Film-Tech Forum ARCHIVE: Magnetic Pattern Viewer

This is topic Magnetic Pattern Viewer in forum Film-Yak at Film-Tech Forum ARCHIVE.

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Posted by Dave Macaulay (Member # 813) on 10-12-2001, 09:25 AM:

Years ago I used 2 commercial products to view the magnetic patterns on recorded magnetic tape. I believe these were made to allow jumpless blade splices in videotape, where the splice has to be made in sync with the video data.
One was a viewer thing about 2 inches around, laying it on the tape revealed the magnetization in a blurry pattern visible in some fluid between two plastic sheets. The other was a colloidal fluid in a bottle, this was painted directly on the tape and showed a very detailed image when dry.
A customer wants something like this to look at 35mm fullcoat and find out what format is recorded on it - single, 2, 3, or 6 track. I've done some internet searching but I can't find anything.
Does anyone else remember this stuff? Does anyone know if/where I can get some?

Posted by John Pytlak (Member # 331) on 10-12-2001, 09:57 AM:

Here is a link to Sprague "magnetic developer":
http://www.sprague-magnetics.com/library/sprgmag.pdf

Here are links to "magnetic viewers"
http://www.sigma-hc.co.jp/english/magnet_viewer.html
http://www.darylscience.com/3DMag.html
http://www.magnetsales.com/Otherprod/Measure.htm#field
http://www.sigma-hc.co.jp/english/

Here are some links to historical information:
http://www.sssm.com/editing/museum/lobby.html
http://www.sssm.com/editing/museum/smith/smith.html
One brand was Ampex "Edivue Diluent (developer)"
http://www.xs4all.nl/~levend/tvmuseum/tvmuseumedit/edit05.htm
http://www.magneticimage.com/people/Harry/Quads/quads.html
http://www.screeneditors.com/news/issue49.htm details the method:

"Whatever method you used to find the cut point, you then developed an image of the recorded tracks using a suspension of iron dust in benzine. This required a fair degree of skill, even when magnetic developer pens came on the market. If you applied too little of the mixture you couldn’t see the tracks, and if you applied too much you obliterated them. Either way you had to start again, wiping down the tape and redeveloping until you could reliably read the track information."

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Dave Macaulay (Member # 813) on 10-12-2001, 04:24 PM:

Thanks John!
I found all those links except the useful ones - everything I came up with seemed to be about looking a 3D magnetic fields from bar magnets... not terribly useful. And I think the studio would frown on pouring iron filings in baby oil on a customer's mag track!
Hopefully the Japanese guys will sell into Canada - that card thing is exactly what we need.

Posted by Dick Vaughan (Member # 540) on 10-13-2001, 03:28 PM:

Hi DW

I remember having the very same viewer back around '83 when we opened the museum in Bradford. We intended to use it to show magnetic information on credit card stripes but came across a problem I think to do with stopping the viewer drying out(?) Can't be more specific. A lot of loops have rolled through the projector since then.

I do remember the viewer was made by 3M but with all the reorganisation that company has undergone since then I am not sure which division would have information.