Nancy on sun 2 mar 08
What is the difference between Lithium, Calcium and Strontium
carbonates? I have one glaze recipes that calls for a little Lithium
and a little Calcium....
Any input would be greatly appreciated!
Nancy
John Post on mon 3 mar 08
Bruce,
The fact that Hamer states that strontium acts in a manner similar to
calcium makes wonder how thorough his research is on it. Many potters
use it as a substitute for barium in recipes and Hamer says it acts in
a manner similar to calcium. Is this like saying rattlesnake or
alligator tastes like chicken? I have worked with strontium and in
the glazes I worked with it did not promote crystal growth during slow
cooling like calcium does. It does yield a matt surface, but it has a
different feel than that of a calcium matt.
John Post
Sterling Heights, Michigan
http://www.johnpost.us :: cone 6 glaze website ::
http://www.wemakeart.org :: elementary art website ::
On Mar 3, 2008, at 10:47 AM, Bruce Girrell wrote:
>> What is the difference between Lithium, Calcium and Strontium
>> carbonates?
>
> Strontium carbonate is useful as a flux at temperatures above about
> 2000 F
> and acts in a manner similar to calcium (Hamer and Hamer).
> Bruce Girrell
>
Ben Shelton on mon 3 mar 08
Posting the recipe would help.
As to the various carbonates.. They all start with a diferent basic
ingredient and add on carbon and oxygen. They are all completely different.
To relate it to cooking it would be like the difference in wheat flour and
corn flour. Both are flours but both are completely different
Ben
Bruce Girrell on mon 3 mar 08
> What is the difference between Lithium, Calcium and Strontium
> carbonates?
Well, the difference is Lithium, Calcium, and Strontium. It is actually the
carbonate that makes no difference, as it is all lost as carbon dioxide (or
maybe monoxide) during firing.
Lithium is often added to a recipe to reduce its expansion of the glaze to
control crazing. It is effective above about 1550 F. Like other alkalis, it
is a good flux and it has good color response, but can produce very
different colors (Britt).
Calcium is a flux used in many, if not most, medium to high fire glazes. It
becomes active above 2000 F and helps add strength, hardness, durability and
resistance to scratching (Britt)
Strontium carbonate is useful as a flux at temperatures above about 2000 F
and acts in a manner similar to calcium (Hamer and Hamer). It tends to help
some strong colors. It is often used as a substitute for barium carbonate.
The books that I referenced contain much more detail on these and other
glaze materials. Britt's book is organized around specific groups and colors
of glazes. Hamer's book is a reference book, organized by topic. No plot at
all, but still fascinating reading.
Bruce Girrell
Britt, John, The Complete Guide to High-Fire Glazes
Hamer, Frank and Hamer, Janet, The Potter's Dictionary of Materials and
Techniques
Steve Slatin on mon 3 mar 08
Nancy --
In each case, during firing the carbonate will
'burn off' leaving an oxide. To understand
what these various materials do, check a
periodic table of the elements.
Lithium is in group I -- it has one molecular
attachment available, like sodium or potassium.
Calcium is in group II. Like magnesium, strontium and
barium, it has two 'attachments.' (Chemists
and physicists alike are probably groaning
at this point, but you don't need to know
more than this to do the chemistry, and
the idea of attachments is sufficient and
you don't start getting all quacked up about
the difference between electrons and
electron holes and such like.)
For this reason, it takes half as many
atoms of calcium or strontium to perform
the same function in a glaze that sodium
or lithium would.
So ... when you're altering a glaze, you
might change one bunch of sodium
atoms for the same number of potassium
atoms, but you'd need twice as many
of either to substitute for calcium or
strontium.
If this settles in well, and you have glaze
calc software, just keep this in mind and
watch your molar totals when you change
things around and you'll be fine. If you
want to recalculate things by hand, let
me know and I'll try to give some better
advice (though others may be more
capable in leading you through that
particular minefield).
Now here's the thing -- not all atoms even
in the same group are equal in effects.
