Craig Martell on sat 3 dec 05
Ivor was asking:
>I would like to know if anyone has heard of including additions of
>Magnesium Carbonate or Zinc Oxide in a batch mix. It seems these two
>substances can enhance the mechanical strength of the ceramic and improve
>its transmission of visible light.
>So, what is the word from the "Big Think Tank"
Hello Ivor:
I don't know anything about the Big Think Tank but here's a small tidbit
from the Peanut Gallery.
I was reading Mimi Obstler's book, Out of The Earth Into the Fire and came
across a recommendation of a flux combination for cone 6 porcelain. She
recommends a mix of Nepheline Syenite, Dolomite, and a small amount of
Potash Feldspar. Dolomite is the only magnesia bearing mineral outside of
talc that I've heard about as a porcelain addition. But I should add in
saying that, I don't get out all that much.
regards, Craig Martell Hopewell, Oregon
Ivor and Olive Lewis on sat 3 dec 05
Upsurge in popularity of Southern Ice Porcelain prompted me to think =
about why this clay should have such wonderful optical qualities.
Knowing that dirty minerals (Iron oxides) and high refractive minerals =
(Titanium dioxide) mitigate against whiteness and translucency and that =
the only other optical blockers are open voids it should not be =
difficult to find materials that are low in these defective materials =
and flux well enough to get rid of the bubbles.
But recent reading has suggested additional avenues.
I would like to know if anyone has heard of including additions of =
Magnesium Carbonate or Zinc Oxide in a batch mix. It seems these two =
substances can enhance the mechanical strength of the ceramic and =
improve its transmission of visible light.
So, what is the word from the "Big Think Tank"
On the same note, is anyone using and of the North Cape Nepheline =
Syenites or Felspars in either Glazes or clay bodies?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
-------------------------------------------------------------------------=
-------
marianne kuiper milks on sat 3 dec 05
Hello again, Ivor.
Dumb question I don't know enough about porcelain,so that's re the "?"
When one decides to add these ingredients to change the chemical balance, would that be done as a "+", or do you exchange for other materials (oxides) you don't want?
How do you know...simply by experimenting?. Ok, not so simple, I understand.
I have always found that to be a very confusing issue.If you substitute is it a 1-on-1 bases? If you have a sec, I'd like some light on that.
A really technical question: when you live down under, do the chemicals fall out of the bowl? Ours stay, we're north. With the possible pole shifting, are we potentially in trouble?
Enjoy your day, Marianne
Ivor and Olive Lewis wrote:Upsurge in popularity of Southern Ice Porcelain prompted me to think about why this clay should have such wonderful optical qualities.
Knowing that dirty minerals (Iron oxides) and high refractive minerals (Titanium dioxide) mitigate against whiteness and translucency and that the only other optical blockers are open voids it should not be difficult to find materials that are low in these defective materials and flux well enough to get rid of the bubbles.
But recent reading has suggested additional avenues.
I would like to know if anyone has heard of including additions of Magnesium Carbonate or Zinc Oxide in a batch mix. It seems these two substances can enhance the mechanical strength of the ceramic and improve its transmission of visible light.
So, what is the word from the "Big Think Tank"
On the same note, is anyone using and of the North Cape Nepheline Syenites or Felspars in either Glazes or clay bodies?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
--------------------------------------------------------------------------------
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Jim Murphy on sat 3 dec 05
on 12/3/05 12:00 AM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> Upsurge in popularity of Southern Ice Porcelain prompted me to think about why
> this clay should have such wonderful optical qualities.
Hello Ivor,
Although I don't have the "recipe" [for Southern Ice], I'm thinkin' its
translucency is due - in large part - to use of ultra-white, fine-grained
Halloysite Clay [as opposed to kaolinic clays used in most other porcelain
claybodies].
> I would like to know if anyone has heard of including additions of Magnesium
> Carbonate or Zinc Oxide in a batch mix.
For porcelain bodies, I haven't heard these may enhance mechanical strength
and improve its transmission of visible light.
Are you referring to some form of eutectic reaction which may limit crystal
growth "size" in the glassy-phase ?
