piedpotterhamelin@COMCAST.NET on sat 6 dec 03
bisqued at 05 and glazed at 04 may have more tendency to craze than a pot
> that was bisqued at 04 and glazed at 06
I wrote that wrong. I meant to say bisqued at 05 and glazed at 06 may have more tendency to craze than a pot
> that was bisqued at 04 and glazed at 06
Sorry about that.
--
"Many a wiser men than I hath
gone to pot." 1649
> I don't think that I used the term shrinkage wisely. My intentions were a visual
> aid by using the term "shrinkage". More complete fusion is more appropriate.
> Parmelee and Harman refer to Rieke's finding that the coefficient of exp of
> porcelain glazes vary from 27 to 42 and stoneware (vitreous all clay body) from
> 57-96 (x10-7).
> It suggests to me that as temperature increases (and so to the fusion of the
> clay) this promotes reducing the expansion of the clay body in the second firing
> and hence bringing the fired clay towards fitting the glaze.
> My books don't discuss this relationship of the co-eff of expansion of the
> fired bisqueware to a glaze or as a factor in making the glaze fit, other than
> the Zamek and Hamer comments already stated.
> Now Parmelee and Harman were not concerned with the earthenware range in this
> article and I acknowledge that the glaze body interface (which is more
> completely formed in this heat range than that of earthenware) forms more
> completely and is more forgiving in these upper temperatures. I am merely
> suggesting (maybe questioning) that the potentially higher expansion rate of a
> pot bisqued at 05 and glazed at 04 may have more tendency to craze than a pot
> that was bisqued at 04 and glazed at 06. By Zamek, Hamer and Harman's notes, I
> sense that the expansion rate of a body is not constant across the cones but
> reduces as temperature increases. And that can benefit glaze fit.
> Well, there it is .
>
> "Many a wiser men than I hath
> gone to pot." 1649
> > >Mr Roy, if the pot is fired higher, then would it not have more of a
> > >complete fusion and more shrinkage towards fitting the glaze? Increasing
> > >the shrinkage being the same as your suggestion of raising the body
> > >contraction.
> >
> > Hi:
> >
> > "Shrinkage", has nothing to do with glaze fit. Glaze fit, or lack of glaze
> > fit, is determined by the expansion rates of both the claybody and
> > glaze. It's important to remember that shrinkage and expansion are not the
> > same thing.
> >
> > regards, Craig Martell Hopewell, Oregon
> >
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> ______________________________________________________________________________
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