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From: krboyce@athena.mit.edu (Kevin R Boyce)
Newsgroups: sci.electronics,rec.audio,rec.video
Subject: Re: What is the life-time of magnetic tape?????
Summary: Where's Bill Vermillion when you need him?
Keywords: tape, back-coating
Message-ID: <1991Jan22.171622.10250@athena.mit.edu>
Date: 22 Jan 91 17:16:22 GMT
References: <1991Jan17.183902.24474@watdragon.waterloo.edu> <1991Jan17.191341.12193@zoo.toronto.edu> <38204@cup.portal.com>
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mmm@cup.portal.com (Mark Robert Thorson) writes:
>It seems to me that the "imprinting" phenomenon which slowly destroys
>magnetic tape recordings could be eliminated by winding two tapes onto
>a spool headed for storage: one tape holding the data and a second tape
>with something to diffuse the magnetic field such as nickel metallization.
>Or maybe a fairly thick tape, say 1 mil, would be enough to separate the
>tape layers and prevent imprinting.  Or maybe just winding a blank tape
>onto the same spool would be enough.  Has any of these ideas been tried?

The thick tape is called "back-coated", and is used in the industry.
Actually, I get my knowledge of this from a college radio station (soon
to be 15,000 watts at 600 feet!), where the only tape we could afford was 
stuff that got sent to us free with programs on it, so I don't know how 
common back-coated tape really is.  I suspect it is the most commonly used
type.  It is about 1 mil thick, normally, and certainly is much more immune
to print-through, though not completely.  Also easier to mark with a grease
pencil for splicing.  Eewww, physical analog splices!
--------
Kevin		boyce@amo.mit.edu
War.  Good God, y'all.                Absolutely       Say it again...
  HUH!           What is it good for?      NUTHIN!