FWIW, I have read about MgO being investigated in Alumina and Anorthite
Liquid composition to suppress "abnormal grain growth".
Best wishes,
Jim Murphy
David Beumee on sun 4 dec 05
Ivor,
I received a letter from Val Cushing which talked about the benefit of addding 1% calcium to a porcelain body, not only as a flux but as a aid in flocculation of the body! I'm very excited at your mention of the use of MgO and ZnO as additions to a porcelain body to aid mechanical strength and translucency. I assume you're talking about very low percentage additions. I don't know. I know that David Pier porcelain uses non traditional flux materials, but David is keeping these materials and percentages proprietary. It's a very nice body and an excellent addition to the availability of throwing porcelain in the US. Aardvark in California is exercizing excellent quality control in producing the body.
Translucency of Southern Ice is no doubt greatly enhanced with the use of ultra fine ryolitic NZ kaolin. Too bad the price of NZ kaolin here in the states is in the stratosphere. My test of NZ kaolin produced the whitest-burning fired bar I've ever seen. It's brilliance makes fired Grolleg, Standard Porcelain or Super Standard test bars look gray by comparison. No wonder Southern Ice fires to such amazing translucency at cone 10. NZ kaolin must be very low in titania, and the presence of iron must be close to non existent.
Don't know a thing about North Cape neph sy or spar. I assume we're talking about southern hemisphere mines.
David Beumee
Lafayette, CO
www.davidbeumee.com
-------------- Original message ----------------------
From: Ivor and Olive Lewis
> Upsurge in popularity of Southern Ice Porcelain prompted me to think about why
> this clay should have such wonderful optical qualities.
> Knowing that dirty minerals (Iron oxides) and high refractive minerals (Titanium
> dioxide) mitigate against whiteness and translucency and that the only other
> optical blockers are open voids it should not be difficult to find materials
> that are low in these defective materials and flux well enough to get rid of the
> bubbles.
> But recent reading has suggested additional avenues.
> I would like to know if anyone has heard of including additions of Magnesium
> Carbonate or Zinc Oxide in a batch mix. It seems these two substances can
> enhance the mechanical strength of the ceramic and improve its transmission of
> visible light.
> So, what is the word from the "Big Think Tank"
> On the same note, is anyone using and of the North Cape Nepheline Syenites or
> Felspars in either Glazes or clay bodies?
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.
>
>
> --------------------------------------------------------------------------------
>
> ______________________________________________________________________________
> 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.
Ivor and Olive Lewis on sun 4 dec 05
Dear Marianne ,
You are being Cheeky! You know the wind blows in the opposite direction, =
water goes down the hole anticlockwise and Gravity is reversed so we =
Aussies float through life with gay abandon.
This is not about substitutions or alterations to existing recipes or =
products, but getting down to the nitty gritty of making a better =
product by applying some well known and well tried technologies and =
using Information from the scientific data base.
In this case, it is ensuring on one hand that raw materials with the =
best constitution to achieve a specific purpose are selected then adding =
other materials to enhance the Physical Properties of the basic clay =
body. For Porcelain in particular it is about altering the Transmission =
of Light through the materials and enhancing the Reflectivity.
Have a good week.
Best regards,
Ivor
Michael Wendt on sun 4 dec 05
Interesting:
Janet Gleeson's book "The Arcanum" ISBN 0-446-52499-9 copyright 1998
mentions that Boettger first used ground alabaster as his flux in an attempt
to recreate the imported Chinese porcelains and got beautiful translucent
results although not ones that matched the color of the Chinese imports
(warm ivory rather than cold white).
Another interesting tidbit, Phil Nisbet, who is a geologist for i-minerals
group here in Idaho, called me earlier this week to ask me if I had heard of
the latest developments in high temperature talc-kaolin bodies. No, I
hadn't.
Talc is magnesium silicate...
