[Videolib] RE: Heavy bronzing (David Wright)

dewright@rubberdisc.com
Tue, 28 Mar 2006 13:56:07 -0000 (UTC)

Here's a site to look at www.CD Rot.com

CD Rot, How & Why it Happens

HOW CD ROT HAPPENS

CD Rot occurs in some older disks that were manufactured in the
technologies early days. The aluminum layer that reflects the light of
the player’s laser is separated from the CD label by a thin layer of
lacquer. If the manufacturer applied the lacquer improperly, air can
penetrate to oxidize the aluminum, eating it up much like iron rusts in
air.

The problem being that when the discs were cut the aluminum layer was too
close to the edge of the disc and not sealed properly from the
environment, thus exposing it to oxidation. The indexing information of a
CD is on the inside the disc, i.e. nearest the center, and that the discs
are read from the center out. This explains why in discs that succumb to
CD Rot, the last tracks on the discs are first affected, i.e. because they
are on the outside edge of the disc and hence the first to be subjected to
oxidation.

A second cause was that some labelling inks used in the silk-screening
process were chemically active even after UV curing. This interfered with
the reflective layer, again, causing readback problems.

So how can you tell whether one of your disks is infected with CD Rot?
Firstly, the silver color on the “label” side of the CD will have started
to change to a color variously described as bronze, copper, golden-brown
or rusty-orange color. The discoloration doesn’t necessarily show up on
the “playing” side of the CDs. This symptom happens on 100% of “rotting”
discs, the worse the “rot” - the more pronounced the discoloration will
be.

On playing the disc, there will be an inordinate amount of “static-like”
background noise. The level of noise that can be heard rises and falls
with the volume of the music on the disc. The louder the actual music, the
more apparent the background noise will be. This symptom is not apparent
at the outset, but eventually creeps in and gets worse and worse over
time. This also seems to show up earliest on tracks towards the end of a
disc rather than at the beginning.

Unofficial estimates put the number of affected discs at between one and
10 per cent, however the good news is that both the issues of ink and
aluminium layers were solved for pressed CDs several years ago, and the CD
manufacturers made changes to their manufacturing process and material
selection. As a result, CD Rot should not be a common problem in the
future.

Hope this helps.
David Wright
Rubberdisc.com
303.250.8455

_______________________________________________
Videolib mailing list
Videolib@library.berkeley.edu
http://www.lib.berkeley.edu/mailman/listinfo/videolib