how does black iron oxide compare to other fluxes?

updated fri 9 nov 07

Paul Borian on thu 1 nov 07

i have been using small amounts of black iron oxide in my slip glazes for
a while now and i just bought 50 lbs of it so i will likely be using
larger amounts of it. Even with the shipping it was less than 1/2 what i
would pay for it locally - supposedly the world supply and demand for it
has caused the price to go up quite a bit kind of like copper but not as
extreme. Aside from the interesting color response i get at cone 11
reduction with it (when i use just the right amount combined with just the
right balance of silica, calcium and magnesium) my impression is that it
is a much stronger flux than the other two mentioned and thus does a
really nice job of smoothing out pinholes in layered glazes that would
otherwise need more of the other fluxes, thereby increasing the expansion
of the glaze. But, this is just an impression i have, i plan to really
test it out more and i am not totally sure this is correct. Can anyone
elaborate?
thanks,
Paul

Ivor and Olive Lewis on fri 2 nov 07

Dear Paul Borian,
You ask an interesting question which seems to hinge on your definition =
of "Flux". What do you mean ? From what you say I infer that you do not =
mean that it contributes to the melting behaviour of the glaze batch but =
that it modifies fluid qualities such as Viscosity, Capillarity and =
Surface Tension once the Ferrous oxide has dissolved in the melt.
Perhaps you would care to clarify.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

Sabri Justin Douglas Ben-Achour on fri 2 nov 07

I think you are right about it being a stronger flux, assuming you mean tha=
t it causes the glaze to begin melting sooner and more quickly.=20

Black Iron Oxide is Fe3O4, a mixed oxide of Fe2+ and Fe3+ ions (and oxygen,=
obviously). Red Iron Oxide is just Fe2O3, whose iron is all in the Fe3+ f=
orm. Fe3+ is a less reduced form of iron than Fe2+. The presence of Fe2+ =
ions makes a glass or crystal green (think Basalt, Olivine, many other mine=
rals, or Scott's Iron Green Glaze, Celadons, etc). Fe3+ ions give reddish =
orange (think rust, red clay, or shino). =20

Iron can be in the Fe2+ or Fe3+ forms depending on: how it was added to the=
glaze, what other things are in the glaze with it (calcium will favor Fe2+=
, it would appear), and the atmosphere of the kiln (oxidizing will favor Fe=
3+).

What does this have to do with being a better flux? Well, one way fluxes w=
ork is by breaking up the network of silicas, aluminas, other things, and o=
xygens that make up the glass. if something is bound to two oxygens, it is=
part of the chain that holds the glaze together. if that something is bou=
nd to just one oxygen, it's broken the chain, since that oxygen is either c=
onnected only to it or at best with just one other element. if you have a =
lot of these somethings breaking up the oxygen network by stealing oxygens =
for themselves, the chain/network will become flimsy and wiggle around and =
be more, well, liquidy. that's what a flux does.=20

Fe2+ is happy being bound with just one oxygen and could grab it for itself=
, whereas Fe3+ can bind to three oxygens and share all three of them with s=
omething else. That would make Fe2+ more of a flux, and Fe3+ less of one.

Now, there is more to this than what i've mentioned (the different forms of=
iron sometimes - not always - have different geometries of connection, Fe3=
+ crystallizes, etc), but still have a stack of things to read on just this=
matter so i'm not comfortable talking about these other issues just yet. =
and i hope someone will correct me if i'm wrong about anything i've said.