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
skiasonaranthropos@FSMAIL.NET on sun 4 dec 05
Hello Ivor,
A few points in response to your questions:
=93Southern Ice Porcelain=94 is based on halloysite from New Zealand; a clay=
which fires to exceptional whiteness and translucency. Further information
can be found at www.nzcc.co.nz
North Cape nepheline syenite: as its name suggests is mined at The North
Cape which is within the Arctic Circle in Norway. In some ways it is
superior to that produced in Canada. Ceramic use includes vitreous bodies,
although feldspars are preferred for porcelain. Of possible interest for
history buffs is that the deposit is located at the Alta fjord very close
to where the German battleship Tirpitz was famously sunk in 1944
No feldspar products are produced in North Cape but the same company mines
both potassium and sodium feldspar in the south of the country, both are
low in iron and titanium. The potassium grade is very widely used in
porcelain
Of course youre correct to note that iron oxides reduces whiteness and
titanium dioxide the same for translucency but the latter also lowers
whiteness. Pores do increase diffraction and hence translucency but so do
crystals within the body
Also you describe =93 ... recent reading has suggested additional
avenues ... Magnesium Carbonate or Zinc Oxide in a batch mix.=94 ... can you=
give these references?
Thank you,
Antony
Ivor and Olive Lewis on mon 5 dec 05
Dear Jim Murphy,
Thanks for your note.
Information points to the North Island Clay. Though Halloysite might =
have the optical properties I would have thought it would impart =
limitations on its working properties as a plastic material. But then, =
that has not been unusual with some of the Porcelains over time.
<crystal
growth "size" in the glassy-phase ?>>..... Eutectic reactions would be =
doubtful from either ZnO-Al2O3-SiO2 or the MgO-Al2O3-SiO2 systems. Most =
of the Eutectic points are over Cone 10 in both systems. Nor do we have =
ready access to the raw materials. Anyway, a Eutectic Fusion would be a =
very rare events in any Potter's life and not something to wish for in a =
clay body.
I wonder if there will be any more interest.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on mon 5 dec 05
Dear Craig Martell,
I will have to ask the library if they can get hold of a copy of that =
book by Mimi Obstler.
But it shows people are thinking about things to change a clay.
Neither do I ! but a few weeks ago on my day out I ran into an old =
potter friend and shouted him a fish lunch. Always good to have an =
attentive ear.
Best regards,
Ivor.
Ivor and Olive Lewis on mon 5 dec 05
Dear Michael Wendt,
Another title to add to my reading list for next year.
Alabaster is Calcium Sulphate, a form of Gypsum. I happen to have a ten =
Kilo lump of the stuff for carving. If I ever do that I will save the =
off cuts.
Talc bodies have been used for ages as casting slip. are the new ones =
Plastic ?
Thanks for the information.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Steve Mills on mon 5 dec 05
North Cape Nepheline Syenite is just about the only one available in the
UK at the moment. The previous version commonly available (I forget the
manufacturer) went out of favour when they more than doubled the import
price.
Steve
Bath
UK
In message , Ivor and Olive Lewis writes
>Upsurge in popularity of Southern Ice Porcelain prompted me to think =3D
>about why this clay should have such wonderful optical qualities.
>Knowing that dirty minerals (Iron oxides) and high refractive minerals =3D
>(Titanium dioxide) mitigate against whiteness and translucency and that =3D
>the only other optical blockers are open voids it should not be =3D
>difficult to find materials that are low in these defective materials =3D
>and flux well enough to get rid of the bubbles.
>But recent reading has suggested additional avenues.
>I would like to know if anyone has heard of including additions of =3D
>Magnesium Carbonate or Zinc Oxide in a batch mix. It seems these two =3D
>substances can enhance the mechanical strength of the ceramic and =3D
>improve its transmission of visible light.
>So, what is the word from the "Big Think Tank"
>On the same note, is anyone using and of the North Cape Nepheline =3D
>Syenites or Felspars in either Glazes or clay bodies?
>Best regards,
>Ivor Lewis.
>Redhill,
>South Australia.
