joyce on tue 1 jul 08
Technically you are certainly correct about the particle shapes, but the
>"spheres" analogy is a good one when discussing the effect of particle size
>on plasticity and working structure in claybodies. Certainly the particles
>are not really spheres. I am travelling, and thus have not followed this
>thread, so forgive me if the following is something that was already
>discussed. I expect it was, given the subject line "Density of packed
>spheres." The common version is the "Room full of basketballs," which is
>full of basketballs but can still accept thousands of golf balls. Then it
>could be said to be full, except that it could accept tens of thousands of
>marbles and then hundreds of thousands of B-Bs and then millions of grains
>of sand. The whole idea has to do with the elimination of unnecessary
>voids, which reduces drying and firing shrinkage, and the increase in the
>number of contact points between particles, which increases the friction we
>rely upon for working structure and also increases dry and bisque strength.
>The clay particle has an affinity for water and that encourages lubrication
>and slipping that translate to plasticity, but without contact points we'd
>have no working structure. A broad distribution of particle sizes (as in
>the spheres analogy, but with the variable shapes we would expect in ceramic
>materials), is one of the most important considerations in designing the
>best claybodies.
>- Vince
>
>Vince Pitelka
>Appalachian Center for Craft
>Tennessee Tech University
>vpitelka@dtccom.net; wpitelka@tntech.edu
>http://iweb.tntech.edu/wpitelka
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