cream breaking red and strontium carbonate

updated sat 11 sep 04

Gaye Sekula on sun 29 aug 04

Is there a trick to mixing in strontium carbonate? Did I get a bad batch or
is it always so granulated? I did a test firing yesterday to ^6, which is
what the recipe states, and the strontium grains are still obvious. Maybe
I should fire it higher?
Thanks,
Gaye Sekula
San Antonio

John Hesselberth on mon 30 aug 04

Hi Gaye,

I would say you got a bad batch, a cheaper/coarser grade, or a
different material was accidentally substituted when your supplier was
weighing it out. My strontium carbonate has just a hint of graininess
when I rub it between my fingers, but it very quickly and easily
becomes a very fine powder. It disperses easily in glaze suspensions
and I have never encountered strontium grains in a fired glaze.

Regards,

John
On Sunday, August 29, 2004, at 01:05 PM, Gaye Sekula wrote:

> Is there a trick to mixing in strontium carbonate? Did I get a bad
> batch or
> is it always so granulated? I did a test firing yesterday to ^6, which
> is
> what the recipe states, and the strontium grains are still obvious.
> Maybe
> I should fire it higher?
> Thanks,
> Gaye Sekula
> San Antonio
>
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

Mary K on tue 31 aug 04

Dear John,

I would love to know what the graininess is in that recipe (Cream Breaking Red).....is it the RIO, or do you think maybe it was on an iron bearing clay? (baby steps, still learning) Mary K

John Hesselberth wrote:
Hi Gaye,

I would say you got a bad batch, a cheaper/coarser grade, or a
different material was accidentally substituted when your supplier was
weighing it out. My strontium carbonate has just a hint of graininess
when I rub it between my fingers, but it very quickly and easily
becomes a very fine powder. It disperses easily in glaze suspensions
and I have never encountered strontium grains in a fired glaze.

Regards,

John
On Sunday, August 29, 2004, at 01:05 PM, Gaye Sekula wrote:

> Is there a trick to mixing in strontium carbonate? Did I get a bad
> batch or
> is it always so granulated? I did a test firing yesterday to ^6, which
> is
> what the recipe states, and the strontium grains are still obvious.
> Maybe
> I should fire it higher?
> Thanks,
> Gaye Sekula
> San Antonio
>
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

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John Britt on tue 31 aug 04

Ivor,

Strontium Carbonate decomposes to Strontium Oxide at around 1100 C (2012
F).

JOhn Britt
www.johnbrittpottery.com

Ivor and Olive Lewis on tue 31 aug 04

Dear Gaye Sekula
I suggest you get a pestle and mortar and mull your material for a
while before adding it to your dry glaze batch.
Strontium Carbonate is tricky stuff. Unlike its cousins, Barium and
Calcium Carbonate, from the same family of elements, it does not
decompose within the temperature range in which we fire our ceramics.
It decomposed with heat at 1340=BA C, say around 2450=BA F, well below
your cone 6 maturity temperature.
So, to make it work in a glaze we would have to consider a new
chemistry. Even if you had access to Strontium Oxide which by
inference is necessary to make the glaze you would be faced with a
problem. Strontium Oxide melts only when you heat it to 2430=BA C (4400=BA
F).
So we are faced with a profound question......What is the Chemistry of
Strontium Carbonate in a glaze ? Please, would those who propose its
use as a substitute of Barium Carbonate enlighten all of us ?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.



fire our goodies ----- Original Message -----
From: "Gaye Sekula"
To:
Sent: Monday, 30 August 2004 2:35
Subject: Cream Breaking Red and Strontium Carbonate


> Is there a trick to mixing in strontium carbonate? Did I get a bad
batch or
> is it always so granulated? I did a test firing yesterday to ^6,
which is
> what the recipe states, and the strontium grains are still obvious.
Maybe
> I should fire it higher?
> Thanks,
> > San Antonio
>
>
______________________________________________________________________
________
> 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.

John Hesselberth on tue 31 aug 04

On Monday, August 30, 2004, at 09:42 PM, Ivor and Olive Lewis wrote:

> Strontium Carbonate is tricky stuff. Unlike its cousins, Barium and
> Calcium Carbonate, from the same family of elements, it does not
> decompose within the temperature range in which we fire our ceramics.
> It decomposed with heat at 1340=BA C, say around 2450=BA F, well below
> your cone 6 maturity temperature.

Hi Ivor,

While I am sure this is true for the pure material, what happens when=20
it is dissolved or suspended in a glaze melt? I think using handbook=20
values for decomposition temperatures could be very misleading in this=20=

situation.