>
>
>-------------------------------------------------------------------------=
>=3D
>-------
--
Steve Mills
Bath
UK
Antoinette Badenhorst on mon 5 dec 05
Hi Ivor. Northern Cape nephline syenite comes from South Africa. I wish =
I
paid more attention to it when I used it while living there. I am mad at
myself for not remembering the name of the potter that wrote her masters
degree about South African ceramic materials and I am even madder for =
not
bringing the book with me. (I thought I will not need it here) If I =
remember
her name I will try to get the information you need.=20
There is another kaolin that we used in the making of porcelain in SA,
called serena kaolin. I remember there was some environmental dispute =
about
the mining of this kaolin, but it was considered as quite white burning
kaolin. I wonder if there is a South African potter on the list that can =
get
information on this for us. At the time I was just too happy that I =
could
mix porcelain and did not care about anything but translucency. Boy do =
we
learn as we go!
By the way in the US the word "sassy" would mean cheeky.....had to =
learn
that among other words and expressions here. =20
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ivor and =
Olive
Lewis
Sent: Saturday, December 03, 2005 12:01 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Porcelain. New Insights on whiteness and translucency
Upsurge in popularity of Southern Ice Porcelain prompted me to think =
about
why this clay should have such wonderful optical qualities.
Knowing that dirty minerals (Iron oxides) and high refractive minerals
(Titanium dioxide) mitigate against whiteness and translucency and that =
the
only other optical blockers are open voids it should not be difficult to
find materials that are low in these defective materials and flux well
enough to get rid of the bubbles.
But recent reading has suggested additional avenues.
I would like to know if anyone has heard of including additions of =
Magnesium
Carbonate or Zinc Oxide in a batch mix. It seems these two substances =
can
enhance the mechanical strength of the ceramic and improve its =
transmission
of visible light.
So, what is the word from the "Big Think Tank"
On the same note, is anyone using and of the North Cape Nepheline =
Syenites
or Felspars in either Glazes or clay bodies?
Best regards,
Ivor Lewis.
Redhill,
South Australia.
-------------------------------------------------------------------------=
---
----
_________________________________________________________________________=
___
__
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.
Jim Murphy on mon 5 dec 05
Ivor,
I have read an "abstract" - from the Whiteware Research Center [Albany,
N.Y.] - entitled "Effects of Auxiliary Fluxes on Whiteware Bodies" whereby
Magnesium Carbonate was noted to be an effective auxiliary flux in terms of
maturation temperature reduction. Having read only the abstract, I'm not
sure though which whiteware body composition or firing temperature was
investigated nor to what extent, if any, Magnesium Carbonate may have on
"translucency" in whiteware bodies.
There is, however, a branch of "glass-ceramics" developing products based o=
n
the SiO2-Al2O3-ZnO-MgO (Spinel, Gahnite) system, e.g., work done by Beall
and Pinckney, where both MgO and ZnO constituents are key spinel crystal
formers [(Mg,Zn)Al2 O4] in glass-ceramic produced below ~1200=BAC.
Best wishes,
Jim Murphy
on 12/5/05 12:44 AM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> Eutectic reactions would be doubtful from either ZnO-Al2O3-SiO2 or the
>MgO-Al2O3-SiO2 systems. Most of the Eutectic points are over Cone 10 in bo=
th
>systems. Nor do we have ready access to the raw materials. Anyway, a Eutec=
tic
>Fusion would be a very rare events in any Potter's life and not something =
to
>wish for in a clay body.
=20
skiasonaranthropos@FSMAIL.NET on mon 5 dec 05
Hi Steve,
The two most openly available sources world wide of nepheline syenite are
from Norway and Canada, and both are owned and operated by the same
company; Unimin
Regards,
Antony
Ivor and Olive Lewis on tue 6 dec 05
Dear Steve,
I did a "Google" on North Cape.
Reading their Sales Promotional stuff seems to suggest that they are
doing a lot of separating, beneficiation and blending to get
consistent products. This can have a colossal effect on production
costs. In addition, currency exchange rates make things bad for
importers.
I would have thought that you might have had some good local deposits
in the north, Scotland perhaps.
never the less, the information I put forward should be of interest to
people who are considering making their own Porcelain bodies.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
----- Original Message -----
From: "Steve Mills"
To: "Ivor and Olive Lewis" ; "Clayart"
Sent: Monday, 5 December 2005 10:31
Subject: Re: Porcelain. New Insights on whiteness and translucency
> North Cape Nepheline Syenite is just about the only one available in
the
> UK at the moment. The previous version commonly available (I forget
the
> manufacturer) went out of favour when they more than doubled the
import
> price.
