Jeff Brown on thu 8 dec 11
Dear Clay Art Community, I am hoping that I can get some insight to a
problem I have been challenged with most recently. My students and I have
been getting a lot of black coring and as a result of the weakened clay
body from the black coring some of the the glazes (glossy and celadon -
temoku) have been shivering and compressing the forms causing dunting or
cooling cracks.
Bisquing is not as issue as we fire slow with soaking periods. At one
point I thought I might be firing the reduction cone 10 kiln to fast in the
early part of the firing as high as 300 degrees/hr. I have since slow down
to approximately 200 degrees/hr. I believe this helped but not entirely as
the black coring still exists.
I used to think I was reducing the kiln to early. I have changed this and
instead of cone 012 I start between cone 010 and 08. Again this may have
helped but still having issues with the black coring.
I then started thinking about the materials in the clay body. We use a
very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old Hickory #5
Ball Clay, and about 7% Custer Feldspar. After reading some of the posts
concerning materials I am more convinced that the issue is the materials.
We also use a porcelainous clay and do not have issues.
Now the ultimate question - what material is the culprit? People have
suggested the ball clay. We have used this clay recipe for years and have
never had so many issues as we are now. I like using this clay body as it
is easy for students to mix but may need to change to something more
reliable.
Any thoughts?
Thank you
Jeff
--
Jeff Brown
Associate Professor of Art
Nicholls State University
Thibodaux, LA
John Britt on thu 8 dec 11
I seriously doubt if it is he materials. Even though you start later (whi=
=3D
ch is good)=3D20
how heavy are you reducing. You may try easing up on the reduction and st=
=3D
art=3D20
later (like you are).
High iron bodies in heavy reduction will all black core if you do it earl=
=3D
y and heavy.
What do the low iron bodies look like>
johnbrittpottery.com
Ron Roy on thu 8 dec 11
Hi Jeff,
I need you to describe what you mean by black coring - a description
would help. I would also refer you to the Hamer dictionary which has a
good description of causes and cures.
Your problem with shivering is probably related to the lower alkali
content of the current custer spar - you have less than the
recommended % of spar to start with. You should download the Sohngen
article to understand this.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
If I am correct that clay body would need 14% of the low potash custer
or 10% of G200 HP spar.
Glad to do a dilatometer test of the current clay to see if
ristobalite is the problem - let me know if you want to make the bars
and I'll send instructions - easy to do.
If you need to test my recommended replacement clay I can send testing
instructions - to see if the body will be too tight.
RR
Quoting Jeff Brown :
> Dear Clay Art Community, I am hoping that I can get some insight to a
> problem I have been challenged with most recently. My students and I hav=
e
> been getting a lot of black coring and as a result of the weakened clay
> body from the black coring some of the the glazes (glossy and celadon -
> temoku) have been shivering and compressing the forms causing dunting or
> cooling cracks.
>
> Bisquing is not as issue as we fire slow with soaking periods. At one
> point I thought I might be firing the reduction cone 10 kiln to fast in t=
he
> early part of the firing as high as 300 degrees/hr. I have since slow do=
wn
> to approximately 200 degrees/hr. I believe this helped but not entirely =
as
> the black coring still exists.
>
> I used to think I was reducing the kiln to early. I have changed this and
> instead of cone 012 I start between cone 010 and 08. Again this may have
> helped but still having issues with the black coring.
>
> I then started thinking about the materials in the clay body. We use a
> very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old Hickory #5
> Ball Clay, and about 7% Custer Feldspar. After reading some of the posts
> concerning materials I am more convinced that the issue is the materials.
> We also use a porcelainous clay and do not have issues.
>
> Now the ultimate question - what material is the culprit? People have
> suggested the ball clay. We have used this clay recipe for years and hav=
e
> never had so many issues as we are now. I like using this clay body as i=
t
> is easy for students to mix but may need to change to something more
> reliable.
>
> Any thoughts?