Regards,

John

John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

John Hesselberth on tue 31 aug 04

On Tuesday, August 31, 2004, at 10:34 AM, Mary K wrote:

> I would love to know what the graininess is in that recipe (Cream
> Breaking Red).....is it the RIO, or do you think maybe it was on an
> iron bearing clay? (baby steps, still learning) Mary K
Hi Mary,

I don't know the recipe so I can't answer your question. If you want to
send it to me off list I could take a guess. Most of our materials,
though, if bought from a high quality supplier will be finely enough
ground to avoid graininess. One exceptions is Wollastonite--it will
disperse but takes a little extra work. Cobalt oxide and red copper
oxide can be difficult to dispense uniformly but, again, it can be done
with some extra work and/or the help of a wetting agent. Zinc oxide
gives some people fits but, so far as I can tell, that only happens if
it has gotten wet or is in a very humid climate. I've never had a
problem with it.

Some materials are, of course, sold in less finely ground state so they
will produce some spots of color--or they are intended for use in clay
bodies and people use them in glazes. You usually want 200 mesh or
finer for glazes.

I always put my glazes through an 80 mesh screen at least twice
(usually 3 times, sometimes 4 if wollastonite is involved) and I don't
have problems with graininess.

Regards,

John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

John Britt on wed 1 sep 04

Ivor,

I used Hamer, and here are web links:

http://www.axxousa.com/srco3_m.html

Here is Digital fire:


Strontium Carbonate
Chemistry
SrO 70.200
Volatiles
CO2 29.800


No Mineralogy defined
Significant Temperatures
1100C: Melts
723C: Decomposition

Strontium Carbonate is a slightly soluble source of SrO used in glazes.
Some sources claim it decomposes at 1075C (others at 1340C) as follows:

SrCO3 -> SrO + CO2

However, the 'Ceramic Industry Materials Handbook' states that it starts
to disassociate as early as 800C in a purely oxidizing atmosphere, whereas
a CO2 atmosphere might delay break-down until around 1220C. This
information is supported by the fact that when the more stable calcium and
barium carbonate are added to bodies, pinholing and blistering are greater
than bodies containing strontium.

And here is another: from www.solvaychemicals.us

http://216.239.41.104/search?q=cache:tDXXjlexV-
YJ:www.solvaychemicals.us/pdf/Stroncarb-
1003.pdf+strontium+carbonate+decomposition&hl=en

Hope that is enough?

JOhn Britt
www.johnbrittpottery.com

Ivor and Olive Lewis on wed 1 sep 04

Dear John,
I also wonder about the same idea relating to the behaviour of
Strontium Carbonate <<, what happens when it is dissolved or
suspended in a glaze melt? I think using handbook values for
decomposition temperatures could be very misleading in this
situation. >>
I do not know !! I would say that no one knows, and I do mean that as
it relates to being part of a glaze formulation. This information may
never have been revealed by experimental exploration.
There are several scenarios which can be considered. You hit on two,
one is that the stuff does nothing, just sits there opacifying the
glaze, the second that it does dissolve into the glaze as a carbonate
without doing anything else. A third proposition would be the there is
a chemical reaction between the Strontium carbonate and free silica,
freeing Carbon dioxide and creating the potential for Strontium
Orthosilicate (Sr2SiO4, CAS No. 12138-28-2, mp.???) to crystallise on
cooling. If you could find the relevant thermodynamic constants,
calculation would show if this was feasible and the optimum
temperature at which the reaction would happen. Such behaviour would
mimic the other elements in Group 2, both Calcium and.Barium form
Orthosilicates.
By the way, I believe that Handbook values for the properties of the
materials we use are an important resource. Used with intelligence
they guard against making unqualified assumptions and drawing
unwarranted conclusions. I say this with the caveats that those who
choose to use them have some background in the Principles of Chemistry
and those who choose to ignore them refrain from inventing plausible
pseudo-scientific explanations for events or observations to mask
their ignorance.
If I say "I do not know" in spite of having information at my
fingertips I mislead no one.
Thanks for asking.
My best regards,
Ivor.

Ivor Lewis.
Redhill,
S. Australia.


----- Original Message -----
From: "John Hesselberth"
To:
Sent: Wednesday, 1 September 2004 1:02
Subject: Re: Cream Breaking Red and Strontium Carbonate


On Monday, August 30, 2004, at 09:42 PM, Ivor and Olive Lewis wrote:

> Strontium Carbonate is tricky stuff. Unlike its cousins, Barium and
> Calcium Carbonate, from the same family of elements, it does not
> decompose within the temperature range in which we fire our
ceramics.
> It decomposed with heat at 1340=BA C, say around 2450=BA F, well below
> your cone 6 maturity temperature.

Hi Ivor,

While I am sure this is true for the pure material, what happens when
it is dissolved or suspended in a glaze melt? I think using handbook
values for decomposition temperatures could be very misleading in this
situation.

