Ron Roy on sun 29 sep 02
> I'm not so sure that David Henley's discussion on vitreous stonewares
>is applicable. Yes, in some circumstances (Oil Lamps,etc.) it is desirable
>to have a vitreous body, but in others it is not, Pizza stones for example.
>It's hardly a mandatory requirement. If you were to say that all
>'stonewares' had to be water tight, would everything else have to be
>designated as an Earthenware????
The definition of stoneware has to do with temperature - not vitrification.
We say Earthenware up to about cone 1 - between cone 1 and cone 11 is
stoneware and above 11 porcelain.
A loose definition of course because there are stonewares above cone 11 and
some porcelains below cone 11.
The difference between earthenware and stoneware has to do with the
temperature mullite starts to form (1100C approx.) which makes stoneware
more resistant to chipping than earthenware.
All clays - no matter what temperature they are fired at will have a
certain water absorbency - or none - none means vitrified. 3% means enough
to not pose a problem for functional ware - above 3% and the problems
progress according to much water gets in. I say keep the absorption below
2% for stoneware - that way - the natural fluctuation of our raw materials
will be taken into account - most of the time.
As a consultant to 2 clay companies - actually it's more than that now - it
is my job to review the test data on every batch of clay they make. I can
then occasionally adjust a body to make sure the absorption and shrinkage
is within tolerances. All the clays I work on are advertised to fire at one
specific cone. There is some leeway - cone 10 starting to fall and tip
touching would be the proper leeway as far as I am concerned.
As an example: There are many times I have adjusted a cone 10 body down to
cone 9 because a customer has been firing a cone 10 at cone 9 and found -
eventually - complaints about leaking. Glaze is not a cure for an
underfired body - the water still gets in through the foot - crazing is the
eventual result - and leaking. Counting on a perfect seal from glaze is
unrealistic - one pin hole or one craze line and the water gets through.
The reasons stoneware should be vitrified enough to exclude water at the
advertised maturing temperature are important to potters making functional
ware. If water can get into the clay - under the glaze (read through the
foot) the clay will gradually rehydrate and grow - that will cause crazing.
It will also water stain tables - and it will become a hazard in the
microwave. If the clay is underfired enough and glazed inside and out it
may also be a problem in ordinary ovens.
There is no reason clay makers should not publish the temperature at which
their clays mature - become water proof - admit no more than 3% water. I
don't see the problem here. Tell us what we need to know to make proper
functional ware - it's not complicated.
On the other hand - potters should be testing their clays for absorption if
the supplier will not. It's not complicated - takes little time and is
wonderful for your peace of mind.
Anyone who wants to know how to test for absorbency let me know - I'll post
the instructions to the list if there are enough interested.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Martin Rice on sun 29 sep 02
Ron:
I for one would very much like to know about testing for absorbency. I'd
also like to know if it's at all possible for a ^04 fired piece to be water
resistant enough for functional ware, particularly the recipe that you were
good enough to help me with.
Thanks,
Martin
Chris Clyburn on mon 30 sep 02
Ron,
I am interested in knowing how to test for water absorbancy.
Chris Clyburn
Ms Noel on mon 30 sep 02
Yes, Ron, please give us your test for absorbency for stoneware. I was not
too concerned as most of my pieces are decorative. But, another potter told
the art director of a show that my work was not stoneware (^6) because it
didn't "ring" right. I know there was a thread about that which I will
check out.
I use Kickwheel's 271 white stoneware ^6 with a variety of commercial and
home mixed glazes. I have not had leaking problems (that I know of) but it
would be nice to be able to check my pieces out...just to be sure!
Noel, in bucolic North Georgia
----- Original Message -----
From: "Martin Rice"
To:
Sent: Sunday, September 29, 2002 7:08 PM
Subject: Re: Stoneware vitrification
> Ron:
>
> I for one would very much like to know about testing for absorbency. I'd
> also like to know if it's at all possible for a ^04 fired piece to be
water
> resistant enough for functional ware, particularly the recipe that you
were
> good enough to help me with.
>
> Thanks,
> Martin
>
>
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melpots@pclink.com.
Jon Pacini on mon 30 sep 02
Greetings all---Ron Roy wrote:
"The definition of stoneware has to do with temperature - not
vitrification."
I hate to disagree with someone as knowledgeable as Ron, but I can't
recall ever seeing a definition or having of a discussion on the topic of
earthenware, stoneware and porcelain that did not include parameters on the
absorption rate.
Granted, for functional stoneware that is going to hold water, 3% or
less absorption is an excellent target for absorption. I couldn't agree
more. And as Ron stated, there are lots of bodies out there that meet that
target at ^5, Laguna makes a dozen of them.
Ws 4 is not one of them and I don't think it's mandatory that every ^5
stoneware meet that narrow criteria. As someone who has consulted for only 2
clay companies, I have found that some potters want a body with a higher
level of porosity for whatever reason, to the tune of 4-5 hundred tons a
year. That's why we make that clay body, it serves a segment of the market
place.
That Ron doesn't feel it's necessary for the clay companies he consults
for to serve that segment is OK with me. To demand to list that Ws 4 matures
at ^7 or ^8 or whatever because that is the temperature that it reaches 3%
absorption fails to take into account that it was designed to have 5%
absorption at ^5. It's supposed to be that way.
I don't know why it would be so big a leap to understand that when you
make 140 stock clay bodies and over 3000 specials, that one of them would
meet this particular criteria, that evidently, a fair number of potters
want. From the simple fact that we make that many different bodies it should
be apparent that what one potter calls a great body, another one calls ill
firing and ill fitting. So be it.
If we all had the same taste and used the same criteria for the optimal
clay we'd only need one clay body.
I don't think you're performing any kind of service to potters by not
delivering up to them the clays they request to be made.
Jon Pacini
Clay Manager
Laguna Clay Co
Maid O'Mud on mon 30 sep 02
Jon Pacini said in part
To demand to list that Ws 4 matures
> at ^7 or ^8 or whatever because that is the temperature that it reaches 3%
> absorption fails to take into account that it was designed to have 5%
> absorption at ^5. It's supposed to be that way.
I don't use your clay bodies. Question - does your advertising re: this
clay body plainly state the absorption at 5% at ^5? If so, then buyer
beware.
*IF* it's simply listed as a ^5 stoneware, I know that I, as a production
potter, would be right pissed as I figure any stoneware clay body listed as
a ^5 should meet stoneware requirements (ie. under 3%).
Tuckers solves all these problems by listing the absorption rates for their
clay bodies at the cone values listed. This is very important to _me_ .
This absorption issue is obviously huge. Why does Laguna choose to list a
^8 stoneware at ^5 anyway? Why not simply list it as a ^8 stoneware? If I
want the clay I'm using to be more porous, I'll simply purchase a higher
firing clay and fire it lower.
sign me confused in the country
Sam - Maid O'Mud Pottery
Melbourne, Ontario CANADA
"First, the clay told me what to do.
Then, I told the clay what to do.
Now, we co-operate."
sam 1994
http://www.ody.ca/~scuttell/
Jon Pacini on tue 1 oct 02
Greetings all-- As I watch potters from around the country and the world
weigh in on this subject, it occurs to me that "stoneware" clay bodies with
higher absorption rates are a some-what regional Phenomenon.
They've been common here on the West Coast since the 1940's. They appear
to be growing in use in Europe, but much of the North American Continent is
unaware of their use. And for some reason cannot fathom of what use they
would be.
Well, there's a very large contingent of potters 'out there' who do use
these types of bodies and it's not because they are somehow ignorant of what
a "stoneware" body is "supposed" to be, at least according to this or that
definition.
I should have had a clue to this regionalization (is that really a
word?) by looking at our Miller clay bodies which are produced at our Ohio
facility. Excluding the low fire earthenwares, all of the bodies are quite
dense, even the 'coarser' throwing bodies have very little grog or sand and
all are pugged quite soft. This is in comparison to our Western clays, which
if you look at the ones that have the most longevity, have lots of sand and
grog, tend to be more open and are pugged quite firm.
Why these two very different philosophies of body composition have
occurred may be based in the types of work produced regionally or in the
materials available, but none the less, there are very divergent
philosophies at work here.
Though I can certainly concur that for Dinnerware and many other types
of "functional" ware, a smooth dense body is superior to a coarse open one.
However, I don't see the point in abandoning these types of bodies or
branding them inferior because they don't fit into this category or that, or
because some potters are unaware of their value.
Anyway, it's been loads of fun. I doubt we're going to reach a
consensus, but boy, isn't this a great forum.
Jon Pacini
Clay Manager
Laguna Clay Co
where it's finally cool and we might get some rain
Ron Roy on wed 2 oct 02
>Yes, Ron, please give us your test for absorbency for stoneware. I was not
>too concerned as most of my pieces are decorative. But, another potter told
>the art director of a show that my work was not stoneware (^6) because it
>didn't "ring" right. I know there was a thread about that which I will
>check out.
