Homebrew PCBs

>
>This toner no doubt has a blend of traditional toner elements
>combined with some magnetic metal (I don't know what metal).

Iron, like the black ink in US currency.

>It is also likely this toner would become reactive to the etchant,
>defeating the purpose of the toner as an etch resist.

It would probably be most amusing.

>I also do not believe the MICR characters are raised.  Feel along the
>bottom of one of your checks where the MICR printing is. The MICR
>printing consists of the block style numbers.

They aren't raised, that would be a disaster. They are read with a magnetic 
head that looks exactly like what you'd find in a 1/4" tape deck.  There 
are differences, but that gets a bit esoteric.