>
> Thank you
> Jeff
>
> --
> Jeff Brown
> Associate Professor of Art
> Nicholls State University
> Thibodaux, LA
>
William & Susan Schran User on thu 8 dec 11
On 12/8/11 9:38 PM, "Jeff Brown" wrote:
> Bisquing is not as issue as we fire slow with soaking periods. At one
> point I thought I might be firing the reduction cone 10 kiln to fast in t=
he
> early part of the firing as high as 300 degrees/hr. I have since slow do=
wn
> to approximately 200 degrees/hr. I believe this helped but not entirely =
as
> the black coring still exists.
>
> I used to think I was reducing the kiln to early. I have changed this and
> instead of cone 012 I start between cone 010 and 08. Again this may have
> helped but still having issues with the black coring.
I would suspect not so much the clay body, but too much reduction, too
early.
How are the primary air disks on the burners set?
Are they closed down, 1/2 open, etc?
Are you firing with natural gas or propane?
How much gas pressure?
Damper setting?
Any flame or smoke from spy holes or flue during early reduction?
Getting back pressure at bottom spy hole at the 012 temperature range?
I fire fast - over 1000F in 2 hours, but kept in oxidation - I keep the
damper open more than I used to.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Steve Mills on fri 9 dec 11
For what it's worth.=3D20
I work with pretty dirty clay, so to avoid your problem biscuit to 06 in a =
w=3D
ell vented Kiln (i.e. vent hole in the lid which is open throughout the fir=
i=3D
ng. The fumes are considerable), and begin reduction at 07. If I start redu=
c=3D
ing earlier I'm asking for trouble. If I block the vent during the bisc I g=
e=3D
t bloats as well in the glaze firing.=3D20
Worth a try?
Steve M
Sent from my iPod
On 9 Dec 2011, at 02:38, Jeff Brown wrote:
> Dear Clay Art Community, I am hoping that I can get some insight to a
> problem I have been challenged with most recently. My students and I hav=
e=3D
> been getting a lot of black coring and as a result of the weakened clay
> body from the black coring some of the the glazes (glossy and celadon -
> temoku) have been shivering and compressing the forms causing dunting or
> cooling cracks.
>=3D20
> Bisquing is not as issue as we fire slow with soaking periods. At one
> point I thought I might be firing the reduction cone 10 kiln to fast in t=
h=3D
e
> early part of the firing as high as 300 degrees/hr. I have since slow do=
w=3D
n
> to approximately 200 degrees/hr. I believe this helped but not entirely =
a=3D
s
> the black coring still exists.
>=3D20
> I used to think I was reducing the kiln to early. I have changed this and
> instead of cone 012 I start between cone 010 and 08. Again this may have
> helped but still having issues with the black coring.
>=3D20
> I then started thinking about the materials in the clay body. We use a
> very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old Hickory #5
> Ball Clay, and about 7% Custer Feldspar. After reading some of the posts
> concerning materials I am more convinced that the issue is the materials.
> We also use a porcelainous clay and do not have issues.
>=3D20
> Now the ultimate question - what material is the culprit? People have
> suggested the ball clay. We have used this clay recipe for years and hav=
e=3D
> never had so many issues as we are now. I like using this clay body as i=
t=3D
> is easy for students to mix but may need to change to something more
> reliable.
>=3D20
> Any thoughts?
>=3D20
> Thank you
> Jeff
>=3D20
> --
> Jeff Brown
> Associate Professor of Art
> Nicholls State University
> Thibodaux, LA
Snail Scott on fri 9 dec 11
On Dec 8, 2011, at 8:38 PM, Jeff Brown wrote:
> ... My students and I have
> been getting a lot of black coring...
I know you say you are doing a long slow bisque, but
is is a clean atmosphere? If the kiln is even slightly into
reduction, you will not be burning out the necessary
organics. I'd look to your air/gas mixture or damper
settings for the likely culprit here. More air!
-Snail
Ric Swenson on fri 9 dec 11
As I understand carbon coring .... it is from too much reduction on most bo=
dies of clay containing iron...except those with very low iron content...
differ or not..RR or Ivor=A1=A3=A3=BF
maybe...... I maybe right..or I am wrong?
would not be the first time...but...
iron causes carbon coring in high reduction?
does your your ball clay have eough iron to cause it?
or excesssive reduction
lack of oxygen duiring firing ?
dirty clay means...more iron in it?
experiment could help..record results.......learn something .... oy
what a concept....learn and record results....
ric
Ric Swenson, B.F.A, M.F.A.
