This has been updated 2007-06. Please look here, but there is still good information, below.
Two ways of seeing tracks on a tape are listed here. We’re collecting more in the comments.

The Arnold/Plastiform Magnetic Viewer
Marie Rundell
Plastiform Division of Arnold
1000 E. Eisenhower Ave.
Norfolk, NE 68701
PH: 402 371 6100 ext. 176
FX: 402 371 6124
As of mid-2003 these were $88.00 in quantities of one.

Kyread DIP-C-141B Magnetic Tape Developer
See this post: (Updated 2011-05-30)

Comments:

From Chris Goosman Posted Mar 8, 2006 5:33 PM

Richard, something I\’ve never seen the answer to is do these chemicals damage the tape at all? My guess is no, but before I dumped something on the tape I\’d like to know that I\’m not hurting anything.

I replied Mar 8, 2006 5:50 PM

Hi, Chris,

Thanks for stopping by.

The Kyread is just iron powder in a quick-evaporating carrier. I think the carriers used to be Freon(tm), but now I don\’t know precisely what they are.

The beauty of the Plastiform viewer is that it\’s a very thin aluminum foil that touches the tape surface (no sharp edges) and the slurry is on the other side. Nothing touches nor stays on the tape. I use that _much_ more than the Kyread. I think it\’s a bit more sensitive, too.

FerroFluids also makes some very, very expensive materials that I\’ve never looked into. Some people make their own.

Gibbs from Univ of Washington left this on Mar 13, 2006 5:01 PM:

Sprague Magnetics in Sylmar California also sells a magnetic developer \”Sprague-Mag\” SM-2 (liquid in bottle) and SM-1 (spray).