May Luk on thu 18 nov 04
Hi all;
Following my HA currie grid test, I'd like to see if I can improve the
crazing of the glaze. I don't think there's a real cure in HA glaze. It is
what it is, but I'd like to check out the strategies that Mike Bailey
suggested in his book [page 72 Cone 6 glazes] I fire to cone 8 though.
I started with A [HA1 without zinc]
Soda Spar __________15
High Alkaline Frit__47
China Clay__________10
Lithium Carb________2
Whiting_____________6
Quartz______________18
Copper Carb_________2
Then I made tiles with
B=A+2 Calcium Borate Frit
C=A+4 Calcium Borate Frit
D=A+6 Calcium Borate Frit
E=A+8 Calcium Borate Frit
The results did not indicate any real improvement in crazing. The COE went
from 99.3 [A] to 95.91 [E]
The Subtotal Alkalis from 0.673 [A] to 0.609 [E]
Although Si:Al ratio went from 10.50 [A] to 10.31 [E] The glaze is runnier
in E. I guess I have less si and al than the original recipe, which is the
opposites of the strategy!
Next I think I'm going to try adding magnesia in the place of calcia, and
slow the firing above 1100. If you have any suggestions, I would appreciate
it.
Many thanks
May
London, UK
Ron Roy on fri 19 nov 04
Hi May,
Very difficult to get rid of crazing in the high alkaline glazes - the one
way you can do it is sub in Li2O for the KNaO - best to use Spodumene - you
can use lithium carb as well but no more than 2%.
The colour response will change however.
RR
>Following my HA currie grid test, I'd like to see if I can improve the
>crazing of the glaze. I don't think there's a real cure in HA glaze. It is
>what it is, but I'd like to check out the strategies that Mike Bailey
>suggested in his book [page 72 Cone 6 glazes] I fire to cone 8 though.
>
>I started with A [HA1 without zinc]
>Soda Spar __________15
>High Alkaline Frit__47
>China Clay__________10
>Lithium Carb________2
>Whiting_____________6
>Quartz______________18
>Copper Carb_________2
>
>Then I made tiles with
>B=A+2 Calcium Borate Frit
>C=A+4 Calcium Borate Frit
>D=A+6 Calcium Borate Frit
>E=A+8 Calcium Borate Frit
>
>The results did not indicate any real improvement in crazing. The COE went
>from 99.3 [A] to 95.91 [E]
>The Subtotal Alkalis from 0.673 [A] to 0.609 [E]
>Although Si:Al ratio went from 10.50 [A] to 10.31 [E] The glaze is runnier
>in E. I guess I have less si and al than the original recipe, which is the
>opposites of the strategy!
>
>Next I think I'm going to try adding magnesia in the place of calcia, and
>slow the firing above 1100. If you have any suggestions, I would appreciate
>it.
>
>Many thanks
>May
>London, UK
>
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Ron Roy
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David Hewitt on fri 19 nov 04
Hi May,
When you say you want to 'improve' crazing I am assuming that you want
to reduce it. If this is not so, then please let me know.
The COE of this recipe is indeed high and so it will need a significant
change to bring the COE into likely range of not crazing.
If you added 20 parts of Calcium Borax Frit rather than 8 parts you can
see that there is a useful reduction in COE. Alternatively you could
reduce the High Alk Frit from 47 to 27 and get a similar reduction.
What either of such changes would do to other aspects of this glaze only
testing will show. I would favour starting with reducing the High Alk
Frit first.
What body are you using?
David
In message , May Luk writes
>Hi all;
>
>Following my HA currie grid test, I'd like to see if I can improve the
>crazing of the glaze. I don't think there's a real cure in HA glaze. It is
>what it is, but I'd like to check out the strategies that Mike Bailey
>suggested in his book [page 72 Cone 6 glazes] I fire to cone 8 though.
>
>I started with A [HA1 without zinc]
>Soda Spar __________15
>High Alkaline Frit__47
>China Clay__________10
>Lithium Carb________2
>Whiting_____________6
>Quartz______________18
>Copper Carb_________2
>
>Then I made tiles with
>B=A+2 Calcium Borate Frit
>C=A+4 Calcium Borate Frit
>D=A+6 Calcium Borate Frit
>E=A+8 Calcium Borate Frit
>
>The results did not indicate any real improvement in crazing. The COE went
>from 99.3 [A] to 95.91 [E]
>The Subtotal Alkalis from 0.673 [A] to 0.609 [E]
>Although Si:Al ratio went from 10.50 [A] to 10.31 [E] The glaze is runnier
>in E. I guess I have less si and al than the original recipe, which is the
>opposites of the strategy!
>
>Next I think I'm going to try adding magnesia in the place of calcia, and
>slow the firing above 1100. If you have any suggestions, I would appreciate
>it.
>
>Many thanks
>May
>London, UK
--
David Hewitt
Web:- http://www.dhpot.demon.co.uk
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