Ceramist, Artist and Teacher.
Jing De Zhen Ceramic Institute
Jing De Zhen City,
Jiang Xi Province
China
Mobile: 86-13767818872
> Date: Fri, 9 Dec 2011 10:00:05 +0000
> From: original.mudslinger@GMAIL.COM
> Subject: Re: Issues with Black Coring
> To: Clayart@LSV.CERAMICS.ORG
>
> For what it's worth.
> I work with pretty dirty clay, so to avoid your problem biscuit to 06 in =
a well vented Kiln (i.e. vent hole in the lid which is open throughout the =
firing. The fumes are considerable), and begin reduction at 07. If I start =
reducing earlier I'm asking for trouble. If I block the vent during the bis=
c I get bloats as well in the glaze firing.
>
> Worth a try?
>
> Steve M
>
>
> Sent from my iPod
>
> On 9 Dec 2011, at 02:38, Jeff Brown wrote:
>
> > Dear Clay Art Community, I am hoping that I can get some insight to a
> > problem I have been challenged with most recently. My students and I ha=
ve
> > been getting a lot of black coring and as a result of the weakened clay
> > body from the black coring some of the the glazes (glossy and celadon -
> > temoku) have been shivering and compressing the forms causing dunting o=
r
> > cooling cracks.
> >
> > Bisquing is not as issue as we fire slow with soaking periods. At one
> > point I thought I might be firing the reduction cone 10 kiln to fast in=
the
> > early part of the firing as high as 300 degrees/hr. I have since slow d=
own
> > to approximately 200 degrees/hr. I believe this helped but not entirely=
as
> > the black coring still exists.
> >
> > I used to think I was reducing the kiln to early. I have changed this a=
nd
> > instead of cone 012 I start between cone 010 and 08. Again this may hav=
e
> > helped but still having issues with the black coring.
> >
> > I then started thinking about the materials in the clay body. We use a
> > very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old Hickory #=
5
> > Ball Clay, and about 7% Custer Feldspar. After reading some of the post=
s
> > concerning materials I am more convinced that the issue is the material=
s.
> > We also use a porcelainous clay and do not have issues.
> >
> > Now the ultimate question - what material is the culprit? People have
> > suggested the ball clay. We have used this clay recipe for years and ha=
ve
> > never had so many issues as we are now. I like using this clay body as =
it
> > is easy for students to mix but may need to change to something more
> > reliable.
> >
> > Any thoughts?
> >
> > Thank you
> > Jeff
> >
> > --
> > Jeff Brown
> > Associate Professor of Art
> > Nicholls State University
> > Thibodaux, LA
jonathan byler on fri 9 dec 11
it is the reduction of the iron to FeO... there is probably not a =3D20
whole lot of carbon in there causing the black color. FeO is black =3D20
iron oxide. if you have bloating problems, that is a carbon issue =3D20
from my understanding. that said, carbon causes this "problem" as =3D20
carbon, or more likely carbon monoxide, which I think is more active =3D20
chemically is what is reducing the iron from red iron oxide to black =3D20
iron oxide.
we have this "problem" because we like some carbon trapping on our =3D20
shinos and reduce pretty heavy pretty early (still no smoke, though). =3D2=
0=3D
I say "problem" in quotes, because it hasn't been one for us. the =3D20
clay is not bloating, and our wares seem to hold up well to daily use =3D20=
=3D
and dishwashing.
as always, YMMV
On Dec 9, 2011, at 8:21 AM, Ric Swenson wrote:
> As I understand carbon coring .... it is from too much reduction on =3D20=
=3D
> most bodies of clay containing iron...except those with very low =3D20
> iron content...
>
>
> differ or not..RR or Ivor=3DA1=3DA3=3DA3=3DBF
>
> maybe...... I maybe right..or I am wrong?
>
>
> would not be the first time...but...
> iron causes carbon coring in high reduction?
>
> does your your ball clay have eough iron to cause it?
>
> or excesssive reduction
>
> lack of oxygen duiring firing ?
>
>
> dirty clay means...more iron in it?
>
> experiment could help..record results.......learn something .... oy
>
> what a concept....learn and record results....