Regards,

John

John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

______________________________________________________________________
________
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.

John Hesselberth on wed 1 sep 04

On Wednesday, September 1, 2004, at 01:32 AM, Ivor and Olive Lewis
wrote:

> A third proposition would be the there is
> a chemical reaction between the Strontium carbonate and free silica,
> freeing Carbon dioxide and creating the potential for Strontium
> Orthosilicate (Sr2SiO4, CAS No. 12138-28-2, mp.???) to crystallise on
> cooling.

Hi Ivor,

There is some circumstantial evidence that something like this happens.
It is possible to formulate a glaze (Weathered Bronze Green) that has a
flux system of SrO 0.475, alkalis 0.49, and the rest being a bit of
calcium and magnesium. Silica is 2.8 and alumina 0.58--no boron.
Weathered Bronze Green melts at cone 6 and is quite stable to copper
extraction even with 5% copper carbonate loading. It is also quite
matte. It melts better and is more durable than I would have predicted
based on my work with glazes high in calcium. That limited data leads
me to speculate that strontium (in whatever form it is) is a more
active "flux" than calcium.

Remove the strontium carbonate and I don't believe the above glaze will
melt. I haven't tried it but will when I get a chance.

Regards,

John

John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

Ivor and Olive Lewis on thu 2 sep 04

Dear John Britt,
Thank you for those contacts. I will follow them through as best I can
with the resources available to me.
From those you give, which would you regard as Prime Sources and which
provide references to the information they give?
Yes, true, the partial pressure of a gas can influence the reactions
of compounds which yield that gas on decomposition.
Interesting that one of your quotes give a decomposition temperature
which is lower that the melting temperature provided. Could this be
correct ? Does your source explain this anomaly?
Does the 'Ceramic Industry Materials Handbook' cite the sources for
its information? The chemistry you give. Would this apply to the other
elements in the Alkali Earth Group? What are the concequences when
Whiting or Dolomite are being used in a glaze batch
You say " Hope that is enough?". I would say, "If you had to answer a
problem in an examination which could affect your future, whcih one
would you, or could you trust?"
Chemistry is such a tantalising subject.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.


.

Ron Roy on thu 2 sep 04

There is no doubt that strontium carb is a flux in middle and high
temperature ranges.

I am quoting from Taylor and Bulls "Ceramic Glaze Technology"

"The use of Strontium in conjunction with Barium and Calcium gives benefits
beyond what might be expected from the mixed base effect when there is need
to control crystallization in glazes. Indirect comparison with barium oxide
alone, strontium oxide produces brighter and more fusible glazes. Strontia
is known to improve the chemical resistance of glazes when introduced at
the expense of lead and zinc oxide, but it's primary role is to facilitate
the development of low temperature glazes. Using strontium oxide as the
flux, glazes with high gloss, firing at 1145C can be made with good crazing
resistance due in part to the highly developed glaze-body reaction layer."

Hamer reports disassociation of the carbonate (gives up CO2) at 1075C -
which makes sense with the above statement by Taylor and Bull - that it is
useful as a flux starting at 1145.

A more useful subject for a discussion of this kind - I would think - is
what effect does the overall mix of fluxes - in a glaze or clay - have on
dissolution temperatures.

Any body got any hard info on that?

RR


>Strontium Carbonate is tricky stuff. Unlike its cousins, Barium and
>Calcium Carbonate, from the same family of elements, it does not
>decompose within the temperature range in which we fire our ceramics.
>It decomposed with heat at 1340=BA C, say around 2450=BA F, well below
>your cone 6 maturity temperature.
>So, to make it work in a glaze we would have to consider a new
>chemistry. Even if you had access to Strontium Oxide which by
>inference is necessary to make the glaze you would be faced with a
>problem. Strontium Oxide melts only when you heat it to 2430=BA C (4400=BA
>F).
>So we are faced with a profound question......What is the Chemistry of
>Strontium Carbonate in a glaze ? Please, would those who propose its
>use as a substitute of Barium Carbonate enlighten all of us ?

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20

Ivor and Olive Lewis on thu 2 sep 04

Thanks for that note John.
I am suspicious of making claims about melting for any of the elements
which have refractory oxides. But I am certain that chemical activity
in the solid phase provides one potential pathway to generate unusual
material mixtures which, in a serendipitous way, do give us mixtures
which activate along "Join Lines" which are shown in Equilibrium Phase
Diagrams.
I have said this before about nascent Calcium Oxide derived from
Whiting or Dolomite reacting with Nascent Silicon Dioxide given up
when Kaolinite decomposes to silica and Mullite. Unfortunately I do
not have a complete phase diagram for SrO-Al2O3-SiO2 which might
reveal the potential for this to take place. In the Binary system
SrO-SiO2, melting is always above 1350=BA C.
You may well be right about the example glaze you describe. But how
would we explain the result without some serious analytical work.
There is certainly for at least one of the Alkali Earth Orthosilicates
to give mixtures with free silica which will melt at Cone 6 where
alumina is present in the recipe. So why not another.
Keep up the good work.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.

