Fara Shimbo on wed 23 apr 03
Hi, Ellie, Dan, and everyone,
Re the number of crystals you get with a glaze, I've done lots of
experiments and this is what I've found:
> Each formula has its own bell curve, wherein it forms crystal
seeds on the way up to peak temperature. Just as an example, one
glaze may form a few seeds at, say, 1250C, and a whole lot at
1260 ... and after that the seeds formed begin to dissolve again
and do not _seem_ to reform on the way down, so far as I can tell.
So if you're getting too many crystals, you can try firing half a
cone higher than you normally do; this will dissolve some of the
seeds. I don't recommend going half a cone lower because in my
experience you get "lumps" of crystals that grow perpendicular to
the surface of the piece, which feels awful. You'll need to experiment
to find where the max-nucleation point is for each formula; a good
deal of it seems to depend on the amount of titanium diox in the
glaze.
> Sometimes you can get too many crystals because your surface is
too rough. I've taken to bisquing my stuff to cone 016 and then
going over the whole thing with 400 grit wet-dry sandpaper.
Then wipe the whole thing with a wet sponge. Any grit left over
will tend to seed a crystal. This reduces the overall number of
crystals but not always by a lot.
> One last thing to try, reduce the amount of TiO2 in the glaze
by half a percent at a time until you get what you want.
You shouldn't need a "seeding agent" in a crystalline glaze unless
you are trying to deliberately put a crystal in a specific place.
What exactly are you using?
Hope this helps,
Fa
Ellie Blair on wed 23 apr 03
Hi Fa,
I don't know if this matters or not but I found that running my dry
ingredients thru a 80 mesh screen twice and the zinc I sieve three times
then I moisten the dry ingredients to a thin frosting consistency and
screened them one more time before the final water addition. I noticed a
drop in crystals in every glaze I did this to. I really agree with the
surface needing to be smooth. I sand my pieces in their green state with
320 grit wet dry sandpaper and wipe the surface clean and bisque to 08.
Then I sand the pieces again with 400 grit and wipe clean with a damp cloth
before I glaze them. What is the difference in firing to 016? Does it
allow more of the glaze to penetrate the piece?
I also wanted to ask you if there was a good place to post a couple pictures
of my work to get some feedback?
Thanks
Ellie :)
----- Original Message -----
From: "Fara Shimbo"
To:
Sent: Wednesday, April 23, 2003 11:56 AM
Subject: Numbers of Crystals in a Crystalline Glaze
> Hi, Ellie, Dan, and everyone,
>
> Re the number of crystals you get with a glaze, I've done lots of
> experiments and this is what I've found:
>
> > Each formula has its own bell curve, wherein it forms crystal
> seeds on the way up to peak temperature. Just as an example, one
> glaze may form a few seeds at, say, 1250C, and a whole lot at
> 1260 ... and after that the seeds formed begin to dissolve again
> and do not _seem_ to reform on the way down, so far as I can tell.
> So if you're getting too many crystals, you can try firing half a
> cone higher than you normally do; this will dissolve some of the
> seeds. I don't recommend going half a cone lower because in my
> experience you get "lumps" of crystals that grow perpendicular to
> the surface of the piece, which feels awful. You'll need to experiment
> to find where the max-nucleation point is for each formula; a good
> deal of it seems to depend on the amount of titanium diox in the
> glaze.
>
> > Sometimes you can get too many crystals because your surface is
> too rough. I've taken to bisquing my stuff to cone 016 and then
> going over the whole thing with 400 grit wet-dry sandpaper.
> Then wipe the whole thing with a wet sponge. Any grit left over
> will tend to seed a crystal. This reduces the overall number of
> crystals but not always by a lot.
>
> > One last thing to try, reduce the amount of TiO2 in the glaze
> by half a percent at a time until you get what you want.
>
> You shouldn't need a "seeding agent" in a crystalline glaze unless
> you are trying to deliberately put a crystal in a specific place.
> What exactly are you using?
>
> Hope this helps,
>
> Fa
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
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>
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>
Pettina Hetherington on sat 26 apr 03
Hi Fa,
At the present time I'm having good results with snow flake base glaze. I am
using up to 5% titanium.
I have also been experimenting with the amount of time it takes the kiln to
fire the last 100degrees. If fired at 100% it takes approx 30 mins to make
the temperature, but it produces large amounts of crystals. When firing time
for the last 100degrees is reduced to 45mins a much better result is
attained.
Do you have any further suggestions/thoughts?
thankyou for your help,
Dan
-----Original Message-----
From: Fara Shimbo [mailto:shimbo@CRYSTALLINE-CERAMICS.INFO]
Sent: Thursday, 24 April 2003 2:57 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Numbers of Crystals in a Crystalline Glaze
Hi, Ellie, Dan, and everyone,
Re the number of crystals you get with a glaze, I've done lots of
experiments and this is what I've found:
> Each formula has its own bell curve, wherein it forms crystal
seeds on the way up to peak temperature. Just as an example, one
glaze may form a few seeds at, say, 1250C, and a whole lot at
1260 ... and after that the seeds formed begin to dissolve again
and do not _seem_ to reform on the way down, so far as I can tell.
So if you're getting too many crystals, you can try firing half a
cone higher than you normally do; this will dissolve some of the
seeds. I don't recommend going half a cone lower because in my
experience you get "lumps" of crystals that grow perpendicular to
the surface of the piece, which feels awful. You'll need to experiment
to find where the max-nucleation point is for each formula; a good
deal of it seems to depend on the amount of titanium diox in the
glaze.
> Sometimes you can get too many crystals because your surface is
too rough. I've taken to bisquing my stuff to cone 016 and then
going over the whole thing with 400 grit wet-dry sandpaper.
Then wipe the whole thing with a wet sponge. Any grit left over
will tend to seed a crystal. This reduces the overall number of
crystals but not always by a lot.
> One last thing to try, reduce the amount of TiO2 in the glaze
by half a percent at a time until you get what you want.
You shouldn't need a "seeding agent" in a crystalline glaze unless
you are trying to deliberately put a crystal in a specific place.
What exactly are you using?
Hope this helps,
Fa
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Fara Shimbo on sun 27 apr 03
Hi, Dan,
I'm not familiar with the Snow Flake base glaze. Who makes it?
(I'm trying to collect them all).
Whatever rate of heat climb gives you the results you want is
the one to use, so long as your kiln can maintain it. If it
gets to past an hour (if you're using an electric kiln) then
your results might grow disappointing.
Other Suggestions ... hmmm, donno. Have you got pictures?
(Send them to me off list if you do, I get the digest and
pictures don't come with it.)
Good luck,
Fa
--
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Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-----------------------------------------------------------
Shimbo Pottery, P.O. Box 41, Hygiene, Colorado 80533 USA
720.272.0442 7AM to 2 PM, Mountain Time
www.crystalline-ceramics.info www.shimbopottery.com
Silly Science Fiction: http://klysadel.net
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