amanda watson-will on sat 11 oct 08
Hi! I'm having a couple of problems with my unglazed porcelain (Southern Ic=
e). I made a concertina shape and fired to cone 9 on a bed of alumina hydra=
te. On the side which lay in contact with the alumina=2C a clear glaze has =
formed. Do you think this is due to over-firing=2C or a reaction with the a=
lumina? In addition=2C there is powdery alumina adhered to the piece. I hav=
e seen this before=2C but I was wondering what others use to remove it? Is =
there anyway to remove the glaze too? I wondered if anyone has tried using =
some sort of sanding attachment on a dremel for this type of application?
Thanks for any advice you can offer.
Amanda
blog: amandawatson-will.blogspot.com
photos: http://www.flickr.com/photos/amandaw-w/
John Rodgers on sat 11 oct 08
Amanda,
I may be wrong about this, but as I recall about alumina hydrate - it
begins to become a melter as it nears cone ten. At cone 9 you may be
experiencing some of that action beginning to start. You may need to
find another more refractory material for your purpose.
Regards,
John Rodgers
Chelsea, AL
amanda watson-will wrote:
> Hi! I'm having a couple of problems with my unglazed porcelain (Southern Ice). I made a concertina shape and fired to cone 9 on a bed of alumina hydrate. On the side which lay in contact with the alumina, a clear glaze has formed. Do you think this is due to over-firing, or a reaction with the alumina? In addition, there is powdery alumina adhered to the piece. I have seen this before, but I was wondering what others use to remove it? Is there anyway to remove the glaze too? I wondered if anyone has tried using some sort of sanding attachment on a dremel for this type of application?
>
> Thanks for any advice you can offer.
> Amanda
>
>
>
>
> blog: amandawatson-will.blogspot.com
>
> photos: http://www.flickr.com/photos/amandaw-w/
>
>
>
Bill Merrill on sat 11 oct 08
If you can melt alumina at cone 10, you have something other than
alumina hydrate. You can sift alumina hydrate on a kiln shelf, put a
pot on the shelf and salt fire it without the pot sticking. Alumina
hydrate melts at 3000 centigrade. See
http://ceramic-materials.com/cermat/material/42.html
The question is, did you really use alumina hydrate?
Bill Merrill billm@pcadmin.ctc.edu
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of John
Rodgers
Sent: Saturday, October 11, 2008 6:59 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: [Suspected Spam] Re: Glaze forming on unglazed porcelain
Amanda,
I may be wrong about this, but as I recall about alumina hydrate - it
begins to become a melter as it nears cone ten. At cone 9 you may be
experiencing some of that action beginning to start. You may need to
find another more refractory material for your purpose.
Regards,
John Rodgers
Chelsea, AL
amanda watson-will wrote:
> Hi! I'm having a couple of problems with my unglazed porcelain
(Southern Ice). I made a concertina shape and fired to cone 9 on a bed
of alumina hydrate. On the side which lay in contact with the alumina, a
clear glaze has formed. Do you think this is due to over-firing, or a
reaction with the alumina? In addition, there is powdery alumina adhered
to the piece. I have seen this before, but I was wondering what others
use to remove it? Is there anyway to remove the glaze too? I wondered if
anyone has tried using some sort of sanding attachment on a dremel for
this type of application?
>
> Thanks for any advice you can offer.
> Amanda
>
>
>
>
> blog: amandawatson-will.blogspot.com
>
> photos: http://www.flickr.com/photos/amandaw-w/
>
>
>
Ivor and Olive Lewis on sun 12 oct 08
Dear John Rodgers,
It would be easy to validate your hypothesis. A fusion button test of
a pure sample should give an answer.
Since we do not have a list of ingredients that are used in Southern
Ice it is difficult to say why these pieces are forming a glaze.
If SI contains a high proportion of Potash felspar then a
decomposition reaction of K2O.Al2O3.6SiO2 to Leucite,
(K2O.Al2O3.4SiO2) and Silica at 1150+/- 20 deg C (2102 +/- 68 F) may
create conditions where sintering would accelerate and lead to melting
at cone 9. Such a notion would be highly speculative and contrary to
common sense.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
jean szostek on sun 12 oct 08
hi des and jan,
what is "soft" alumina? i now alumina oxide and hydrate
greatings jean
----- Original Message -----
From: "Des & Jan Howard"
To:
Sent: Saturday, October 11, 2008 10:50 PM
Subject: Re: Glaze forming on unglazed porcelain
> John
> You must have 'soft' alumina, my text shows 2050oC or 3722oF
> as the melting point of alumina.
> Des
>
> John Rodgers wrote:
>> I may be wrong about this, but as I recall about alumina hydrate - it
>> begins to become a melter as it nears cone ten. At cone 9 you may be
>> experiencing some of that action beginning to start. You may need to
>> find another more refractory material for your purpose.
>
> --
> Des & Jan Howard
> Lue Pottery
> Lue NSW
> Australia
> 2850
>
> 02 6373 6419
> www.luepottery.hwy.com.au
--------------------------------------------------------------------------------
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15:59
John Rodgers on sun 12 oct 08
Hi Ivor,
There was a bit of a qualifier in my remarks.