>
> Steve
> Bath
> UK
>
>
> In message , Ivor and Olive Lewis writes
> >Upsurge in popularity of Southern Ice Porcelain prompted me to
think =3D
> >about why this clay should have such wonderful optical qualities.
> >Knowing that dirty minerals (Iron oxides) and high refractive
minerals =3D
> >(Titanium dioxide) mitigate against whiteness and translucency and
that =3D
> >the only other optical blockers are open voids it should not be =3D
> >difficult to find materials that are low in these defective
materials =3D
> >and flux well enough to get rid of the bubbles.
> >But recent reading has suggested additional avenues.
> >I would like to know if anyone has heard of including additions of
=3D
> >Magnesium Carbonate or Zinc Oxide in a batch mix. It seems these
two =3D
> >substances can enhance the mechanical strength of the ceramic and
=3D
> >improve its transmission of visible light.
> >So, what is the word from the "Big Think Tank"
> >On the same note, is anyone using and of the North Cape Nepheline
=3D
> >Syenites or Felspars in either Glazes or clay bodies?
> >Best regards,
> >Ivor Lewis.
> >Redhill,
> >South Australia.
> >
> >
>
>---------------------------------------------------------------------
----=
> >=3D
> >-------
>
> --
> Steve Mills
> Bath
> UK
Ivor and Olive Lewis on tue 6 dec 05
Dear David,
The big problems with Nepheline Syenite is always the Sodium ions that
are released when it comes into contact with water. They seems to act
as a deflocculant. But in the case of a casting slip this might be a
plus.
As you suggest, one of the frits might be a good idea. My thoughts
would be to look for something with a lower Boric oxide level and
high Aluminium oxide so that melting was near to the chosen maturity
temperature.
Where to start with the practical exercise ? Possibly with the classic
recipe using selections from a graded line blend of frit and regular
flux.
But if you do wish to go for slip manufacture why not explore the new
Talc/Kaolin blends or even the old Bone China formulations.
All the best,
Ivor
skiasonaranthropos@FSMAIL.NET on tue 6 dec 05
Hello Antoinette,
I think similar names may have confused you: North Cape nepheline syenite
is produced in the north of Norway, my earlier reply noted it was near the
Alta fjord within the Arctic circle. Have a look at:
www.highbeam.com/library/doc0.asp?DOCID=1G1:43367668&refid=holomed_1
There is however some nepheline syenite at the Northern Cape Province in
SA, near Spitskop if memory serves correctly. Up to just a couple of years
ago this was being mined as an aggregate with no ceramic or glass
applications, and whilst this may have changed recently no exports are
reported
Regards,
Antony
Lee Love on tue 6 dec 05
John Reeves (My favorite Canadian potter. Don't have a clue who the best
one is), did extensive research on translucent porcelain in England. He
publshied something on it in Studio Potter on porcelain years ago. I
have a photocopy of the article (I got it from him at the workshop I
attended), but it is in storage in Minneapolis. Look at back issues.
--
李 Lee Love 大
愛 鱗
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
http://ikiru.blogspot.com/ Zen and Craft
"The way we are, we are members of each other. All of us. Everything.
The difference ain't in who is a member and who is not, but in who knows
it and who don't."
--Burley Coulter (Wendell Berry)
skiasonaranthropos@FSMAIL.NET on tue 6 dec 05
Hello Ivor,
Re. El-Meliegy, E. M. and Saleh, H. I., "Preparation and Microstructure of
Protoenstatite from Egyptian Raw Materials". INTERCERAM, 2005 - 5,
September, Vol 54. pp 332-335
Thank you for the above reference. Whilst not the most readable of
articles I found it of some interest over this mornings coffee, not least
as it highlights a porcelain body prepared without any clay which in this
case is just talc and feldspar. Talc has a long established use in
ceramics, with uses including steatite porcelain for electrical insulators
and lowering firings temperature by the formation of a eutectic. However
in article there was no mention of, to quote from your original
post, =93... enhance the mechanical strength of the ceramic and improve its=
transmission of visible light=94 Have you another source describing these
benefits, and ideally the mechanism?