>I use Kickwheel's 271 white stoneware ^6 with a variety of commercial and
>home mixed glazes. I have not had leaking problems (that I know of) but it
>would be nice to be able to check my pieces out...just to be sure!
>Noel, in bucolic North Georgia
Hi Noel, here they are - let me know if you have questions - RR
Testing clays.
Make several bars of the body - 6" long, 1" wide and 1/2 " thick.
Mark a line 10 something long - any scale but it is so much easier if the
scale is in tenths. I use a line 5" long and use an inch scale with 20
graduations per inch. You can use a centimeter scale - it will be divided
into 10ths - It's a little shorter so not quite as accurate but it will do
fine.
When you move the "bar" around be very careful to NOT bend it in anyway. If
you bend or twist clay it remembers and unbends during drying and firing
and you will get a false report of warping.
Dry carefully - I prefer under a single sheet of newspaper till it is not
cold on your cheek. Leaving the bars in a warm place after they appear dry
will get more moisture out.
Measure the line to see how much dry shrinkage - line is now 9.5 CM means
it shrank 5%
Fire the bar - you can bisque it first if you want - that would be the most
accurate way. If you single fire better go slow or get the bar really dry -
you can blow up thick clay easily if you go too fast. Best to have a cone
beside the bars - always do 2 bars for each temperature you are going to
fire the clay at.
When you take them out of the kiln - Mark the cone bend right on the bar
then weigh them right away - preferably when they are warm - we don't want
atmospheric moisture getting into the clay and giving us a false reading.
Mark the weight right on the bar with something that will resist boiling
water - a marker will probably work. Leave room above it for the wet
weight.
Boil the bars - covered with water (don't let the water get below the bars)
for two hours. Run cold water in till the bars are cold. Dab off any
surface water and weigh again.
Lets say the dry weight is 150 and the wet is 165. Subtract the dry weight
from the wet (15.0) - then divide the difference (15) by the dry weight and
multiply by 100.
15 divided by 150 = 0.1 times 100 = 10% absorbency. Too high to exclude
water at that temperature.
For stoneware clays it is best between 3% and 1% - Porcelains often have none.
Measure the shrinkage line to get overall dry and fired shrinkage. If your
scale says 8.8 it means the clay shrinkage is 12%.
Throwing clays should be kept around 12% overall shrinkage.
Ron Roy - Oct 2001.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Marni Turkel on wed 2 oct 02
A few years ago I was having problems with my clay sweating and went
to work to fix it. I worked with great help from both Ron Roy and
Jonathan Kaplan. I started out following Ron's advice (posted on the
list again yesterday) to test the % of absorption. Since I can't boil
water at work, it ment taking the tests and a scale home to do the
work. After quite a number of tests and boiling and weighing I
decided I wanted something a little more immediate. Since I don't
sell the clay I make, I have only myself to please and my own
standards to meet.
My goal was a casting slip that would not sweat no matter what the
characteristics of the glaze. So I decided that it would be enough
for me to fire a small cup or bowl with a circular foot (bisqued and
glazed with regular work, not in a test kiln) and then put water in
it. If it didn't sweat, I was ok. If you've never done this with your
clay, it can be an eye opener.
When I got a claybody that didn't discolor on the outside from water,
I started putting a piece of colored typing or xerox paper under the
cup. The colored paper makes it easier to see if the foot is
transferring moisture since it will darken with moisture or wrinkle
it. After that, I kept adjusting the formula until I got a body that
doesn't wrinkle the paper in 48 hours. On some of the tests bodies I
tried, they were really tight, but so vitreous that I had trouble
with warpage on larger pieces, so I backed off on the flux.
It was really a long process for me, but I am so glad I did it.
Earlier this year I had to start looking for a substitute for the
Ione kaolin that I had been using. None of the kaolins I tested kept
the degree of vitrification that I wanted. Using the cup and water
routine I was able to easily find a blend of new ingredients that
gave the same results as the Ione. I periodically put in test cups
next to a visual cone to be sure that my clay is consistent with
results from the past. It gives me peace of mind.
Marni
--
Marni Turkel
Stony Point Ceramic Design
2080 Llano Rd 1B
Santa Rosa, CA 95407
Phone: 707-579-5567
Fax: 707-579-1116
http://www.marniturkel.com
Ron Roy on fri 4 oct 02
For definitions of clays see Rhodes Clay and Glazes - chapter 5 - all
editions including Hoppers latest. First book I ever bought and an eye
opener in the early days - still good basic information for those starting
out.
The point of letting potters know what cone clays vitrify at is basic. If
you don't do that then they are going to have to learn the hard way. At
least warn them that clays need to be tested before use to ascertain what
leaks and what doesn't.
The problem is of course that when clays are listed at a range of
temperatures of course they are going to be under vitrified at some of
those temperatures and perhaps even over fired at the top temperature. To
expect potters to be aware of that is asking too much I am sorry to say.
It is absolutely wrong to say the companies I work for do not fill the
needs of any potter - we give them what they want and if that is 5%
absorption they get it. What we will not do is sell clay to potters making
functional work that leaks. In fact we make hundreds of custom bodies -
test them all to make sure they do work - for what ever the customer wants.
No body is doing potters a favour selling them clays that are not going to
work for the kind of ware they make. Nobody wins when a clay body is
unsatisfactory.
Clay companies should realize - the better their clays work the more
successful potters will be - every body wins - clay supplier, potter and
customer.
I encourage every potter to test their clays - no matter who makes them -
including their own mixes. It is simple to do and will ensure a better
product.
RR
>Greetings all---Ron Roy wrote:
> "The definition of stoneware has to do with temperature - not
>vitrification."
>
> I hate to disagree with someone as knowledgeable as Ron, but I can't
>recall ever seeing a definition or having of a discussion on the topic of
>earthenware, stoneware and porcelain that did not include parameters on the
>absorption rate.
> Granted, for functional stoneware that is going to hold water, 3% or
>less absorption is an excellent target for absorption. I couldn't agree
>more. And as Ron stated, there are lots of bodies out there that meet that
>target at ^5, Laguna makes a dozen of them.
>
> Ws 4 is not one of them and I don't think it's mandatory that every ^5
>stoneware meet that narrow criteria. As someone who has consulted for only 2
>clay companies, I have found that some potters want a body with a higher
>level of porosity for whatever reason, to the tune of 4-5 hundred tons a
>year. That's why we make that clay body, it serves a segment of the market
>place.
> That Ron doesn't feel it's necessary for the clay companies he consults
>for to serve that segment is OK with me. To demand to list that Ws 4 matures
>at ^7 or ^8 or whatever because that is the temperature that it reaches 3%
>absorption fails to take into account that it was designed to have 5%
>absorption at ^5. It's supposed to be that way.
>
> I don't know why it would be so big a leap to understand that when you
>make 140 stock clay bodies and over 3000 specials, that one of them would
>meet this particular criteria, that evidently, a fair number of potters
>want. From the simple fact that we make that many different bodies it should
>be apparent that what one potter calls a great body, another one calls ill
>firing and ill fitting. So be it.
> If we all had the same taste and used the same criteria for the optimal
>clay we'd only need one clay body.
>
> I don't think you're performing any kind of service to potters by not
>delivering up to them the clays they request to be made.
>
>Jon Pacini
>Clay Manager
>Laguna Clay Co
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 4 oct 02
This has nothing to do with some potters being unaware of the value of open
bodies. No body even commented about that.
What we are talking about is giving potters a clear choice when buying
clay. Will it work for what they want to make. No amount of argument will
get around that. If I make a cup with this clay will it leak is the
question. If I fire this clay to cone 6 will it be underfired for
functional ware.
Perhaps a short note included in the description of the clay in the
catalogue to say - fire to cone ? for proper vitrification for functional
ware - what could be simpler?
RR
> Though I can certainly concur that for Dinnerware and many other types
>of "functional" ware, a smooth dense body is superior to a coarse open one.
>However, I don't see the point in abandoning these types of bodies or
>branding them inferior because they don't fit into this category or that, or
>because some potters are unaware of their value.
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 7 oct 02
Greetings all and Ron R.--- The Laguna catalog lists the absorption levels
for all of the stoneware clays at the cones they were designed to be used
at. They are listed at ^10 or ^5 firing levels, which ever one is that
specific claybodies' designated firing temperature. The absorption levels
for the stonewares listed vary from .5% up to 8%.
Ron, I'm surprised you think it's more valuable to list that a body
reaches 3% absorption at ^8 3/4 than to state that it's absorption is 2% at
^10 or 5% at ^5. I would think that more potters are interested in the
absorption rate at the temperatures glazes are traditionally fired at than
at what specific temperature a clay reaches any given level of absorption.