hope that helps

sabri

www.thesabritree.com



> Date: Thu, 1 Nov 2007 19:45:39 -0500
> From: paul@BLANKETCREEK.COM
> Subject: how does black iron oxide compare to other fluxes?
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> i have been using small amounts of black iron oxide in my slip glazes for
> a while now and i just bought 50 lbs of it so i will likely be using
> larger amounts of it. Even with the shipping it was less than 1/2 what i
> would pay for it locally - supposedly the world supply and demand for it
> has caused the price to go up quite a bit kind of like copper but not as
> extreme. Aside from the interesting color response i get at cone 11
> reduction with it (when i use just the right amount combined with just th=
e
> right balance of silica, calcium and magnesium) my impression is that it
> is a much stronger flux than the other two mentioned and thus does a
> really nice job of smoothing out pinholes in layered glazes that would
> otherwise need more of the other fluxes, thereby increasing the expansion
> of the glaze. But, this is just an impression i have, i plan to really
> test it out more and i am not totally sure this is correct. Can anyone
> elaborate?
> thanks,
> Paul
>=20
> _________________________________________________________________________=
_____
> Clayart members may send postings to: clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at melpots2@visi=
.com

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Duff bogen on fri 2 nov 07

Ivor
Its been a puzzlement to me fore a long time. If FeO fits the form of RO/R2O as in the "unity formula" does it act as a flux? What about manganese- Britanica sez there are "five oxides of manganese" does MnO act as a flux? Does MnO2 act as a glass former? My suspicion is that the answer to these three questions is "sometimes".
Duff


Ivor and Olive Lewis wrote:
Dear Paul Borian,
You ask an interesting question which seems to hinge on your definition of "Flux". What do you mean ? From what you say I infer that you do not mean that it contributes to the melting behaviour of the glaze batch but that it modifies fluid qualities such as Viscosity, Capillarity and Surface Tension once the Ferrous oxide has dissolved in the melt.
Perhaps you would care to clarify.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

______________________________________________________________________________
Clayart members may send postings to: clayart@lsv.ceramics.org

You may look at the archives for the list, post messages, or change your
subscription settings here: http://www.acers.org/cic/clayart/

Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com


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Ivor and Olive Lewis on sat 3 nov 07

Dear Duff,

You ask a very interesting question and I have no doubt my response will =
enrage some readers

<RO/R2O as in the "unity formula" does it act as a flux? What about =
manganese- Britanica sez there are "five oxides of manganese" does MnO =
act as a flux? Does MnO2 act as a glass former? My suspicion is that the =
answer to these three questions is "sometimes".>>

As I stated in my response to Paul Borian, there are several meanings =
that can be conveyed by the term "Flux". I think two of them are =
important to our community. The first is that Fluxes may be compounds =
which melt at a relatively low temperature and acts as solvents for the =
remaining ingredients. The second definition relates to the way in which =
a solute, something that can dissolve into a solvent, alters physical =
properties such as fluidity, viscosity, surface tension or capillary =
activity.

So the important fact to consider is their melting or fusion point and =
the way that the glaze behaves with or without a given ingredient. It is =
my experience that a base glaze will reach fusion point and cool to =
congeal as a vitrified glass without the presence of Iron oxides. I have =
not noticed that adding Iron oxide causes glazes my glazes to melt at a =
lower temperature, as indicated by the reflective appearance of the =
glaze surface during firing. Nor does my high (15% RIO) iron glaze run =
from the pot.

In the case of the suite of Iron oxides, Haematite, Fe203 melts at 1594 =
deg C, Magnetite, Fe3O4 (FeO.Fe2O3) melt at 1597 deg C and Wustite, FeO =
melts at 1337 deg C.The suite of Manganese Oxides has Manganese Monoxide =
MnO, melting at 1840 deg C, Manganese II/III oxide Mn2O3, decomposing at =
1080 deg C, Manganese oxide MnO2 decomposing at 535 deg C and Manganese =
oxide Mn2O7 which appears to be unstable and can be detonated ! There is =
also Mn3O4 mp 1567 deg C which forms during the decomposition of =
Manganese dioxide. So it would seem as though none of the oxides of Iron =
and Manganese could, of themselves, provide a molten environment lower =
than the melting temperatures of Frits or Alkali Felspars. However, I do =
not discount the potential for alternative chemistries.

