Caleb Long on wed 7 jul 99
I am testing a number of crystalline glazes. The compositions
a correct but to date I haven't been able to get more than a hint of
crystals. A few and very small. Some have run to matte which
seems like it could be a crystalline response, but not what we're
after. We are using a Skutt 1227 firing a normal glaze cycle up to
2272 (^8) then drop at the kilns normal cooling rate (takes about a
hour) to 2072 hold there for 3 hours and then drop to 2000 and hold
for another hour. We usually end up bending ^9 by the time the
holds are complete. One of our glaze does develop a a nice golden
sparkle in a slip gloss brown that is clearly crystalline and very
nice but it only works on a very mature clay (a commercial 5-6 buff
@ ^8-9 it does nothing on ^10-12 sandstone) and wasn't even
formulated to crystallize. It amazes me how different my glazes
can be from one clay to another that are fairly similiar other than
maturity. The interface is important. Anyway back to the point
can anyone help me with the firing cycle? I"ve tried a few. Do I
need to lengthen the hold? At what temperature? Do I need to cool
slower through the lower temperature? Lower the holding
temperature? Could it be related to the application thickness? Do
crystalline glazes tend to need thick or thin applications? I've read
everything I can find in print including the archives but I'm still
stuck. As near as I can tell I'm doing everything "right" but I must
be missing something. Any help and understanding would be
greatly appreciated.
Rob Reeve
Warsaw, Mo
LeRoy Price on thu 8 jul 99
Hi Rob:
I know the frustation that you are feeling -- it took us awhile before
getting our first good crystals. I have the following suggestions:
1. Do your initial firing to 2325 to 2375, reaching that temperature
as quickly as possible. This may require that you reformulate your glaze,
but give your present glaze a try.
2. Hold the temperature there from 0 to 30 minutes.
3. Drop to about 2100; hold for 2 to 6 hours.
2. Apply the glaze very thickly; 2 mm if you can do it without the glaze
cracking during drying. (And be sure to have large catch basins to
hold all of the glaze that runs off.)
LeRoy Price
On Wed, 7 Jul 1999, Caleb Long wrote:
> ----------------------------Original message----------------------------
> I am testing a number of crystalline glazes. The compositions
> a correct but to date I haven't been able to get more than a hint of
> crystals. A few and very small. Some have run to matte which
> seems like it could be a crystalline response, but not what we're
> after. We are using a Skutt 1227 firing a normal glaze cycle up to
> 2272 (^8) then drop at the kilns normal cooling rate (takes about a
> hour) to 2072 hold there for 3 hours and then drop to 2000 and hold
> for another hour. We usually end up bending ^9 by the time the
> holds are complete. One of our glaze does develop a a nice golden
> sparkle in a slip gloss brown that is clearly crystalline and very
> nice but it only works on a very mature clay (a commercial 5-6 buff
> @ ^8-9 it does nothing on ^10-12 sandstone) and wasn't even
> formulated to crystallize. It amazes me how different my glazes
> can be from one clay to another that are fairly similiar other than
> maturity. The interface is important. Anyway back to the point
> can anyone help me with the firing cycle? I"ve tried a few. Do I
> need to lengthen the hold? At what temperature? Do I need to cool
> slower through the lower temperature? Lower the holding
> temperature? Could it be related to the application thickness? Do
> crystalline glazes tend to need thick or thin applications? I've read
> everything I can find in print including the archives but I'm still
> stuck. As near as I can tell I'm doing everything "right" but I must
> be missing something. Any help and understanding would be
> greatly appreciated.
>
> Rob Reeve
> Warsaw, Mo
>
David Woodin on thu 8 jul 99
We get excellent results by firing our Skutt 1027 to top temperature as fast
as it will go hold 5 to 10 minutes drop the temperature as fast it goes to
2012 and hold for 4 hours, then shut the kiln off. In our case top
temperature is 2345 deg F. The crystals are the size of quarters.
David
Mike Bailey on thu 8 jul 99
Dear Rob,
You seem to be holding the kiln at too high a soaking temp. Try dropping
fast to around 1075 deg C (sorry I can't think in F) allowing 4 hour
drop to 1050 deg C or even 1025 deg C. For later sophistication to get
the halos you need to go back up in temp. There's an excellent new book
by Peter Illsley just come out called "Macro-crystalline Glazes - The
Challenge of Crystals" ISBN 1 86126 120 9 which would be very helpful.
Agree about the clay/glaze effect. 10 clays = 10 different glazes!
Cheers,
Mike Bailey.
