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Subject: Damage to electronic media by magnetic fields

Damage to electronic media by magnetic fields

From: Jim Lindner <vidipax>
Date: Monday, October 23, 1995
Sonya Koros <smkst13 [at] lis__pitt__edu> writes

>one of my duties has been
>to photocopy the cases of incoming CDs for record-keeping purposes.
>I have been wondering whether copying the cases with the CDs still
>inside could possibly damage the CDs.  My thinking is based on the
>possibility that the magnetic field generated by the copier may
>someone cause the electronic data on the CD to "shift".

The material that "holds" the data in  most audio CD's is usually
aluminum, and the way that the data is stored is through "pits" or
tiny holes in the media.  Other types of CD's use dye layers to
"expose" these pits, and still others use gold and other substrates
to hold the data.  As such, most CD's are basically immune to
magnetic fields unless they are *extremely* powerful.  There are
other types of CD's that do use magnetics (the Magneto-Optical CD
for one) that could theoretically be affected, but it would need a
far higher strength magnetic field for a long period of time than
you would properly have. It is improbable that you would come into
contact with these media in a music library (unless perhaps they are
CD master pressings which are used to actually make the CD's at the

I doubt that a copier has a very strong magnetic field at all where
you would normally be placing the materials.  The power supply and
motors would probably be the source of such a field, and these
components are probably at the bottom of the machine.  Even if these
fields were extremely strong, the time of exposure would be so short
as to make the exposure negligible. Of far greater concern would  be
old 1/4" reel to reel magnetic tapes that could be damaged by being
exposed at close proximity to a strong field over a long period of
time (years).

Jim Lindner
The Magnetic Media Restoration Company

                  Conservation DistList Instance 9:37
                Distributed: Thursday, October 26, 1995
                        Message Id: cdl-9-37-009
Received on Monday, 23 October, 1995

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