Regarding the Unity Formula. This is a convenient way of representing =
the chemical composition of a glaze batch which allows us to make =
comparisons and draw conclusions about the "potential" behaviour of a =
glaze.=20

If you need to ask more questions please do so.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Ivor and Olive Lewis on sun 4 nov 07

Dear Sabri Justin Douglas Ben-Achour,

You suggest << I think you are right about it being a stronger flux, =
assuming you mean that it causes the glaze to begin melting sooner and =
more quickly>>

Perhaps you would explain why ?

What you have written tells me that if I increase the rate at which I =
heat my kiln, adding Iron oxides to my glazes will cause them to mature =
in less time. Hence, I can use a Pyrometric Cone of lower value to tell =
me the reactions leading to glaze maturity are complete.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Sabri Justin Douglas Ben-Achour on sun 4 nov 07

if you increase the rate at which you heat your kiln, your glazes will matu=
re in less time regardless of whether or not you have added iron oxides. i=
f you use the same rate of heating for two glazes, one with Fe3O4 and one =
without, the former will melt more and sooner. of course glasses don't hav=
e melting points, they have glass transition temperatures, which is a broad=
stretch of temperatures over which they begin to soften. so one can't tal=
k really about having an exact melting point. a glaze can become glossy and=
still be extremely viscous.



> Date: Sun, 4 Nov 2007 13:54:22 +1030
> From: iandol@WESTNET.COM.AU
> Subject: Re: how does black iron oxide compare to other fluxes?
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Dear Sabri Justin Douglas Ben-Achour,
>=20
> You suggest << I think you are right about it being a stronger flux, assu=
ming you mean that it causes the glaze to begin melting sooner and more qui=
ckly>>
>=20
> Perhaps you would explain why ?
>=20
> What you have written tells me that if I increase the rate at which I hea=
t my kiln, adding Iron oxides to my glazes will cause them to mature in les=
s time. Hence, I can use a Pyrometric Cone of lower value to tell me the re=
actions leading to glaze maturity are complete.
>=20
> Best regards,
>=20
> Ivor Lewis.
> Redhill,
> South Australia.
>=20
> _________________________________________________________________________=
_____
> Clayart members may send postings to: clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at melpots2@visi=
.com

_________________________________________________________________
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Ron Roy on sun 4 nov 07

Hi Paul,

Reduced iron is more of a melter than red iron - but using black iron to
start with does not make sense to me - because I think black iron re
oxidizes when heated in a kiln before it gets reduced again.

That is just what I think and I have no direct evidence to support that.
Perhaps a few experiments are called for.

It is somewhat common to use black iron added to a clay body - because it
does not stain like red iron. It is also true that the black gives a
different sort of colour in clay but again I do not know why.

If you care to do some experiments I would be interested in any results. Be
happy to help design some experiments.

RR

>i have been using small amounts of black iron oxide in my slip glazes for
>a while now and i just bought 50 lbs of it so i will likely be using
>larger amounts of it. Even with the shipping it was less than 1/2 what i
>would pay for it locally - supposedly the world supply and demand for it
>has caused the price to go up quite a bit kind of like copper but not as
>extreme. Aside from the interesting color response i get at cone 11
>reduction with it (when i use just the right amount combined with just the
>right balance of silica, calcium and magnesium) my impression is that it
>is a much stronger flux than the other two mentioned and thus does a
>really nice job of smoothing out pinholes in layered glazes that would
>otherwise need more of the other fluxes, thereby increasing the expansion
>of the glaze. But, this is just an impression i have, i plan to really
>test it out more and i am not totally sure this is correct. Can anyone
>elaborate?
>thanks,
>Paul