>
> ric
>
>
>
>
>
>
> Ric Swenson, B.F.A, M.F.A.
> Ceramist, Artist and Teacher.
> Jing De Zhen Ceramic Institute
> Jing De Zhen City,
> Jiang Xi Province
> China
> Mobile: 86-13767818872
>
>
>
>> Date: Fri, 9 Dec 2011 10:00:05 +0000
>> From: original.mudslinger@GMAIL.COM
>> Subject: Re: Issues with Black Coring
>> To: Clayart@LSV.CERAMICS.ORG
>>
>> For what it's worth.
>> I work with pretty dirty clay, so to avoid your problem biscuit to =3D20=
=3D
>> 06 in a well vented Kiln (i.e. vent hole in the lid which is open =3D20
>> throughout the firing. The fumes are considerable), and begin =3D20
>> reduction at 07. If I start reducing earlier I'm asking for =3D20
>> trouble. If I block the vent during the bisc I get bloats as well =3D20
>> in the glaze firing.
>>
>> Worth a try?
>>
>> Steve M
>>
>>
>> Sent from my iPod
>>
>> On 9 Dec 2011, at 02:38, Jeff Brown wrote:
>>
>>> Dear Clay Art Community, I am hoping that I can get some insight =3D20
>>> to a
>>> problem I have been challenged with most recently. My students and =3D2=
0=3D
>>> I have
>>> been getting a lot of black coring and as a result of the weakened =3D2=
0=3D
>>> clay
>>> body from the black coring some of the the glazes (glossy and =3D20
>>> celadon -
>>> temoku) have been shivering and compressing the forms causing =3D20
>>> dunting or
>>> cooling cracks.
>>>
>>> Bisquing is not as issue as we fire slow with soaking periods. At =3D20=
=3D
>>> one
>>> point I thought I might be firing the reduction cone 10 kiln to =3D20
>>> fast in the
>>> early part of the firing as high as 300 degrees/hr. I have since =3D20
>>> slow down
>>> to approximately 200 degrees/hr. I believe this helped but not =3D20
>>> entirely as
>>> the black coring still exists.
>>>
>>> I used to think I was reducing the kiln to early. I have changed =3D20
>>> this and
>>> instead of cone 012 I start between cone 010 and 08. Again this =3D20
>>> may have
>>> helped but still having issues with the black coring.
>>>
>>> I then started thinking about the materials in the clay body. We =3D20
>>> use a
>>> very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old =3D20
>>> Hickory #5
>>> Ball Clay, and about 7% Custer Feldspar. After reading some of the =3D2=
0=3D
>>> posts
>>> concerning materials I am more convinced that the issue is the =3D20
>>> materials.
>>> We also use a porcelainous clay and do not have issues.
>>>
>>> Now the ultimate question - what material is the culprit? People =3D20
>>> have
>>> suggested the ball clay. We have used this clay recipe for years =3D20
>>> and have
>>> never had so many issues as we are now. I like using this clay =3D20
>>> body as it
>>> is easy for students to mix but may need to change to something more
>>> reliable.
>>>
>>> Any thoughts?
>>>
>>> Thank you
>>> Jeff
>>>
>>> --
>>> Jeff Brown
>>> Associate Professor of Art
>>> Nicholls State University
>>> Thibodaux, LA
ivor and olive lewis on sat 10 dec 11
Dear Ric Swenson,
No argument from me. But there are complexities and some facts that are not
well known.
For example, The iron content may not be visible as an obvious terra cotta
hue in the clay. Some clays are grey but contain significant proportions o=
f
Iron in the form of Iron Pyrites. A strongly oxidising atmosphere is needed
to drive out the sulphur. If the iron is in oxide of hydroxide form and it
is reduced to the Ferrous state it can react with any free silica in a clay
body forming Iron Silicate which melts in the 1200 Deg C range.
There is a good discussion about Black coring by W.E Brownell in "Structura=
l
Clay Products" pp 145-149. ISBN 0-387-81382-9
Regards,
Ivor Lewis,
REDHILL,
South Australia
Lee on sat 10 dec 11
Early sealing shinos encourage it also.