It is absolutely wrong to say the companies I work for do not fill the
needs of any potter - we give them what they want and if that is 5%
absorption they get it. What we will not do is sell clay to potters making
functional work that leaks.
Well Ron, If I misread your earlier post I apologize, but I could have
sworn you stated you adjusted all the stonewares for the companies which you
consult to 3% absorption. But since those companies do have higher
absorption clays available, how in the world do you keep a potter from
buying one of your clays and using it any way that they decide to try and
use it???
For definitions of clays see Rhodes Clay and Glazes - chapter 5 - all
editions including Hoppers latest. First book I ever bought and an eye
opener in the early days - still good basic information for those starting
out.
Correct me if I'm wrong again, but to me it seems what Rhodes is
defining in Chapter 5 of his book, 'Clay and Glazes for the Potter',(my
edition is the 13th from 1971) are raw materials which can be used to
develop clay bodies, not the bodies themselves. Chapter 5 is entitled
'Kinds of Clay' and describes Kaolins, Ballclays, Fireclays ect. and does
indeed include Stoneware clay and Earthenware clay, but as Raw or refined
Minerals that are dug from the ground and that can be used in clay body
composition. As an example Jordan clay is/was, a 'stoneware' type clay
mineral that comes to mind.
In Chapter 6 Rhodes describes how to developed a body from those
minerals. He does give some sample stoneware bodies with absorption rates,
stating 5% as not being quite dense enough and 2% being too dense.
What Rhodes does not state is that Stoneware needs to be any specific
porosity rate, though he does give the above range. Which I would guess
leaves 4-3% absorption as "ideal". Though I don't believe it's "ideal" for
all purposes and Rhodes never actually states that it is.
In my opinion, the level of vitrification should not be the only gauge
used to determine at what temperature a clay body should be fired and I'm
not sure it would be the best way to categorize clays. Apparently there are
those who think by cone is a less than ideal method. I suppose there are too
many variables in ceramics and to use any single characteristic to
categorize clays is certainly an imperfect method.
As I have stated, the levels of vitrification are listed in our catalog
for the approximate cones at which the clays were designed to function. So
are shrinkage, texture and color and a wealth of other pertinent info. The
more info you can digest before you start to work, the better off you are.
This type of info is indeed basic and should be available to those who are
going to use the clay. At least I can be in agreement with Ron on that
point.
In closing-----You should always test your clays, glazes and minerals before
you commit to production, if they're not appropriate, try something else.
Life's too short to force the issue. Ron, I hope you come to San Diego for
NCECA and that you like to drink beer!!!
Jon Pacini
Clay Manager
Laguna Clay Co
where I thought it was going to be winter for a few days, but it's summer
again
Ron Roy on fri 11 oct 02
It is in the interest of education rather than an ongoing argument with any
individual that I submit the following. When choosing clays be forewarned -
especially in the face of conflicting information - test your clays to make
sure they are suitable for the ware you want to make unless the make of
those clays can show some accurate test data - even so I recommend building
you own data. Remember - having a record of any particular clay body - over
a period of time will tell you how well designed the body is and how
resistant to variation over time.
>Greetings all and Ron R.--- The Laguna catalog lists the absorption levels
>for all of the stoneware clays at the cones they were designed to be used
>at. They are listed at ^10 or ^5 firing levels, which ever one is that
>specific claybodies' designated firing temperature. The absorption levels
>for the stonewares listed vary from .5% up to 8%.
In the Laguna catalogue WC398 (WS-4) is described as follows. Keep in mind
- a customer complained this clay leaked when fired to cone 5.
Page 11- Clay application Charts - WS4 clearly indicated for tableware and
ovenware. It clearly states in the header that these recommendations are
based on lab testing
Page -16 - cone 5 stoneware clays - Similar to WS5 but with added flux for
lower absorption - good to cone 8.
(WS5 - care should be taken when used for functional ware - not totally
vitrified in most cone 5 firings)
RR comments - a range of 4 cones (45C or 113C) so it has to be either
underfired to the point of leaking at 5 or overfired at cone 8 or both.
Page 20 - approx. cone 5 Avr. water absorption plus or minus 2% = 1.5.
RR comments - Jon says the 1.5 is a misprint and should be 5% - the burning
questions are - what is the actual % absorption at cone 5 and 8 for this
body.
I'm not surprised that the person who sold this clay to Imzadi had no idea
that this clay would not be suitable at cone 5 for the job - unless they
had access to current test data. I can't think of any other reason than
there is no current test data on this body.
> Ron, I'm surprised you think it's more valuable to list that a body
>reaches 3% absorption at ^8 3/4 than to state that it's absorption is 2% at
>^10 or 5% at ^5. I would think that more potters are interested in the
>absorption rate at the temperatures glazes are traditionally fired at than
>at what specific temperature a clay reaches any given level of absorption.
Why not say what the absorption rate is for every cone the body is
recommended - or at least the upper and lower cones? That way anyone can
choose the right clay they need.
>It is absolutely wrong to say the companies I work for do not fill the
>
>needs of any potter - we give them what they want and if that is 5%
>
>absorption they get it. What we will not do is sell clay to potters making
>
>functional work that leaks.
>
> Well Ron, If I misread your earlier post I apologize, but I could have
>sworn you stated you adjusted all the stonewares for the companies which you
>consult to 3% absorption. But since those companies do have higher
>absorption clays available, how in the world do you keep a potter from
>buying one of your clays and using it any way that they decide to try and
>use it???
I never said that - I adjust each body to what I consider the right
absorption rate for the cone it is to be fired at - usually under 2% - less
for porcelains. Even our sculpture clays don't leak.
Any one who wants clays with higher absorption get them as a special order
- we don't sell them to anyone else - don't stock them. We also test all
special orders and advise the customer if we fell it is necessary - for
their application.
If we did stock it we would clearly note the absorption rates in our
catalogue and the test data would be available - any time - to any one - on
any clay we make.
>For definitions of clays see Rhodes Clay and Glazes - chapter 5 - all
>
>editions including Hoppers latest. First book I ever bought and an eye
>
>opener in the early days - still good basic information for those starting
>
>out.
>
> Correct me if I'm wrong again, but to me it seems what Rhodes is
>defining in Chapter 5 of his book, 'Clay and Glazes for the Potter',(my
>edition is the 13th from 1971) are raw materials which can be used to
>develop clay bodies, not the bodies themselves. Chapter 5 is entitled
>'Kinds of Clay' and describes Kaolins, Ballclays, Fireclays ect. and does
>indeed include Stoneware clay and Earthenware clay, but as Raw or refined
>Minerals that are dug from the ground and that can be used in clay body
>composition. As an example Jordan clay is/was, a 'stoneware' type clay
>mineral that comes to mind.
The definition of stoneware is by temperature and over all shrinkage - a
raw material can be classified as a stoneware - like a fire clay with
enough plasticity to be thrown for instance. Jordan was not a stoneware by
definition - for instance at cone 10 - to high shrinkage and too tight - it
varied a lot so I can't say with certainty that it would not be at cone 6
as well I'm sure not - it was a very sticky clay.
>
> In Chapter 6 Rhodes describes how to developed a body from those
>minerals. He does give some sample stoneware bodies with absorption rates,
>stating 5% as not being quite dense enough and 2% being too dense.
> What Rhodes does not state is that Stoneware needs to be any specific
>porosity rate, though he does give the above range. Which I would guess
>leaves 4-3% absorption as "ideal". Though I don't believe it's "ideal" for
>all purposes and Rhodes never actually states that it is.
I believe 4% is too high - and 3% does not give enough leeway for variation
of raw materials. I try to keep the stonewares between 1 and 2%. I learned
the hard way but in the back of my mind was the fact that potters were
relying on me to do it right - or they had to pay - and it's difficult
enough to make it as a potter without having to try to do it with clay that
is not right. I am very fortunate to have business men who agree with that
and pay me to do it.
>
> In my opinion, the level of vitrification should not be the only gauge
>used to determine at what temperature a clay body should be fired and I'm
>not sure it would be the best way to categorize clays. Apparently there are
>those who think by cone is a less than ideal method. I suppose there are too
>many variables in ceramics and to use any single characteristic to
>categorize clays is certainly an imperfect method.
What would be a better way than to gauge by cone?
> As I have stated, the levels of vitrification are listed in our catalog
>for the approximate cones at which the clays were designed to function. So
>are shrinkage, texture and color and a wealth of other pertinent info. The
>more info you can digest before you start to work, the better off you are.
>This type of info is indeed basic and should be available to those who are
>going to use the clay. At least I can be in agreement with Ron on that
>point.
>
>In closing-----You should always test your clays, glazes and minerals before
>you commit to production, if they're not appropriate, try something else.
