[PADG:906] Re: Mechanical Damage to DVDs

[Joe_Iraci@xxxxxxxxx]

The likely cause of the problem is dirty equipment. There is no physical
contact between the reading device and the disc when it is being played.
The reader is a laser. Between the laser and the disc is a lens. This lens
gets fairly close to the disc, but does not touch it. However, if the
equipment is dirty, debris can accumulate on the lens and then contact will
be made with the disc leading to the formation of circular scratches. The
other possibility is that the disc wobbles in the drive and this causes
contact with the laser.

The thicker chemical coating of CDs mentioned below is to the top side of
the CD and the not the side from which the disc gets read. These chemical
coatings are there to protect the metal layer within the CD, which resides
very close to the label side or top side of the CD. These coatings would
have no effect on preventing the damage mentioned in this post. For DVDs,
no such coatings are necessary because the metal layer resides deep in the
disc matrix and not close to the label or top side.

Joe Iraci
Senior Conservation Scientist
Canadian Conservation Institute



                                                                           
             Tom Teper                                                     
             <tteper@xxxxxxxx>                                             
             Sent by:                                                   To 
             owner-padg@xxxxxx         padg@xxxxxxx                        
             g                                                          cc 
                                                                           
                                                                   Subject 
             13/03/2006 04:22          [PADG:903] Mechanical Damage to     
             PM                        DVDs                                
                                                                           
                                                                           
             Please respond to                                             
               padg@xxxxxxx                                                
                                                                           
                                                                           




I have a question from one of our residence hall libraries about a
circulating DVD collection (appended below). Apparently, they are receiving

many returned with very deep circular scratches that frequently render the
discs unreadable. They are speculating that students are using their gaming

systems to play the discs, rather than a conventional DVD player. Has
anyone heard of similar problems with their collections?

Tom

-----
I'm wondering if you encounter DVDs with deep, circular scratches.  It's
become quite a problem for us, sometimes a DVD is rendered totally
unuseable
after only one check-out.  Clearly the scratches are not the result of
being
dropped or tossed into a backpack because of the totally symmetrical
patterns.  The scratches are too deep to be cleaned.

I've asked [others] who have their own DVD collections, but no one seems to

have this problem but
me.  I'm wondering if it is the result of people using their gamestations
to
play DVDs, as I know they can be harsher on  DVDs than CD-ROMS.  Apparently
CD-ROMS have a thicker chemical coating than makes them not as fragile as
DVDs, according to some websites I've read.




Head of Preservation and Assistant Professor,
         John "Bud" Velde Endowed Professorship
University Library
246F Main Library
University of Illinois at Urbana Champaign
1408 West Gregory Drive
Urbana, IL      61801

Telephone:      217-244-8755
Fax:            217-244-4358