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if a ba ion falls in the woods (a very light mouse might eat it

updated wed 30 apr 97


John Baymore on wed 16 apr 97


Gavin Stairs wrote (in part):

Date: Mon, 14 Apr 1997 09:47:17 EDT
From: Gavin Stairs
Subject: Re: if a Ba ion falls in the woods

Slight addition to my previous post.

Bill Walker wrote me off list to tell me that this glaze is pretty much
within limits for a glaze of this cone. I agree. So what went wrong?


This discussion points up the complexity of this glaze formulation,
batching, application, and firing issue, for sure. If it were such a
simple thing, God wouldn't have created ceramic engineers.

>> .....pretty much within limits for a glaze......<<

This brings me to think about those "accepted limit formulas" too. There
are many "versions" published in many different places, some slightly
different than others. We all seem to take these published formulas as a
"decree from God". So...... who is God?

Just exactly WHO came up with these originally (if we can ever identify
which craft pottery books hold the original ones), and more particularly
WHEN. I know that we can go back to the work done by Seger published in
the early 1900's, Warren with great stuff in the 30's, and also folks like
Lawrence, Kingrey, Norton, Singer, Parmalee, and Shaw in the 60's and early
70's, but who more recently? The same basic "general limit formulsa" have
been kicking around pot shops ever since I started serious clay work in the
late 60's.

When there is a variation in a craft pottery book...... who the %$#@
established that the new ones are "more correct" than the ones in another

And exactly WHO has done leaching tests on the glazes devised within these
"limit formulas". When was this done? (the 50's !!!!!) And most
importantly, to what set of leaching standards were they compared? Where
are the published results?

The investigations into this area that I have seen (the craft potter stuff)
indicate that these "accepted" limits seem to be based only on a "macro"
observation of the glaze for things like general melt, surface, body fit,
etc. Sort of the ........."if it looks like a glaze, smells like a glaze,
etc........ it must be a glaze approach". Just a tad better than doing a
triaxial blend and looking at the tiles and saying "oh boy, I've got three
new glazes to use".

I certainly have seen many limited focus industrial investigations
(non-craft oriented ceramics texts, J.AmerCer Soc, and so on) into certain
pretty narrow areas that go into depth about all levels of testing of the
matricies formed, and how variations in composition, batching, and firing
affect end result.

But I haven't seen this type of stuff at all for the tables so commonly
published in the "craft pottery" texts. Are we (authors of craft orineted
glaze publications running from class handouts to formal books)......myself
included, just passing on yet another "myth" of ceramics to be passed on by
the next generation?

So in addition to the possible formulation problems with the batch or with
firing control that Gavin so accurately reiterated, I just have to wonder a
bit here if..............

............the frequently published limit formulas for craft potters are
not accurate with respect to leaching issues?????

Along another track here............ I think potters also tend to take
these formulas as "fact" rather than "suggestion". Blends of materials of
the complexitey of most glazes are probably subject to the occasional
anamoly (sp?) jumping in just to catch us (God has a wierd sense of humor
). This points up the importance of actual leach testing if a glaze
is destined for functional ware and contains any particularly toxic



PS: Seems to me there is a technical type thesis project possibly hiding
in here somewhere . Any takers? (Boy, I wish I were younger, had a
good lab at my disposal at a university, and a solid budget.)

John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA