Timakia@AOL.COM on wed 17 apr 02
Hi everybody. I made a few tests on feldspatic glazes ^9-10 this week. As
one
could have predicted almost all of them crazed. Does anyone have some advice
on how to improve the fit of these glazes on porcelain clays? What I found
interesting was that some crazed more than the others. Made me think some of
the oxides improved the expansion. Can that be? The one where I added rutile
and copper carbonate did not craze at all. Then one that I just addes
rutile,
crazed less than the others.
Thanks.
Antoinette.
(who is mostly in the dark when talking about glazes LOL)
Antoinette Badenhorst
http://hometown.aol.com/timakia
105 Westwood circle
Saltillo, MS
38866
Hank Murrow on wed 17 apr 02
>Hi everybody. I made a few tests on feldspatic glazes ^9-10 this week. As
one
>could have predicted almost all of them crazed. Does anyone have some
advice
>on how to improve the fit of these glazes on porcelain clays? What I found
>interesting was that some crazed more than the others. Made me think some
of
>the oxides improved the expansion. Can that be? The one where I added
rutile
>and copper carbonate did not craze at all. Then one that I just addes
rutile,
>crazed less than the others.
>Thanks.
>Antoinette.
>(who is mostly in the dark when talking about glazes LOL)
dear Antoinette;
Suggest you get Ian Currie's book, "Revealing Glazes" and do
a grid set with your desired fluxes and the feldspar in the C corner.
After the fire, you WILL find several cells where the melt is good
AND the crazing disappears. Those are good for further study. I often
do a mini grid set around the center of interest from the larger grid
tile. It is a GREAT way to zero in on the qualities you want in your
glaze.
Good Luck! Hank in Eugene
Roger Korn on wed 17 apr 02
I'd like to add: Ian Currie's grid system guarantees that your tests won't
miss the
desired fit and surface. That's the beauty of the system. So many times over
the
years, I've organized series of line blends, only to find that the result
I've
sought lay between two of the mixes or two of the series. By varying both
silica
and alumina (kaolin) systematically with Ian's system, the answer WILL
occur. The
system takes a little time to learn (get to one of his workshops, if
possible) but
you will stop wasting time chasing down dead ends and save a huge amount of
time in
the long run.
You can order the Revealing Glazes book from Ian's website
http://ian.currie.to/ ,
and even though he lives well "back of beyond the black stump", the book
will
arrive in about a week. The US Postal System should work so well...
Roger
Hank Murrow wrote:
> >Hi everybody. I made a few tests on feldspatic glazes ^9-10 this week. As
one
> >could have predicted almost all of them crazed. Does anyone have some
advice
> >on how to improve the fit of these glazes on porcelain clays? What I
found
> >interesting was that some crazed more than the others. Made me think some
of
> >the oxides improved the expansion. Can that be? The one where I added
rutile
> >and copper carbonate did not craze at all. Then one that I just addes
rutile,
> >crazed less than the others.
> >Thanks.
> >Antoinette.
> >(who is mostly in the dark when talking about glazes LOL)
>
> dear Antoinette;
>
> Suggest you get Ian Currie's book, "Revealing Glazes" and do
> a grid set with your desired fluxes and the feldspar in the C corner.
> After the fire, you WILL find several cells where the melt is good
> AND the crazing disappears. Those are good for further study. I often
> do a mini grid set around the center of interest from the larger grid
> tile. It is a GREAT way to zero in on the qualities you want in your
> glaze.
>
> Good Luck! Hank in Eugene
>
>
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Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
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North Plains, OR 97133
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Ron Roy on sat 27 apr 02
Hi Antoinette,
I assume the amount of feldspar is high - many of the glazes we use have
feldspar in them and can therefore be called feldspathic glazes.
At any rate - feldspars contribute sodim and potasium oxide to glazes - and
they have the higest expansion rates of all the oxides we use. This does
not mean they cannot be countered with low expansion oxides like silica
magnesium and boron - how ever it becomes more difficult as the KNaO
content increases.
The other part is - porcelains are more difficult to fit glazes to and stop
crazing. What I need to have is the recipe to see if it is possible - send
it to me along with the temperature you are firing to and I will advise if
I think it is possible to get rid of the crazing.
RR
>Hi everybody. I made a few tests on feldspatic glazes ^9-10 this week. As
one
>could have predicted almost all of them crazed. Does anyone have some
advice
>on how to improve the fit of these glazes on porcelain clays? What I found
>interesting was that some crazed more than the others. Made me think some
of
>the oxides improved the expansion. Can that be? The one where I added
rutile
>and copper carbonate did not craze at all. Then one that I just addes
rutile,
>crazed less than the others.
>Thanks.
>Antoinette.
>(who is mostly in the dark when talking about glazes LOL)
>Antoinette Badenhorst
>http://hometown.aol.com/timakia
>105 Westwood circle
>Saltillo, MS
>38866
Ron Roy
RR #4
15084 Little Lake Road
Brighton
Ontario
Canada - K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Timakia@AOL.COM on sun 28 apr 02
Hi Ron, thank you for your response. I saw several referals to feldspatic
glazes and found in Frank Hammers potters dictionary and in clay and glazes
for the potter that these glazes contains an extra high feldspar content. I
ran into several receipes with between 40-85% feldspar. The one that I
tested
was the one from Hammer which reads as follows:
Feldspar 66, (I used G 200)
Silica (#325) 10
Whiting 23
To this I added :
3 copper carb
1 red iron
The color was good (a deep glassy turqoiuse green, with some dryer, matt
spots) I like the reaction in textured areas, but it crazed very badly ans
will need more aluminia.
1nickel
1rutile
This combination created a beige/transparent color. It crazed very badly.
5 rutile
This one gave a beautiful blue white with some yellowish specks where thick.
It also crazed
1red iron gave a light brown with some blue/purple flashes where thick.It
also crazed. I would not do more with this particular combination, but
wonder
what will happen if I add some opacifier.
The one that seems to be the most succesful was the following:
5 copper carb.
4 rutile
This one barely crazed. It will need more aluminia, since it puddled a
little
in the bottom of the test bowl. The color is almost a 'celadon" green where
thin, blue-green in the bottom of the bowl with a surfaced yellowish green.
All of these are tested at ^9 in an electric kiln(3cub ft)
The reason why I chose to use this recipe, was because in SA, whiting was
known to improve glazes that crazed .
I also see some of these recipes contain much less whiting, with some zinc
added. I am not interested in cristalline effects and I understand that zinc
usually promotes that.On the other hand there are other usefull qualities in
zinc that I would like to use, like the color effect with some oxides.
Whoouw, now, I really showed you how little I know about glazes, but I
appreciate your suggestions.
Thanks.
Antoinette.
Antoinette Badenhorst
http://hometown.aol.com/timakia
105 Westwood circle
Saltillo, MS
38866
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