Ben Shelton on tue 23 aug 05
temp)
I have done some experiments with iron and rutile and titanium in glazes at
cone 10 reduction. I have added these to clear or white "base" glazes just
to see what they look like. I have a result that I like the color of with
about 4% ea of iron and rutile.
The only problem is that the glaze seems over fired at ^10. I wondered if
there is a general way to calculate the fluxing effects of iron at this temp
or just some general guidelines for raising the matuation temp of a glaze.
Logic would point me towards increasing the silica and alumina in relation
to the fluxes (or lowering the flux content) BUT the other day I was reading
up on Eutectic effects. WHOOOOOOAAA that throws a monkey wrench into it.
If I had the glaze recipe with me, I'd post it. I'll have to do that later
but for now, is there any general info that might benefit my understanding
of why a white, non-gloss glaze would be overfired when adding 4% iron and
rutile?
Thanks
Ben
Ben Shelton on fri 26 aug 05
temp)
I'll be using Glaze master if ever I get my "shop" computer up and running.
I don't know if it has this feature or not.
Lee Love's suggestions from Leach is add 0.5% Kaolin for every 1% of added RIO.
This should be enough for a nice test. I never really expect calculations to
be 100% accurate when tested out. They do provide a great place to start for
a test of this nature. I am sure that I will have to run a series of tests
with added kaolin above and below the calculated value. Now I have abetter
idea of a point to start from and a feel for what size increments to use for
the tests.
Thanks
Ben
John Hesselberth on fri 26 aug 05
temp)
On Aug 26, 2005, at 8:19 AM, Ben Shelton wrote:
> I'll be using Glaze master if ever I get my "shop" computer up and
> running.
> I don't know if it has this feature or not.
Hi Ben,
It does, but not in a straightforward way. Put iron oxide as an
ingredient instead of as an additive. That will pick it up in a normal
unity calculation. Then go to the Clay Body screen. There is an option
(a button to click on in the lower central part of the screen) there to
include iron in flux unity. You can toggle between alumina unity
(sometimes used in clay body calculations) and iron in flux unity.
In a future upgrade (not the one I am planning to release this Fall) I
may make that a little more straightforward to do if enough people want
it.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Anne Melvin on fri 26 aug 05
temp)
Hi John,
I'm fairly convinced that adding different oxides to the same glaze changes the eutectics as much as a couple of cones. Is there any way of predicting what will happen? I still do crystalline glazes which require an involved firing schedule. It seems that cobalt in a glaze makes it mature at a lower cone. Nickel requires a higher cone. The different iron concentrates in ilminite, rutile and titanium also seem to make a difference. I can't put pots with different oxides as colorants in the same glaze kiln firing if I want the same size crystals on each pot because the melting of the glaze is different.
As you suggested, I'll try to use GlazeMaster to see what changes in the calculations.
Also, it seems that the different oxides change the amount of water required in the same glaze. Cobalt in glaze seems make the glaze thicker. Do the oxides floc/defloc? Or am I way off base? Could you tell me where I can research this?
Hope I'm not asking too much. I read every msg you write here on ClayArt. I really appreciate your common sense and your expertise.
Anne Melvin in Connecticut
John Hesselberth on fri 26 aug 05
temp)
On Aug 26, 2005, at 5:27 PM, Anne Melvin wrote:
> I'm fairly convinced that adding different oxides to the same glaze=20
> changes the eutectics as much as a couple of cones.=A0 Is there any =
way=20
> of predicting what will happen?
Hi Anne,
I have observed some of the same effects, but I know of know way to=20
predict it at the current state of our knowledge--well maybe a bit with=20=
iron in reduction, but not with cobalt and other colorants. I have, for=20=
example, seen it with copper. It is almost as if copper makes a glaze=20
more elastic and prone to fit a wider variety of bodies. Is that a fact=20=
or just my imagination--I don't know.
You, of course, are working with glazes high in zinc and the=20
combination of zinc with some of those colorants may give more of an=20
effect than the typical boron-containing glazes I usually work with. I=20=
have seen some other things with macro-crystalline glazes that puzzle=20
me. In the relatively few results I have seen for leach testing they=20
are considerably more durable than I would predict from the other work=20=
I have done. It is almost as if those glazes are in a different=20
compositional domain where the 'rules' we normally apply to glazes are=20=
no longer valid--new ones may need to be developed. You are working in=20=
an area that could benefit from careful research--it sounds like you=20
should take that on as a project.