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he land
of eternal youth is behind the house, a beautiful land fluent within
itself." -- John O'Donohue
Ron Roy on sat 10 dec 11
Hi Ric,
Probably one of the most misunderstood issues we have to deal with.
The more iron the bigger the problem can be - iron is easily reduced =3D20
to black which is a strong flux and can lead to bloating because the =3D20
clay is over fluxed.
Black coring to me in when there are different colours inside a fired =3D20
iron bearing body. The most common would be black inside with grey =3D20
towards the outside indicating carbon not having enough oxygen inside =3D20
a body to burn off - so - it takes the iron it needs from Fe2O3 =3D20
reducing it to FeO. That explains the darker colour in black coring. =3D20
That would also explain the lighter coloured clay towards the outside =3D20
in which the organics did have more oxygen to work with.
If the iron in reduced in a bisque firing that black iron has a much =3D20
longer time to flux the clay than if it was reduced during a glaze =3D20
firing. That may explain why starting reduction later during a glaze =3D20
firing may lessen a problem during a glaze firing. It would also in my =3D2=
0
opinion - indicate the clay is over fluxed to start with. You should =3D20
be able to start reduction early an many potters do so without =3D20
problems - especially with clay with little iron.
It is my opinion that you cannot over reduce - either the iron is =3D20
reduced or not . It may also be true that there is reduced iron and =3D20
unreduced iron in the same ware - which would explain black coring.
Glad to discuss this further - never a bad idea to brain storm a =3D20
problem like this.
RR
Quoting Ric Swenson :
> As I understand carbon coring .... it is from too much reduction on =3D20
> most bodies of clay containing iron...except those with very low =3D20
> iron content...
>
>
> differ or not..RR or Ivor=3DE3=3D80=3D82=3DEF=3DBC=3D9F
>
> maybe...... I maybe right..or I am wrong?
>
>
> would not be the first time...but...
> iron causes carbon coring in high reduction?
>
> does your your ball clay have eough iron to cause it?
>
> or excesssive reduction
>
> lack of oxygen duiring firing ?
>
>
> dirty clay means...more iron in it?
>
> experiment could help..record results.......learn something .... oy
>
> what a concept....learn and record results....
>
> ric
>
>
>
>
>
>
> Ric Swenson, B.F.A, M.F.A.
> Ceramist, Artist and Teacher.
> Jing De Zhen Ceramic Institute
> Jing De Zhen City,
> Jiang Xi Province
> China
> Mobile: 86-13767818872
>
>
>
>> Date: Fri, 9 Dec 2011 10:00:05 +0000
>> From: original.mudslinger@GMAIL.COM
>> Subject: Re: Issues with Black Coring
>> To: Clayart@LSV.CERAMICS.ORG
>>
>> For what it's worth.
>> I work with pretty dirty clay, so to avoid your problem biscuit to =3D20
>> 06 in a well vented Kiln (i.e. vent hole in the lid which is open =3D20
>> throughout the firing. The fumes are considerable), and begin =3D20
>> reduction at 07. If I start reducing earlier I'm asking for =3D20
>> trouble. If I block the vent during the bisc I get bloats as well =3D20
>> in the glaze firing.
>>
>> Worth a try?
>>
>> Steve M
>>
>>
>> Sent from my iPod
>>
>> On 9 Dec 2011, at 02:38, Jeff Brown wrote:
>>
>> > Dear Clay Art Community, I am hoping that I can get some insight to =
=3D
a
>> > problem I have been challenged with most recently. My students and I=
=3D
have
>> > been getting a lot of black coring and as a result of the weakened c=
=3D
lay
>> > body from the black coring some of the the glazes (glossy and celado=
=3D
n -
>> > temoku) have been shivering and compressing the forms causing duntin=
=3D
g or
>> > cooling cracks.
>> >
>> > Bisquing is not as issue as we fire slow with soaking periods. At on=
=3D
e
>> > point I thought I might be firing the reduction cone 10 kiln to =3D20
>> fast in the
>> > early part of the firing as high as 300 degrees/hr. I have since slo=
=3D
w down
>> > to approximately 200 degrees/hr. I believe this helped but not entir=
=3D
ely as
>> > the black coring still exists.