If you look on the inside cover of the journal youll see an advertisement
for North Cape Minerals, including the nepheline syenite you mentioned.
And at this point it might be worth trying to clear up some confusion:
The two most openly available sources world wide of nepheline syenite are
Norway and Canada. Both are owned and operated by Unimin, with the North
Cape name often used for the Norwegian material. The name shoudlnt be
confused with Nofloat which is the trade name of the companys feldspars;
Altaflux is used for the nepheline syenite products. Markets supplied from
Norway are not likely to see material from Canada
You note =93In recent years the Egyptians have put a lot of effort into the
exploitation of their own raw minerals industries.=94 Egypt has a very
active ceramics industry, and a number of manufacturers are easily world
class. Considering the volumes produced it is of course only sensible
economics for domestic raw materials to be considered, and whilst these
are used as there are problems with consistency and the required
technically parameters imports are still considerable with some feldspars
from Turkey and kaolins from England. And there is some nepheline syenite
in the country; which should be a surprise when you consider the route of
the word syenite!
Kind regards,
Antony
Antoinette Badenhorst on tue 6 dec 05
Antony you are right. Thanks for the correction. This makes me think of
driving pass Egypt earlier today....Egypt Mississippi. As far as I =
know,the
mineral market in SA is very fragile in general and I have to say that I =
was
surprized to see neph. sye. That I thought came from SA.The areas that =
you
talked about was earlier very rich in copper, but there were word that =
the
copper mines shut down. It sounds like you are familiar with these =
regions.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
skiasonaranthropos@FSMAIL.NET
Sent: Tuesday, December 06, 2005 2:59 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Porcelain. New Insights on whiteness and translucency
Hello Antoinette,
I think similar names may have confused you: North Cape nepheline =
syenite
is produced in the north of Norway, my earlier reply noted it was near =
the
Alta fjord within the Arctic circle. Have a look at:
www.highbeam.com/library/doc0.asp?DOCID=3D1G1:43367668&refid=3Dholomed_1
There is however some nepheline syenite at the Northern Cape Province in
SA, near Spitskop if memory serves correctly. Up to just a couple of =
years
ago this was being mined as an aggregate with no ceramic or glass
applications, and whilst this may have changed recently no exports are
reported
Regards,
Antony
_________________________________________________________________________=
___
__
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.
Ivor and Olive Lewis on wed 7 dec 05
Dear Antoinette Badenhorst,=20
I think there is a difference between North Cape which is Scandinavian =
and Northern Cape which is, if I recall my geography correctly, a =
Province of the Republic of South Africa.=20
But I would not doubt that there are some excellent ceramic minerals =
produced in that part of the World.
Best regards,
Ivor
Ps. I make my own tools and use a special alloy to prevent ware.
Ivor and Olive Lewis on wed 7 dec 05
Dear Jim Murphy,
Thanks for your information=20
This article could be interesting! Do you have the full citation ?
Knowing the Batch Formulations of Beall and Pinckney might reveal a lot =
that would be of interest to the others . Do you have more information?
Best regards,
Ivor
Ivor and Olive Lewis on thu 8 dec 05
Thanks Lee=20
Can you give a clue as to the year of that Studio Potter ? Then someone =
with a collection might be able to sort it out and give us all a precis =
of the information.
Best regards,
Ivor
Jim Murphy on thu 8 dec 05
Hi Ivor,
The abstract I previously referenced is as follows, however, bear in mind it
is only an "abstract" with very limited details:
"Effects of Auxiliary Fluxes on Whiteware Bodies" T-00-015-WRC
Martin Reynolds (M.S.), Advisor: William M. Carty and James Varner
April, 2000
"The purpose of this work was to provide detailed comparisons of auxiliary
flux effects on whiteware bodies. Seven auxiliary fluxes were used in this
study: zinc borate, zinc oxide, calcium borate, calcium carbonate, calcium
silicate, magnesium carbonate, and magnesium silicate."