Actually, my one experience with this happening is something I would not
want to repeat - but I got a similar response when I fired one of my
electric kilns to cone 10 just to see the results of cone 10 on a piece
of work. Firing that high works the kiln far to hard to suit me. But I
did get a similar reaction. Just how pure the Alumina was - who's to
say. There may have been a problem with the clay - it came not from my
usual sources but from a friend who had a bit of cone 10 clay in a bag
left over. So what I did definitely was not a definitive test. but
simply my experience. I virtually never fire above cone 6 these days, so
I use alumina all the time without question. Not much point in firing
above cone 6 in my book. Energy consumption is to high to go the extra
distance.to cone 10. And now energy just became more precious. The
regional electrical power company just requested of the Public Services
Commission new rate hikes to compensate for energy costs to them. It
seems that with the downward financial spiral we are in here, inflation
is accelerating. What a nightmare!
It would be interesting though, if someone who does fire to cone ten and
above would actually put some alumina through it's paces and report back
the results. That would be a big plus.
Regards,
John Rodgers
Ivor and Olive Lewis wrote:
> Dear John Rodgers,
> It would be easy to validate your hypothesis. A fusion button test of
> a pure sample should give an answer.
> Since we do not have a list of ingredients that are used in Southern
> Ice it is difficult to say why these pieces are forming a glaze.
> If SI contains a high proportion of Potash felspar then a
> decomposition reaction of K2O.Al2O3.6SiO2 to Leucite,
> (K2O.Al2O3.4SiO2) and Silica at 1150+/- 20 deg C (2102 +/- 68 F) may
> create conditions where sintering would accelerate and lead to melting
> at cone 9. Such a notion would be highly speculative and contrary to
> common sense.
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.
>
>
>
Michael Wendt on sun 12 oct 08
yup, clock reset itself to 1999 again, damned thing.
Amanda,
I believe there must be substantial sodium
in the Southern Ice. At high temperatures,
the sodium vapor pressure is sufficient to form a
cloud of vapor around the piece.
Normally it is free to spread out and gets
carried away by the kiln atmosphere but
the alumina traps it at the surface, causing
a glazed appearance. I get the same thing
with my Helmer body at times which causes
it to flash in the affected area and attribute
it to the use of Nepheline Syenite as a major
flux component. I think it also explains plucking
since the foot literally glazes itself to the shelf
with this vapor buildup.
To see if this is the reason, make a clay support
that looks like a conventional ceramic stilt but
with several points. Coat just the tips with alumina
while soft and plastic and place the piece on the
"stilt". If it is vapor buildup, the condition will
disappear because there was room for the vapor
to dissipate.
If the texture would be acceptable, have you tried
sand blasting? Harbor freight sells small spot
sand blasters for just this kind of job. You might
even enjoy masking in patterns and using this as
a special decorative element to surprise people.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
Amanda asked:
Hi! I'm having a couple of problems with my unglazed
porcelain (Southern Ice). I made a concertina shape and
fired to cone 9 on a bed of alumina hydrate. On the
side which lay in contact with the alumina, a clear
glaze has formed. Do you think this is due to
over-firing, or a reaction with the alumina? In
addition, there is powdery alumina adhered to the
piece. I have seen this before, but I was wondering
what others use to remove it? Is there anyway to remove
the glaze too? I wondered if anyone has tried using
some sort of sanding attachment on a dremel for this
type of application?
Thanks for any advice you can offer.
Amanda
Des & Jan Howard on sun 12 oct 08
John
You must have 'soft' alumina, my text shows 2050oC or 3722oF
as the melting point of alumina.
Des
John Rodgers wrote:
> I may be wrong about this, but as I recall about alumina hydrate - it
> begins to become a melter as it nears cone ten. At cone 9 you may be
> experiencing some of that action beginning to start. You may need to
> find another more refractory material for your purpose.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
Ivor and Olive Lewis on mon 13 oct 08
Dear John Rodgers,
I am progressing towards a firing at Cone 8/9. What I will do is to
put a sample of my Aluminium Hydrate at a warmer spot in contact with
my usual Cone 8 porcelain.
All the best,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on mon 13 oct 08
Des ,
Potash Felspar 50 % ?
Seems to me to be a high proportion.
Were we not told at some time or other that the clay content included
an unspecified amount of NZ Halloysite ? Do you have an assay for that
material ?
Interesting facts about some Sodium compounds, from Kaye and Laby's
tables.
Sodium boils at 900 deg C (1652 F) Sodium Monoxide sublimes at 1275
deg C (2327 F)
Best regards,
Ivor Lewis.
Redhill,
South Australia.
amanda watson-will on mon 13 oct 08
Michael and all the others who have replied=2C
Thanks for your thoughts. I will give your experiment a try when I get a ch=
ance. At the moment I am still trying to salvage the piece. Sandblasting co=
uld be an option=3B or I think I could use the silicon carbide attachments=
for my father's Dremel. Another idea I had was to try the etching creme us=
ed for etching glass. Has anyone ever used this stuff or the dremel for a s=
imilar application?