>Life's too short to force the issue.
>Jon Pacini
>Clay Manager
>Laguna Clay Co
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 14 oct 02
Greetings All---Ron wrote: "Any one who wants clays with higher
absorption get them as a special order
- we don't sell them to anyone else - don't stock them. We also test all
special orders and advise the customer if we fell it is necessary - for
their application"
Let me explain just exactly how a clay body becomes a stock clay body
for Laguna. First off we don't pluck stock bodies out of the air because we
need one to fill a hole in our catalog.
All of the Stock bodies we produce started out as specials, for schools,
for potters. If a potter who has developed a clay that is then made by us,
and he does workshops or just by word of mouth, recommends that body to
other potters and those other potters purchase that clay and they recommend
it to others, then that body may eventually get to the point where we are
making so much of it that we ask permission to put it in the catalog.
The same goes for bodies developed by instructors at schools and made by
us. After the students leave school, they may wish to use in their studio,
the clay that was used at the school. If they continue to recommend it to
others and production warrants it, then that clay may eventually get to be a
stock body.
This is where our stock bodies come from. Potters continually
requesting a specific body. We don't take some potters special clay body out
of the blue and make it a stock body---that's absurd to even insinuate. All
'specials' are kept strictly confidential and they are not made for anyone
else without permission from the original customer.
Ron wrote: "Why not say what the absorption rate is for every cone the body
is
recommended - or at least the upper and lower cones? That way anyone can
choose the right clay they need."
Laguna's clay bodies have listings for ^06, ^5 and ^10 and data is
published for those temperatures. Give me a break Ron. We have customers
that use ^10 porcelains to pit fire with. They raku ^5 and ^10 clays. God
only knows what torture some of these bodies go through. I'd have to list
all the data for every clay body at every possible cone temperature. Your
position is absurd. If someone is in a quandary over which of our clays to
use, please call me, 626-330-0631 x228, I will do my best to match you up
with something that will work for you. If we don't have a stock body that
meets your needs, we will make you something to test.
Laguna doesn't try to jam any clay body down anyone's throat, nor do we
tell them that they have to use a specific clay in a specific way. We do try
to match them up with what has worked best in the past for other potters.The
recommendations in Laguna's catalog are based not only on the input of the
technical staff, but by the potters who use the bodies and that statement is
at the top of the application chart.
This discussion was precipitated by an attempt to define what
constitutes a stoneware and there have been a few definitions looked at. As
for WS 4, it's a stoneware. It has a higher absorption rate than what Izmadi
expected and Ron prefers, but lots of potters use that body successfully, as
demonstrated by their continued voting with their wallets.
And finally----
Ron wrote: 'The definition of stoneware is by temperature and over all
shrinkage - a
raw material can be classified as a stoneware - like a fire clay with
enough plasticity to be thrown for instance. Jordan was not a stoneware by
definition - for instance at cone 10 - to high shrinkage and too tight - it
varied a lot so I can't say with certainty that it would not be at cone 6
as well I'm sure not - it was a very sticky clay.'
Well, not that I don't appreciate Ron's opinion, I do, but I'll hang in
with the Rhodes' I cited on this one.
Jon Pacini
Clay Manager
Laguna Clay Co
Jose A. Velez on fri 18 oct 02
Mr. Pacini:
> You can put whatever amount of info in the catalog you want, but
> ultimately, Potters individually have to learn all the twists and turns.
> They have to physically do it themselves. Test your materials!!!!
>
I am an amateur potter and do not have at stake what professional potters
do, but believe me I am flabbergasted by your very defensive message of a
position that frankly is indefensible. What you are advocating is similar
to say a fasteners manufacturer only has the obligation to classify its
bolts as "fat" or "skinny" and is up to the user to measure and classify
them so they can meet his/her needs. I think the request for a minimum of
information that provides the parameters that are essential to the user of
any product is a very reasonable one. Sure, for a product that has such a
wide variety of applications, and where the criteria for success is rather
subjective only the individual user can tell if the product meets his or her
needs, but that does not relieve the supplier of the obligation to provide
the necessary information that describe the capabilities of the product. If
you do not provide that information you are simply avoiding your
responsibility.
Respectfully,
Jose A. Velez
Ron Roy on fri 18 oct 02
I don't think Jon is implying I pick bodies out of the air - but just in case.
The great majority of the bodies made by Tuckers are my bodies - made over
a period of 30 years - developed using data from all the bodies made over
the years - all tested for workability, shrinkage and absorbency before
they are added to the stock body list.
They are made with a eye on the test data from our testing of individual
raw clays complied over the years. This means we use raw clays that are the
most stable whenever we can - this dramatically cuts down on the number of
surprises potters get.
There is no guessing or borrowing or grabbing out of the air.
As for my absurd positon on publishing absorption and shrinkage rates for
the recommended cone range for clays - I say it would help any potter
choose the clays they need - would make any clay makers job much easier,
result in less problems for potters and clay producers, result in better
pots with more satisfied customers - in other words better for everyone.
That does not sound absurd to me - in any way - in fact it sounds like the
way it should be.
RR
> Let me explain just exactly how a clay body becomes a stock clay body
>for Laguna. First off we don't pluck stock bodies out of the air because we
>need one to fill a hole in our catalog.
> All of the Stock bodies we produce started out as specials, for schools,
>for potters. If a potter who has developed a clay that is then made by us,
>and he does workshops or just by word of mouth, recommends that body to
>other potters and those other potters purchase that clay and they recommend
>it to others, then that body may eventually get to the point where we are
>making so much of it that we ask permission to put it in the catalog.
> The same goes for bodies developed by instructors at schools and made by
>us. After the students leave school, they may wish to use in their studio,
>the clay that was used at the school. If they continue to recommend it to
>others and production warrants it, then that clay may eventually get to be a
>stock body.
>
> This is where our stock bodies come from. Potters continually
>requesting a specific body. We don't take some potters special clay body out
>of the blue and make it a stock body---that's absurd to even insinuate. All
>'specials' are kept strictly confidential and they are not made for anyone
>else without permission from the original customer.
>
>Ron wrote: "Why not say what the absorption rate is for every cone the body
>is
>recommended - or at least the upper and lower cones? That way anyone can
>choose the right clay they need."
>
> Laguna's clay bodies have listings for ^06, ^5 and ^10 and data is
>published for those temperatures. Give me a break Ron. We have customers
>that use ^10 porcelains to pit fire with. They raku ^5 and ^10 clays. God
>only knows what torture some of these bodies go through. I'd have to list
>all the data for every clay body at every possible cone temperature. Your
>position is absurd. If someone is in a quandary over which of our clays to
>use, please call me, 626-330-0631 x228, I will do my best to match you up
>with something that will work for you. If we don't have a stock body that
>meets your needs, we will make you something to test.
>
> Laguna doesn't try to jam any clay body down anyone's throat, nor do we
>tell them that they have to use a specific clay in a specific way. We do try
>to match them up with what has worked best in the past for other potters.The
>recommendations in Laguna's catalog are based not only on the input of the
>technical staff, but by the potters who use the bodies and that statement is
>at the top of the application chart.
>
> This discussion was precipitated by an attempt to define what
>constitutes a stoneware and there have been a few definitions looked at. As
>for WS 4, it's a stoneware. It has a higher absorption rate than what Izmadi
>expected and Ron prefers, but lots of potters use that body successfully, as
>demonstrated by their continued voting with their wallets.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jon Pacini on fri 18 oct 02
Greetings All---- Good Morning Ron-----There is no doubt in my mind you
labor very intensely on your formulations and barring any major lapses in
your chain of supply or manufacture, I'm sure you get few surprises. We have
not gotten into the positions we are in from doing shoddy craftsmanship.
What we do have is a differing of philosophies. I agree that info on clay
bodies is important and should be published in catalogs, but I believe that
published info is only a guide to what for and how a clay body can be used.
I can understand that when a clay body is developed, that the natural
inclination is to categorize it and print, "This body is a smooth dinnerware
body and has 1.5% absorption at ^10" in the catalog.
What I have found out in my 30+ yrs in the biz, is that once a body is out
on the market, the vast majority of potters just don't deal with a clay body
in such a rigid manner. Individually some may, but many potters are going to
wood fire that body to ^12 and a lot are going to pit fire it at ^012 and
many will torture it in other various ways. Eventually that info filters
it's way into our catalog for better or worse. Usually it ends up on the
Application Chart. Sometimes on the description pages. One of my former
asociates more than likely worked with some potters who wanted to use WS4 at
^8 and it worked. I wouldn't doubt that is how the notation got into the
description. Should we list all of the data for all of these firing
temperatures?? No, It's just too unwieldy. Should we restrict what we say
the clays can be used for? No, not if it's being used for those purposes.