"Thermal gradient analysis, dilatometry, differential thermal analysis,
thermal gravimetric analysis, deflection testing, modulus of rupture
testing, helium pycnometry, x-ray diffraction were all used to study the
behavior of auxiliary fluxes at 1-3 mole percent additions."
"Zinc borate and magnesium carbonate were the most effective auxiliary
fluxes in terms of maturation temperature reduction. Zinc borate appears to
be the better choice over magnesium carbonate due to their differences in
pyroplastic deformation. Magnesium carbonate increases pyroplastic
deformation more than three times as much compared to zinc borate."
> Knowing the Batch Formulations of Beall and Pinckney might reveal a lot that
> would be of interest to the others . Do you have more information?
Ivor, I believe those Batch Formulations are "classified". ;o)
What's really intriguing, is "Glass-ceramics" [produced by controlled
crystallization in a base glass] can produce "translucent" material at much
lower temperature than standard porcelains.
Magnesium compounds are sometimes used [in glass-ceramic compositions] to
control crystal growth behavior.
Best wishes,
Jim Murphy
Jim Murphy on sat 10 dec 05
Hi Ivor,
With regard to "translucent" porcelains, I brought up "glass-ceramics" due
to controlled crystal growth behavior. Not-so-much the state of "fusion" per
se, but rather, the type & size of crystals growing into a base "glass".
Kaolin-based porcelains may tend to develop the longer needle-like Mullite
crystals [during thermal decomposition] which is not-so-good for
"translucency". Of course, there are kaolin-based porcelain recipe
exceptions!
Whereas, a Halloysitic-based "porcelain" - like Southern Ice - would have
different crystal growth behavior, presumably with LESS Mullite.
Best wishes,
Jim Murphy
on 12/9/05 9:55 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> I take it that the difference between our Porcelain and the "Glass Ceramic"
> that is the basis of this investigation is that the latter is always brought
> to a state of full fusion and develops into a two phase material during
> cooling, whereas Porcelain, being a traditional "Ceramic", is never allowed to
> fully fuse but becomes a multi phase material by having unmelted relict
> materials embedded in a glass phase.
Ivor and Olive Lewis on sat 10 dec 05
Dear Jim,
Thanks for your precis.
I take it that the difference between our Porcelain and the "Glass =
Ceramic" that is the basis of this investigation is that the latter is =
always brought to a state of full fusion and develops into a two phase =
material during cooling, whereas Porcelain, being a traditional =
"Ceramic", is never allowed to fully fuse but becomes a multi phase =
material by having unmelted relict materials embedded in a glass phase.
So they are playing with hot moulding materials
I am sure the key to understand the results depends on knowledge of the =
original batch, especially the nature of the Primary Fluxing Agents that =
initiate the melting phase.
Given that the melting point of Zinc Borate (2ZnO.3B2O3) is stated as =
being 980=BA C and the MP of Magnesium Oxide is 2826=BA C (MgCO3 =
decomposes above 350=BA C) I think making predictions or drawing =
conclusions about fusion points of body compositions without all of the =
information would be foolhardy.
But, on the other hand, Potters know that Magnesium compounds in a =
stoneware glaze increase fluidity. So aggravated pyroplasticity might =
have been anticipated.
Now, when are we to be allowed play with the "Helium Pycnometer"
All the best and good wishes for the Festive Season,
Ivor
Ivor and Olive Lewis on thu 15 dec 05
Yes Jim,
I was reading about that last week.
Some of these Glass-Ceramics are transparent, the reason being that the =
individual crystals are so small that they measure a fraction of the =
wavelength of light and therefore do not interfere with its passage =
through their substance.
<'could'
be used to develop a more translucent porcelain, but, the "mechanism" =
may
very well be due to control of crystal growth [rather than as an aux. =
flux]=3D>>
I believe the intention is to introduce Protoenstatite into the =
structure. This has optical qualities similar to those of the other =
minerals. It also has better physical qualities than Mullite and so =
improves the strength.
Amazing how we exploit the minerals of the Earth.
Have a good Festive Season.
Best regards,
Ivor
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