Gail Dapogny on fri 4 jul 03
I've been having aproblem with several glaes but one in particular on our
porcelain:
fine glaze cracking (horizontal) , particularly down near the base.
Having hammered a couple of these pots at the fine-crack places, I realize
that they are dunts -- I can see the tiny fissures in the body, there's no
glaze in the cracks, they are very fine but slightly sharp.
And finally, these dunting cracks appear with some other glazes also -- on
this porcelain.
So...how do I tackle these? I assume that in the long run, the porcelain
should be modified . In the short run, is there anything I can do within
the glaze to help with the problem? Specifically is the silica (flint)
too high?
The Porcelain body is as follows:
Custer 25
Grolleg 17
EPK 23
OM4 7
Flint 13
Bentonite 8
(Total 100)
The glaze in question is:
Bev's Red-Brown
Custer 39
Whiting 12
Alberta Slip 6
Flint 28
EPK 5
Talc 3
Bone Ash 7
Total 100
Red Iron 13
Formula on Insight:
CaO .69
MgO .10
KNaO .21
Al2O3 .29
SiO2 3.19
Fe203 .26
Th Expansion: 7.67
I sent this problem to Ron Roy, but thought that others on Clayart might be
interested in any interchane that takes place.
Hope to hear from you, and thanks in advance.
Gail Dapogny
Gail Dapogny
Ann Arbor, Michigan
gdapogny@umich.edu
http://www.silverhawk.com/ex99/dapogny (single historical photo - no longer
registered with Silverhawk)
| |
|