You could turn a catalog into an encyclopedia with all the info available
on the materials Laguna sells. As I say, it would be absurd. Where would it
end. A catalog is not meant to be a textbook either. Education is better
left to those who don't have a monetary interest in what material you are
going to purchase. That doesn't infer that potters shouldn't get product
support, but a supplier is not a substitute for a good curriculum at a
university, years of being an apprentice to a master or a great reference
library.
Laguna inherited a system of categorizing clays and glazes into groups of
temperature ranges. And therefore give the info on individual bodies within
those groupings. You can find this info on the Characteristics Chart in the
Laguna catalog. Every supplier should decide how they wish to do it, but
they should do it!
Somehow out of all of this, I get the feeling that the act of purchasing
clay is to be reduced, in effect, to shopping at Wal-mart. Drive to the
store, buy a package of striped underware and a ovenware claybody. Ceramics
is a Craft! It takes years to master. Purchasing clay is not going to the
store and buying hankies. Granted, a catalog should give you an 'Idea' for
what kind of clay you want to use, but it can't throw and fire the clay for
you. It can't tell you, 'such and such a clay', is perfect for you. That's a
very personal decision and Potters have to do that on their own.
Having been a production thrower in a factory and a Studio Potter on my
own, I know you have to work with the materials to learn what they are going
to do under your own particular circumstances. There is no other way to
learn that other than by doing it. You're not going to get that knowledge
from a catalog no matter how 'complete' it is. And it's not any different
for any other Craft. Woodworkers carefully select the woods they use, and
stoneworkers do the same. Sure, a catalog says it's oak or granite , but a
Craftsman has to feel the grain, turn the stone in the hand. I find it
amazing that potters take clay home from a store without even looking at it,
without opening a bag and rolling a coil, feeling the texture. I guess it's
a testament to the job we do producing bodies, but where does this attitude
about purchasing clay come from. In no other Craft could you get away with
that, how can anyone expect to do so Ceramics??
You can put whatever amount of info in the catalog you want, but
ultimately, Potters individually have to learn all the twists and turns.
They have to physically do it themselves. Test your materials!!!!
Ron--it's been loads of fun ---you can have the last word----I'll defer to
my elders--HA!!!
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: Ron Roy [mailto:ronroy@total.net]
Sent: Thursday, October 17, 2002 11:09 PM
To: Jon Pacini
Subject: Re: stoneware vitrification
I don't think Jon is implying I pick bodies out of the air - but just in
case.
The great majority of the bodies made by Tuckers are my bodies - made over
a period of 30 years - developed using data from all the bodies made over
the years - all tested for workability, shrinkage and absorbency before
they are added to the stock body list.
They are made with a eye on the test data from our testing of individual
raw clays complied over the years. This means we use raw clays that are the
most stable whenever we can - this dramatically cuts down on the number of
surprises potters get.
There is no guessing or borrowing or grabbing out of the air.
As for my absurd positon on publishing absorption and shrinkage rates for
the recommended cone range for clays - I say it would help any potter
choose the clays they need - would make any clay makers job much easier,
result in less problems for potters and clay producers, result in better
pots with more satisfied customers - in other words better for everyone.
That does not sound absurd to me - in any way - in fact it sounds like the
way it should be.
RR
> Let me explain just exactly how a clay body becomes a stock clay body
>for Laguna. First off we don't pluck stock bodies out of the air because
we
>need one to fill a hole in our catalog.
> All of the Stock bodies we produce started out as specials, for
schools,
>for potters. If a potter who has developed a clay that is then made by us,
>and he does workshops or just by word of mouth, recommends that body to
>other potters and those other potters purchase that clay and they recommend
>it to others, then that body may eventually get to the point where we are
>making so much of it that we ask permission to put it in the catalog.
> The same goes for bodies developed by instructors at schools and made
by
>us. After the students leave school, they may wish to use in their studio,
>the clay that was used at the school. If they continue to recommend it to
>others and production warrants it, then that clay may eventually get to be
a
>stock body.
>
> This is where our stock bodies come from. Potters continually
>requesting a specific body. We don't take some potters special clay body
out
>of the blue and make it a stock body---that's absurd to even insinuate. All
>'specials' are kept strictly confidential and they are not made for anyone
>else without permission from the original customer.
>
>Ron wrote: "Why not say what the absorption rate is for every cone the body
>is
>recommended - or at least the upper and lower cones? That way anyone can
>choose the right clay they need."
>
> Laguna's clay bodies have listings for ^06, ^5 and ^10 and data is
>published for those temperatures. Give me a break Ron. We have customers
>that use ^10 porcelains to pit fire with. They raku ^5 and ^10 clays. God
>only knows what torture some of these bodies go through. I'd have to list
>all the data for every clay body at every possible cone temperature. Your
>position is absurd. If someone is in a quandary over which of our clays to
>use, please call me, 626-330-0631 x228, I will do my best to match you up
>with something that will work for you. If we don't have a stock body that
>meets your needs, we will make you something to test.
>
> Laguna doesn't try to jam any clay body down anyone's throat, nor do
we
>tell them that they have to use a specific clay in a specific way. We do
try
>to match them up with what has worked best in the past for other
potters.The
>recommendations in Laguna's catalog are based not only on the input of the
>technical staff, but by the potters who use the bodies and that statement
is
>at the top of the application chart.
>
> This discussion was precipitated by an attempt to define what
>constitutes a stoneware and there have been a few definitions looked at. As
>for WS 4, it's a stoneware. It has a higher absorption rate than what
Izmadi
>expected and Ron prefers, but lots of potters use that body successfully,
as
>demonstrated by their continued voting with their wallets.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jon Pacini on sat 19 oct 02
Hi Jose--Greeting All---
You are missing the point entirely Jose. The information regarding the
temperatures, shrinkage, absorption, etcetera, IS IN the Laguna Catalog for
the all the stock clay bodies, as it should be. Every clay Catalog should
have this info!!!! I've written this time and again. Not only in this
thread, but a dozen others. I'm not disputing that.
What Ron proposes is that if ANY mention of use at ANY temperature is
included in a catalog, then all attendant info must also be in the catalog.
Or if the body doesn't meet HIS criteria (1-2% absorption) then the cone
should be included for where it does meet his criteria, along with all the
attendant specifications, I hold that is absurd.
Ron cited Rhodes to back up his assertion that 1-2% absorption is basic
info, but Rhodes doesn't back him up. Rhodes says 2% is too tight, let alone
1%. Susan Peterson in her book "Art and Craft of Clay" classifies stonewares
at 2-5% absorption. These are the two most prominent educators in the
ceramics field I can think of. Neither of whom back Ron up in defining
Stonewares at the narrow range of 1-2% absorption.
The body that started this all off is WS 4. It's absorption at ^5 is 5%,
it's in our newest catalog that way and according to Peterson that qualifies
it as Stoneware. If Ron wants to dispute her, that's his call not mine. As
far as I can tell, Susan invented firing at ^5. WS 4 was not intended to
work at ^8 when it was developed. What it's specs are at that temp is
anyone's guess. That it is used at that temperature, is beside the point.
Every single clay body can be fired under dozens of conditions.
If you have followed this discussion closely you would realize that potters
do not work solely at the specified temperatures that are listed in
catalogs. And that the info in, at least Laguna's catalog, is only intended
as a guideline for working at the temperature that the bodies were designed
to work at and it is so stated. If I put in all the temperatures and
attendant specs, for all the clays, that all the potters we deal with are
using and working at, the catalog would be the size of a phone book. And
once again --that is absurd.
As for Amateur /professional---- I don't see that it makes a difference---
No professional potter would base his production on the basis of a
description in a catalog----it is my assertion that NO amateur should
either. As Craftsmen, you have an obligation to do the research, it makes no
difference if you are a pro or an Amateur. If in fact Ron believes his
catalog is a text potters can live and die by ---that's great for him. But
I wouldn't base my production on any info from a catalog. I would do the
work!!---Being involved in ceramics is much more dependent on your own
knowledge of the materials than anything a catalog or book can tell you or
EVER will tell you. If you don't do the work, you WILL have to learn the
Hard Way, by getting yourself in trouble.
Jose, to assert that I'm saying a clay need only be described as "fat or
skinny" is ludicrous. Reread the entire thread and see how many times I give
the data that pertains to the body in question. How many times I've written,
" The data is in the catalog for the temperature the clay is intended to be
fired at." Is that statement somehow incomprehensible???
I'm sorry Ron, I was willing to call it a day on this thread ---
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: Jose A. Velez [mailto:potter785@cox.net]
Sent: Friday, October 18, 2002 5:38 PM
To: Jon Pacini; CLAYART@LSV.CERAMICS.ORG
Subject: Re: Re: stoneware vitrification
Mr. Pacini:
> You can put whatever amount of info in the catalog you want, but
> ultimately, Potters individually have to learn all the twists and turns.
