the refractory kaolin content. Mid range terra
> cottas are also possible, and don't have the associated problems of terra
> cottas in the earthenwar range. (perhaps the useage of the name terra cotta
> is slightly erroneous. They are really midrange red clay bodies).
>
> High Temperature Range cone 6-10
>
> Porcelain and stoneware clay bodies in this range work best with a ratio of
> 70 parts plastic materials and 30 parts non-plastic materials. 80/20 bodies
> work well also. The full range of materials are useable at this temperature
> range. Enough feldspar must be present to disolve the flint into a glassy
> matrix. Otherwise free silica will cause dunting. Diversifying ball clay
> content, kaolin content, even fireclay content is beneficial. Again, use
> finer grinds of fireclay such as Greenstripe or Sutter. Use of red clays
> such as Newman and Red Art is fine, but kept at a low percentage. Choose
> clays with low LOI contents, especially with the choice of ball clays. The
> full range of plastic abilities are possible for pressing bodies, jiggering
> bodies, etc. etc.
>
> Casting Bodies (all temperature ranges)
>
> Thes bodiese are half plastics and half non plastics. Low temperature
> fluxes are talc, again, and some pyrophyllite can be used. Kaolins can be
> used also. Red clays need to be cut with kaolins to diversify the partice
> size to achive a good casting rate. Medium range non-plastics are feldspars
> in conjuntion with flint and pyrophyllite. Diversificaton of clay content
> essential. Same applies to high temperature range. Casting rates can be
> adjusted by choice of clays with varying particle sizes. Velvacast is
> particularly useful.
>
> I hope these generalizations help you to ask the right questions of your
> clay in the box suppliers.
>
> Good reads for more details are Rhodes, Tichane,Hansen etc.
>
> Jonathan
>
> Jonathan Kaplan, president
> Ceramic Design Group LTd/Production Services
> PO Box 775112
> Steamboat Springs, CO 80477
> (970) 879-9139 voice and fax
> http://www.sni.net/ceramicdesign
>
> UPS: 1280 13th St. Unit13
> Steamboat Springs, CO 80487
--
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake, WI 53075
silvercreek@execpc.com
http://www.execpc.com/silvercreek
Ron Roy on mon 4 oct 99
30 mesh is good enough for screening lime out of clays.
There are 3 types of pyrophyllite. Best to choose the right one for body
making. I don't use it so I can't advise on it's use.
Pyrophyllite is not a substitute for feldspar or silica. It is more like a
calcined clay.
I have never seen a body where all the free quartz is melted.
I'm sure this will lead to further questions - I will try to answer as they
come.
RR
>----------------------------Original message----------------------------
>-Would you consider AP Green fireclay acceptable if it were screened as it goes
>into the mixer?
>
>-Is 50 mesh screening of suspect coarse materials what it takes to eliminate
>lime pop-outs in cone 10 ware?
>
>-When and why is pyrophyllite used as a substitute for feldspar and flint?
>
>-Would you include grog/kyanite/sand as fillers in the 80/20 and 70/30 ratio
>of plastics to fillers- especially in a coarse tile type body?
>
>-Is there a general rule-of-thumb ratio of feldspar to flint in a stoneware
>body to take all the flint into solution? or is this too dependent on the
>amount of free silica in the clays?
>
>I've learned much about glazes from this list as they seem to be discussed in
>the most minute detail. I want to have the same amount of control over my clay
>but I still feel like my clay body testing is often led by blind guessing as
>most published information I've seen is vague generalizations and clay body
>composition doesn't seem to generate as much interest. I've assumed that part
>of this is that raw clays are available on a more regional basis then glaze
>materials, but the comparison of specific clays by Jonathan is very helpful.
>Thank you.
>Sylvia
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Jonathan Kaplan on mon 4 oct 99
Sylvia Mondloch has asked for some specific clay body information.
>-Would you consider AP Green fireclay acceptable if it were screened as it goes
>into the mixer?
Yes. However, if you use fireclay in your clay body consider diversifying
the fire clay content with AP Green and Greenstripe, or Sutter, or all
three. Screen it at 50 mesh. This is true with all the plastic ingredients
in the mix. Diversify the mix.
>
>-Is 50 mesh screening of suspect coarse materials what it takes to eliminate
>lime pop-outs in cone 10 ware?
Yes, but it is no guarentee. My experience is that it is sufficient. Some
have wondered if this will change the working qualities of the clay body,
going from lets say 28 mesh to 50 mesh or 60 mesh. I never have.
>
>-When and why is pyrophyllite used as a substitute for feldspar and flint?