Ivor and Olive Lewis on fri 3 sep 04

Dear Ron Roy,
Hamer's value differs by 325=BA C from those I have already given. I
distrust his value of 1075=BA C. Check his list of references. Where
does he get this knowledge from?
Statements about the maturation of a glaze only make sense if the
context in which the term "Flux" is being used is defined in an
unambiguous way and if it takes into account the substances which are
created when Strontium Carbonate dissociates.
If it is to Strontium Oxide and Carbon dioxide, the ACS give a melting
point of 2420=BA C for Strontium oxide (attributed to E.E. Schumacher,
1926) on the 1948 International Scale (Levin and others 1979).
Anyone who has access to the archives of the American Chemical Society
might like to consult the CAS data base and ascertain the melting
point of Strontium Ortho-Silicate, Sr2SiO4, (CAS No.13597-55-2). I am
unsure if Strontium forms a metasilicate which is analogous to
Wollastonite but there is information (ACS) to suggest that it does.
No doubt the empirical observations of Turner and Bull are, prima
facie, facts. But they tell us nothing about what is happening in
terms of Chemical Principles.
Dare I say that, at times, it would seem our community suffers from
myopic tunnel vision when we discuss the science and technology of our
craft. I often wonder how many glaze commentators and writers of
glazing books have really studied the teachings of Prof Kingery and
his Co-authors, especially Ch 10.
And yes, I agree with your suggestion <discussion of this kind - I would think - is what effect does the
overall mix of fluxes - in a glaze or clay - have on dissolution
temperatures. >> if you change one word; change "Fluxes" a term which
damns us to following the train tracks of history, to "Substances".
Best regards,
Ivor Lewis.
Redhill,
S. Australia.

Hi Ivor,

When you say "myopic" are you referring to mine or yours?

I have to agree - there are flaws in the literature we have - yours and
mine - how can it possibly be that so many writers disagree on the
disassociation temperature of the carbonates we use? Could it be that there
is a general misunderstanding about this? Could it be that the system in
which disassociation takes place has a profound affect on the temperature
at which this happens and could it be that the process is so complicated
that the only way to find out is to construct the experiments and do the
melting - as is the case with phase diagram research.

Dragging into the discussion melting points is a red herring - we all
understand - or should - that when you combine any materials - the
inevitable happens - the melting temperature is lowered. To use the fact
that SrO melts at whatever temperature is to muddy the water. I again must
mention the fact that Seger calls the alkaline earths fluxes at the middle
range of our temperatures and up. There is no doubt about that - and we
also know that Strontium Carbonate must disassociate on order to be a flux
at those temperatures. Explain it what ever way you want but for the sake
of discussions with other potters - why not use the terms we at least are
familiar with?

RR


>Hamer's value differs by 325=BA C from those I have already given. I
>distrust his value of 1075=BA C. Check his list of references. Where
>does he get this knowledge from?
>Statements about the maturation of a glaze only make sense if the
>context in which the term "Flux" is being used is defined in an
>unambiguous way and if it takes into account the substances which are
>created when Strontium Carbonate dissociates.
>If it is to Strontium Oxide and Carbon dioxide, the ACS give a melting
>point of 2420=BA C for Strontium oxide (attributed to E.E. Schumacher,
>1926) on the 1948 International Scale (Levin and others 1979).
>Anyone who has access to the archives of the American Chemical Society
>might like to consult the CAS data base and ascertain the melting
>point of Strontium Ortho-Silicate, Sr2SiO4, (CAS No.13597-55-2). I am
>unsure if Strontium forms a metasilicate which is analogous to
>Wollastonite but there is information (ACS) to suggest that it does.
>No doubt the empirical observations of Turner and Bull are, prima
>facie, facts. But they tell us nothing about what is happening in
>terms of Chemical Principles.
>Dare I say that, at times, it would seem our community suffers from
>myopic tunnel vision when we discuss the science and technology of our
>craft. I often wonder how many glaze commentators and writers of
>glazing books have really studied the teachings of Prof Kingery and
>his Co-authors, especially Ch 10.
>And yes, I agree with your suggestion <>discussion of this kind - I would think - is what effect does the
>overall mix of fluxes - in a glaze or clay - have on dissolution
>temperatures. >> if you change one word; change "Fluxes" a term which
>damns us to following the train tracks of history, to "Substances".
>Best regards,
>Ivor Lewis.
>Redhill,
>S. Australia.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20