> They have to physically do it themselves. Test your materials!!!!
>
I am an amateur potter and do not have at stake what professional potters
do, but believe me I am flabbergasted by your very defensive message of a
position that frankly is indefensible. What you are advocating is similar
to say a fasteners manufacturer only has the obligation to classify its
bolts as "fat" or "skinny" and is up to the user to measure and classify
them so they can meet his/her needs. I think the request for a minimum of
information that provides the parameters that are essential to the user of
any product is a very reasonable one. Sure, for a product that has such a
wide variety of applications, and where the criteria for success is rather
subjective only the individual user can tell if the product meets his or her
needs, but that does not relieve the supplier of the obligation to provide
the necessary information that describe the capabilities of the product. If
you do not provide that information you are simply avoiding your
responsibility.
Respectfully,
Jose A. Velez
Gavin Stairs on sat 19 oct 02
At 03:44 PM 14/10/2002 -0700, Jon Pacini wrote:
> Let me explain just exactly how a clay body becomes a stock clay body
>for Laguna. First off we don't pluck stock bodies out of the air because we
>need one to fill a hole in our catalog.
> All of the Stock bodies we produce started out as specials, for schools,
>for potters.
Hi Jon,
Now I begin to understand why so many posts to Clayart talk about
idiosyncratic clay bodies that come from Laguna, and they (the potters)
have some sort of a problem or another. There's no system to your
system. It just grew like Topsy, and you keep making whatever body gets
ordered. Sounds like the good old American way, but it doesn't have any
predictability. You're not contributing to your customers' educations or
improving their working methods. You're just feeding their habits. I
would have hoped that a large firm like Laguna would have researched the
available raw materials, made decisions about what would be a good mix of
same, and designed bodies that would suit the various needs based on
that. A simple statement at the end of such a designed body list would
cover all the rest of the requests you get. Like "If none of our carefully
designed bodies fits your needs, we will make a ton of whatever you like."
Most firms making art materials strive for some sort of order and
predictability in their products, and also seek to apply the expertise that
they presumably develop over the years to benefit their customers. From
your statements, it would seem that you don't believe you have any such
advantage, and "the customer is always right" is the maxim that covers all
situations.
Well, so be it. I think I prefer Ron's idea of how best to serve the clients.
Gavin
Jose A. Velez on sun 20 oct 02
Mr. Pacini, Ron et al
> Hi Jose--Greeting All---
> You are missing the point entirely Jose. The information regarding
the
> temperatures, shrinkage, absorption, etcetera, IS IN the Laguna Catalog
for
> the all the stock clay bodies, as it should be. Every clay Catalog should
> have this info!!!! I've written this time and again. Not only in this
> thread, but a dozen others. I'm not disputing that.
>
I apologize, it looks as if I "shot from the hip". I think I am
oversensitive to this issue of not been able to obtain basic information
concerning clay and other materials. Some potters elect to use raw
materials as they are found in nature and the unpredectability or the
originality of results is something they want, others do want to have
materials that behave the same way every time they use them. Although I
have not been involve in this for too long, it appears to me some suppliers
hide behind the first group to avoid the legitimate requirements of the
second group. Catchy names and subjective descriptions substitute for
information that should be quite specific. It would make sense to me for a
"users group" with sufficient commercial power to define the minimum
information required, with definitions for those parameters and protocols
for testing. For instance your discussion: is "maturity" temperature of
stoneware associated with 2% porosity or is it 5%? How is that tested? If
we had those standards available and published for all suppliers to see,
then we could speak with our $$$ and favor those suppliers that provide the
information. Is NCECA that organization? Can Clayart be the spearhead?
Best regards,
Jose A. Velez
Craig Martell on sun 20 oct 02
Charles said:
>Reduction forces carbon into the clay body; if the reduction is
>quite heavy, the body can be weakened (because carbon is softer?). I have
>on occasion broken a reduction-fired pot only to find that the walls under
>the glaze were gray-black.
Hi Charles:
As you say above, carbon weakens the claybody. When we are firing in
reduction we are hopefully dealing with CO or carbon monoxide and not C,
pure carbon. But it's an imperfect world and even the most careful potter
can, and probably has overdone it a bit. A case in point would be the salt
firing I did last thursday. Fortunately, the ware was all porcelain which
is now porcelain with carbon trapping. So it goes!
regards, Craig Martell Hopewell, Oregon
Liz Willoughby on sun 20 oct 02
Dear Clayarters,
Regarding Jon Pancini's statement challenging Ron Roy's preference
for stoneware absorbency in which he said:
" Ron cited Rhodes to back up his assertion that 1-2%
absorption is basic
info, but Rhodes doesn't back him up. Rhodes says 2% is too tight, let alone
1%. Susan Peterson in her book "Art and Craft of Clay" classifies stonewares
at 2-5% absorption. These are the two most prominent educators in the
ceramics field I can think of. Neither of whom back Ron up in defining
Stonewares at the narrow range of 1-2% absorption."
I turned to my Potter's Dictionary by Frank and Janet Hamer, which as
we all know is a very well respected book. Under "Stoneware" they
state,
"Potters who make stoneware tableware aim to get an end-product which
is theorectically vitrified and therefore is non-porous. This takes
the body near to its point of deformation. With most clays this
vitrification also fires a brittleness or lack of resilience. It is
preferable that the body shall have an absorbency of 1% or even 2%.
In this state it has resilience and can withstand physical knocks.
Below 1% absorbency, most stoneware clays decrease in strength to the
point of vitrification where they may be only half as strong as at 1
%."
So it seems that this book supports Ron. Why have I jumped in here?
I have used clays formulated by Ron for 30 years. I have worked at
Tucker's in their lab, testing raw materials, and all their clay
bodies, and have seen the care and concern, that Ron has shown over
the years helping potters solve their clay problems, and their clay
and glaze fit problems. His concern is always for the potter, making
sure that the clay that they use is reliable, especially for
functional work. I have seen many satisfied customers, and am one
myself. Ron has so much experience dealing with clays that I would
trust his judgement without reserve. He knows his stuff.
Meticky Liz
Liz Willoughby
RR 1
2903 Shelter Valley Rd.
Grafton, On.
Canada
K0K 2G0
e-mail lizwill@phc.igs.net
Craig Martell on sun 20 oct 02
Buenos Dias:
I have to agree with Ron Roy with regard to the aborbtion for stonewares
being best at 1 to 2%.
Porcelain is pretty strong and durable, provided it's a well formulated,
balanced body, at near zero percent absorbtion. What's the difference, and
why is this so when stonewares are brittle and chip and break easily when
vitrified to this point? Basically, from the reading and testing I've done
with various bodies, brittleness is most often related to the amount of
iron oxide, FeO, present in the fired stonewares. If a body contains
enough iron and that iron is reduced to form FeO, the body glass system is
rendered brittle at vitrification. Most stonewares and porcelains are
fluxed with potash feldspar. Potassium will make brittle glass in the
presence of FeO (Hamer and Hamer, iron oxide).
It seems that types of clay and firing conditions have a lot to do with the
durable condition of the finished ware. You can use clays that are very
low in iron and, or, you can control the atmosphere of the kiln to cut or
eliminate the reduction and conversion of Fe2O3 to FeO. When I fired
oxidation many years back I made some stoneware bodies that were pretty
durable and were very tight. If they were fired in reduction, they were
less durable and quite brittle. These are only my observations and
thoughts and are, of course, subject to round filing.
regards, Craig Martell Hopewell, Oregon
Charles Moore on sun 20 oct 02
Craig,
I realize that you have a lot more experience and knowledge about clays than
I do, but I would like to add one thought--which seems to bear out one of
your last statements about stoneware fired under reduction and under
oxidation. Reduction forces carbon into the clay body; if the reduction is
quite heavy, the body can be weakened (because carbon is softer?). I have
on occasion broken a reduction-fired pot only to find that the walls under
the glaze were gray-black.
The reaction of porcelain to reduction is, of course, quite different as you
explained.
Perhaps these observations are only good for round filling as you noted.
Long been an admirer of your pots.
Charles
Sacramento
----- Original Message -----
From: "Craig Martell"
To:
Sent: Sunday, October 20, 2002 11:17 AM
Subject: Re: stoneware vitrification
> Buenos Dias:
>
> I have to agree with Ron Roy with regard to the aborbtion for stonewares
> being best at 1 to 2%.
>
> Porcelain is pretty strong and durable, provided it's a well formulated,
> balanced body, at near zero percent absorbtion. What's the difference,
and
> why is this so when stonewares are brittle and chip and break easily when
> vitrified to this point? Basically, from the reading and testing I've
done
> with various bodies, brittleness is most often related to the amount of
> iron oxide, FeO, present in the fired stonewares. If a body contains
> enough iron and that iron is reduced to form FeO, the body glass system is
> rendered brittle at vitrification. Most stonewares and porcelains are
> fluxed with potash feldspar. Potassium will make brittle glass in the
> presence of FeO (Hamer and Hamer, iron oxide).
