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Date: | Wed, 1 Dec 1999 20:28:22 -0500 |
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Just to add a bit of confusion: small <1" diameter marbles (made of
marble rather than glass) can be the discarded by product of an early
20th century ball mill. (Then again, how early are ball mills?) Ball
mills are basically drums, larger than 55 gal drums, and set to rotate
about the long axis. They're filled with marble balls of at least
baseball size and mixed with smaller ones. Pigment blocks are added and
are ground to powder, the larger balls gradually decrease to marble size
while the larger types are added as needed to keep the mix stable.
Due to the rotating motion, the "marbles" are nearly perfectly
spherical. Some I have seen have bands of pigment adhering to the
outside surface which may otherwise distinguish them from "real"
marbles. A ball-mill dump site is quite spectacular. They would be
expected anywhere there was an industry which needed powdered products
for their purposes such as paints, graphite, varnish, etc.
Of course, they're not going to be in small numbers on rural domestic
sites, but otherwise, their genesis needs to be ascertained.
Lyle
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