Steve Slatin on thu 23 feb 06
Lori --
There are several reasons why it might work and several why it
might not.
Why it might work --
You've only got 10% clay in this recipe. Subbing one clay
for another is going to be much less significant than when
you've got 20 or 30 percent clay in a recipe. It's based on
a potash spar and not a soda spar; soda spar glazes in my
limited experience are more sensitive to substitutions of
clay than potash spar glazes. And the recipe gets lots of
its silica from the spar and plain silica; so silica concentration
is not so important.
Why it might not --
Kaolin and OM#4 aren't all that much alike. EPK (if it's
the Kaolin you use) has 31% alumina; OM#4 has 22%.
EPK is 66% silica; OM#4 is 74%. There's also a significant
difference in the particles found in these clays; 97% of OM4
particles are 10 microns or smaller; only 90% of EPK
particles are. This will have quite a bit to do with glaze
suspension, the way it flows if brushed, and so on.
Why it's worth trying a small batch to find out --
It's the only way to know for sure. Watch for suspension
problems; be ready to use something to adjust it if necessary;
if it doesn't work the first time out remember it's 10% of the
glaze and it's 10% higher in silica and 10% lower in alumina
(more or less! gimmee a break!) and that's all of 1% in
absolutes, so adjust 1% at in the silica if you must ...
but this is a cone 8 - 10 glaze. Few glazes like this
fail completely from being off 1% in silica or alumina.
Be brave! Do a small batch, just a 100 g or so, and put it
on a small waste piece or a test tile, and see what it does.
If it's OK, you're a hero. If not, it's still useful information.
Let us know what happens.
Best wishes -- Steve Slatin
Lori Doty wrote:
I have been beating my head against the wall on this one and since I
know very little about glaze making would like to know if it would be
ok (within usable parameters) to use OM4 (a ball clay) instead of
kaolin in a glaze recipe as a one for one substitute or am I courting
danger here? The recipe from Brad Sondahl's web site calls for kaolin
in the amount listed below.
Steve Slatin --
In watermelon sugar the deeds were done and done again
as my life is done in watermelon sugar.
---------------------------------
Yahoo! Autos. Looking for a sweet ride? Get pricing, reviews, & more on new and used cars.
Lori Doty on thu 23 feb 06
I have been beating my head against the wall on this one and since I=20
know very little about glaze making would like to know if it would be=20
ok (within usable parameters) to use OM4 (a ball clay) instead of=20
kaolin in a glaze recipe as a one for one substitute or am I courting=20
danger here? The recipe from Brad Sondahl's web site calls for kaolin=20
in the amount listed below.
Glaze name: H38-40 (black gloss)
Cone: 8 - 10
Firing: Ox. or Red.
Testing: Untested
Date: 6/3/96
Recipe: (Percent, Batch)
Potash feldspar=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 38.92=A0=A0=A0=A0=A0=A0 =
38.92
Silica=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
28.02=A0=A0=A0=A0=A0=A0 28.02
Kaolin=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
10.06=A0=A0=A0=A0=A0=A0 10.06
Dolomite=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
4.55=A0=A0=A0=A0=A0=A0=A0 4.55
Bone ash=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
4.55=A0=A0=A0=A0=A0=A0=A0 4.55
Whiting=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
13.91=A0=A0=A0=A0=A0=A0 13.91
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
--------=A0=A0=A0 --------
Totals:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 =
100.00=A0=A0=A0=A0=A0 100.00
Also add:
Red iron oxide=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 4.55=A0=A0=A0=A0=A0=A0=
=A0 4.55
Cobalt carbonate=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 1.00=A0=A0=A0=A0=A0=A0=A0=
1.00
Copper carbonate=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0.55=A0=A0=A0=A0=A0=A0=A0=
0.55
Thanks for any input.
Lori Doty
Nurse/Potter
Slowly turning the tide
Rolla, Missouri=
Taylor, in Rockport TX on thu 23 feb 06
Dearest Lori:
Please do not beat your head agains any hard, unyielding objects...not even
if they are nice fellow clayarters. You'll need your noodle to figure out
your glazes.
Dave F. suggested on list awhile back that replacing some or all of the
kaoline in a recipe to see how it affected glaze slop might be a productive
experiment. I thought so to and replaced all the kaoline in my the four
'base' glazes I first started out testing. I could tell no major difference
in the look of the fired glazes. They look almost identical on my test
tiles. My notes on the glaze preparation and sieving record the slight
improvement in suspension of the glaze slop. I had one hellish hardpanner
and the OM4 only slightly helped with that.
As for the chemical compostion of the different clays, I will defer to those
with more background in this sub to esplain. Kaoline (EPK is what I use) did
raise my silica number and lower my alumina number within my calc program
for my tested glazes.
What are your "usable parameters"?