Pyrophyllite is a hydrous alumina silicate, Al2O3:4SiO2:H2O.It decreases
thermal expansion and a substitute for all or part of the flint or feldspar
in a body. I have used it in clay bodies ranging from cone 06 to cone 10,
in plastic bodies as well as casting bodies. There is no rule. Try halving
the flint quantity with pyrophyllite. Remember that while we all think a
zero expansion clay body is highly desireable, such a clay body will
alter the fit of the glaze.
>
>-Would you include grog/kyanite/sand as fillers in the 80/20 and 70/30 ratio
>of plastics to fillers- especially in a coarse tile type body?
I would add grog as a percentage over the total amount of the clay body
(100 ) and definitely not include it as a part of the non plastics. Same
with sand. I would include kyanite though.
>
>-Is there a general rule-of-thumb ratio of feldspar to flint in a stoneware
>body to take all the flint into solution? or is this too dependent on the
>amount of free silica in the clays?
No. I have seen bodies with no flint and lots of spar, some with all flint
and no spar, and allvariations in between. I have seen some with twice the
amount of spar as flint and some with twice the amount of flint as spar. A
good point to start for testing is half and half, and test it for glaze fit
and absorption. Once you have a workable body and your glazes fit, have a
DTA test run on the body which will show the expansion and contraction of
the body upon heating and cooling
and show if there will be problems wioth free silica
Good Luck
Jonathan
>
>
Jonathan Kaplan, president
Ceramic Design Group LTd/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
Lorraine Pierce on tue 5 oct 99
thanks Jonathon...your messages are very helpful. My local clay supplier doesn't
carry Greenstripe or Sutters' Fireclay, only AP Green at $20 a bag and Hawthorne
Bond at $10, Goldart at $11.Are they western clays? Didn't find them in my old
Alfred Materials List either.Is there a current source book of materials you wou
recommend? Lori in New Port Richey
Jonathan Kaplan wrote:
> ----------------------------Original message----------------------------
> Sylvia Mondloch has asked for some specific clay body information.
>
> >-Would you consider AP Green fireclay acceptable if it were screened as it go
> >into the mixer?
>
> Yes. However, if you use fireclay in your clay body consider diversifying
> the fire clay content with AP Green and Greenstripe, or Sutter, or all
> three. Screen it at 50 mesh. This is true with all the plastic ingredients
> in the mix. Diversify the mix.
> >
> >-Is 50 mesh screening of suspect coarse materials what it takes to eliminate
> >lime pop-outs in cone 10 ware?
>
> Yes, but it is no guarentee. My experience is that it is sufficient. Some
> have wondered if this will change the working qualities of the clay body,
> going from lets say 28 mesh to 50 mesh or 60 mesh. I never have.
> >
> >-When and why is pyrophyllite used as a substitute for feldspar and flint?
>
> Pyrophyllite is a hydrous alumina silicate, Al2O3:4SiO2:H2O.It decreases
> thermal expansion and a substitute for all or part of the flint or feldspar
> in a body. I have used it in clay bodies ranging from cone 06 to cone 10,
> in plastic bodies as well as casting bodies. There is no rule. Try halving
> the flint quantity with pyrophyllite. Remember that while we all think a
> zero expansion clay body is highly desireable, such a clay body will
> alter the fit of the glaze.
> >
> >-Would you include grog/kyanite/sand as fillers in the 80/20 and 70/30 ratio
> >of plastics to fillers- especially in a coarse tile type body?
>
> I would add grog as a percentage over the total amount of the clay body
> (100 ) and definitely not include it as a part of the non plastics. Same
> with sand. I would include kyanite though.
> >
> >-Is there a general rule-of-thumb ratio of feldspar to flint in a stoneware
> >body to take all the flint into solution? or is this too dependent on the
> >amount of free silica in the clays?
>
> No. I have seen bodies with no flint and lots of spar, some with all flint
> and no spar, and allvariations in between. I have seen some with twice the
> amount of spar as flint and some with twice the amount of flint as spar. A
> good point to start for testing is half and half, and test it for glaze fit
> and absorption. Once you have a workable body and your glazes fit, have a
> DTA test run on the body which will show the expansion and contraction of
> the body upon heating and cooling
> and show if there will be problems wioth free silica
>
> Good Luck
>
> Jonathan
> >
> >
>
> Jonathan Kaplan, president
> Ceramic Design Group LTd/Production Services
> PO Box 775112
> Steamboat Springs, CO 80477
> (970) 879-9139 voice and fax
> http://www.sni.net/ceramicdesign
>
> UPS: 1280 13th St. Unit13
> Steamboat Springs, CO 80487
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