Snail Scott on mon 16 sep 02
At 09:57 PM 9/15/02 -0500, you wrote:
>...THe clay runs with more grog added were appreciably more
>stiff than those with less grog. I always thought...that the grog was
absorbing water. I know what
>grog is so this is not what infact was occurring.
>Explanations?
Two factors, I suspect.
One: The grog, though non-absorbent, still has surfaces
which must be wetted, using water which had previously
contributed to the squishiness of the wet clay.
Two: The grog itself, being a larger particle size than
the clay (even if it's a small mesh), reduces plasticity
by increasing the average particle size of the clay body.
Plasticity is largely a combination of moisture content
and particle size. (Some people consider the particle-
size factor to be the 'real' source of plasticity, but
it won't work without the water!) And by adding grog
to a clay body already at its optimum consistency, you
are affecting both factors.
I suppose that by coating the grog with a waterproofer
(as suggested), you could eliminate the surface-wetting
factor, but it seems more efficient to just wet the
grog before adding it. Or start with a wetter clay.
-Snail
| |
|
