ivor and olive lewis on sun 29 jul 12
Oxides from Group 1 and Group 2 two elements are known to influence the
viscosity of glazes. One way to explain this that they introduce non
bridging oxygen anions into the silicate framework.
This raises ideas about other anions being introduced as terminating groups=
.
Weyl and Marboe suggest candidates would be Calcium Fluoride, which could
insert Fluorine anions into the Silicate structure. The second is Water
vapour, even at atmospheric pressure would contribute Hydroxyl anions.
.
Our travelling library delivered a small treasure trove this week. Two
volumes by A. B. Searle ; "The Glazers Book" (1935) and "The Clayworker's
Handbook" (1929). The third volume was "Understanding Pottery Glazes"
(1963) by David Green. Bibliography is interesting. He acknowledges Glen
Nelson, A.B. Searle and Daniel Rhodes as sources.. At the end of the book
is a series of tables including a Periodic Table of the Elements.
From time to time questions arise on Clayart about potential glazes for
clays that seem to fall outside the popular firing ranges. David Green
presents a series of tables for firings ranging from 800 deg C to 1400 deg =
C
in 25 degree intervals, suggesting Seger proportions of Alumina and Silica
with subsidiary fractions of all the popular Fluxing oxides. For those who
do not have a computer there are instructions for using a Slide Rule to
convert Seger Ratios to recipe percentages masses or weights. Problems wit=
h
Pinholes in Borosilicate glazes, no worries. Soak for 1100 deg C for 4 hour=
s
!
Regards,
Ivor Lewis,
REDHILL,
South Australia
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