iandol on wed 9 oct 02
Dear Jon Pacini,
In talking about measuring porosity, to what extent are Apparent Density =
and Theoretical Density taken into account in the tests and =
determination of porosity.
Am I correct to believe that even a porcelain clay will not attain its =
Theoretical Density when fully vitrified yet it will be totally =
impervious to the penetration of fluids?
Am I also correct to suggest that a stoneware body may be impervious but =
show a degree of adsorption from a soaking test because of incomplete =
identification from either sintering or partial vitrification?
Best regards,
Ivor Lewis.
Jon Pacini on fri 11 oct 02
Hi Ivor--greetings All-----I don't use Theoretical Density calculation in
determining porosity levels that are to be published. I've found that unless
you have very amazing control over your entire process, (and everyone
elses)Theory calculation is best left as guide line.
Concerning a porcelain body, For all practical purposes it's porosity
level will only be as high as the unvitrified portions of the composition
will allow it to be. If fully vitrified, it takes on the attributes of a
glass like substance as far as it's imperviousness to and absorbtion of
fluids. It's density level on the other hand, may be varied by firing in a
vacuum or under pressure. In that way you could control any gas voids in the
body and therefore it's true density.
A Stoneware or any clay for that matter, may show higher apparent
absorption because of the textural qualities of the clay surface. That is
voids in the surface that could hold water, but not necessarily allow it to
penetrate or pass thru. For that reason a soak or boiling test is not always
the most accurate test for absorption. For very open bodies it's quite
effective, for tighter ones, how much fluid penetration you get is certainly
open to debate, Though there are certainly more sophisticated instruments
available, I prefer an antique pressure cooker, (personal preference), for
porosity testing.
Jon Pacini
Clay Manager
Laguna Clay Co
-----Original Message-----
From: iandol [mailto:iandol@tell.net.au]
Sent: Tuesday, October 08, 2002 11:46 AM
To: Jon Pacini
Cc: clayart@LSV.CERAMICS.ORG
Subject: : stoneware vitrification
Dear Jon Pacini,
In talking about measuring porosity, to what extent are Apparent Density and
Theoretical Density taken into account in the tests and determination of
porosity.
Am I correct to believe that even a porcelain clay will not attain its
Theoretical Density when fully vitrified yet it will be totally impervious
to the penetration of fluids?
Am I also correct to suggest that a stoneware body may be impervious but
show a degree of adsorption from a soaking test because of incomplete
identification from either sintering or partial vitrification?
Best regards,
Ivor Lewis.
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