Ron Roy on fri 14 dec 01
Hi Les,
Wise words - and don't forget - the materials we use to make clay are them
selves variable in ways we cannot anticipate. We do know from our testing
program that there is variability but we can only guess at the reasons why.
We cannot test for the oxide makeup of the raw materials - no one would be
able to afford such clays. As it is - the testing for absorbency and
shrinkage adds to the cost but gives a price advantage to those who do not
have a testing program.
It may be that there are two kinds of migration - soluble Lithium in the
raw glaze on bisque during drying and again during firing - Craig often
refers to this last situation but I don't know why. Perhaps you could
expand on the reasons you think this is true Craig.
What we need is someone to do some testing - a glaze with lithium carb and
one with a frit, Spodumene or Petalite.
Another complicating factor is the solubility of some frits in the glaze
slop. If the Lithium is sourced from a frit and it does release soluble
lithium into the raw glaze - does it release more or less than the
carbonate?
You can see how your question is not easily answered - this is not really a
question of opinion but needs some investigation.
First we need a glaze/clay combination using the carbonate that shows the
problem - then we need to substitute another source of lithium for all or
part of the carbonate.
The figure of 2% carbonate as a safe level came from a series of
experiments I did with David Hewitt. I dilatometered bars of clay and glaze
- some with just the glaze and others with the lithium carbonate bearing
glaze scraped off the clay after it had dried. The experiments did not give
us any clues.
David had run into the problem - a glaze which was shivering and crazing -
he finally came to the conclusion that 2% was as much lithium carb he would
ever want to put in a glaze. I wonder now if he still thinks so - after
seeing the results of his glazes I would not be surprised if he avoided
lithium carb completely.
I cannot understand anyone wanting to risk this kind of glaze fit problem -
I don't think I could sleep very well if I was imagining what was happening
to all those pots I had sold to others once the complaints started coming
in.
I am not trying to be alarmist or exaggerating to make a point - I am just
repeating facts that have lead me to believe - in this case - that there
can be problems with lithium that we cannot predict and we should be
careful.
I recently did an experiment - I replaced - gradually - all the KNaO in a
cone 10 glaze with Lithium - to find out the effect of increasing lithium
on expansion. Some where I had read that Lithium - up to 20% replacement
for KNaO would lower expansion of a glaze. After 20% replacement - this
trend would reverse itself. In other words the expansion would start to
rise again. I did not find this so but had to discontinue the experiment
because the Spodumene was contaminated with iron and the melting was too
strong (reduced iron is a big time flux.)
There was no sign of any fit problems however - and the expansion was
moving continually downward.
I will do this experiment again when time allows.
If anyone wants to do the experiment at cone 6 I will be glad to help them
design the glaze tests - what we need is a clay/glaze combination that
shows the problem to start with.
RR
> The glazes that we use might be just on the cusp of
>this glaze defect, and that can be just enough to send it over the
>proverbial edge. The last part was a bit of a rant from a very, very bad
>experience. The point is this glaze looks and feels great. Ronald, I know
>you're out there somewhere twiddling with some sort of "delapitator" but
>what I would like to know is: Do you still suggest only 2% lithium when a
>frit is employed? Will not the frit solve the migration problems with
>lithium carb. Is F-493 soluble?
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Craig Martell on fri 14 dec 01
Hello Ron:
Where does one start with all of this? I wonder too if there are many
folks reading Clayart that have much of an interest in these sorts of
topics. The good thing is that the delete key is always there if we need it.
As you've seen from experience, lithium can cause some really drastic
problems in clay and glazes. It's categorized as a "low expansion oxide"
but there are others that have a lower COE that don't cause the problems
that lithium will. To name a few, Zinc, Magnesia, and Boron have a lower
COE than lithium. Lithium feldspathoids are another matter. Petalite has
a really low COE because of it's other components, alumina and silica which
are low expanders.
The reason I think that lithium causes problems during firing is related to
the above but also the solubility thing which isn't agreed upon by
everyone. Hamer says that lithium carbonate is only "slightly soluble" and
that lithium oxide is very soluble. If this is true, we have to look at
the coefficient of diffusion as being more relevant to problems related to
lithium. Lithium is the lightest metal oxide. It has a very small atom
with a strong charge which means it is very reactive. My sources for this
are: Lawrence and West-Ceramic Science for the Potter, Hamer and Hamer, W D
Kingery-Introduction to Ceramics (don't let this title fool you) and Mimi
Obstler-Out of the Earth and Into the Fire. Forgot one, Cullen
Parmelee-Ceramic Glazes. Obstler also cites the "slightly soluble" thing
with regard to lithium carbonate and gives her source as a bulletin from
Foote Minerals. Obstler also cites problems in the clay/glaze interface
with highly reactive lithium forging it's way into the claybody causing
more aggressive fluxing of the clay rendering it brittle and weak. This
would also set up a perfect scenario for shivering. Michael Banks has put
forth the idea in a past post that lithium carb could form spodumene at the
interface by reacting with the alumina and silica in the clay. I believe
this is a strong possiblity. Jim Robinson has talked about changes in his
glazes on lithium fluxed claybodies due to lithium migrating the other way,
from clay to glaze. This idea from Jim R isn't written anywhere. It's
from a conversation I had with him.
