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We have a pretty nice one that I helped prototype and design for our  
Forces That Shape the Bay exhibit.  Ours uses abrasives/sandblasting  
materials, an idea we borrowed from a sedimentation tube at the  
Smithsonian that some of us saw at one point.

The contents are silicon carbide, garnet, and glass beads (in  
water).  Unfortunately I don't have complete specs on all three  
materials.  The SiC was a free sample that our administrative  
assistant sweet-talked out of a local abrasives company; the garnet  
is 220-HPX; and the glass beads were the "fine" glass beads that we  
use in our bead blaster (from McMaster or Grainger or some such place).

We put the SiC and garnet through a stack of sieves and tried many,  
many combinations of different particle sizes of each of the three  
materials (we didn't seive the glass beads, as they were pretty  
monodisperse to begin with).  The 19th sample apparently worked  
pretty well, as that's where my notes stop.  :-)

One crucial step was rinsing (and rinsing, and rinsing, and rinsing)  
the garnet to get rid of the dust and other fine particles.

The tube itself is a tempered glass tube with Teflon end caps held on  
with six stainless steel rods around the circumference.  It's mounted  
to a shaft at its center and it has knobs on each end so that  
visitors can rotate it back and forth to stir up the contents and  
then leave it in a vertical (or oblique) postion to watch the  
settlement.  We have one of our patented eddy-current dampers on the  
back of the shaft to keep the thing from spinning out of control.

It has held up nicely outside for the past five years and it works  
quite well.  The only thing about it is that the contents tend to get  
compacted together if the tube sits in one position for a long time,  
so you have to do some pretty vigorous shaking and stirring if you're  
the first person to use it for a while.


On Aug 18, 2008, at 3:04 PM, Mike Levad wrote:

> Hey Everybody,
>
> We are building a sediment model which consists of a tube with a  
> clear fluid
> in it and different sized particles. When you turn it over the  
> bigger stuff
> hits the bottom first and the little stuff stays on top.  I have  
> seen this
> in a few different places.  Is anybody willing to share what works  
> best for
> the clear fluid and the sediment particles?
>
> Thanks,
>
> Mike
>

~~~~~~~~~~~~~~~~~~~~~~~~~
Allan Ayres
Exhibit Developer
Lawrence Hall of Science
University of California, Berkeley
Berkeley, CA 94720-5200
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