I still use KyRead (older 70s era versions were Magnasee and Visomag), which are applied directly to the magnetic medium. Basically a mixture of micron-sized pyrolytic iron powder and an inert, rapidly-evaporating carrier. Shake the bottle up and drop some on the medium. As the carrier evaporates the magnetic features become visible.
What hit the vendors of such stuff was the Montreal protocol ban on CFCs, such as Freon TF. Kyros adapted initially by using an HCFC, but as those were sunsetted, went to some sort of ether. You can still get the stuff. Be prepared to be shocked on shipping charges. I've suggested to an overseas friend that a mixture of methanol and pyrolytic iron powder might work without damaging the medium. He reports that it works, but the methanol does take a bit of time to evaporate. The viewing films aren't terribly useful for magnetic tapes, but do show the features of a credit-card magnetic stripe (lower bit density). But get the Japanese film, not the common green stuff, as it's not very sensitive. Mostly what I use the Kyread for here is separating 7- from 9-track tapes and verifying that a tape had been degaussed. Here, for example is what a 7-track tape looks like using a simple webcam to take the photo: https://i.imgur.com/wKuTXZH.jpg --Chuck On 6/27/19 8:46 AM, Warner Losh via cctalk wrote: > On Thu, Jun 27, 2019 at 9:42 AM Al Kossow via cctalk <cctalk@classiccmp.org> > wrote: > >> >> >> On 6/27/19 8:21 AM, Warner Losh via cctalk wrote: >>> I saw this >>> half-dollar sized plastic fob on the desk and asked what it was for. >> >> http://qicreader.blogspot.com/p/track-visualization.html >> >> shows a couple of them >> > > Yea, the plastiform magnetic viewer was the thing that I saw. Nice article, > including pictures of the bits on a credit card... > > Warner > -- --Chuck Sent from my digital computer
