Craig Martell on sat 6 jan 01
Ian commented:
>Ababi just posted some crystalline glazes with the comment that in
>one of them the lithium seemed to be softening the glaze. I have not
>heard of this. Does it happen? I had a clear that crazed on one of
>my clays, so I substituted spodumene for the pot spar to lower
>expansion. It worked well, but the glaze stains with coffee. Is
>this an example of above?
Hi:
The short answer is: Damifino! Glazes need to be looked at with regard
to everything that makes up the glaze. There may be problems with certain
materials and if used incorrectly, lithium can raise hell with glazes. So
the longer answer is that one needs to look at the entire glaze makeup to
get an idea of what may be problematic when faults or undesireable
properties are seen.
What may have happened to your glaze by subbing spodumene for potash
feldspar is a less aggressive fusion which could possibly make the glaze
"softer" and allow staining. Especially if this glaze was used at a lower
temperature than cone 9-10. I wouldn't sub spodumene for all of the
feldspar in any glaze. Spodumene isn't even classed as a mineral due to
the fact that it doesn't have a set melting point, but a range of temp
where it usually melts. It's not as powerful as potash spar in regard to
melt. But, again, you have to know what else is in the glaze to even
predict this.
There are several other materials and approaches that one might take to
lower expansion that are more likely to yield positive results. But it
depends on temp, atmosphere, desired color response, texture, and a lot of
other stuff that can only be determined by looking at the "whole" glaze.
I guess the long answer is that there is no quick or short answer most of
the time.
regards, Craig Martell in Oregon
Ian Macmillan on sat 6 jan 01
Happy New Year
Ababi just posted some crystalline glazes with the comment that in
one of them the lithium seemed to be softening the glaze. I have not
heard of this. Does it happen? I had a clear that crazed on one of
my clays, so I substituted spodumene for the pot spar to lower
expansion. It worked well, but the glaze stains with coffee. Is
this an example of above?
Ian
Ababi Sharon on sun 7 jan 01
Yes, I know I might use it wrong. My good adviser told me, that the lithium
makes the crystals, to be washed away, perhaps that was the right way to
write. Anyway, the first time I made that glaze I changed the B2O3 that was
in frit 3110 into lithium carbonate, in away that I kept the expansion. I
did not have any other tool to decide how much low expansion material to add
instead the Boron that I decided to remove it as might disturb
crystallization So I took The Li2O temporary out of the flux unity and
played only as the expansion was Perhaps, there was my mistake, but on my
"test cylinders"these hat looks saucers, was great. In the very first test I
made even with7 Lithium carb. and got "needles". In the next test probably
two or three month ahead I will try something else.
Now in my mind this glaze, tell me if I made a great discovery, or I am
going to dump (my favorite word) another 100gram batch of our beloved earth:
crystalline2120^6
=================
ENGLISH KAOLIN(Puraf 4.2 4.20%
FRIT 2120........... 29.1 29.11%
QUARTZ.............. 31.1 31.08%
ZINC OXIDE.......... 25.9 25.93%
TITANIUM DIOXIDE.... 7.4 7.38%
BONE ASH............ 2.3 2.31%
========
100.0
CaO 0.11* 3.06%w 3.67%m
K2O 0.00* 0.13%w 0.09%m
Na2O 0.26* 8.03%w 8.73%m
ZnO 0.63* 25.93%w 21.46%m
TiO2 0.18 7.38%w 6.22%m
Al2O3 0.04 2.31%w 1.52%m
P2O5 0.01 1.06%w 0.50%m
SiO2 1.70 51.56%w 57.79%m
Fe2O3 0.00 0.03%w 0.01%m
Cost/kg 11.20
L.O.I. 0.51
Si:Al 37.94
SiB:Al 37.94
Expan 9.10
Notes:
>From Lana Wilson's book page 50
Good base: fire to 1222C then cool fast to 1055C live to soak 1 hour then
cool normally. some people do it different see in the book! Here is changing
to 2120. to keep the expansion I added bone ash instead of B2O3
The Crystalline glaze are life time job.
I don't have life time for crystalline.
but still it is fun
Ababi Sharon
ababisharon@hotmail.com
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/index.html
* * * * * * * *
www.photoisland.com
ID: sharon@shoval.org.il
Password:clay
----- Original
Message -----
From: "Ian Macmillan"
To:
Sent: Saturday, January 06, 2001 11:47 PM
Subject: lithium softening glazes?
> Happy New Year
>
> Ababi just posted some crystalline glazes with the comment that in
> one of them the lithium seemed to be softening the glaze. I have not
> heard of this. Does it happen? I had a clear that crazed on one of
> my clays, so I substituted spodumene for the pot spar to lower
> expansion. It worked well, but the glaze stains with coffee. Is
> this an example of above?
>
> Ian
>
>
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Wade Blocker on sun 7 jan 01
Ian,
Lithium fluxes a glaze. If there is too much lithium in a glaze it
become runny. To keep the glaze from being runny, cutting back on the
lithium does the trick. Mia in sunny ABQ
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