Maybe the thing we should keep in mind is that lithium, for many reasons,
is an oxide to use with care and respect. Then we won't have to run myriads
of tests and experiments to find out the states that are the most
problematic. The reason I say this is that most of us need to spend time
making pots to feed the bottom line. I'd love to figure this stuff out but
it takes a lot of time and energy.
regards, Craig Martell in Oregon
John Hesselberth on sat 15 dec 01
on 12/14/01 9:18 PM, Craig Martell at ashglaze@WVI.COM wrote:
> The reason I think that lithium causes problems during firing is related =
to
> the above but also the solubility thing which isn't agreed upon by
> everyone. Hamer says that lithium carbonate is only "slightly soluble" a=
nd
> that lithium oxide is very soluble.
To add a little data to the conversation, The Handbook of Chemistry and
Physics reports that lithium carbonate is soluble to the extent of 1.33
grams per 100 ml of water at 20=B0C. Since we use about 90-100 ml of water
per 100 grams of dry glaze this means more than half of the lithium would b=
e
in solution when, say, 2% lithium carbonate or less is in a glaze. When yo=
u
had, say, 20% in a glaze less than 10% of the lithium would be in solution.
I think this supports your point, Craig, that something goes on with lithiu=
m
that may we quite different from a pure solubility in water issue. I do
find it difficult to believe, though, that anything migrates very far in th=
e
brief time these molecules or ions are mobile during firing. These are
pretty viscous liquids we are talking about. And if they did migrate they
would move in the direction of uniformizing composition--not toward creatin=
g
pockets of nonuniformity. Movement into the clay, though, is an idea that
intrigues me. Interesting. I agree with you Craig that, while we can
speculate until the cows come home, it is best for now to regard lithium as
something that should be used with great care. The experiments required to
sort this out would likely be very difficult and expensive to do right.
Regards,
John
web sites: http://www.masteringglazes.com and http://www.frogpondpottery.co=
m
EMail: john@frogpondpottery.com
"Pots, like other forms of art, are human expressions: pleasure, pain or
indifference before them depends upon their natures, and their natures are
inevitably projections of the minds of their creators." Bernard Leach, A
Potter's Book.
Joyce Lee on sat 15 dec 01
Craig said:
"Where does one start with all of this? I wonder too if there are many
folks reading Clayart that have much of an interest in these sorts of
topics. The good thing is that the delete key is always there if we need
it."
----------------------------------------------------------
I hope I'm speaking for those of us who are interested but do not begin to
understand the ins&outs of more than superficial glaze chemistry. I always
read every befuddling word of yours, Ron's, Tom's etc chemical descriptions.
They are part of clay..... the very clay by which I am personally obsessed.
I want to hear.... and often get more than simply somewhat of a nodding
awareness... although that alone would be worth the reading. My
understanding of "Out of the Earth, Into the Fire" is enhanced by such
posts.
For example, in today's post it was important
for me to hear that "lithium is an oxide to use with care and respect." I
can't recall just why I ordered lithium but I did. I like spotting it here
and there on a pot, especially a flat-surfaced one such as a platter. I
like that at ^11 it flattens out into a surrealistic flower form... and that
at ^9 it's a cindery looking round blob which appears fragile but isn't. I
like that adding water causes certain reactions on the pot ..... and that
applying dry lithium to wet glaze results in other looks. I like that
lithium on specific glazes results in a beige rutile-like feathered halo
which surrounds silver, with a slightly raised dark metallic gray in the
center.
At the moment I can't absorb WHY this happens but I can comprehend that
maybe I want to be a little more careful when flicking
bits of lithium here&there... and consider what kind of function the pot is
destined to serve.
Fortunately, almost nobody else with money in their wallets finds these
looks more than just interesting .... so there are no pots lurking, waiting
to do a lithium raid on any body except mine.
Thank you for sharing with the list rather than confining your more esoteric
discussions to private posts.
Joyce
In the Mojave loving this time when I can feel perfect in snuggly sweats,
but still barefoot it comfortably across the house's tiled floor areas ....
if I'm speedy......