Regards=2C
Amanda
Des & Jan Howard on mon 13 oct 08
Ivor
Converted to generic equivalents Southern Ice has this recipe.
kaolin 50
potash feldspar 30
silica 20
dolomite 1
limestone 0.5
Des
Ivor and Olive Lewis wrote:
> Since we do not have a list of ingredients that are used in Southern
> Ice it is difficult to say why these pieces are forming a glaze.
> If SI contains a high proportion of Potash felspar then a
> decomposition reaction of K2O.Al2O3.6SiO2 to Leucite,
> (K2O.Al2O3.4SiO2) and Silica at 1150+/- 20 deg C (2102 +/- 68 F) may
> create conditions where sintering would accelerate and lead to melting
> at cone 9. Such a notion would be highly speculative and contrary to
> common sense.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
Des & Jan Howard on mon 13 oct 08
Jean
It was a joke. I was teasing John about his
faulty recollection of melting points.
Des
jean szostek wrote:
> hi des and jan,
> what is "soft" alumina? i now alumina oxide and hydrate
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
John Rodgers on mon 13 oct 08
Ivor,
That's great. it will be interesting to learn of the outcome.
Regards,
John Rodgers
Chelsea, AL USA
Ivor and Olive Lewis wrote:
> Dear John Rodgers,
> I am progressing towards a firing at Cone 8/9. What I will do is to
> put a sample of my Aluminium Hydrate at a warmer spot in contact with
> my usual Cone 8 porcelain.
> All the best,
> Ivor Lewis.
> Redhill,
> South Australia.
>
>
>
Hank Murrow on tue 14 oct 08
Dear Des & Ivor:
A very pure halloysite is mined from an highly altered rhyolite
occurrence in New Zealand. Rhyolite is an igneous, volcanic
(extrusive) rock, of felsic (silicon-rich) composition (typically
>70% SiO2, <20% Al2O3, ~7% KNaO. In the case of the New Zealand
deposit, there has been considerable weathering and alteration which
along with considerable benefication, reduces the alkali content to
0.5% and the Silica content to 50%. Thus, it makes a translucent body
with the addition of plasticizers and a little alkali. More on the NZ
halloysite can be found here:
http://www.minerals.co.nz/html/main_topics/resources_for_schools/
industrial_minerals/indmin_cs_halloysite.html#what_is_halloysite
& http://www.halloysite.com/technical1.htm
There are three major deposits of halloysitic clay in the USA. CO,
UT, & IN.
Hope this helps,
Cheers, Hank
On Oct 14, 2008, at 1:59 PM, Des & Jan Howard wrote:
>
> I gather Southern Ice contains an halloysitic clay.
> No analysis is available to me for this clay.
> Ivor and Olive Lewis wrote:
>
>> Ivor asks: Were we not told at some time or other that the clay
>> content included
>> an unspecified amount of NZ Halloysite ? Do you have an assay for
>> that
>> material ?
Ivor and Olive Lewis on wed 15 oct 08
Dear Hank Murrow,
Thanks for your information.
I was barred from the Schools site but got into the commercial pages
you suggested.
Given a 50/50 Al2O3/SiO2 and so little alkali in the Halloysite that
substance would not account for surface melting and glass formation in
contact with Aluminium Hydrate.
Best regards,
Ivor
Des & Jan Howard on wed 15 oct 08
Ivor
I gather Southern Ice contains an halloysitic clay.
No analysis is available to me for this clay.
The SI % analysis when converted, using materials easily
available to me, gives the generic recipe I posted.
% analysis of Southern Ice
K2O 3.83
Na2O 1
CaO 0.79
MgO 0.31
Al2O3 23.37
SiO2 70.25
Fe2O3 0.1
TiO2 0.02
kaolin 50
potash feldspar 30
silica 20
dolomite 1
limestone 0.5
Des
Ivor and Olive Lewis wrote:
> Were we not told at some time or other that the clay content included
> an unspecified amount of NZ Halloysite ? Do you have an assay for that
> material ?
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
Neon-Cat on thu 16 oct 08
According to Sasha Wardell's very nice and inspiring book (great photos and
informative text), "Porcelain and Bone China", The Crowood Press, 2004,
Southern Ice contains local kaolin from Tonganah (near Scottsdale) and
commercially produced materials for the remainder of the recipe:
50% Tonganah kaolin
30% Potash Feldspar
20% Silica 300
5% bentonite
Further info:
"Ceramic Technical", No. 1, 1995, and "Ceramic Art and Perception", Vol. 24,
1996.
The clay resources of Tasmania:
(the end of this site has more on Tonganah kaolin in appendix 2)
http://www.mrt.tas.gov.au/mrtdoc/dominfo/download/UR1995_02/UR1995_02.pdf
Industrial Minerals in Tasmania:
http://www.mrt.tas.gov.au/mrtdoc/dominfo/download/UR1992_07/UR1992_07.pdf
Marian
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