Lithium is a more successful melter
in small quantities than sodium or
potassium (the latter two are about
equal, I believe). Calcium is a more
reluctant melter than magnesium.
You don't need to get into why, it's
just the way things are.
Similarly, lithium has a more favorable
effect (again, in small quantities) on
expansion than sodium. Potassium
is somewhere in the middle. Lithium
readily creates crystals (small, but
visible), calcium never has for me.
Every decent glaze I've ever used
has had ingredients from group I and
group II. The better glazes often have
several of each. Much of what happens
inside of a melting (or hardening) glaze
is not well known. There's plenty of
room for study, if you wish to do it.
Best wishes -- Steve S
For each
Nancy wrote:
What is the difference between Lithium, Calcium and Strontium
carbonates? I have one glaze recipes that calls for a little Lithium
and a little Calcium....
Any input would be greatly appreciated!
Nancy
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John Britt on tue 4 mar 08
John,
Nice. Finally someone understands that "acts like" or "is in the same
column" does not means "the same as". The UMF cannot make carob taste
like chocolate no matter what Ron says.
Oxides have individual physical properties as well as chemical properties
that are unique.
Rock on,
(I finally have a reasonably good cone 6 oil spot that I may have you test
for me if you are still interested in that.)
John Britt
John Post on tue 4 mar 08
Hi John,
I'm interested in testing your oil spot glaze. When you have time,
please send it.
I have a little Aim test kiln that I hooked up to an Orton computer
controller I got on e-bay. I have it set up so the results are
comparable to what I get when I fire in my larger electrics. It's fun
to be able to load 4 tiny pots in it and get a real quick turnaround
with the results.
John Post
Sterling Heights, Michigan
http://www.johnpost.us :: cone 6 glaze website ::
http://www.wemakeart.org :: elementary art website ::
> (I finally have a reasonably good cone 6 oil spot that I may have
> you test
> for me if you are still interested in that.)
>
> John Britt
Ivor and Olive Lewis on thu 6 mar 08
Dear John Post,
You inquire <similar to calcium makes (me) wonder how thorough his research is on it. =
>>John Post.
One way to find out is to write to him via his publisher (or perhaps one =
of the Welsh Clayarters can supply his address) and ask about his work =
on this topic. Alternatively, you might check through the references he =
gives in his bibliography. I have the 1975 (first) edition and he =
mentions some impressive names...Rhodes, Parmellee, Cardew, Singer.
I noticed some time ago when the more recent edition was published that =
this list had been shortened.
What might concern me if I did my own trials, as you have done, and =
obtained differing results, would be that I might distrust my own =
observations and reach an incorrect conclusion based on an unreliable =
text book information.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
John Post on thu 6 mar 08
My wondering was mostly rhetorical. I looked up Strontium in Hamer
before I started testing with it to see what he had to say about it.
There was not very much in the way of details.
I trust my own fired results. I really don't have to worry about
whether or not my results apply to other people's firings since I am
not doing research for others. I'm just curious about what works in my
kilns with my firing cycles.
John Post
Sterling Heights, Michigan
http://www.johnpost.us :: cone 6 glaze website ::
http://www.wemakeart.org :: elementary art website ::
On Mar 6, 2008, at 12:10 AM, Ivor and Olive Lewis wrote:
> Dear John Post,
>
> You inquire <> manner similar to calcium makes (me) wonder how thorough his
> research is on it. >>John Post.
>
> One way to find out is to write to him via his publisher (or perhaps
> one of the Welsh Clayarters can supply his address) and ask about
> his work on this topic. Alternatively, you might check through the
> references he gives in his bibliography. I have the 1975 (first)
> edition and he mentions some impressive names...Rhodes, Parmellee,
> Cardew, Singer.
>
> What might concern me if I did my own trials, as you have done, and
> obtained differing results, would be that I might distrust my own
> observations and reach an incorrect conclusion based on an
> unreliable text book information.
>
> Best regards,
>
> Ivor Lewis.
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