In message , Caleb Long writes
>----------------------------Original message----------------------------
> I am testing a number of crystalline glazes. The compositions
>a correct but to date I haven't been able to get more than a hint of
>crystals. A few and very small. Some have run to matte which
>seems like it could be a crystalline response, but not what we're
>after. We are using a Skutt 1227 firing a normal glaze cycle up to
>2272 (^8) then drop at the kilns normal cooling rate (takes about a
>hour) to 2072 hold there for 3 hours and then drop to 2000 and hold
>for another hour. We usually end up bending ^9 by the time the
>holds are complete. One of our glaze does develop a a nice golden
>sparkle in a slip gloss brown that is clearly crystalline and very
>nice but it only works on a very mature clay (a commercial 5-6 buff
>@ ^8-9 it does nothing on ^10-12 sandstone) and wasn't even
>formulated to crystallize. It amazes me how different my glazes
>can be from one clay to another that are fairly similiar other than
>maturity. The interface is important. Anyway back to the point
>can anyone help me with the firing cycle? I"ve tried a few. Do I
>need to lengthen the hold? At what temperature? Do I need to cool
>slower through the lower temperature? Lower the holding
>temperature? Could it be related to the application thickness? Do
>crystalline glazes tend to need thick or thin applications? I've read
>everything I can find in print including the archives but I'm still
>stuck. As near as I can tell I'm doing everything "right" but I must
>be missing something. Any help and understanding would be
>greatly appreciated.
>
>Rob Reeve
>Warsaw, Mo
>
--
Mike Bailey
Pamala Browne on sat 10 jul 99
A question about crystals--- We had what we considered to be several
successful firings. We got too many crystals and not any BIG
ones,however.Lots of halos due to raising and lowering the temp during the
end hold. Now, should we take the temp up higher to burn off more crystals
or does the burning off come from the hold at the top temp? We had lots of
disscussion on this and never reached a final consensus.If someone out there
can help me get this straight in my head ,I would be grateful.We will be
doing lots more with lots of experimenting and I know that crystals can be
the most challenging of all glazes, so many variations, but surely these top
holds and drops do something specific every time. Oh, we were firing in a
gas kiln to ^8 to ^11.
----- Original Message -----
From: Mike Bailey
To:
Sent: Thursday, July 08, 1999 5:38 AM
Subject: Re: crystalline firing cycle
> ----------------------------Original message----------------------------
> Dear Rob,
>
> You seem to be holding the kiln at too high a soaking temp. Try dropping
> fast to around 1075 deg C (sorry I can't think in F) allowing 4 hour
> drop to 1050 deg C or even 1025 deg C. For later sophistication to get
> the halos you need to go back up in temp. There's an excellent new book
> by Peter Illsley just come out called "Macro-crystalline Glazes - The
> Challenge of Crystals" ISBN 1 86126 120 9 which would be very helpful.
>
> Agree about the clay/glaze effect. 10 clays = 10 different glazes!
>
> Cheers,
>
> Mike Bailey.
>
> In message , Caleb Long writes
> >----------------------------Original message----------------------------
> > I am testing a number of crystalline glazes. The compositions
> >a correct but to date I haven't been able to get more than a hint of
> >crystals. A few and very small. Some have run to matte which
> >seems like it could be a crystalline response, but not what we're
> >after. We are using a Skutt 1227 firing a normal glaze cycle up to
> >2272 (^8) then drop at the kilns normal cooling rate (takes about a
> >hour) to 2072 hold there for 3 hours and then drop to 2000 and hold
> >for another hour. We usually end up bending ^9 by the time the
> >holds are complete. One of our glaze does develop a a nice golden
> >sparkle in a slip gloss brown that is clearly crystalline and very
> >nice but it only works on a very mature clay (a commercial 5-6 buff
> >@ ^8-9 it does nothing on ^10-12 sandstone) and wasn't even
> >formulated to crystallize. It amazes me how different my glazes
> >can be from one clay to another that are fairly similiar other than
> >maturity. The interface is important. Anyway back to the point
> >can anyone help me with the firing cycle? I"ve tried a few. Do I
> >need to lengthen the hold? At what temperature? Do I need to cool
> >slower through the lower temperature? Lower the holding
> >temperature? Could it be related to the application thickness? Do
> >crystalline glazes tend to need thick or thin applications? I've read
> >everything I can find in print including the archives but I'm still
> >stuck. As near as I can tell I'm doing everything "right" but I must
> >be missing something. Any help and understanding would be
> >greatly appreciated.
> >
> >Rob Reeve
> >Warsaw, Mo
> >
>
> --
> Mike Bailey
>
DAN JOHNSTON on sun 11 jul 99
For what it is worth, I have found that I can decrease the *number* of
crystals by starting the crystal seeding and growth at 2012 f, holding for
45 minutes then taking it up to 2025-2050 for the remaining soak of 3-4
hours. This stops the continued crystal formation (seeding) but allows the
crystals present to grow to quarter size. Again, if you soak too long the
crystals present will all grow together and dominate the pot loosing the
individual elegance. Good luck!