Taylor, in Rockport TX
On Thu, 23 Feb 2006 19:06:57 -0600, Lori Doty wrote:
>I have been beating my head against the wall on this one and since I
>know very little about glaze making would like to know if it would be
>ok (within usable parameters) to use OM4 (a ball clay) instead of
>kaolin in a glaze recipe as a one for one substitute or am I courting
>danger here? The recipe from Brad Sondahl's web site calls for kaolin
>in the amount listed below.
Ron Roy on fri 24 feb 06
Hi Lori,
Ball Clay (OM4 in this case) always has less alumina and more silica than
kaolin - so it takes more ball clay to get the same amount of alumina -
then you have too much silica so you need to remove some.
To get the same glaze use 14 OM#4 and reduce the silica to 25.
Replacing kaolin with ball clay helps suspend glazes better and also will
reduce powdering.
Ball clay works better with bentonite and epsom salts to cure glazes that
settle out too quickly.
RR
>Glaze name: H38-40 (black gloss)
>Cone: 8 - 10
>Firing: Ox. or Red.
>Testing: Untested
>Date: 6/3/96
>
>Recipe: (Percent, Batch)
>Potash feldspar 38.92 38.92
>Silica 28.02 28.02
>Kaolin 10.06 10.06
>Dolomite 4.55 4.55
>Bone ash 4.55 4.55
>Whiting 13.91 13.91
> -------- --------
>Totals: 100.00 100.00
>Also add:
>Red iron oxide 4.55 4.55
>Cobalt carbonate 1.00 1.00
>Copper carbonate 0.55 0.55
>
>
>Thanks for any input.
>
>Lori Doty
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Hendley on fri 24 feb 06
The short answer: it probably won't make a noticeable difference
in this glaze.
There are all sorts of subtitles between kaolin and ball clay both
in the working qualities of the raw glaze and the final fired glaze,
but don't worry about it until you have a little more experience.
However, either my good buddy Taylor or his glaze calculation
program got it backwards - kaolin has a higher alumina
to silica ratio, and ball clay has a higher silica to alumina ratio.
That means that, theoretically at least, the ball clay should give
a slightly shinier glaze, and kaolin, more matt.
David Hendley
Old Farmhouse Pottery
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
>I have been beating my head against the wall on this one and since I
> know very little about glaze making would like to know if it would be
> ok (within usable parameters) to use OM4 (a ball clay) instead of
> kaolin in a glaze recipe as a one for one substitute or am I courting
> danger here? The recipe from Brad Sondahl's web site calls for kaolin
> in the amount listed below.
> Recipe: (Percent, Batch)
> Potash feldspar 38.92 38.92
> Silica 28.02 28.02
> Kaolin 10.06 10.06
> Dolomite 4.55 4.55
> Bone ash 4.55 4.55
> Whiting 13.91 13.91
Taylor, in Rockport TX on fri 24 feb 06
On Fri, 24 Feb 2006 00:03:11 -0600, David Hendley wrote:=
...
>However, either my good buddy Taylor or his glaze calculation
>program got it backwards - kaolin has a higher alumina
>to silica ratio, and ball clay has a higher silica to alumina ratio.
David is always right, and I'm more often that not very left. Guess I can't=
tell the difference. Here's the side by side unities of my cone 5/6 test.
Less than 8% clay in the recipe, btw. I like to play.
Base 3
w/EPK w/OM4
Unity Oxide Unity
.118 Na2O .118
.124 K2O .125
.317 MgO .317
.341 CaO .34
.1 ZnO .1
1.000 Total 1.000
.378 Al2O3 .352
.006 Fe2O3 .007
4.023 SiO2 4.041
.001 TiO2 .004
0 P2O5
10.6 Ratio 11.5
63.6 Exp 63.6
Comments: Taylor can't tell his
left from his right.
Crazes on my Armadillo bodies.
-----------------------------------
Calculations by GlazeMaster=99
www.masteringglazes.com
------------------------------------
Taylor, in Rockport TX
wi
Michael Wendt on sat 25 feb 06
If you are making a glaze that is colored, try Helmer Kaolin as the kaolin
and see if it works better as a suspending agent. We never add bentonite to
our glazes, not even chun which is only 5% Helmer and the glaze is still
suspended and does not hard pan during settling.
I use it for clear and white but the 1.2% iron content might bother some
people's color.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Ron Roy wrote:
Hi Lori,
Ball Clay (OM4 in this case) always has less alumina and more silica than
kaolin - so it takes more ball clay to get the same amount of alumina -
then you have too much silica so you need to remove some.
To get the same glaze use 14 OM#4 and reduce the silica to 25.
Replacing kaolin with ball clay helps suspend glazes better and also will
reduce powdering.
Ball clay works better with bentonite and epsom salts to cure glazes that
settle out too quickly.
RR
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