Re: Substance blocks magnetism but also reacts to it

Hi,
     The only material that actually blocks a DC magnetic field is a 
superconductor.  That requires extreme cold and very special materials.
     The other way to "block" magnetic fields is to cancel them out by 
moving an easily magnetized body like a sheet of iron close to the point 
you want to shield.  The best way to do it is to put a soft iron box 
around what you want to shield.  That is not a perfect shield but will 
reduce the field perhaps a factor of 100 or more depending on the details.
     There is no way that I know of to shield a magnetic field with a body 
that does not react to the field.