>
> It seems that types of clay and firing conditions have a lot to do with
the
> durable condition of the finished ware. You can use clays that are very
> low in iron and, or, you can control the atmosphere of the kiln to cut or
> eliminate the reduction and conversion of Fe2O3 to FeO. When I fired
> oxidation many years back I made some stoneware bodies that were pretty
> durable and were very tight. If they were fired in reduction, they were
> less durable and quite brittle. These are only my observations and
> thoughts and are, of course, subject to round filing.
>
> regards, Craig Martell Hopewell, Oregon
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
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melpots@pclink.com.
iandol on mon 21 oct 02
Dear Craig Martell,
Porcelain clay bodies are formulated with a high proportion of primary =
Kaolin. They also have ample flux to create the environment for Reactive =
Liquid Sintering.
Clays used to compound Stoneware bodies seem to be based on disordered =
Kaolinite (Fireclay, Ball clay) in which other elements substitute for =
Aluminium. So, there may be a reduced proportion of Alumina in the =
overall composition of a stoneware body. This will reduce or diminish =
the volume of Mullite formed during the decomposition phase of the =
disordered Kaolinite. If, as you say there is a higher proportion of =
Iron oxides then Iron silicates may form. Otherwise fragments of iron =
oxide will exist as inclusions in the vitreous phase.
Without the interwoven structure provided by the extensive background of =
acicular Mullite the impact strength of the fired body will deteriorate.
It seems to me that where there is empirical evidence to support either =
view, it has not, as yet, been tested by investigations which would =
validate the propositions. Hence my earlier inquiry about the =
relationship between porosity and theoretical density.
Best regards,
Ivor Lewis, Redhill, South Australia
Jon Pacini on mon 21 oct 02
Greetings All----Hi Gavin ---
Laguna Clay Co is currently comprised of S. Paul Ward Ceramic Supply,
Westwood Ceramic Supply, Mineral Ceramic Products, Miller Clay Co and the
original, Laguna Clay Co. The history of these firms dates back to 1932.
Each company had it's own philosophy for developing clays for it's
customers, so each one brought something different to the table when it was
incorporated into the Laguna Clay family of companies. How many individual
engineers, chemists, potters and educators have contributed to the thousands
pages of lab notebooks, thousands of clay and glaze formulas we produce and
have in our library is anybodies guess.
Miller Clays' philosophy was very much likes Ron's and the clay bodies it
produced reflect that. Westwood's bodies reflected what the Southern
California Teaching population wanted for it's Ceramics classes and for the
alumni that went on to pot professionally. Laguna itself originally only
made "special bodies" for potters and manufacturers, in later years it drew
from those specials for "stock clays".
Laguna still produces clays from each of these companies. And does so
because the demand from our customers does not allow us to say, "You can't
use that clay because it doesn't fit our corporate criteria for what a clay
body should be". Our "MCP" CN 301 formula can be dated back to the 1930's.
I'm not sure I would develop a clay formulation like it today, but it is
still a strong performer. We will produce it till no one buys it any longer.
I don't think you realize that to drop a body from production or "stock",
disrupts the lively hood of the potters who use that body. I would consider
it irresponsible to do so, particularly on the basis of "Theoretical
Idealism". I think it is rather our responsibility to produce that clay to
the best of our ability!!
Our tech staff is very capable of developing 'Theoretically Ideal' clay
bodies. We do a great deal of research into raw material use, their
function and stability. We have dilatometers, a gradient furnace, X-Ray
diffraction equipment, MOR equipment, seven electric kilns and two gas kilns
and we fire them daily to do QA, basic research and product development. I
have a library of mineral specifications from the mines that date back to
the 1930's and do new tests daily.
But I'm not going to modify a clay body that was developed 50 years ago by
Susan Peterson, that hundreds of potters use on a daily basis, because it
doesn't meet my, or somebody else's, personal criteria. I might have to if
it strays from spec, but not because it doesn't meet some "Theoretical
Ideal".
We here are not unaware of traditional parameters set down from the
thousands of years of Ceramic History. Quite the opposite is true. It is
precisely because SO MUCH can be done with clay, that we have so many clays
that a potter can choose from.
Education is a necessary part of being a Craftsman. If you aspire to be a
Craftsman, you must seek out the knowledge of your materials and tools. That
is what defines a Craftsman, his/her Knowledge of their tools and materials.
That Ron has taken it upon himself to Educate potters is marvelous. Clayart
wouldn't be the same without him. If you partake of his particular
philosophy, that is your decision. His is certainly not the only philosophy
to pot by, nor is the one I subscribe to.
From nearly the beginning of this discussion I have noted a differing of
philosophies. Laguna has never looked upon itself as a source of a MFA
Degree in Ceramics. We have personnel here who can solve virtually any
difficulties you may be having and can certainly help you with our products,
but we don't teach university courses in ceramics. Though we are proud you
purchase our clay, we don't think its our place to tell potters how to make
pots and certainly not that there is only our way to make pots.
Liz W. brought up a reference from Hamer's book that gives 1-2% as
preferable for stoneware. Well, on the preceding page the Hamers' list 'less
than 5%' as being their high end for absorbency for Stoneware, even they
have conflicts. It should also be noted that I have no beef about somebody
using a clay body as Ron describes it. Laguna makes plenty of them to those
specs. I have no particular beef with Ron other than our notions of what
defines a stoneware differ, and of course, what role a Supply company should
fill in the market place.
Personally I think you should have the option to use what ever clay meets
your needs and to deride a particular clay only on the basis that it doesn't
meet your specific criteria, is rather narrow minded and very short sighted.
That is after all, where this thread started. And besides, you never know
when that discarded funky test is exactly what a customer is going to ask
for.
If you are interested in Laguna clays and the catalog does not give you the
info you need, please give me a call and I'll try to help you out.
626-330-0361-x228, I have lots of duties out in production, so leave me a
voice mail if I'm out.
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: Gavin Stairs [mailto:stairs@stairs.on.ca]
Sent: Saturday, October 19, 2002 2:32 PM
To: Ceramic Arts Discussion List
Cc: Jon Pacini
Subject: Re: stoneware vitrification
At 03:44 PM 14/10/2002 -0700, Jon Pacini wrote:
> Let me explain just exactly how a clay body becomes a stock clay body
>for Laguna. First off we don't pluck stock bodies out of the air because
we
>need one to fill a hole in our catalog.
> All of the Stock bodies we produce started out as specials, for
schools,
>for potters.
Hi Jon,
Now I begin to understand why so many posts to Clayart talk about
idiosyncratic clay bodies that come from Laguna, and they (the potters)
have some sort of a problem or another. There's no system to your
system. It just grew like Topsy, and you keep making whatever body gets
ordered. Sounds like the good old American way, but it doesn't have any
predictability. You're not contributing to your customers' educations or
improving their working methods. You're just feeding their habits. I
would have hoped that a large firm like Laguna would have researched the
available raw materials, made decisions about what would be a good mix of
same, and designed bodies that would suit the various needs based on
that. A simple statement at the end of such a designed body list would
cover all the rest of the requests you get. Like "If none of our carefully
designed bodies fits your needs, we will make a ton of whatever you like."
Most firms making art materials strive for some sort of order and
predictability in their products, and also seek to apply the expertise that
they presumably develop over the years to benefit their customers. From
your statements, it would seem that you don't believe you have any such
advantage, and "the customer is always right" is the maxim that covers all
situations.
Well, so be it. I think I prefer Ron's idea of how best to serve the
clients.
Gavin
Jon Pacini on mon 21 oct 02
Hi Jose--keep putting your concerns on Clayart. We hear them.
a Porosity/absorption test can be found in the archives, Ron gave a good
one- he boils, I pressure cook. Other wise the test is the same---your
call.
The definition of stoneware, vitreous, maturing, at what % of absorption
it all relates to and a bunch of other vague terms we potters commonly use,
is what we are sparing around about. Ron has his philosophy and I have
mine--it's always good to have loyal opposition--your call again.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: Jose A. Velez [mailto:potter785@cox.net]
Sent: Sunday, October 20, 2002 8:54 PM
To: Jon Pacini; CLAYART@LSV.CERAMICS.ORG
Subject: Re: Re: stoneware vitrification
Mr. Pacini, Ron et al
> Hi Jose--Greeting All---
> You are missing the point entirely Jose. The information regarding
the
> temperatures, shrinkage, absorption, etcetera, IS IN the Laguna Catalog
for
> the all the stock clay bodies, as it should be. Every clay Catalog should
> have this info!!!! I've written this time and again. Not only in this
> thread, but a dozen others. I'm not disputing that.