And thanks for your generous comments. I'm glad you find my writings=20
helpful.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Lawrence Ewing on sun 28 aug 05
temp)
Hi Ben,
Your interest in the fluxing effect of RIO caught my interest so I
thought I would use Matrix to calculate some comparisons.
It would seem that the suggestion that adding 0.5% kaolin for each 1%
RIO falls quite a long way short of returning the proportions of Al2O3
and SiO2 to those that existed in the recipe before RIO is added. I am
assuming that this was the purpose of increasing the clay content.
As John pointed out there is also a problem with the change in the Al:Si
ratio that occurs when just kaolin is added.
You can see these calculation comparisons at
http://www.matrix2000.co.nz/Illustrations_1.htm
Cheers,
Lawrence Ewing
Ben Shelton wrote:
>I'll be using Glaze master if ever I get my "shop" computer up and running.
>I don't know if it has this feature or not.
>Lee Love's suggestions from Leach is add 0.5% Kaolin for every 1% of added RIO.
>
>This should be enough for a nice test. I never really expect calculations to
>be 100% accurate when tested out. They do provide a great place to start for
>a test of this nature. I am sure that I will have to run a series of tests
>with added kaolin above and below the calculated value. Now I have abetter
>idea of a point to start from and a feel for what size increments to use for
>the tests.
>
>Thanks
>
>Ben
>
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>
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>
>
Bruce Girrell on mon 29 aug 05
temp)
I didn't see this message get posted. Sorry if this is a repeat post.
Ron Roy wrote:
>Some glaze programs allow you to include the Fe2O3 (It's FeO after being
>reduced) as a flux - that should give you a better picture of what to do.
>If you are using Insight there is a "reduction" button that include iron in
>with the fluxes.
But how does that tell you anything about the melt temperature? I can
compare my unity formula with published limits, but how do we get from
clicking the "reduction" checkbox in Insight to something like "adding 1%
RIO will drop my maturation temperature by 20 degrees"?
Is there any way at all to predict a maturation temperature using any of the
glaze calc programs?
Bruce "babes in the forest" Girrell
John Hesselberth on wed 31 aug 05
temp)
On Aug 28, 2005, at 11:21 PM, Tom at Hutchtel.net wrote:
>
> Hi John,
>
> Talk to me a bit more about how using an alumina unity works in
> formulating
> a clay body.. Are there limit guidelines, and if so, where are these
> found.
>
> I understand that you can't really use calculation software for clay
> bodies,
> other than directionally, but how can it be legitimately used to
> assist in
> clay body work? Ron or others, chime in if you would
Hi Tom,
Ron has given you a much better answer than I could as I don't develop
clay bodies. Mostly the preferred display of compositional information
depends on which was used by your teacher when you were in the
'student' phase of your clay life. It is all the same information
displayed in different formats. Flux unity is the most common among
studio potters, but some people use mole percents or weight percents.
And a rare few seem to use alumina unity for clay bodies. I built it
into the GlazeMaster program just to give people a choice. I think Ron
is right that alumina unity was more widely used for clay bodies in the
early days of computers when computational power was limited. There was
some aspect of flux unity calculations--I never have tried to figure
out which--which bogged down computers of the day when alumina and
silica were so much higher than the fluxes.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Lee Love on thu 1 sep 05
temp)
On Aug 28, 2005, at 11:21 PM, Tom at Hutchtel.net wrote:
>
>
> Talk to me a bit more about how using an alumina unity works in
> formulating a clay body.. Are there limit guidelines, and if so,
> where are these found.
Tom,
Iron in the clay body, of course, can have an effect on the fluxing of
the glaze. My nami glaze I use on my iron body has additions of kaolin
added. At my teacher's workshop, we used his standard ash glaze with
kaolin added according to where the work would be placed in the kiln.
Anywhere from 5% to 25% in the hottest parts of the noborigama. So it
is a proven method.
Claybody can be experimented with using the traditional lineblend
methods too. What I did with my new Mashiko Nami clay from the quarry,
was added enough keibushi (refractory ball clay) bring the alumina up
to the levels of Shigaraki nami. There is no way I can get an accurate
analysis of the quarry clay, so these empirical methods work better
than the theoretical ones.
I ended up using the nami clay straight, though I might add keibushi
for dishes. I am also using it mixed half & half with Aka tsuchi (red
clay that is actually ocher colored) from the quarry. My method of
choosing the ratios was to mix different amounts until the results was
the same milk chocolate color as my teacher's iron clay.
--
Lee Love
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
"We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep."
--PROSPERO Tempest Shakespeare
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