Khaimraj Seepersad on sun 16 dec 01
Good Day to All ,
[ BIG thank you for the lithium topic ]
Joyce ,
please get in line . I ordered 5lbs of the stuff and
went out on the town , making alkaline frits , alkaline
glazes [ heavy cullet use ] and low Egyptian paste
bodies.
I was having a great time , all of a sudden I had
these alkaline frits maturing at around 1100deg.c
[ orton cone 04 ] , and flowing as an applied glaze
at 650 to 850 deg.c [ about 020 to 015 small cone
orton ]. I was in heaven .
50 to 68 % Si02 and so clear.
Liquid frit shattering into finely particled glass , less
than 1 mm .
[ a ball miller's dream ]
Cullet glazes at 930 deg.c and E.Paste bodies at
910 deg.c [ 011 to 010 orton small cone ]. Very high
silica glazes and bodies.
I was the cat's meow , the bees' knees.
Then I saw what Lithium Oxide could do to the human
system and I backed way off.
So now I play nicely and the lithium carbonate is reserved
for developing enamels for Aluminium.
Khaimraj
Presently raining and cool , lawn grass is now lawn jungle.
* Note Well ---- West Indies ----CARIBBEAN !
Not India.
West Indies [ W.I ] is the proper postal code for the Islands
surrounding the Caribbean sea .
-----Original Message-----
From: Joyce Lee
To: CLAYART@LSV.CERAMICS.ORG
Date: 15 December 2001 12:59
Subject: Re: Lithium Carb in glazes Graig and David please read
>Fortunately, almost nobody else with money in their wallets finds these
>looks more than just interesting .... so there are no pots lurking, waiting
>to do a lithium raid on any body except mine.
>
>Thank you for sharing with the list rather than confining your more
esoteric
>discussions to private posts.
>
>Joyce
>In the Mojave loving this time when I can feel perfect in snuggly sweats,
>but still barefoot it comfortably across the house's tiled floor areas
....
>if I'm speedy......
Wanda Holmes on sun 16 dec 01
Ron, Craig, John, Paul, et al. Please DO post these discussions. With
every one, the fog is diminished a bit and one day, thanks to all of you, I
might truly understand all I'm learning about clay and glaze chemistry.
Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Craig Martell
Sent: Friday, December 14, 2001 8:18 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Lithium Carb in glazes Graig and David please read
Hello Ron:
Where does one start with all of this? I wonder too if there are many
folks reading Clayart that have much of an interest in these sorts of
topics. The good thing is that the delete key is always there if we need
it.
As you've seen from experience, lithium can cause some really drastic
problems in clay and glazes. It's categorized as a "low expansion oxide"
but there are others that have a lower COE that don't cause the problems
that lithium will. To name a few, Zinc, Magnesia, and Boron have a lower
COE than lithium. Lithium feldspathoids are another matter. Petalite has
a really low COE because of it's other components, alumina and silica which
are low expanders.
The reason I think that lithium causes problems during firing is related to
the above but also the solubility thing which isn't agreed upon by
everyone. Hamer says that lithium carbonate is only "slightly soluble" and
that lithium oxide is very soluble. If this is true, we have to look at
the coefficient of diffusion as being more relevant to problems related to
lithium. Lithium is the lightest metal oxide. It has a very small atom
with a strong charge which means it is very reactive. My sources for this
are: Lawrence and West-Ceramic Science for the Potter, Hamer and Hamer, W D
Kingery-Introduction to Ceramics (don't let this title fool you) and Mimi
Obstler-Out of the Earth and Into the Fire. Forgot one, Cullen
Parmelee-Ceramic Glazes. Obstler also cites the "slightly soluble" thing
with regard to lithium carbonate and gives her source as a bulletin from
Foote Minerals. Obstler also cites problems in the clay/glaze interface
with highly reactive lithium forging it's way into the claybody causing
more aggressive fluxing of the clay rendering it brittle and weak. This
would also set up a perfect scenario for shivering. Michael Banks has put
forth the idea in a past post that lithium carb could form spodumene at the
interface by reacting with the alumina and silica in the clay. I believe
this is a strong possiblity. Jim Robinson has talked about changes in his
glazes on lithium fluxed claybodies due to lithium migrating the other way,
from clay to glaze. This idea from Jim R isn't written anywhere. It's
from a conversation I had with him.
Maybe the thing we should keep in mind is that lithium, for many reasons,
is an oxide to use with care and respect. Then we won't have to run myriads
of tests and experiments to find out the states that are the most
problematic. The reason I say this is that most of us need to spend time
making pots to feed the bottom line. I'd love to figure this stuff out but
it takes a lot of time and energy.
regards, Craig Martell in Oregon
____________________________________________________________________________
__
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.
