iandol on wed 24 may 00
Paul Lewing asks: is this a Bristol glaze? Is it only the fact that it's =
a Zn base that makes a glaze a Bristol glaze, or is there some further =
criterion? I can't find any in any of my books.
Paul
My knee jerk reaction is to say this is not a traditional Bristol Glaze =
because of the presence of Gerstley Borate. I don=92t think this rock =
was mined when this glaze type was first invented. Reading Hamer as well =
as Rhodes, Cooper and Royle leads to a definition of an opaque glaze in =
the range 1100-1300C where zinc oxide has replaced Lead oxide or =
carbonate as the principle flux. Representative Bristol Glaze recipes =
show a much higher content of felspar than the one you have worked out, =
over 60%.
Having said that, if it works well in the firing range you have chosen =
and you are satisfied with colour responses, opacity and texture I =
cannot see why it should not be valued by others for the effects it =
gives. However, being a person who likes lots of reduction, I would not =
use it because of the volatility of metallic zinc which forms so readily =
when zinc oxide is reduced.
It might be an interesting exercise to do a quad tile test, blending =
your felspar, whiting silica and kaolin and adding a constant proportion =
of dense zinc oxide to each mixture. I prefer this empirical approach to =
glaze research. Then I know.
Should you need more information about quad blend proportions for this =
one, contact me off list.
Regard, Ivor Lewis
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