RE: [AV Media Matters] Writing on the inner hub area of a CD -R?

[e.ha.zwaneveld@nfb.ca]

Greetings,

 <mailto:Linda.Tadic@hbo.com> Linda.Tadic@hbo.com
[mailto:Linda.Tadic@hbo.com]  asked:

But what about writing on the plastic inner hub of the CD-R, where the
manufacturer's serial
number is located? I haven't heard any sources say that this practice could
potentially increase deterioration of the CD, since it doesn't involve
writing on a surface close to the metal reflective layer. Of course there's
always the argument that the CD-R could be mishandled or scratched while
writing the number on the hub. But if an institution requires identification

beyond the serial number, writing the identification on the plastic inner
hub
with an archival pen seems to be the "safest" archivally (if such a concept
exists). Are there any tests or sources that prove that this practice can
endanger the CDs?

Response: The compact optical disc system is a beautiful piece of
micro-engineering. But the disc is also
vulnerable when handled.
There is no evidence that writing on the disc surface immediately adjacent
to the hub will cause
damage due to the ink or soft tipped pen. Of course one should instruct the
individual doing the marking,
to place the disc reading surface on a clean and soft surface. This side is
made of unprotected
polycarbonate. In the process of writing on the hub area, the disc will
probably be turned around a little.
If that is done while the pen is pressing down on the disc, the side facing
the desk surface which is the reading side,
could get scratched in a circular fashion. A circular scratch is the worst
kind of scratch.
Also, finger nails, rings and watch bands can inadvertently rest or rub over

the label side of the disc while writing. Fingerprint acid should not
contact the disc surface being marked. Therefore,
wear non-dusting nylon gloves when marking compact optical discs, just as is
prescribed when handling motion picture film.
Where DVD media consist of two disc halves that are bonded together,
it is useful to note that the area immediately around the hub is typically
not bonded.
This means that the two halves are separated by an unsupported air gap. When
writing, minimize the pressure applied, to
avoid causing the adhesive in the rest of the disc sandwich to be loosened
up, or the disc halve being written on, to
become damaged with microscopic cracks, making it a potential area of oxygen
entry (and oxidation) into the sandwich.
Because the area immediately surrounding the hub is typically not bonded and
vulnerable, the single disc halves of frequently
used discs, can become chipped as a result of the removal of the disc
without pushing on the center register in its jewel case.
But archival discs are not typically used, hence this source of wear will
not cause problems, but it illustrates the vulnerability
of the partially unbonded disc halves.
I trust that this is useful advise.
Best regards,
Ed H. Zwaneveld,
Technological Research and Development
National Film Board of Canada
Tel: +1-514-283-9143
May 7, 2001

Moderators Comment:
One additional point - the index track on a CD is the inner most area
closest to the hub. If you lose the index track the entire disk is
compromised so I agree that it is best to stay completely away from the
neighborhood of the hub.