Ababi on thu 18 jul 02
Hello Ron.
Now I understand mor.
One of the reasons I use mainly kaolin, is probably that while using
software I adjust
the way I will get the alumina silica the way it was before.
In some of the very many raku recipes I made I found out that in a given
recipe when I
used 85 frit and 15 kaolin I got white, ( clear) glaze while with ball clay
I got it gray (
clear). It is possible that the gray happened because of crackles that after
the
reduction looked like a gray mesh, perhaps because of the less alumina?
When I started to read The Magic Of Fire , of Tony Hansen I counted the ball
clays I
was surprise from the so many kinds. At that time Ball Clay was a
meaningless
name of a powder so kaolin and the others. Imagine to yourself every music
CD you
have is the same!
After reading Mike Bailey's book I have learnt that one should have at list
two kinds of
Ball clay in order to use different amount, relations of alumina silica.
Dear clayarters.
Do not catch me in my words. I might explain it bad but I understand it
correctly!
One kind I use is AK 33.3% Alumina and 512.2% silica the way I keep it in
Insight LOI
11.7
The second Gleason 26.2% Alumina and 58 silica 11.6 LOI
The third kind has either alumina or silica has (can or bottle) LOI 100% it
is the Schlitz
Ababi
---------- Original Message ----------
>Hi Bill,
>Yes - I am posting this to ClayArt.
>The difference would be a bit more shine - less alumina and more silica
>will raise the Si/Al ratio somewhat and that usually results in more gloss.
>The difference may not be as noticeable in balanced glazes but you would
>notice it more in a matte glaze for instance. It may as well be less
>noticeable in slow cooled glazes because the formation of crystals is aided
>by more silica and less alumina.
>The main advantages of using ball clay instead of kaolin are better
>suspension in the bucket and better dry strength of the ball clays (most of
>them) which counters glaze cracking and the resulting crawling. Ball clay
>works better with bentonite as well to counter settling when only small
>amounts of raw clay are present in a glaze recipe.
>Lets take the following glaze as an example - I have just made this up to
>illustrate - this is not a real glaze - although it may turn out to be one.
>Frit 3134 - 25.0
>G200 spar - 20.0
>Whiting - 20.0
>EPK - 15.0
>Silica 20.0
>Total 100.0
>Ratio - 9.46
>Expan - 547.03
>Same recipe with OM4
>Frit 3134 - 25.5
>G200 spar - 20
>Whiting - 20
>OM4 - 21.0
>Silica 16.5
>Total 103.0
>Ratio - 9.48
>Expan - 549.97
>I have not retotaled the OM4 recipes because I did not want to introduce
>another factor - thinking - simple is better at this point. Note the small
>addition of Frit because new total is over enough that I need to add some
>boron to keep it the same.
>As you can see the ratios and expansion are very close - so I would expect
>both glazes to look and act pretty well the same. There is more iron and
>titanium in the second and this might have some slight effect on some very
>sensitive glazes - but not necessarily unwelcome changes.
>If I had to make up a general rule for this exchange with this Kaolin and
>this ball clay I would say for every one EPK taken out add 1.4 OM4.
>I can't figure out how to calculate the amount of silica to subtract - will
>someone explain it to me please.
>2nd example
>Frit 3134 - 25.0
>G200 spar - 20.0
>Whiting - 20.0
>EPK - 10.0
>Silica 25.0
>Total 100.0
>Ratio - 12.44
>Expan - 539.45
>Same recipe with OM4
>Frit 3134 - 25.0
>G200 spar - 20.0
>Whiting - 20.0
>OM4 - 14.0
>Silica 23.0
>Total 100.0
>Ratio - 12.43
>Expan - 539.44
>The reason adding ball clay helps with crawling has to do with the MOR
>(modulus of rupture) of various clays. MOR is simply how much force it
>takes to break a bar of dried clay - all clays are tested this way at the
>mine.
>EPK has a MOR of 300
>Pioneer - 300-400
>OM#4 has a MOR of 850, 825
>Bell dark has a MOR of 690
>Naturally the MOR of any given clay will vary depending on the batch but we
>can be sure that the ball clays will be stronger dry than the kaolins.
>Adding bentonite to both kaolins and ball clays will make them stronger but
>it works better with ball clays they say.
>RR
>>Roy - Read your comments on Clayart regards kaolin vs. ball clay. Got
>>your "Mastering Cone 6 Glazes" (with the free shipping) a while back
>>and have been using it, in part, teaching my students about the
>>importance of stable/durable glazes for functional ware. I have
>>subbed EPK & OM4 Ball Clay back and forth in equal amounts in some
>>glazes and have not seen much difference in the glazes. I'd be
>>interested in your recommended percentage substitutions of these two
>>materials, given the silica/alumina differences. You may post you
>>comments to Clayart for others to learn.
>>Thanks, Bill
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
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Ababi on thu 18 jul 02
>One kind I use is AK 33.3% Alumina and 512.2% silica
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
A bit less Silica:52.2
Ababi
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