Jeff Lawrence on thu 23 aug 01
John Hesselberth was suggesting that my bubbly glaze was
overfluxed
Thanks for your comments, John -- this is an interesting
thought for me, because I expect overfluxed glazes to just
run for the shelf. In this case, the glaze on the edge
(vertical) of the test tile did not appear to run at all,
though it did bubble there. Also, when I look at the limits
Insight provides, this glaze looks like it is within them
for all oxides.
Looking at a thick tome on Micas that I forgot I had, I
find the following formulae for two common varieties:
biotite K(Mg0.6-1.8Fe2.4-1.2)(Si3Al)O10(OH,F)2
muscovite KAl2(Si3Al)O10(OH,F)2
Among other polysyllabic truths, it says F can substitute
for the OH, even to the exclusion of OH. I am suspecting now
that F is a bubble factor. Do all those OH's and O's turn
into chemical water that outgasses during firing?
I like Paul Lewing's suggestion of calcining to eliminate
bubbles, but still wonder how to keep and even increase them.
Jeff Lawrence jml@cybermesa.com
Edouard Bastarache on thu 23 aug 01
Hello Jeff,
Fluorine materials are recomended in order to make
"crater glazes", if they crater , they bubble.
Later,
Edouard Bastarache
Irreductible Quebecois
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://www.absolutearts.com/portfolios/e/edouardb/
Paul Lewing on thu 23 aug 01
on 8/23/01 5:51 PM, Jeff Lawrence at jml@SUNDAGGER.COM wrote:
> I like Paul Lewing's suggestion of calcining to eliminate
> bubbles, but still wonder how to keep and even increase them.
Jeff, I forgot to mention that, when calcining stuff, especially something
that seems to have as high a LOI as this stuff, you should calculate for the
LOI and compensate for its loss when you remix the glaze.
To increase the bubbles, you could always add some silicon carbide powder.
One or two percent should make any glaze bubble.
Paul Lewing, Seattle
John Hesselberth on thu 23 aug 01
on 8/23/01 1:51 PM, Jeff Lawrence at jml@SUNDAGGER.COM wrote:
> Among other polysyllabic truths, it says F can substitute
> for the OH, even to the exclusion of OH. I am suspecting now
> that F is a bubble factor. Do all those OH's and O's turn
> into chemical water that outgasses during firing?
Hi Jeff,
Not necessarily--there are lots of Os in the final glaze. The answer to
this is the same as to the question Paul asked you. What is the LOI. Find
or measure that to get a better idea of what is happening.
John
Web site: 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.
John Hesselberth on thu 23 aug 01
on 8/23/01 1:51 PM, Jeff Lawrence at jml@SUNDAGGER.COM wrote:
> Also, when I look at the limits
> Insight provides, this glaze looks like it is within them
> for all oxides.
This is why we all say limits are guidelines only. When you push KNa toward
the top of the limits AND also boron toward the top AND have only a modest
level of silica you may well have a pretty liquid glaze.
John
Web site: 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.
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