chemical analysis data sheets

updated thu 13 jan 05

mailtoandrew@FSMAIL.NET on mon 10 jan 05

Hello Ivor,

I m reading both the EPK v Grolleg and Chemical Analysis Data Sheets
threads with great interest, and I think some extremely valid points have
been raised. Whilst I might throw in a few points of my own shortly I d
like to respond to one of your comments:

You stated: =94The EPK v Grolleg debate. Perhaps even with those degrees of
shrinkage and adsorption there is no vitrification happening in these
clays at cone 10. If this statement seems unbelievable, think carefully
before condemning my idea.=94

At cone 10, for which I taking 1300*C as being typical, a kaolin with an
alkali content such as found in Grolleg will be on the very cusp of the
onset of vitrification, or at least the beginning of glass formation.

Regards,

Andrew

Ivor and Olive Lewis on mon 10 jan 05

Dear Ron Roy,
I have a great deal of sympathy for the opinion expressed by Jon when
he says <chemical analysis report and living and dieing with it. Not that the
variations are always catastrophic, but that the typical part of the
analysis, at least to me seems very misleading. How can you rely on a
bunch of oxide percentages to do glaze calculation when those
percentages don t really reflect what material is in the bag you are
using. >>
The following facts support this view.
1 An analysis expressed as percentages, or molecular proportions, of
molecular oxides is an abstraction, a code which tells only about the
elements that are present in a representative sample
2 This information, useful though it may be in simplifying numerical
calculations, does not describe the true chemical nature of the
components, the substances which comprise the mixtures under review.
3 Information about Molecular oxides tells us nothing about the
distribution of those entities among the mineral constituents.
4 One of the components in the Molecular oxide representation or
analysis sheet, LOI or Loss on Ignition, conflates vital information,
concealing useful knowledge about the gases that are discharged during
heating.
5 Absence of Mineral analyses denies knowledge which can be used in a
predictive way or for problem solving.
6 One "Oxide" may be present in several constituents. But without
knowing the identity of these compounds we cannot make an estimate of
their effect in a clay body.
7 Knowing the names of the contributing minor or residual minerals in
a substance such as Kaolin or Ball Clay assists in predicting that
minerals behaviour.
8 Knowing the identity of the minerals means we have access to further
information, Crystal structure, Melting Points, Density, decomposition
products, thermodynamic behaviour. All of these may influence ceramic
processing.
9 Some of the elements we use are readily available to enter into =
reactions when they are in one mineral form but totally unreactive at =
our maturing temperature in another mineral or compound.
10 Where the molecular oxide analysis reveals only a very small fraction =
of a normally useful low melting point oxide we do not know, without a =
mineral analysis if the metallic atoms are present in a mineral compound =
or contained as interstitial inclusions, contaminants or inclusions in =
the crystal structure of a major ingredient=20

With regard to Substitutes for Gerstly Borate. I would ask, how much was =
known about the original material other than its Molecular Oxide =
Composition ? The answer to the question as to why it seemed difficult, =
if not impossible to duplicate its properties may have something to do =
with the molecular structure of the chemical compounds in the original =
mineral(s). Although books describing minerals and Potters books show =
Boron compounds has having lots of H2O's in their molecular formula, as =
they do for Kaolin, this misrepresents the structural nature of these =
compounds
As an example; Borax is known to potters as Na2O.2B2O3.10H2O. A better =
representation indicating chemical structure is Na2[B4O5(OH)4]8H2O . I =
would put the lack of success down to inadequate research. Mimicking =
Molecular Oxide compositions will not achieve physical and chemical =
properties of the original compound.
The EPk v Grolleg debate. Perhaps even with those degrees of shrinkage =
and adsorption there is no vitrification happening in these clays at =
cone 10. If this statement seems unbelievable, think carefully before =
condemning my idea.

Best regards,
Ivor Lewis.
Redhill,
S. Australia.