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Subject: Storing DVDs

Storing DVDs

From: Jonathan Farley <j.farley>
Date: Friday, October 24, 2003
Barbara Summers <bsummers [at] lib__siu__edu> writes

>Does anyone have experience using products like d_skin
><URL:http://www.d-skin.com/> or Disc Shields
><URL:http://www.audiovideosupply.com/Security.htm> to protect DVD's
>and CD's from scratching? ...

D-Skin despite the snazzy flash presentation seem not to understand
that the sensitive part of CDs and DVDs is actually the label side,
not the read side. The laser can focus through all but the most
deliberate scratches on the read side of the disc, but scratches to
the label side may cause serious problems.

Disc readers are able to focus through scratches on the read side of
up to 14 microns for a DVD and 20 microns for a CD, the average
'scuffing' scratch is around 5 microns, so I wouldn't worry too much
(unless you have some real careless people using the discs, that
is!). On the other hand, a five micron scratch on the label side
will destroy the disc (the average depth from the surface of the
label to the data layer is three microns for a CD).

Despite the claims that there will be no distortion and no skipping,
I find this doubtful. Polycarbonate can polarise light, and can have
different refractive indices. Two distinct layers therefore could
introduce an interference moire pattern at worst, or reduce the
returned light at best, each of which will cause miss-reads and a
greater reliance on error correction, ergo a higher possibility of
distortion and skipping.

At least Disc Shield are protecting the correct part of the disc. I
would on the other hand be extremely worried about the use of any
shield that is advertised as non-removable. The adhesive is probably
extremely aggressive and consequently a damage risk in itself.

I think the Disc Shield system is designed for high use items with
an intended short lifespan. D-skin on the other hand is based on an
erroneous assumption and no help at all. I would treat both products
and their beneficial claims with extreme caution, especially in any
kind of archival setting.

You are likely to have more trouble from acidic off-gassing from the
jewel cases and keep cases they are being stored in.

Jon Farley


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                  Conservation DistList Instance 17:37
                 Distributed: Monday, October 27, 2003
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Received on Friday, 24 October, 2003

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