Ivor and Olive Lewis on fri 20 feb 04
Dear Andrew,
I am still waiting for Ryan and Radford but I have had Rado on loan
several times. I like his work. Agreed, it is a worthwhile read for
anyone interested in the practicalities of claywork.
Your comment about the stacking of Kaolinite crystals is interesting.
I have seen some of the images on web sites. Are you telling us that
when our plastic potter's clay dries this is how the crystals move
together to create those "Stacks".
The "Secrets of Flocs" ? So far I have not seen any images, other than
those which come from the imagination of their creators, which present
us with facts about the nature of "Flocks". As you suggest, depending
on the origin and nature of a natural clay, there are many component
materials which contribute to the quality of the stuff we work with.
So, what is a "Floc" ? Is the "Water Hull" of Lawrence and West a
"Floc". Or are "Flocs" accumulations of "Water Hulls" encasing the
other solids?What happens to "Flocs" when we pug, wedge and knead a
mass of clay? How do they function during the throwing and other
shaping processes. If it is because water provides lubrication is this
a similar effect to an ice skate moving on solid ice lubricated by a
film of water which seemingly refreezes as the pressure is past.
There seems to be a lot known about Clay/Water systems when they are
absent. But how much do we know about "Flocs" when they exist in
Clay/Water systems which contain only sufficient water to engineer
plasticity?
You seem to have access to a much wider knowledge base than I do, so
perhaps you have the answers to such questions.
Enjoy your weekend.
Best regards,
Ivor Lewis. Redhill, South Australia
Andrew Sugden on mon 23 feb 04
Dear Ivor,
When dug from the ground the kaolinite particles in kaolin are more often
found as stacks of hexagons rather than as discrete individuals, they are
sometimes also called books or veriforms. As I don=92t know how to post
pictures to ClayArt I can not show my own SEM images hopefully the
following web reference will suffice:
http://originoflife.net/information/
The stacks, which are formed during crystal growth, can reach lengths of
up to 100um. The delamination of the stacks by physical action can
significantly alter properties, and is a major contributory factor to the
increased plasticity of reworked clay compared to virgin material.
Delamination is irreversible.
A dictionary definition of flocculate is to aggregate in tufts, flakes or
cloudy mass. Drifting well away from the point remember flocc wall paper?
Consider a slip appropriately doped to cause edge to face attraction of
the individual particles, the resultant agglomerations are the floccs.
This slip is viscous and stiring of it breaks apart the floccs and
consequently leads to increased fluidity. After the removal of the
shearing action the fluidity decreases as the floccs reform. This is the
phenomenon of thixotropy. On dewatering to a plastic, and ultimately dry
state, the arrangement of the clay particles will alter, but will not be
the same as that which results from drying a deflocculated system.
Off to get my hands dirty on some clay....
Regards,
Andrew
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