Mike Bailey on sat 12 jun 99
Hello,
A couple of days ago there was a posting about a high lithium glaze and
shivering. Unfortunately, I've deleted the daily digest so this is from
memory. The glaze mentioned had 10% lithium carb in the recipe and an
explanation was put forward that, as lithium has a low coefficient of
expansion, this caused the glaze to shiver off.
I don't think this is quite right. Lithium is similar to the other
alkalis; Potassium and Sodium - they actually all have high expansion
figures - its just that lithium' RTE is lower (usefully) than the other
two. But still much greater than: alumina, boron, magnesia or silica.
One problem that we all have arises from the coefficient of expansion
figures used in the computer programs - just how 'good' Lithium is
depends on which figures are used. A worker in this field called Appen
gives a higher figure than some of the other people. Observations would
favour his higher figure.
There is something else going on with glazes high in Lithium too. I've
got a series of test tiles that were done with my glaze testing buddy
David Hewitt. We tested an increasing progression of Lithium Carbonate.
They were all crazed and began to flake off in sheets with the higher
amounts of Lithium. Under a hand lens one could see that the glaze had
pulled away from the clay. This seems to be a characteristic similar to
the silica inversions where there is a sudden contraction / expansion at
a specific temperature. I've understood this as an example of quantum
mechanics - where what we are seeing is the result of an electron
falling down (or jumping up) between electron orbitals.
About 5% by weight of Lithium carb seems to be approaching the practical
limit that one can put in a glaze.
Best regards to all and apologies for losing the original posting.
Mike.
--
Mike Bailey
Bath. U.K.
Craig Martell on sun 13 jun 99
HI:
Mike Bailey wrote:
>A couple of days ago there was a posting about a high lithium glaze and
>shivering. Unfortunately, I've deleted the daily digest so this is from
>memory. The glaze mentioned had 10% lithium carb in the recipe and an
>explanation was put forward that, as lithium has a low coefficient of
>expansion, this caused the glaze to shiver off.
>I don't think this is quite right. Lithium is similar to the other
>alkalis; Potassium and Sodium - they actually all have high expansion
>figures - its just that lithium' RTE is lower (usefully) than the other
>two. But still much greater than: alumina, boron, magnesia or silica.
I've looked at many posts on Clayart in the past few years dealing with
shivering and shattering of pots. The common factor in all the glazes was
that they contained some sort of lithium material. While it may not always
be true that lithium is the primary culprit, I would venture to say that in
a lot of cases it is. We must not forget to take the entire clay-glaze
system into account though. There needs to be an examination of the clay
mechanics as well as the total glaze composition. The most recent posting
from Earl was in regard to a glaze the contains both lithium carb and
magnesia, which are both of lower expansion than potassium or sodium. I
would still maintain that the lithium in this glaze is causing the shivering
and I do feel that it is of a low enough expansion when compared to potash
and soda that it will cause a marked difference in expansion properties. I
would add that the problem with Lithium carb also stems from the fact that
it is one of the lightest metals and 10% in a glaze will contribute a lot of
lithium molecules. Much more than the same percentage of other oxides.
Lithium has a high coefficient of diffusion too which means that it can
easily penetrate the interface or boundary layer between the clay and glaze
and cause shivering to occur there. Michael Banks sent a very thoughtful
post in regard to this not too long ago and it should be available in the
archives. One other thought about the high coefficient of diffusion thing
is in regard to why lithium can and will move around so much. I was
thinking that since so many molecules are contributed by any given
percentage of lithium in contrast to say potash, soda, calcium, magnesium,
there may not be enough silica and alumina in the glaze to accomodate all
these lithium ions so the excess lithium will migrate into the interface and
clay which would contain more alumina and silica.
Another thought I had was that if lithium is similar to potash and soda, why
can't flameware bodies be compounded with potash and soda spars? Why do
glazes that are made to fit flameware bodies have to contain such high
amounts of lithium compounds to fit the clay? The expansion numbers that we
see may not accurately describe the expansion differences between lithium
materials, in this case Petalite and Spodumene, and other alumino silicates
used as body fluxes. I fired fusions of all the spars and alumino silicates
that I have and the lithium materials didn't craze while the potash and soda
spars all did. These were prepared by dry packing into half inch crucibles
to form the button and then I fired the buttons to cone 10 reduction.
This is my last post on lithium. I'm sounding like a broken record and I
quit!
fire some tests, Craig Martell in Oregon
Janet Kaiser on mon 14 jun 99
I too deleted the original question, because I am not a technical guru. But
I did question whether there was an additional bit of the equation omitted?
For example, was the glaze on slip decoration, oxides or plain pot?
Janet Kaiser
Thonas C. Curran on mon 14 jun 99
Craig Martell wrote:
>
> ----------------------------Original message----------------------------
> HI:
>
> Mike Bailey wrote:
>
> >A couple of days ago there was a posting about a high lithium glaze and
> >shivering. Unfortunately, I've deleted the daily digest so this is from
> >memory. The glaze mentioned had 10% lithium carb in the recipe and an
> >explanation was put forward that, as lithium has a low coefficient of
> >expansion, this caused the glaze to shiver off.
>
> >I don't think this is quite right. Lithium is similar to the other
> >alkalis; Potassium and Sodium - they actually all have high expansion
> >figures - its just that lithium' RTE is lower (usefully) than the other
> >two. But still much greater than: alumina, boron, magnesia or silica.