Paul Lewing on sun 16 dec 01
At one point in this discussion, mention was made of seeing both crazing and
shivering on the same piece. I know Ron has seen that, and I believe I
heard Craig say once he had seen that. I have as well, several times. It
was always in a glaze that contained BOTH lithium (as I recall always in the
form of the carbonate) and zinc. Has that been others' experience as well,
or just coincidence for me? If it's not coincidence, why might that be the
case?
Paul Lewing, Seattle
David Hewitt on mon 17 dec 01
I have also seen this. It arose in testing work that Mike Bailey and I
were conducting on cone 6 glazes for his recently published book - 'Cone
6 Glazes'.
The following is an extract from this book.
"... when the amount of Lithium exceeds 10.0% a strange thing happens;
the glaze shivers away from the clay. The potter is left with the
bizarre effect of a crazed glaze that has shivered, faults that are
usually at the opposite ends of a glaze fitting spectrum. A brochure on
'Lithium in Ceramics' by the Lithium Corporation of America notes that
'...Small additions of lithium compounds will react with quartz during
firing and eliminate the alpha-beta quartz transition in the cooling
cycle'. Michael Banks has proposed that this is due to the formation and
phase changes of Spodumene....."
David
In message , Paul Lewing writes
>At one point in this discussion, mention was made of seeing both crazing =
>and
>shivering on the same piece. I know Ron has seen that, and I believe I
>heard Craig say once he had seen that. I have as well, several times. I=
>t
>was always in a glaze that contained BOTH lithium (as I recall always in =
>the
>form of the carbonate) and zinc. Has that been others' experience as wel=
>l,
>or just coincidence for me? If it's not coincidence, why might that be t=
>he
>case?
>Paul Lewing, Seattle
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Ron Roy on sat 22 dec 01
Good man for noticing that Paul,
I just looked up my notes on the experiments David Hewitt and I did on this
subject - yes the glaze we worked on did have Zinc in it - zinc and lithium
are both oxides that can encourage crystallization.
Can anybody else offer confirmation - or have strange fit problems with
glazes containing lithium and no zinc?
Remember - we are not talking about glazes with very low
expansion/contraction rates - they will shiver - but glazes with what we
think are rates within the normal working range.
Any body want to do some experiments on this subject? I will provide the
dilatometry - RR
RR
>At one point in this discussion, mention was made of seeing both crazing and
>shivering on the same piece. I know Ron has seen that, and I believe I
>heard Craig say once he had seen that. I have as well, several times. It
>was always in a glaze that contained BOTH lithium (as I recall always in the
>form of the carbonate) and zinc. Has that been others' experience as well,
>or just coincidence for me? If it's not coincidence, why might that be the
>case?
>Paul Lewing, Seattle
>
>______________________________________________________________________________
>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.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Craig Martell on sat 22 dec 01
RR sez:
>I just looked up my notes on the experiments David Hewitt and I did on this
>subject - yes the glaze we worked on did have Zinc in it - zinc and lithium
>are both oxides that can encourage crystallization.
>
>Remember - we are not talking about glazes with very low
>expansion/contraction rates - they will shiver - but glazes with what we
>think are rates within the normal working range.
Hi Ron:
The subject of LiO and calculated expansion gets more tenuous by the
minute. I hope Nils doesn't mind me saying this via the group(nothing
derogatory here anyway :>) but I looked at two bowls with his LiO plus MgO
glaze and because of the massive development of Pyroxene crystals the glaze
had crazed. In other words, the calculated expansion really didn't apply
to what was actually happening in this case. I wonder what state the glaze
would be in if the pots had been given a very fast cool that didn't allow
crystals to develop. The expansion certainly would have been lower.
The above stuff makes me think too that lowering expansion with MgO is
going to be relative to the amount of MgO in the glaze and the cooling
rate, which both effect the probability of crystal development. I guess
this is one good reason to use "limits" as a guide with some types of glazes.
Glazes with LiO and ZnO can be tricky too, I would think. ZnO has a lower
calculated expansion than LiO so there's a potential problem but they both
favor crystal development which makes it hard to rely on calculated
expansion figures.
Perhaps some dilatometry experiments with low expansion glazes in glassy
and crystalline states would yield some good info. Specifically, fire the
same glaze with two different scenarios, a quick cool to prevent crystals
and a slow cool to encourage them. The actual expansion rates should be
very different and the only way to get some good numbers is with a dilatometer.
Also, I have some free Zinc Oxide if anybody wants it.
regards, Craig Martell in Oregon
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