rballou@mnsinc.com on thu 1 oct 98
Hi all,
Tried to post something before about the blues, but it never made it to the
list. Oh, well... Everyone else has pretty much covered that ground now.
Here's just the bit that might make a difference.
Chun/Iron/Ti and blue: I've done some biaxial blends that confirm what
other posts have mentioned about optical/iron blues. The Fe1 set from Ian
Currie's book will produce iron blues on certain glazes. Rutile blues occur
in the same location if the colorants are changed (I used 1.5 Rutile and
3.5 RIO). Typically, these are low alumina/hi silica glazes. But a mat
rutile blue also showed up in the hi alumina/low silica location.
Relatively small changes in the alumina or silica affect the appearance of
the blue. The greening effect of Ti on iron is also apparent in these
glazes. More tests with different amounts/proportions of rutile/ti/iron
would probably give some more answers.
Biaxial blends are a very useful way to pin down glaze effects. The alumina
and silica in a glaze have a big impact on color, surface, texture in a
glaze. Biaxial blends are a way of quickly pinpointing where you should be
looking. So much of glaze testing that most potter's do is hit or miss.....
like throwing darts blindfolded. Sometimes you'll make the occasional
bullseye. Biaxial blends take off the blindfold. Plus, they help understand
glazes in general. You don't need to know how to do glaze calculation to do
a biaxial blend. Glaze calculation helps understand things even more, but
it's not necessary. Ian has a new website that explains how to do a blend
with existing recipes. There's even a calculation feature for doing the
math. You can find it at http://ian.currie.list.to/index.html
Happy testing!
Ruth Ballou
Silver Spring, MD
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