Gretchen Zinkan on sun 16 dec 01
Wishing you all a peaceful holiday with your family of choice...and a
productive and exciting new year. Thanks to you all for your good humour,
encouragement and great ideas.
My question is this:
Given that petalite and spodomene are also lithium products...do they also
leach the same...and therefore should be avoided where ever possible on
functional wear?
Best wishes,
Gretchen
British Columbia
John Hesselberth on sun 16 dec 01
on 12/16/01 12:29 PM, Gretchen Zinkan at gzinkan@CYBERLINK.BC.CA wrote:
> Given that petalite and spodomene are also lithium products...do they also
> leach the same...and therefore should be avoided where ever possible on
> functional wear?
Hi Gretchen,
The propensity to leach isn't what we have been worrying about. Once any
material is incorporated into a well melted glaze its propensity to leach
shouldn't depend on the material from which it was sourced. It will only
depend on the final fired composition of the glaze and the conditions by
which it was fired. We have very little data on the tendency of lithium to
leach; that would have to be determined by testing.
What we were collectively worrying about was the tendency of lithium in a
glaze to result in unpredictable crazing and/or shivering/dunting. I think
it is fair to say we don't fully understand what is going on here. One
theory is that if lithium is sourced from the partially soluble lithium
carbonate you will have more trouble with this type of defect than if is
sourced from spodumene or petalite which are less soluble. The bottom line,
though, is that we don't know and I think the consensus is that one should
be very cautious with any glaze containing significant amounts of lithium.
Test it very carefully, in particular, before you use it on functional work.
As I'm sure you know, shivering and/or dunting can be very dangerous glaze
defects--in a lot of ways more serious than leaching because someone can get
hurt right now--causing slivers of glaze to pop off or causing a pot to
break very unexpectedly. Crazing, while less of a problem, is still
considered to be undesirable by most people on functional pottery.
Regards,
John
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
iandol on mon 17 dec 01
dear Gretchen Zinkan,
You Say <products.....do they also leach the same...and therefore should be =
avoided where ever possible on functional wear >>
Petalite, a material I buy by the sack in spite of the expense, with an =
accepted formula of Li2O-Al2O3-8SiO2 and Spodumene Li2O-Al2O2-4SiO2 are =
members of the Felspar group of minerals. I believe they must be =
regarded as stable and water insoluble in our time frame though they =
will eventually weather over time, as do all rocks and minerals when =
exposed to environmental influences.
Once incorporated into a stable glaze, that is one which is fully =
vitrified and has an acceptable Alumina to Silica ratio, the size of the =
Lithium Ion is such that this element would be efficiently trapped in =
the silicate matrix. So it might seem that only a small fraction would =
be available for chemical reaction with external solvents.=20
I have no reason to use Lithium Carbonate, but I will continue to =
incorporate Petalite in those of my glazes which might require =
adjustment to fit a specific clay body. Yes, this is for domestic ware =
and yes, we use our own pottery.
Best regards,
Ivor Lewis
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