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0

Sabri Justin Douglas Ben-Achour on sun 4 nov 07

Just because something has a high theoretical melting point doesn't mean th=
at it can't be a flux. Calcium Oxide is a flux, its melting point is 2572=
=B0C. You can't just compare melting points and determine if something is =
a flux or not, that's not how fluxes work. The world - and certainly not s=
omething so messy as a glaze (where there are other issues like eutectic mi=
xes, crystals, and a bunch of other oxides each doing their own thing all a=
t the same time) - doesn't behave so neatly and theoretically. In these ca=
ses you have to see what's actually going on in between the molecules and a=
toms if you're going to explain what you see, and sometimes there are just =
too many things going on to quite know exactly. So, short answer for Mangan=
ese: people should write in with their observations and tell us what it act=
ually does, then others can suggest why it does. My guess is that Manganes=
e can probably act as a flux sometimes.

Although I think I already mentioned this in another email, fluxes work by =
disrupting the network of oxygens and cations (silica) that forms
the glass. =20

1. this happens because different atoms like to bond to
different numbers of oxygens. normally, a glass has silicon attached
to four oxygens, and each oxygen is shared with another silicon atom,
and so on and so on. they form a network. if a flux is introduced, it
may be attached to one or several oxygens and it won't share them with
a silicon, or maybe it will only share one. Either way, just like
someone in a human chain who refuses to hold hands, the flux disrupts
the network of silicon and oxygen, and the whole network becomes more
flimsy and moveable (i.e., more like a liquid). =20


2. Sometimes, the same element or oxide can break the chain OR help take pa=
rt in the network, depending on it's state. Iron is an example of this. Wh=
en its charge is 2+, it will grab an oxygen for itself and disrupt the chai=
n. When its charge is 3+, it can share up to three oxygens with something =
else and help make a network. These can also be affected by the presence o=
f positive ions like sodium, who can balance charge disruptions caused by t=
he iron taking oxygens away from silicon. if you didn't have the sodium i=
ons present, you might see the Fe3+ (in the form of Fe2O3) not taking part =
at all in the silica network and crystallizing out of it entirely.=20

3. Sometimes, there can be something else in the glaze that might alter the=
influence of a flux, because it helps restore the network (alumina), or be=
cause it reacts or interacts with a flux to change it's state (Calcium on I=
ron).

4. Another way the same additive can affect the melt of a glaze is by it's =
shape. Boron is an example of this. Normally, B2O3 that we add to our gla=
zes as borax or borate, is shaped as little triangles, with a B connected t=
o three Oxygens in the same plane. This shape makes it difficult to be par=
t of the silicon-oxygen network because the silicon-oxygen network is arran=
ged in tetrahedra, not triangles. the incompatibility of the shapes is one=
reason B2O3 can do what a flux does even though it can be a good network f=
ormer too. If you add alkali ions, which are small and can move around to =
hard to get to places, where they can help counterbalance charges and allow=
the B2O3 to convert to a tetrahedral shape, the B2O3 will form a better=
glass and mesh into the glass network.

5. Finally, different fluxes will have different other effects because of t=
heir size, their charge, their bond strength, their electronegativity, thei=
r vibration, what other ions they are with, and how they are feeling that =
day.


"and acts as solvents for the remaining ingredients. The second
definition relates to the way in which a solute, something that
can dissolve into a solvent, alters physical properties such as
fluidity, viscosity, surface tension or capillary activity.>"



where did you get your solvent-solute based definition of fluxes? i don't t=
hink those are accurate for glazes, but obviously correct me if i'm wrong. =
fluxes do not
change the behavior of the total mixture just because they dissolve it,
or are dissolved into it, in the way that salt dissolves in water and affec=
ts its freezing point (i.e. fluxes aren't eutectic mixtures), at least not =
all fluxes. for that you just need to see how minute amounts of fluxes wil=
l change the melt of a glaze, clearly not by dissolving it. fluxes change =
the behavior
of the glaze based on how they interact with its network structure which is=
very specific and which i mentioned a few emails ago. The working definiti=
on of a flux as thousands of potters use it is an
empirically based definition of something that makes a glaze more
liquid like (and included in that is fluidity, viscosity, etc). solute sol=
vent issues aren't really involved in a direct way, which is why you are at=
a loss to explain how Iron and Manganese could act as
fluxes based on a definition that relies on solutions. (i.e., you wrote: "=
f
the oxides of Iron and Manganese could, of themselves, provide a molten
environment lower than the melting temperatures of Frits or Alkali
Felspars. However, I do not discount the potential for alternative
chemistries.>")

that's just it, they don't need to in order to behave as fluxes.