>> >
>> > I used to think I was reducing the kiln to early. I have changed thi=
=3D
s and
>> > instead of cone 012 I start between cone 010 and 08. Again this may =
=3D
have
>> > helped but still having issues with the black coring.
>> >
>> > I then started thinking about the materials in the clay body. We use=
=3D
a
>> > very simple clay body of 50% Hawthorne Bond Fireclay, 50% Old Hickor=
=3D
y #5
>> > Ball Clay, and about 7% Custer Feldspar. After reading some of the p=
=3D
osts
>> > concerning materials I am more convinced that the issue is the mater=
=3D
ials.
>> > We also use a porcelainous clay and do not have issues.
>> >
>> > Now the ultimate question - what material is the culprit? People hav=
=3D
e
>> > suggested the ball clay. We have used this clay recipe for years and=
=3D
have
>> > never had so many issues as we are now. I like using this clay body =
=3D
as it
>> > is easy for students to mix but may need to change to something more
>> > reliable.
>> >
>> > Any thoughts?
>> >
>> > Thank you
>> > Jeff
>> >
>> > --
>> > Jeff Brown
>> > Associate Professor of Art
>> > Nicholls State University
>> > Thibodaux, LA
>
ivor and olive lewis on sun 11 dec 11
If you get into the metallurgical knowledge base you will find that in the
presence of free carbon iron oxide will reduce to metallic iron when the
temperature rises above a nominal 600 deg C. Originally Bog Iron was smelte=
d
with charcoal and the result was called sponge Iron. This was forged,
hammered, to consolidate the metal and Silica Sand was used to flux iron
oxides. In the process of Forge Welding Silica sand is still used as a flux
. A need to increase production saw the introduction of Bellows to elevate
the intensity of the fire and raise the temperature. Bog iron was always
contaminated with sand and this gave rise to slag stringers in the forged
metal..
I take a circumspect view of the claim that Black Iron Oxide, nominally FeO=
,
has fluxing properties. My scepticism rises from knowledge of sintering.
Both oxides have Tamman points in the 900 deg C region hence they could be
equally reactive towards each other and sinter to produce Iron Silicate,
Fayalite 2FeO.SiO2 which melts at 1205 deg C.
Regards and Seasonal Greetings to All.
Ivor Lewis,
REDHILL,
South Australia
.
Lee on sun 11 dec 11
Ivor inquired privately about Shinos and black coring. (I didn't know it
was not public until after I sent reply.)
Shinos seal over at cone 012 and below. So with high iron clay, and
heavy reduction, it can be a problem.
There are a number of reasons why tradtional shinos do not have this
problem. First is, that they were not fired in heavy reduction. They
get red color from higher alumina content that only requires a small amount
of iron. They rarely reached above 1100*C, which required firing longer
than a week.
Also, mogusa clay that is used with shino is high alumina and only
has small amounts of iron. When they wanted iron under the glaze, they
used an iron slip on the lighter colored clay. Both, the low levels of
iron and high alumina help avoid coring and bloating problems.
Having the iron in the slip instead of the body is a good
solution for shinos, and it makes them more like what was traditionally
made as shino. They actually give more color variation than a dark body
does.
Another thing you can do is add 10% RIOx to some of you shino (John
Britt brought Robinson's technique to my attention.) You can get some
nice strong reds doing this with Robinson's High Alumina Mino glaze listed
in John's book.
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he land
of eternal youth is behind the house, a beautiful land fluent within
itself." -- John O'Donohue
ronroy@CA.INTER.NET on tue 13 dec 11
Hi Ivor,
Seger says the fluxes are those oxides with one oxygen, CaO, Na2O,
K2O, ZnO etc - Those with two oxygen are glass makers - SiO2
- Those with three oxygen are the are the modifiers - Al2O3, Fe2O3.
Are you saying that when you change (reduce) Fe2O3 into FeO it is not a flu=
x?
Sounds like you are saying Seger is wrong???