>
> I've looked at many posts on Clayart in the past few years dealing with
> shivering and shattering of pots. The common factor in all the glazes was
> that they contained some sort of lithium material. While it may not always
> be true that lithium is the primary culprit, I would venture to say that in
> a lot of cases it is. We must not forget to take the entire clay-glaze
> system into account though. There needs to be an examination of the clay
> mechanics as well as the total glaze composition. The most recent posting
> from Earl was in regard to a glaze the contains both lithium carb and
> magnesia, which are both of lower expansion than potassium or sodium. I
> would still maintain that the lithium in this glaze is causing the shivering
> and I do feel that it is of a low enough expansion when compared to potash
> and soda that it will cause a marked difference in expansion properties. I
> would add that the problem with Lithium carb also stems from the fact that
> it is one of the lightest metals and 10% in a glaze will contribute a lot of
> lithium molecules. Much more than the same percentage of other oxides.
> Lithium has a high coefficient of diffusion too which means that it can
> easily penetrate the interface or boundary layer between the clay and glaze
> and cause shivering to occur there. Michael Banks sent a very thoughtful
> post in regard to this not too long ago and it should be available in the
> archives. One other thought about the high coefficient of diffusion thing
> is in regard to why lithium can and will move around so much. I was
> thinking that since so many molecules are contributed by any given
> percentage of lithium in contrast to say potash, soda, calcium, magnesium,
> there may not be enough silica and alumina in the glaze to accomodate all
> these lithium ions so the excess lithium will migrate into the interface and
> clay which would contain more alumina and silica.
>
> Another thought I had was that if lithium is similar to potash and soda, why
> can't flameware bodies be compounded with potash and soda spars? Why do
> glazes that are made to fit flameware bodies have to contain such high
> amounts of lithium compounds to fit the clay? The expansion numbers that we
> see may not accurately describe the expansion differences between lithium
> materials, in this case Petalite and Spodumene, and other alumino silicates
> used as body fluxes. I fired fusions of all the spars and alumino silicates
> that I have and the lithium materials didn't craze while the potash and soda
> spars all did. These were prepared by dry packing into half inch crucibles
> to form the button and then I fired the buttons to cone 10 reduction.
>
> This is my last post on lithium. I'm sounding like a broken record and I
> quit!
>
> fire some tests, Craig Martell in Oregon
Many moons ago (while I was having trouble with shivering high lithium
glaze) I read somewhere that lithium carb was used in nose cones of
rockets because of low or zero coefficient of expansion. All I know is
that I've only had shivering problems with lithium over the years, and
that's why I posted a reply to this thread last week or so. I agree
with Craig about the lower expansion rates, and I checked Hamer's entry
on lithium materials, but I just mislaid my copy and can't quote from it
right now. Cheers from CNC
Earl Brunner on tue 15 jun 99
The original question had the shivering over cobalt oxide on the rim. The pot
itself destructed from compression stress, as have about 20 % of the other pots
glazed with that glaze before I pulled it from the shelf. You can pull them
apart into little pieces with your bear hands. Ron Roy cautioned against using
the lithium in that form and quantity. I will probably drop the glaze rather
than try to fix it. Liked the purple though.
Janet Kaiser wrote:
> ----------------------------Original message----------------------------
> I too deleted the original question, because I am not a technical guru. But
> I did question whether there was an additional bit of the equation omitted?
> For example, was the glaze on slip decoration, oxides or plain pot?
>
> Janet Kaiser
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Mike Bailey on wed 16 jun 99
Hi,
Ref my reply to the Lithium carb and shivering discussion.
Several Clayarters have been kind enough to contribute, Craig Martell
(who is obviously fed up with answering this question, my apologies),
Michael Banks (off list) and Thonas Curran.
The point I'm making is that if you start off with a crazed glaze and
you then add a low expansion material to this, magnesia, boric oxide
etc. you see the crazing diminish. Eventually one may reduce the
expansion figure for the glaze so that under your firing conditions, not
only has the crazing disappeared but the glaze is now too big for the
clay body and it shivers off. That's my picture of shivering - a glaze
that isn't crazed but has splintered away from the pot i.e. the opposite
of crazing.
We now come to the conundrum (to me at least) where you have a crazed
glaze that has also flaked off the pot. These high Lithium glazes seem
to do both i.e. craze and 'shiver' at the same time!
That why I said 'there's something else going on with Lithium'. Whatever
the reason, it happens at quite a low temperature when the glaze's
fluidity is low.
I don't mean to prolong the discussion and perhaps I'm getting too
involved in the semantics of what is 'shivering' and what is 'flaking'.
Of course the end result is the same, the blasted glaze has fallen off
the pot!
Cheers,
Mike.
--
Mike Bailey
Craig Martell on thu 17 jun 99
Mike Bailey says:
>Ref my reply to the Lithium carb and shivering discussion.
>Several Clayarters have been kind enough to contribute, Craig Martell
>(who is obviously fed up with answering this question, my apologies),
Hello Mike:
No need to apologize for offering your views on a perfectly legitimate and
worthy topic. It's not your fault that I'm cranky from making pots day and
night. I need a beer and a nap I think.
regards, Craig Martell in Oregon
| |
|