But, it is true that components of a glaze or the glaze itself will react m=
ore quickly in a liquid state. glazes - they are glasses - 'melt' over a =
broad range of temperatures. they don't all of a sudden become liquid lik=
e ice and water. so they can become viscous and allow a modifying oxide ("=
flux") to enter into and then modify its network more quickly well below th=
e melting point of a modifying oxide, and well below the point at which a g=
laze is fully liquid.

a low fire glaze in a high fire kiln will melt all over the place. becaus=
e it has more or more powerful fluxes than a high fire glaze, among other r=
easons. so I'm a little confused as to why we're discussing the definition=
of flux.=20

anyway, leaving the realm of theory for just a second, and addressing actua=
l observations:=20



at a lower temperature,> =20

I certainly have. In my experience, I have seen reduced iron oxides behave=
as fluxes and more oxidized iron oxides not do so. But it will depend on =
what else is with the iron, the atmosphere of the kiln, etc etc.=20

hope this helps.

Sabri

http://www.thesabritree.com








> Date: Sat, 3 Nov 2007 17:17:08 +1030
> From: iandol@WESTNET.COM.AU
> Subject: Re: how does black iron oxide compare to other fluxes?
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Dear Duff,
>=20
> You ask a very interesting question and I have no doubt my response will =
enrage some readers
>=20
> <O/R2O as in the "unity formula" does it act as a flux? What about manganese=
- Britanica sez there are "five oxides of manganese" does MnO act as a flux=
? Does MnO2 act as a glass former? My suspicion is that the answer to these=
three questions is "sometimes".>>
>=20
> As I stated in my response to Paul Borian, there are several meanings tha=
t can be conveyed by the term "Flux". I think two of them are important to =
our community. The first is that Fluxes may be compounds which melt at a re=
latively low temperature and acts as solvents for the remaining ingredients=
. The second definition relates to the way in which a solute, something tha=
t can dissolve into a solvent, alters physical properties such as fluidity,=
viscosity, surface tension or capillary activity.
>=20

>=20
> In the case of the suite of Iron oxides, Haematite, Fe203 melts at 1594 d=
eg C, Magnetite, Fe3O4 (FeO.Fe2O3) melt at 1597 deg C and Wustite, FeO melt=
s at 1337 deg C.The suite of Manganese Oxides has Manganese Monoxide MnO, m=
elting at 1840 deg C, Manganese II/III oxide Mn2O3, decomposing at 1080 deg=
C, Manganese oxide MnO2 decomposing at 535 deg C and Manganese oxide Mn2O7=
which appears to be unstable and can be detonated ! There is also Mn3O4 mp=
1567 deg C which forms during the decomposition of Manganese dioxide. So i=
t would seem as though none of the oxides of Iron and Manganese could, of t=
hemselves, provide a molten environment lower than the melting temperatures=
of Frits or Alkali Felspars. However, I do not discount the potential for =
alternative chemistries.
>=20
> Regarding the Unity Formula. This is a convenient way of representing the=
chemical composition of a glaze batch which allows us to make comparisons =
and draw conclusions about the "potential" behaviour of a glaze.=20
>=20
> If you need to ask more questions please do so.
>=20
> Best regards,
>=20
> Ivor Lewis.
> Redhill,
> South Australia.
>=20
> _________________________________________________________________________=
_____
> Clayart members may send postings to: clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at melpots2@visi=
.com

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