Alisa Clausen on thu 3 may 07
This is Brian Gartsides famous clear parts recipe.
I broke it down in to weight because I work better that way. I calculated
it by simple division:
4 into 100,
2 into 25 and
2 into 12.5,
then rounded up on Glaze Master. I left it at totaling 98 because I did not
want
4 decimal places.
Original in parts
4 Frit 3134
4 EPK
2 G-200 Feldspar
2 Silica
1 Talc
1 Whiting
16 Water
Now in weight
Amount Ingredient
28.6 Frit--Ferro 3124 4 parts
28.6 Kaolin--EPK
14.3 Feldspar--G-200 2 parts
14.3 Silica
7.1 Talc 1 part
7.1 Whiting
100 Total
Unity Oxide
.138 Na2O
.074 K2O
.204 MgO
.584 CaO
1.000 Total
.6 Al2O3
.212 B2O3
.006 Fe2O3
3.562 SiO2
.004 TiO2
.001 P2O5
5.9 Ratio
6.5 Exp
Results
Gloss to semi gloss transluscent glaze
See color variations at website, Glaze tests, more tests www.alisapots.dk
My parts base tests crazed on my stoneware. However the weight variation
did not. I think it because my parts measuring by spoon full was much too
variable.
Best regards from Alisa in Denmark
John Sankey on wed 7 nov 07
The original is
4 Frit 3134 by volume
4 EPK
2 G-200 Feldspar
2 Silica
1 Talc
1 Whiting
By weighing ingredients, I get
29 frit,Ferro 3134
24 kaolin,EPK
15 silica
15 feldspar,G-200
9 whiting
8 talc
I calculate a COE of 5.86, which is low enough that crazing
shouldn't be the problem that Alisa saw when it was thick. I
wonder if something else was involved...
--
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Alisa Clausen on wed 7 nov 07
On Wed, 7 Nov 2007 06:06:25 -0500, John Sankey
wrote:
>The original is
>4 Frit 3134 by volume
>4 EPK
>2 G-200 Feldspar
>2 Silica
>1 Talc
>1 Whiting
>
>By weighing ingredients, I get
>
>29 frit,Ferro 3134
>24 kaolin,EPK
>15 silica
>15 feldspar,G-200
>9 whiting
>8 talc
>
>I calculate a COE of 5.86, which is low enough that crazing
>shouldn't be the problem that Alisa saw when it was thick. I
>wonder if something else was involved...
>
>--
>
Dear John
The crazing occured when I did Brians glaze by volume. I just think that
the tests were off because I was not careful enough with measurements (i.e
how level the teaspoon was or not). When I broke it down to grams,
which my version was slightly different, 28,28, 14, 14, 7, 7
I experienced no crazing. I believe I was much more accurate with the
balance of materials in the gram version.
Furthermore, these tests promted me to start asking about oxides. How
much of what can influence a COE enough to make an otherwise crazing base,
not craze? Since most COE information does not factor in the coloring
oxides in the total batch, I can not calculate the difference. However,
from visual results of tests, I can see that most of the colored tests
with Red Iron and some with Cobalt Oxide of an otherwise crazing base, did
not craze.
Best regards, Alisa in Denmark
John Sankey on thu 8 nov 07
"Since most COE information does not factor in the coloring
oxides in the total batch, I can not calculate the difference."
That's why I wrote my own program - glaze programs are black
boxes and we users don't know what goes on inside them.
Especially, we have no clue as to how they invent coefficients
when they claim to be following an author who didn't test many
oxides or whether they use zero for the missing ones.
Colorants make a big difference to expansion, especially iron
because we use so much, barium and strontium because they are so
high. I calculate with everything that melts - glaze programs
should too.
See http://sankey.ws/glazeexpansion.html
--
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Ivor and Olive Lewis on fri 9 nov 07
Dear John Sankey,=20
I'm not sure about the details but I have read somewhere that some of =
the materials we use have negative coefficients so that they contract =
when heated and expand when cooled.
From memory, one of the culprits is Boric Oxide
Ron Roy on sat 10 nov 07
Hi John,
I calculated in my usual way and get a calculated expansion (450) just at
the point when I would expect occasional crazing and/or crazing when the
glaze is thick on many of Tuckers clay bodies.
We can also expect some crazing during a fast cool - even if the glaze
expansion is low enough to not craze otherwise.
RR
>By weighing ingredients, I get
>
>29 frit,Ferro 3134
>24 kaolin,EPK
>15 silica
>15 feldspar,G-200
>9 whiting
>8 talc
>
>I calculate a COE of 5.86, which is low enough that crazing
>shouldn't be the problem that Alisa saw when it was thick. I
>wonder if something else was involved...
>
>--
>Include 'Byrd' in the subject line of your reply
>to get through my spam filter.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
brian on sun 11 nov 07
>John and Ron.
It has been interesting to read comments about a glaze that I
initiated, was calculated by Steve Rumsey in the 1980's and which I
have used for have used for over 20 years.
Ron said he....
>got a calculated expansion (450) just at
>the point when I would expect occasional crazing and/or crazing when the
>glaze is thick on many of Tuckers clay bodies.
>
>We can also expect some crazing during a fast cool - even if the glaze
>expansion is low enough to not craze otherwise.
My question is .......Is there a slight adjustment possible to lower
the COE using the same materials?
And further to that, I would be really interested in hearing comments
about the changes that occur when 10-12% red iron oxide is added
(this is a common procedure)
John said "Colorants make a big difference to expansion, especially
iron" and that he always calculates for this.
I do realise that there was a conversion fron Aust/NZ to American
kaolin and feldspar at the start of the discussion but I am still
interested in your comments
best wishes
Brian
--
Brian Gartside
Pukekohe, New Zealand
http://www.briangartside.com
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