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slip sliding platelets

updated mon 4 aug 03


Lily Krakowski on fri 1 aug 03

Years ago I acquired a small book called "The Natural History of Clay," by
Alfred B. Searle, Cambridge U.P 1912. (Fun to know the manager of the Press
at the time was one Mr Clay). Searle himself is listed as author of several
clay related books, and as Cantor Lecturer on Brickmaking which I assume
means that he knew his stuff.

He cites Johnson and Blake who "supposed that plasticity is due to the clay
being composed of extremely minute plates 'bunched together,'a view which ws
also held by Biederman and Herzfield, Le Chatelier and others. Olschewsky
enlarged this theory by suggesting that the plasticisyt of certain clays is
dependent on the large surface and the interlocking of irregular particles
with the plates just mentionned. These theories of inerlocking are,
however, incomplete, because the tensile streght of clays should accurately
represent teh platicity if interlockign were the sole cause. Zschokke has
shown that tensile strength is only one factor which must be determined in
any attempt to measure plasticity.

"E.H.L Schwarz has suggested that manhy clays are composed of small globular
masses of plates so arranged as to form an open network...which is
sufficiently strong not to be destroyed by pressure. In the presence of
water and much rubbing the paltes are separated and are made to lie flat on
each other, thereby giving a plastic and impermeable mass. if this is
really the case it would explain the porosity and large surface of some
clays and might account for their adsorptive power"

The bibliography either is not very good, or is not what we demand today,
because there is no clue who some of these men [?] were. However for
Johnson and Blake this is given: " 'On Kaolinite and Pholerite' American
Journal of Science. XLIII. 1867" and for Schwarz "'Causal Geology", Blackie
and Sons, Ltd. 1910."

Platelets slipsliding around, then, may have been accepted wisdom, although
Searle goes on with colloidal theories.Interestingly Searle lists himself as
translator of an E. Bourry piece in 1911.

I got to reread that little book yesterday because I was stuck at home as my
truck had broken down....It is ok. Just a wire.

Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389

Be of good courage....

iandol on sat 2 aug 03

Dear Lily Krakowski,=20

Searle had interesting historical perceptions. As far as I know in those =
days they were unable to image Kaolinite suspensions. Much later it was =
possible to make Gold Shadowed Replicas of surfaces for the early =
electron microscopes. Then improved on these with the advent of the =
Phillips Scanning Electron Microscope.

But as yet it seems as though no one has imaged plastic clay bodies used =
by potters. The problem here is that specimens have to be examined in =
vacuum, so the water disappears.

I find it amazing, when they are talking about plastic clay, that the =
Pundits are ignorant of the properties of water. I argued on Clayart =
about three years ago that most of the plastic clays which responded =
well on the potters wheel had a Mass Ratio of water to clay solids in =
the order of 1 to 2 whereas the Volumetric Ratio would be around 2 to 1. =
Incorporate this concept into the current models and it is impossible =
for the solids to be in contact. Adjacent Clay Crystals would be =
separated by a layer of water twice as thick as the crystal depth. It is =
also known that Water which is influenced by Kaolinite assumes a rigid =
structure due to polarisation. This polarisation is destroyed when =
Deflocculants are introduced

Yesterday Olive took water from the fridge. It was frozen into a single =
crystal. How do I know that? There were no internal reflections. Why did =
it behave that way? Because Olive had removed clay nuclei which could =
have triggered precipitation of many crystals. Even more amazing was the =
development of Gas Inclusions which were linear tubes.

Which reminds me. Did I not post a Science and Technology reading list =

Best regards,

Ivor Lewis. Redhill, South Australia