Re: [Phys-l] Magnetism and rust

[John Denker <jsd@av8n.com>]

On 12/04/2010 11:37 AM, Peter Schoch wrote: 
> I have a steel router table.  On it I have a magnetic feather-board
> -- a strong, ceramic magnet in a holder that then has 'fins' on it to
> keep the work being routed tight to the fence.  The table, despite it
> being cold and damp was rust free -- EXCEPT under where the magnet
> was!  As I lifted off the feather-board, I found a perfect rust
> outline of the magnet inside the feather-board!

> I can't explain using any Physics I know...

It's probably chemistry not physics.  I reckon the machine was 
only intermittently damp, and that the moisture evaporated quickly
from most places but more slowly right next to the feather board.
I predict that a non-magnetic object would have had a comparable
effect.