Stephanie Wright on tue 20 feb 07
Hello everyone,
First I have questions that may seem pretty dumb. I am hoping someone can
give me a simple answer that I can wrap my brain around...
What are the essential differences between ball clay and kaolin? I see
both EPK and ball clay called for in glaze recipes, and I am thinking
there must be reason they are not interchangeable.
Regarding ball clay, is there a major difference between ball clay and
dark ball clay? Does dark ball clay contribute more to the color of a
glaze? I have a temmoku recipe that calls for dark ball clay, and we have
none in our classroom supplies.
Second, I just got a recipe for Byron Temple Orange (^10 R). Have any of
you used it? What is your opinion of the glaze, both pre and post firing?
Thanks!
Stephanie
Jon Pacini on wed 21 feb 07
Greetings All---Hi Stephanie--- you wrote--
What are the essential differences between ball clay and kaolin? I see
both EPK and ball clay called for in glaze recipes, and I am thinking
there must be reason they are not interchangeable
There are a number of differences between kaolins and ball clays. If you
really want to delve into the differences pick up a copy of Daniel Rhodes
'Clay and Glazes for the Potter'. It would give you the full run down, but
I'll give you a short if some what incomplete answer here.
Good kaolins tend to fire white, they generally are quite refractory and not
extremely plastic. In a glaze they are generally used as a source of
alumina, imparting hardness in the final glaze.
Ball clays are usually very plastic and can fire light colored or dark
depending on iron content. The raw color can also be light or dark depending
on the organics contained in the material. The amount of and composition of
these organics can have an effect on the plasticity of any given ball clay.
In glazes a ball clay can, like kaolin, be a source of alumina. But
generally when it is added, it is used as a source of plasticity as well. It
will help with keeping the glaze in suspension and with adherence. Bentonite
is commonly used in the latter application also.
Tenmoku glazes can be almost entirely clay. Albany Slip Clay was used
extensively in that purpose. I'm not sure if it could be characterized
technically as a ball clay though --- you might have to check with John
Britt on that particular point.
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co
karen gringhuis on wed 21 feb 07
Stephanie -
FIRST, consider investing in the best reference book -
The Potter's Dictionary by Frank and Janet Hamer.
Even if you find an older edition on ebay for cheap,
it will be very instructive and interesting reading -
I kid you not. Waaay better than "Dictionary" sounds.
(If & when you do this and start browsing, keep a note
pad handy bc you will come up w/ more qns. Which is
what it's all about & a great source of creative
ideas.) If your local library doesn't have one, ask
for it on inter-library loan.
NUTSHELL:
Kaolin - very pure, very white, not so plastic.
Ball clay - less pure therefore less white BUT very
plastic therefore suspending the other materials in
the glaze better than kaolin. You can see why some
glaze recipes incl both clays.
Hamer = "Ball clay is a general term for many clays"
- hence your dark ball clay.
Temmoku - quickly looking at 2 temmoku recipes in
Cushing's Handbook, both get their color from 10% red
iron oxide. They use grolleg (kaolin) or epk and come
out dark. Therefore it seems plain ball clay should
work fine in your glaze. Yes, "dark" ball clay would
contribute some color but I can't see it being as
important as iron ox.
If you really want to see the color differences in
ball clays, take every ball clay you can get your
hands on even a sample of, separately wet them into
wet clay, make a test bar of each & fire them side by
side. See what you get.
Keep asking qns. If I can help more, feel free to
write off list.
Karen G.
------------------
>What are the essential differences between ball clay
and kaolin? I see
both EPK and ball clay called for in glaze recipes,
and I am thinking
there must be reason they are not interchangeable.<
>is there a major difference between ball clay and
dark ball clay? Does dark ball clay contribute more to
the color of a
glaze? I have a temmoku recipe that calls for dark
ball clay, and we have none...<
Karen Gringhuis
KG Pottery
Box 607 Alfred NY 14802
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Ron Roy on thu 22 feb 07
Hi Stephanie,
That tenmoku is probably mine - because I use bell dark ball clay - Old
Mine 4 will work fine. Bell dark is actually one of the lighter burning
ball clays - it's called dark because there is carbon associated with it -
an advantage as carbon helps with plasticity but burns out during firing.
If you look at the analysis of the kaolins you will see - they are quite
high in alumina from 46% up to 48% - if you compare them to ball clays you
will see that the ball clays have a lot less alumina 24 to 30% and
consequently more silica than the kaolins.
Ball clays are also stronger. My tenmoku originally had kaolin in it - and
it crawled a lot - since I replaced the kaolin with ball the crawling has
stopped - because the ball clay is stronger and does not crack up as much
as the glaze is sintering.
So you can use this information to see if subbing ball clay in for kaolin
will help cure problems.
Lets say your glaze has only 5% kaolin and is hard to keep mixed up and
powders off when you handle it - and sometimes crawls. Subbing in ball clay
for all or part of the kaolin will help with all three problems.
You will need more ball clay because you want the same amount of alumina
and you also have to reduce the silica because ball clay always has more
silica than kaolin.
So more ball clay helps to keep the glaze mixed - because ball clay is a
better suspender and there is more of it - and it's stronger so it will
reduce the powdering. It will also work better with bentonite to help
suspend glazes.
Sounds all very complex I know but if you are using a calculation program
it becomes quite simple.
Any questions?
RR
>First I have questions that may seem pretty dumb. I am hoping someone can
>give me a simple answer that I can wrap my brain around...
>
>What are the essential differences between ball clay and kaolin? I see
>both EPK and ball clay called for in glaze recipes, and I am thinking
>there must be reason they are not interchangeable.
>
>Regarding ball clay, is there a major difference between ball clay and
>dark ball clay? Does dark ball clay contribute more to the color of a
>glaze? I have a temmoku recipe that calls for dark ball clay, and we have
>none in our classroom supplies.
>
>Second, I just got a recipe for Byron Temple Orange (^10 R). Have any of
>you used it? What is your opinion of the glaze, both pre and post firing?
>
>Thanks!
>
>Stephanie
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
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>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Snail Scott on mon 26 mar 07
-----Original Message-----
>From: Stephanie Wright
>Sent: Feb 20, 2007 9:59 PM
>What are the essential differences between ball clay and kaolin? I see
>both EPK and ball clay called for in glaze recipes, and I am thinking
>there must be reason they are not interchangeable.
>
>Regarding ball clay, is there a major difference between ball clay and
>dark ball clay?
Ball clay vitrifies at a lower temperature and is
less white than kaolin, and is cheaper in most
places, but the main distinction is that ball clay is
very plastic (due to fine particle size), and has a
correspondingly high shrinkage rate.
So, ball clay is popular in throwing bodies, and in
glazes, but if it needs to be very white, or have a
lower shrinkage, kaolin might be used in place of
some or all of the ball clay.
It's rare for a recipe to call specifically for dark
ball clay, since it's easy to supply a source of
oxide to darken a recipe, and ball clay doesn't
contribute much colorant. It's more common for
a recipe to specify a light ball clay, in order to
avoid that extra colorant where it's not wanted.
I wouldn't worry about seeking out a dark ball
clay specifically; just use what you have on
hand, and if the recipe doesn't come out well,
try adding an extra percent or so of iron oxide.
-Snail
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