>
I apologize, it looks as if I "shot from the hip". I think I am
oversensitive to this issue of not been able to obtain basic information
concerning clay and other materials. Some potters elect to use raw
materials as they are found in nature and the unpredectability or the
originality of results is something they want, others do want to have
materials that behave the same way every time they use them. Although I
have not been involve in this for too long, it appears to me some suppliers
hide behind the first group to avoid the legitimate requirements of the
second group. Catchy names and subjective descriptions substitute for
information that should be quite specific. It would make sense to me for a
"users group" with sufficient commercial power to define the minimum
information required, with definitions for those parameters and protocols
for testing. For instance your discussion: is "maturity" temperature of
stoneware associated with 2% porosity or is it 5%? How is that tested? If
we had those standards available and published for all suppliers to see,
then we could speak with our $$$ and favor those suppliers that provide the
information. Is NCECA that organization? Can Clayart be the spearhead?
Best regards,
Jose A. Velez
Gavin Stairs on tue 22 oct 02
At 01:36 PM 21/10/2002 -0700, Jon Pacini wrote:
>Laguna Clay Co is currently comprised of S. Paul Ward Ceramic Supply,
>Westwood Ceramic Supply, Mineral Ceramic Products, Miller Clay Co and the
>original, Laguna Clay Co. The history of these firms dates back to 1932.
>Each company had it's own philosophy for developing clays for it's
>customers, ... Laguna still produces clays from each of these companies.
>And does so because the demand from our customers does not allow us to
>say, "You can't use that clay because it doesn't fit our corporate
>criteria for what a clay body should be". ... I don't think you realize
>that to drop a body from production or "stock", disrupts the lively hood
>of the potters who use that body. I would consider it irresponsible to do
>so, particularly on the basis of "Theoretical Idealism". I think it is
>rather our responsibility to produce that clay to the best of our ability!!
Dear Jon,
I don't think you have quite caught the gist of what I and others have been
suggesting. I do not want you to quit making clay that people want. I am
suggesting that rather than promoting to new customers the bodies that have
been inherited over the years on an ad hoc basis, you design and promote a
rational set of bodies that would serve your clients better. I am fully
aware that many of your clients who have learned to use one or more of the
"legacy" bodies would be bitter and bereft if you were to arbitrarily cease
production. I am also aware of how much work is involved in carrying a lot
of bodies that essentially duplicate each other in function, but have
sacred recipes handed down from antiquity, etc. There is a matter of
economy, and of utility, to using your expertise in the service of your
clients, rather than just to repeat the past over and over again. I would
imagine that you could select from your current production bodies a subset
that could become your preferred bodies, to be kept up to date and
optimized against currently available raw materials in a rational
manner. Then you could continue to produce the others as long as demand
were strong. However, when new customers would come to you with requests
for a particular type, you could steer them to your preferred set.
You and Laguna seem to prefer the disorder of the inheritance. Well,
that's ok, but new customers, and apparently not a few old ones too, seem
to find it confusing. I'm not surprised.
And by the way, there is no suggestion of some theoretical perfect body in
what we are saying. There's no such thing. We can all agree on that. And
many professionals who have developed their own body will prefer that to
any other, even if it has defects. So also with people who have come to
know a body and do not want to waste time redesigning all their glazes for
a new one for no apparent reason. So for all of us, we hope that you will
keep on serving these people as you have done in the past.
Gavin
Steve Mills on tue 22 oct 02
Interesting this; I was taught to reduce very heavily in order to give
depth to the Celadons and Tenmuku's we used at College. I fact it was
de-rigueur to soak for at least an hour at the beginning of the
reduction phase to *establish body reduction* before allowing the
temperature to start rising. I think on reflection that the bodies that
were weakened most by this were the high iron bearing ones; certainly
more of my pots made with light coloured clays and porcelains have
survived the rigors of everyday use.
Steve
Bath
UK
In message , Craig Martell writes
>Charles said:
>>Reduction forces carbon into the clay body; if the reduction is
>>quite heavy, the body can be weakened (because carbon is softer?). I have
>>on occasion broken a reduction-fired pot only to find that the walls under
>>the glaze were gray-black.
>
>Hi Charles:
>
>As you say above, carbon weakens the claybody. When we are firing in
>reduction we are hopefully dealing with CO or carbon monoxide and not C,
>pure carbon. But it's an imperfect world and even the most careful potter
>can, and probably has overdone it a bit. A case in point would be the salt
>firing I did last thursday. Fortunately, the ware was all porcelain which
>is now porcelain with carbon trapping. So it goes!
>
>regards, Craig Martell Hopewell, Oregon
--
Steve Mills
Bath
UK
David Beumee on fri 25 oct 02
When I think about the proper absorption percentage for mature stoneware, I am reminded of Pete Pinnell's words from his post of last December.
"Absorption is not a good indicator of maturity. Maturity is the point at which a body reaches it's best strength and glaze fit and ' no longer suffers from marked
moisture expansion' ".
As to Craig Martell's post about britltleness related to iron oxide content in a stoneware clay body, I remember Jim Robinson's comments from the Studio
Potter article Fear of Silica, and they agree completely. In a reduction atmosphere where oxidised iron is converted to reduced black iron,
"fluids form quickly, teaming up with feldspathic melts.These liquids can dissolve mullite and quartz, cutting down on their helpful attributes. When these FeO-rich
liquids cool into glass, the glass has a brittle character." Jim Robinson recommends keeping the red iron oxide percentage in a stoneware clay body below 1%, as
does Jim McKinnell in his article "Black Core and Bloating" from Studio Potter Volume 6, number 2.
To Ivor; if incresing the presence of mullite is the answer to a strong stoneware body and the answers haven't been found out, let's set up the
experiments, find some answers and report back to this group. To Ron; I agree that testing isn't complicated or difficult, but it is time consuming. Who will step
up to the plate and help me? In the hundred or so stoneware, white stoneware , and porcelain bodies that I've tested of late, I 've come up with some very good
recipes I'd be happy to share. But I have yet to find a great throwing body that is also truly shock resistant in terms of both thermal expansion and every day wear
and tear.
David Beumee
Earth Alchemy Pottery
Lafayette, Colorado
10/24/02 5:54:29 PM, Ron Roy wrote:
>By now anyone reading this thread should realize - all clay producers are
>not the same - it happens to be true about raw material suppliers as well.
>
>I think the state of education - including most texts, schools and workshop
>presenters do not do very well in this area. In fact - if I were to try and
>pick raw clays to use based on published data I could not make the best
>choices. I would think clay makers should welcome the opportunity to
>educate when ever they can - how ever they can. Better still - develop the
>data we all need to design bodies that do the job better.
>
>When buying clay there are a few questions that need to be asked. You need
>to know what testing - if any - the company you are relying on provide your
>clay needs - are doing.
>
>Any company that tests raw materials or their clays will be happy to show
>you the data. If they say they are but won't show you the data it simply
>means they are not doing the testing - or their product is so variable they
>dare not.
>
>If your clay company will not provide up to date data and how it was fired
>then it is up to you. If they are not watching and neither are you then you
>are going to have problems sooner or later - and you may have an inferior
>product right now. There are just to many variables to assume everything
>will stay the same - thats assuming everything was right to start with.
>
>If you are testing raw materials and/or clay bodies you will do everyone -
>including manufactures - a favour. The sharing of such information is now
>easy thanks to ClayArt.
>
>You may ask - why should I share - they are my competition? It's a valid
>question but it does not take into account the effect of poorly crafted
>ware on the market we all wish was better. Think of anyone buying poorly
>made ware - leaky mugs, cracking casseroles and tea pots, and glazes that
>lose colour in ordinary use - what do they think of hand made pottery after
>an experience like that. Will they rush out and buy another right away - or
>will they never buy another again?
>
>This is all about doing it better, each of us deciding to take a step up
>and sharing what we learn.
>
>When we post to this list we have an obligation to try and make things
>better if we can - at least that is how I feel about it and I am obviously
>not alone.
>
>To those of you who think testing is hard, time consuming and complicated -
>it is not. Remember - you are going to have to pay much more in time and
>loses eventually - it's simply a question of pay now or pay much more
>later.
>
>If anyone is experiencing problems with clays and/or glazes this is the
>place to get help and in doing so - educate thousands of potters and make
>it better for all of us.
>
>RR
>
>
>
>> A catalog is not meant to be a textbook either. Education is better
>>left to those who don't have a monetary interest in what material you are
>>going to purchase. That doesn't infer that potters shouldn't get product
>>support, but a supplier is not a substitute for a good curriculum at a
>>university, years of being an apprentice to a master or a great reference
>>library.
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
>
>______________________________________________________________________________
>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.
>
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