Dan
Farmington, MO
danj@ldd.net
LeRoy Price on tue 13 jul 99
Hi Pamala:
As you know, the crystals form on nuclei, or "seeds". About 1936
Norton did a very impressive study of Zinc-Silicate glazes and exactly
when these seeds form.
To summarize: Most of the seeds form as the temperature is INCREASING,
not as it is decreasing, as is commonly believed. Of course the seeds
do not form without limit, there is simulataneously a seed-destruction
process going on. Above a certain temperature, as the temperature
increases the seed-destruction rate increases much faster than the
seed-formation rate.
What does all this mean? If you have too many crystals (i.e. seeds), you
can reduce their number by either going to a higer temperature or
holding the kiln at its top temperature for a longer period (or both).
Since you are firing in a gas kiln be sure to keep the atmosphere
oxydizing. A reducing atmosphere inhibits crystal growth. As I
understand it, when a glaze is reduced its surface contracts (shrinks)
due to the loss of the oxygen from the molelcules on the surface.
This additional surface force prevents the needed migration of the
crystal-forming elements.
LeRoy Price
On Sat, 10 Jul 1999, Pamala Browne wrote:
> ----------------------------Original message----------------------------
> A question about crystals--- We had what we considered to be several
> successful firings. We got too many crystals and not any BIG
> ones,however.Lots of halos due to raising and lowering the temp during the
> end hold. Now, should we take the temp up higher to burn off more crystals
> or does the burning off come from the hold at the top temp? We had lots of
> disscussion on this and never reached a final consensus.If someone out there
> can help me get this straight in my head ,I would be grateful.We will be
> doing lots more with lots of experimenting and I know that crystals can be
> the most challenging of all glazes, so many variations, but surely these top
> holds and drops do something specific every time. Oh, we were firing in a
> gas kiln to ^8 to ^11.
> ----- Original Message -----
> From: Mike Bailey
> To:
> Sent: Thursday, July 08, 1999 5:38 AM
> Subject: Re: crystalline firing cycle
>
>
> > ----------------------------Original message----------------------------
> > Dear Rob,
> >
> > You seem to be holding the kiln at too high a soaking temp. Try dropping
> > fast to around 1075 deg C (sorry I can't think in F) allowing 4 hour
> > drop to 1050 deg C or even 1025 deg C. For later sophistication to get
> > the halos you need to go back up in temp. There's an excellent new book
> > by Peter Illsley just come out called "Macro-crystalline Glazes - The
> > Challenge of Crystals" ISBN 1 86126 120 9 which would be very helpful.
> >
> > Agree about the clay/glaze effect. 10 clays = 10 different glazes!
> >
> > Cheers,
> >
> > Mike Bailey.
> >
> > In message , Caleb Long writes
> > >----------------------------Original message----------------------------
> > > I am testing a number of crystalline glazes. The compositions
> > >a correct but to date I haven't been able to get more than a hint of
> > >crystals. A few and very small. Some have run to matte which
> > >seems like it could be a crystalline response, but not what we're
> > >after. We are using a Skutt 1227 firing a normal glaze cycle up to
> > >2272 (^8) then drop at the kilns normal cooling rate (takes about a
> > >hour) to 2072 hold there for 3 hours and then drop to 2000 and hold
> > >for another hour. We usually end up bending ^9 by the time the
> > >holds are complete. One of our glaze does develop a a nice golden
> > >sparkle in a slip gloss brown that is clearly crystalline and very
> > >nice but it only works on a very mature clay (a commercial 5-6 buff
> > >@ ^8-9 it does nothing on ^10-12 sandstone) and wasn't even
> > >formulated to crystallize. It amazes me how different my glazes
> > >can be from one clay to another that are fairly similiar other than
> > >maturity. The interface is important. Anyway back to the point
> > >can anyone help me with the firing cycle? I"ve tried a few. Do I
> > >need to lengthen the hold? At what temperature? Do I need to cool
> > >slower through the lower temperature? Lower the holding
> > >temperature? Could it be related to the application thickness? Do
> > >crystalline glazes tend to need thick or thin applications? I've read
> > >everything I can find in print including the archives but I'm still
> > >stuck. As near as I can tell I'm doing everything "right" but I must
> > >be missing something. Any help and understanding would be
> > >greatly appreciated.
> > >
> > >Rob Reeve
> > >Warsaw, Mo
> > >
> >
> > --
> > Mike Bailey
> >
>
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