I took my old cylinder head to my local machine shop to have it resurfaced and have a valve job done to it.  Turns out the head was cracked.  Badly cracked, in fact, its now junk.  I have now done my own porting job on a dual plug cylinder head, but I went back to the machine shop to take some photos of the magnafluxing operation.

The whole operation literally takes seconds. One racing machine shop wanted to charge me $45 per head to have it sent out and magnafluxed.  I imagined that it must require a big machine like an MRI.  Hmmm, not hardly as it turns out.  Really just requires a large electomagnet.  I found a shop that did it for free while I waited.  All three of the 2.3turbo heads I had and two dual plug heads were cracked.  Arrrrghhhhh.
 

In magnafluxing, a strong magnetic field is set up around the part in question.  Fine iron filings (magnetic particles) are then puffed (with a turkey baster type device) onto the part.  They will immediately collect at any disruption in the magnetic field, like a crack.  One side of the crack gets a positive charge while the other side gets a negative charge.  The magnetic iron filings pile up at the crack and quickly make it very obvious.  The yellow in the photo was a paint pen done after the magnaflux for me to see the crack easily.  Iwent back to take pictures again.