RR
Quoting ivor and olive lewis :
> If you get into the metallurgical knowledge base you will find that in th=
e
> presence of free carbon iron oxide will reduce to metallic iron when the
> temperature rises above a nominal 600 deg C. Originally Bog Iron was smel=
ted
> with charcoal and the result was called sponge Iron. This was forged,
> hammered, to consolidate the metal and Silica Sand was used to flux iron
> oxides. In the process of Forge Welding Silica sand is still used as a fl=
ux
> . A need to increase production saw the introduction of Bellows to elevat=
e
> the intensity of the fire and raise the temperature. Bog iron was always
> contaminated with sand and this gave rise to slag stringers in the forge=
d
> metal..
> I take a circumspect view of the claim that Black Iron Oxide, nominally F=
eO,
> has fluxing properties. My scepticism rises from knowledge of sintering.
> Both oxides have Tamman points in the 900 deg C region hence they could b=
e
> equally reactive towards each other and sinter to produce Iron Silicate,
> Fayalite 2FeO.SiO2 which melts at 1205 deg C.
> Regards and Seasonal Greetings to All.
> Ivor Lewis,
> REDHILL,
> South Australia
> .
>
ivor and olive lewis on wed 14 dec 11
Dear Ron,
Greetings for the festive season to you and wishing you a rewarding New
Year.
I am not criticising Herman Seger. He was working from the knowledge base a=
s
it was understood in the late eighteen Hundreds and I would love to access
his writings.
However, the way material oxides were viewed changed early in the twentieth
century. As a result of the work of Arrhenius, Bronsted and Lowry Chemists
gained a new perspective on the nature of those groups of oxides and the
term "Amphoteric" was introduce accepting the some oxides can behave as
acids with respect to basic oxides and behave as basic oxides with respect
to acidic oxides.
Changes in a ceramic system as oxygen is progressively removed from Iron
Oxide, Fe2O3 lead first to a double system Magnetite, FeO.Fe2O3 (Fe3O4).
Continue reducing and the final result is Fe 0.95O (Nominally FeO) Check on
the melting point of this. Almost 1400 deg C and compare it to the MP of
Fe2O3 in excess of 1500 deg C.
What I wrote and intended to be understood was that the solid state reactio=
n
of sintering between Silica and Iron oxide FeO which can commence at
temperatures as low as 900 deg C have the potential to create a compound
called Fayalite 2FeO.SiO2, that has a melting point of 1205 deg C.
If, in a bisque firing, conditions were conducive to the production of
Fayalite that compound would become a melting flux if the glaze firing were
to mature at cone six or higher.
Anyway Ron, you must recall that I disagree with everyone when it comes to
definitions. Recall previous disagreements with everyone about Eutectic as
well as Flux.
Best regards,
Ivor Lewis,
REDHILL,
South Australia
----- Original Message -----
From:
To: "ivor and olive lewis"
Cc:
Sent: Wednesday, December 14, 2011 12:08 PM
Subject: Re: Issues with Black Coring
> Hi Ivor,
>
> Seger says the fluxes are those oxides with one oxygen, CaO, Na2O, K2O,
> ZnO etc - Those with two oxygen are glass makers - SiO2
> - Those with three oxygen are the are the modifiers - Al2O3, Fe2O3.
>
> Are you saying that when you change (reduce) Fe2O3 into FeO it is not a
> flux?
>
> Sounds like you are saying Seger is wrong???
>
> RR
>
>
>
>
> Quoting ivor and olive lewis :
>
>> If you get into the metallurgical knowledge base you will find that in
>> the
>> presence of free carbon iron oxide will reduce to metallic iron when the
>> temperature rises above a nominal 600 deg C. Originally Bog Iron was
>> smelted
>> with charcoal and the result was called sponge Iron. This was forged,
>> hammered, to consolidate the metal and Silica Sand was used to flux iron
>> oxides. In the process of Forge Welding Silica sand is still used as a
>> flux
>> . A need to increase production saw the introduction of Bellows to
>> elevate
>> the intensity of the fire and raise the temperature. Bog iron was always
>> contaminated with sand and this gave rise to slag stringers in the
>> forged
>> metal..
>> I take a circumspect view of the claim that Black Iron Oxide, nominally
>> FeO,
>> has fluxing properties. My scepticism rises from knowledge of sintering.
>> Both oxides have Tamman points in the 900 deg C region hence they could
>> be
>> equally reactive towards each other and sinter to produce Iron Silicate,
>> Fayalite 2FeO.SiO2 which melts at 1205 deg C.
