When I've played with iron filings and magnets in the past,
the effect of friction between the filings and paper has always
seemed obvious. I'm not sure that I would learn anything from
using a low-friction surface instead (what seemed obvious might
not even be real), but I'll try it if I can. Do you have any
suggestions for a low-friction material to put between the
filings and the magnet?

Hmm. Low friction means the filings are going to slide off
and get into the carpet. I'll just have to pick them up again
with the magnet.

The shape of the filings is obviously significant. Do you have
any suggestions for getting filings which are nearly spherical,
and which are not themselves magnetized? Maybe a particular
kind of iron or steel?

Just now I filed a nail with two different sizes of file. The
bigger, slightly coarser file gave bigger filings, but it isn't
clear that the size and shape distribution is different.

One thing that *is* very different: I put twice as much time
and effort in with the smaller file, and got 1/10th the amount
of filings. I need a vise to hold the nail. I need a workbench
to hold the vise. I need a workroom to hold the bench. I need
a house to hold the workroom. I can't afford a vise.

I'm answering my own questions. I made the filings onto a hard
plastic tray from the kitchen. It seems to have lower friction
than some paper. When I apply a magnet, the itty-bitty little
filings climb up on each other's shoulders to do a flea-circus
stunt where they make relatively huge needles (compared to the
size of the filings) which stand up from the tray surface.

-- Jeff, in Minneapolis

..