Ivor and Olive Lewis on tue 6 nov 07
Dear Sabri Justin Douglas Ben-Achour,
As I understand information given in reference books such as the CRC =
Handbook of Chemistry and Physics or Tables of Physical and Chemical =
Constants compiled by the National Physical Laboratory, the =
temperatures quoted for melting and boiling points are practical =
reference points and are not speculative or hypothetical. They are facts =
gained from practical experience.
Best regards,
Ivor
Sabri Justin Douglas Ben-Achour on tue 6 nov 07
no one said that melting points weren't useful because they are theoretical=
or official, if that is what you're getting at. but their melting points =
aren't directly related to whether or not they make good fluxes, which i wa=
s the original point. unclear to me why this is getting shifted to adjectiv=
e choice and drawn out.
but, since you bring it up, another point is that the melting point under p=
erfect, standard conditions and in
isolation isn't always applicable to what will happen in a glaze. the offic=
ial melting points may be from practical experience, but they are tested un=
der very specific conditions that are not always reproduced in the kiln.=20
maybe 'official'
or 'ideal' would have been better words. the salt example is an example of =
how
the usefulness of the official melting point of salt is made more complicat=
ed by the
fact that the salt, in real life, makes other compounds that have
different vapor pressures. or that sometimes they react with a neighbor be=
fore they would reach their melting point and the new product has a new mel=
ting point. or that they decompose before melting (ex mercury oxide). or =
that they become part of a glass.=20
the word 'theoretical' was used for its connotation of limited applicabilit=
y to the 'real' world that we know as potters. =20
> Date: Tue, 6 Nov 2007 17:05:38 +1030
> From: iandol@WESTNET.COM.AU
> Subject: Temperature Scales
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Dear Sabri Justin Douglas Ben-Achour,
> As I understand information given in reference books such as the CRC Hand=
book of Chemistry and Physics or Tables of Physical and Chemical Constants =
compiled by the National Physical Laboratory, the temperatures quoted for =
melting and boiling points are practical reference points and are not specu=
lative or hypothetical. They are facts gained from practical experience.
> Best regards,
> Ivor
>=20
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Climb to the top of the charts!=A0 Play Star Shuffle:=A0 the word scramble =
challenge with star power.
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Ivor and Olive Lewis on sun 11 nov 07
Dear Sabri Justin Douglas Ben-Achour
Sorry for the delay in answering your note of Tue, 6 Nov 2007.
Here are your main points and my comments
:<good fluxes, >> ..... You may well be correct but it would depend on the =
scope of the meanings of the term "Flux".
<conditions and in isolation isn't always applicable to what will happen =
in a glaze.>> ..... I agree. Standard melting points are derived from =
materials that are specially prepared to high degrees of purity. Few, if =
any, materials we buy by the sack load would be purified to that degree =
of refinement. small percentages of contamination can alter the melting =
temperature
<their melting point and the new product has a new melting point. or that =
they decompose before melting (ex mercury oxide). or that they become =
part of a glass.>> .....True, and though students may have learned this =
it is often forgotten. Good examples are the Alkali Earth Carbonates and =
Kaolin which decompose and for those that react before melting, Calcium =
oxide created in the decomposition of Whiting reacts with Silica well =
below the maturity point of a cone 8 glaze.
Perhaps we do share some ideas that might be regarded as =
"Unconventional" among studio potters and ceramic artists.
Best regards
Ivor
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