>> Regards and Seasonal Greetings to All.
>> Ivor Lewis,
>> REDHILL,
>> South Australia
>> .
>>
>
>
>
>
ronroy@CA.INTER.NET on wed 14 dec 11
Dear Ivor,
Best of the season to you as well.
Is there an experiment that we could conduct to see if reduced iron is
a flux in clay bodies?
RR
Quoting ivor and olive lewis :
> Dear Ron,
> Greetings for the festive season to you and wishing you a rewarding New Y=
ear.
>
> I am not criticising Herman Seger. He was working from the knowledge
> base as it was understood in the late eighteen Hundreds and I would
> love to access his writings.
>
> However, the way material oxides were viewed changed early in the
> twentieth century. As a result of the work of Arrhenius, Bronsted
> and Lowry Chemists gained a new perspective on the nature of those
> groups of oxides and the term "Amphoteric" was introduce accepting
> the some oxides can behave as acids with respect to basic oxides and
> behave as basic oxides with respect to acidic oxides.
>
> Changes in a ceramic system as oxygen is progressively removed from
> Iron Oxide, Fe2O3 lead first to a double system Magnetite, FeO.Fe2O3
> (Fe3O4). Continue reducing and the final result is Fe 0.95O
> (Nominally FeO) Check on the melting point of this. Almost 1400 deg
> C and compare it to the MP of Fe2O3 in excess of 1500 deg C.
>
> What I wrote and intended to be understood was that the solid state
> reaction of sintering between Silica and Iron oxide FeO which can
> commence at temperatures as low as 900 deg C have the potential to
> create a compound called Fayalite 2FeO.SiO2, that has a melting
> point of 1205 deg C.
>
> If, in a bisque firing, conditions were conducive to the production
> of Fayalite that compound would become a melting flux if the glaze
> firing were to mature at cone six or higher.
>
> Anyway Ron, you must recall that I disagree with everyone when it
> comes to definitions. Recall previous disagreements with everyone
> about Eutectic as well as Flux.
>
> Best regards,
> Ivor Lewis,
> REDHILL,
> South Australia
>
>
> ----- Original Message ----- From:
> To: "ivor and olive lewis"
> Cc:
> Sent: Wednesday, December 14, 2011 12:08 PM
> Subject: Re: Issues with Black Coring
>
>
>> Hi Ivor,
>>
>> Seger says the fluxes are those oxides with one oxygen, CaO, Na2O,
>> K2O, ZnO etc - Those with two oxygen are glass makers - SiO2
>> - Those with three oxygen are the are the modifiers - Al2O3, Fe2O3.
>>
>> Are you saying that when you change (reduce) Fe2O3 into FeO it is
>> not a flux?
>>
>> Sounds like you are saying Seger is wrong???
>>
>> RR
>>
>>
>>
>>
>> Quoting ivor and olive lewis :
>>
>>> If you get into the metallurgical knowledge base you will find that in =
the
>>> presence of free carbon iron oxide will reduce to metallic iron when th=
e
>>> temperature rises above a nominal 600 deg C. Originally Bog Iron
>>> was smelted
>>> with charcoal and the result was called sponge Iron. This was forged,
>>> hammered, to consolidate the metal and Silica Sand was used to flux iro=
n
>>> oxides. In the process of Forge Welding Silica sand is still used as a =
flux
>>> . A need to increase production saw the introduction of Bellows to elev=
ate
>>> the intensity of the fire and raise the temperature. Bog iron was alway=
s
>>> contaminated with sand and this gave rise to slag stringers in the for=
ged
>>> metal..
>>> I take a circumspect view of the claim that Black Iron Oxide,
>>> nominally FeO,
>>> has fluxing properties. My scepticism rises from knowledge of sintering=
.
>>> Both oxides have Tamman points in the 900 deg C region hence they could=
be
>>> equally reactive towards each other and sinter to produce Iron Silicate=
,
>>> Fayalite 2FeO.SiO2 which melts at 1205 deg C.
>>> Regards and Seasonal Greetings to All.
>>> Ivor Lewis,
>>> REDHILL,
>>> South Australia
>>> .
>>>
>>
>>
>>
>>
>
>
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